ENVIRONMENTAL HEALTH SERIES
                        Air Pollution
     POWER SYSTEMS
FOR ELECTRIC  VEHICLES
  L-OO
U.S. DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE
                    Public Health Service

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                                       AP37
         POWER  SYSTEMS


                    FOR


      ELECTRIC  VEHICLES



              A Symposium sponsored by
             The U. S. Department of Health,
                Education, and Welfare
                Columbia University
                      and
             Polytechnic Institute of Brooklyn

                  April 6-8, 1967

                    Chairman
            H. B. Linford, Columbia University

                  Co-Chairmen
        H. P. Gregor, Polytechnic Institute of Brooklyn
          B. J. Steigerwald, Public Health Service
U. S. DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE
                Public Health Service
    Bureau of Disease Prevention and Environmental Control
         National Center for Air Pollution Control
                  Cincinnati, Ohio

                      1967

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    The ENVIRONMENTAL HEALTH SERIES of reports was estab-
lished  to report the results of scientific and engineering  studies  of
man's  environment:  the community, whether urban, suburban,  or
rural, where he lives,  works,  and relaxes; the  air, water, and earth
he uses and re-uses; and the wastes he produces and must dispose of
in a way that preserves these natural  resources.  This SERIES  of
reports provides for professional users a central source of information
on the intramural research activities of the Centers in the Bureau of
Disease Prevention and Environmental Control,  and on their coopera-
tive activities with state  and local agencies, research institutions, and
industrial organizations.  The general subject area of each report is
indicated by the letters  that appear in the publication  number;  the
indicators are

                 AP — Air Pollution
                RH — Radiological Health
                UIH — Urban and Industrial Health

    Reports in the SERIES  will be distributed to requesters,  as sup-
plies permit. Requests should be directed to the Center  identified  on
the title page.
         Public Health Service Publication  No. 999-AP-37

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                            PREFACE

    The National  Center for Air Pollution Control, the Polytechnic
Institute of Brooklyn, and  Columbia University  sponsored a sym-
posium on Power Systems  for  Electric Vehicles  at  Columbia Uni-
versity April 6, 7,  and 8, 1967. The purpose of the symposium was to
provide a coordinated review of current research activities related to
power systems for electric vehicles.  The meetings were designed both
to define the present  status of our knowledge  and  to  stimulate
research.

    As chairmen of the symposium,  we want to thank  Dr. John H.
Ludwig and Mr. Anthony H. Sweet of the Public  Health Service for
their  cooperation and assistance; Mrs. Anne Cassel, of Dr.  Ludwig's
staff,  provided editorial services in  preparation of these  proceedings.
Finally, the devotion  of Miss Donna McManus, Secretary  of the Sym-
posium, to the never-ending details is greatly appreciated.

                                   Henry B. Linford
                                   Harry P. Gregor
                                   Bernard J. Steigerwald

New York
Washington, D. C.
1967
    This  report  was prepared for publication  at  facilities  oj the
Public Health  Service  in  Cincinnati, Ohio, under  the direction of
Kenneth Cassel, Jr., Publications Officer, National Center for Urban
and Industrial Health.
                                                               iii

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                     CONTENTS
Introduction 	HENRY B.  LINFORD   1

PROBLEMS IN OUR CITIES:  polluted air, tangled  transit;
    why we think about electric vehicles.

Introduction 	RICHARD s. MORSE   3

An Examination of Alternatives to the Gasoline Engine 	
                                         AUSTIN N. HELLER   5

Impact of Electric Vehicles on Urban Problems	
                                         CLARK HENDERSON  13

Impact of  Electric Power Systems on Urban Traffic Flow,
    Control, and Facilities	-	WALTER HELLY  19
TYPES OF POWER SOURCES: reviews of system develop-
    ments, including several kinds of hybrids.

Introduction 	_.	WILLIAM T. REID  25

Hybrid Power Systems for Vehicles 	GEORGE A. HOFFMAN  27

NASA Work on High-Energy-Density Electrochemical Power
    Devices 		ERNST M. COHN  43

Potential Battery Systems in Vehicle Propulsion	
                                         ROBERT C. OSTHOFF  51

Battery-Powered Electric Vehicles	D. THOMAS FERRELL, JR.
                                      and ALVIN j. SALKIND  61

Power Systems for  Electric Vehicles for  Military and Com-
    mercial Use  	EDWARD A. GILLIS  71

Fuel Cell — Battery Power Sources for Electric Cars	
                                       GALEN R. FRYSINNGER  83

Electric Vehicle  Research	HOWARD A.  WILCOX  91

European  Developments  of Power  Sources  for  Electric
    Vehicles	-	M. BARAK 105
AUXILIARY SYSTEMS:  component developments; other
    aspects of the total vehicle system.
Introduction	PAUL L. HOWARD 121

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Electronic Circuits for Speed Control and Braking	
                                             VICTOR WOUK 123

The Mechanical Design of Electric Automobiles 	
                                           CARL A. VANSANT 143

Electrochemical Systems	ANDRE J. de BETHUNE 155

Separator Systems	HARRY P. GREGOR 173
BATTERIES AND FUEL CELLS:  status of current research
    on specific energy-storage systems; how they perform.

Introduction	ARTHUR FLEISCHER 199

Lead-Acid Batteries and Electric Vehicles	DAVID L. DOUGLAS 201

High-Energy Non-Aqueous  Battery  Systems for  Electric
    Vehicles  	M. EISENBERG 209

An Electrically  Rechargeable Zinc-Air Battery  for  Motive
    Power	D. v. RAGONE 225

Zinc-Air Batteries for the Electric Vehicle	NIGEL i.  PALMER 231

Note on Problems Related to High-Energy Batteries	
                                            SAMUEL RUBEN 242

The Atomics International Sodium-Air Cell	L. A.  HEREDY,
                                 H. L. RECHT, D. E. MC KENZIE 245

Aluminum Fuel Cell for Electric Vehicles ....SOLOMON  ZAROMB 255

Performance and Economics of the  Silver-Zinc Battery in
    Electric Vehicles 	GEORGE A. DALIN 269

A Sodium-Sulfur Secondary Battery	T. w. DEWITT 277

Lithium Nickel-Halide Batteries	R. c. SHAIR, A. E. LYALL,
                                               H. N. SIEGER 289

A State-of-the-Art Automotive Fuel Cell 	PHILIP  DANTOWITZ,
                                              LONNY GADDY 297

Direct Hydrocarbon and Methanol-Air Fuel Cells	
                C. E. HEATH, E. H. OKRENT, M. BELTZER, G. CIPRIOS 307

Hydrogen-Air Fuel Cells for Vehicle Propulsion	G. E. EVANS 313
VI

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POWER SYSTEMS
      FOR ELECTRIC VEHICLES
    We have allowed ourselves to so contaminate the air space above
most of our major cities as to endanger the health of the inhabitants.
Although the total  contribution of pollutants emanating from in-
ternal combustion engines is debatable, we do not have to argue about
exact percentages, since there is  almost uniform  agreement that
automobiles are a major contributor.

    The U. S. Department of Health, Education, and Welfare, through
its National Center for Air Pollution Control, asked us to cooperate
with them in arranging to bring together the leaders of the scientific
and engineering world and delineate the state of non-polluting power
systems  existent today.  We  hope to point out where progress can
be made most expeditiously, with the  result  of reducing the lead
time for the commercialization of the electric vehicle.

                                Henry B. Linford
                                Columbia University

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PROBLEMS IN OUR  CITIES: polluted
air, tangled  transit; why  we think about
electric vehicles.
    The air  pollution  problem is more  complex than is  generally
recognized.  It varies in form and intensity throughout the country,
but the  gasoline  automobile is a  principal contributor to the  total
pollution. This country now has over 80,000,000 automotive vehicles;
no simple mechanism can be  suggested to attack a problem of this
magnitude.

    The automotive industry must of course undertake the introduc-
tion  of  improved automotive  engine designs  and emission  control
devices.  Our committee" is receiving excellent cooperation -from the
automobile  companies  and the oil, chemical, and  other  industrial
groups.  I am confident that  the  emission characteristics  of future
automobiles will  be substantially improved.
 ' Mr. Morse is a member of the Technical Advisory Board of the U. S.
 Department of Commerce.  Currently he is chairman of the study panel
 appointed by the  Secretary of Commerce to  deal with  the automotive
 air pollution problem.

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    The public must clearly recognize its responsibility and assume
the necessary costs associated with our country's desire to improve
the environment in which  we live.  The Federal government must
develop early and realistic short- and long-term goals and standards,
both for quality of our air and for the transportation systems them-
selves.

    In retrospect it appears that knowledge and technology available
several  years ago were adequate  to reduce  harmful emissions from
the gasoline engine substantially, but we have only recently initiated
appropriate action at  the national level. Because of the 80,000,000
automotive  vehicles now in use,  the introduction  of new and ad-
vanced propulsion devices can at best reduce air pollution to a limited
extent in the next decade.  It is a sad commentary  indeed that the
very industrial society that is supposed to improve standards of living
has in fact  made many of  our cities uninhabitable relative  to the
quality of air that was known 50 years ago.

    New  types of automotive vehicles must be developed that will
operate without  generating harmful  emissions.  Our panel studies
are specifically directed toward  the identification of  new  types  of
motive  power that  are technically  and economically  feasible and
to which the scientific and industrial capabilities of this country can
be most profitably employed. The immediate needs  of certain areas
such as Los Angeles and New York City  and future  requirements  of
our growing urban society dictate that government and  industry
implement a more effective national program than has been evident
in the past decade.

                                   Richard S. Morse
                                   Massachusetts Institute
                                     of Technology

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                  AN EXAMINATION OF
ALTERNATIVES TO THE  GASOLINE AUTOMOBILE


                        Austin N. Heller

       Commissioner, Department of Air Pollution Control
                        New York, N. Y.

    Right here in  New York City, because of the convenience and
transportation flexibility of the private automobile, New York  auto-
motive vehicles consume a billion gallons of gasoline each 12 months.
Because of the less than perfect efficiency of the internal combustion
engine, about 70 million  gallons of this total is discharged into the
atmosphere  as waste  products —  unburned  hydrocarbons.  This
wasted gasoline costs New  York  City motorists  about $25,000,000
a year at current prices.

    A study of carbon monoxide, hydrocarbons, and oxides of nitro-
gen emissions has  been completed by  the  New York City Depart-
ment  of Air Pollution Control.  I would like to  bring to your atten-
tion some pertinent data, that will be included in the report of the
study.

    For the City of New York, we estimate that each day, automobile
traffic produces 8,300,000  pounds  of  carbon  monoxide, 1,000,000
pounds of hydrocarbons,  and 212,000 pounds of oxides  of nitrogen.
This  information  is  being correlated  with traffic  patterns in the
City,  and the initial  evaluation indicates a direct  relationship be-
tween traffic  congestion and emissions. For example, if the average
route speed of an  autombile is  25 miles per hour, the exhaust gases
on the average contain 3 percent carbon monoxide and 1,275 parts
per million hydrocarbons.

    On another basis of calculation, each  car  emits 0.17 pound  of
carbon monoxide each mile it  travels  at  25  mph.  At 10 mph, the
rate  of emission rises to 0.35 pound of carbon monoxide per mile
traveled.  This  fluctuating rate, crucial to those of us charged with
air  pollution control  in  New York  City, is  due to the  increasing
traffic congestion resulting from more and more automobiles travel-
ing over a static amount of road  space  and crowding  into a fixed
area of land space.

    New York City  traffic Commissioner Henry  Barnes is fond  of
telling people that  the only way to get to the west side of Manhattan
is to be born there. Although things are not that bad, I would like to
emphasize that things are not that bad — yet.

    Since the beginning  of this year, the Department of Air Pollu-
tion Control  has maintained a five-station carbon monoxide moni-
toring program in midtown and lower Manhattan, with the samplers
operating  continuously 24 hours a  day, 7 days a week.  The first  of
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the stations to go into  operation and the one  from which  the  most
data  have been obtained, is located at 45th Street and Lexington
Avenue.  A summary of  data from this site for the first 2 months
showed that during a normal workday the hourly carbon monoxide
concentration average cannot be expected to fall below 15 ppm  from
9:00 a.m. to 7:00 p.m.  The New York State ambient air quality ob-
jective  states that  15  ppm for 8 consecutive  hours should  not be
exceeded more than 15 percent of the time on an annual basis.
    On January 24, at the 45th  Street location, 15 ppm as an hourly
average was exceeded for 11V2 consecutive hours, with a high hourly
average  of 31 ppm. On January 26, 15 ppm was exceeded at 45th
Street for 9 hours, with  the highest hourly average being 30  ppm.
On that  same day, and at the same time in the  morning,  the  high
hour  at Times Square was  21 ppm; at Canal and  Church Streets  it
was 35 ppm; and at Herald  Square it was 25 ppm.
    The influence of traffic upon carbon monoxide values in Man-
hattan cannot be doubted.  The early morning low, followed  by  a
jump in concentrations during  the  rush hour is  easily discernible.
Variations in  traffic flow, not only  on weekdays but on Sundays as
well,  can be  read from the variations in carbon monoxide  readings.

    Nationally,  70  million  automobiles  consume  some 600,000 tons
of gasoline per day  and discharge more  than 270,000 tons of  carbon
monoxide, unburned hydrocarbons, nitrogen oxides, and organic  lead.

    Where  is our  automobile  population  heading?  In 1900,  this
nation's  auto  population  was nil.  Today there are more than 70
million  private motor  cars  in the United States,  and this  figure  is
expected to rise to 120 million by 1980 — approximately a 70 percent
rise.  For New York City, this rise will be a minimum of 70 percent
and I remind you that 1980 is only 13 years away.

    From the standpoint of air pollution control,  I  would like to
examine the various types of  automobile  engines that  are either
presently in existence or  are in a prototype stage.

                     GASOLINE  ENGINES

    The potential sources of air pollutants emitted  from gasoline
engines include blowby gases from the crankcase, exhaust gases, and
evaporative losses from the fuel  tank and carburetor.

    Control of blowby  gasses, i.e.,  the combustion  gases that  blow
past the reciprocating  piston, is being  approached. These blowby
gasses are trapped  in the crankcase and piped to the intake mani-
fold  where  they are  returned to  the  combustion chambers   and
burned.

    Hydrocarbons evaporate from the car's fuel supply system, gas
tank,  and carburetor into  the  atmosphere.  Experimental systems
for control of evaporative losses  of hydrocarbons have been  designed
and appear to be technically feasible.
                              Alternatives to the Gasoline Engine

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    A national  control program  is scheduled  to  begin in  late  1967
with the introduction of 1968 models. These vehicles will be equipped
to control  crankcase  emissions  completely and to control exhaust
emissions to specified levels. Federal regulations for all 1968 models,
with engines greater than 140 cubic inches in displacement, restrict
carbon monoxide concentrations to 1.5  percent  and hydrocarbon  con-
centrations to 275 ppm in the exhaust  stream.

    Since the  vehicles produced  during  1967 will  pollute the air
throughout their 10-year life span, emission controls must  relate to
air quality  standards  and projected  requirements  for  populations
in the year 1977.

    The consideration of air  pollution control devices is far from  a
panacea. A report  issued this  past  December (1966) by  the Cali-
fornia State Motor Vehicle Board points up the very high deteriora-
tion rate of the automotive pollution control  device that  has  been
mandatory in  that State since 1966.

    Tests were conducted on 552 fleet cars  with control devices to
determine whether  they  could  meet California's criteria for hydro-
carbon and carbon  monoxide emissions.  A direct  correlation  in the
testing indicated  that the higher the mileage  of  the vehicle, the
greater the ineffectiveness of the air  pollution control device. Of
227 vehicles driven  less than 2,000 miles, 37 percent failed to main-
tain pollution below state limits.  Of 15 vehicles  driven over  20,000
miles, 13 vehicles,  or 87  percent failed.  From  these data, we can
conclude that  an extension of  this trend indicates  that  at  50,000
miles all of the vehicles will fail to  meet California standards for
hydrocarbon and carbon monoxide emissions.

    Despite this  evidence,  "first generation"  automotive  emission
controls are rather impressive accomplishments and are a significant
step in controlling  air pollution.  However,  it is interesting  to ex-
amine these accomplishments in light of the substantial rise made in
pollution sources during these past 14 years.  Since 1953, the vehicle
population has  increased  64  percent and gasoline  consumption has
increased 73 percent.

    The importance of figures  such as these is that  they  present  a
direct challenge to the various professionals to move  faster than the
expected rise in population and the concomitant rise  in  the auto-
mobile population.  Looking  back,  we  would have  had to  reduce
emissions by at least  70 percent since 1953 just to stand still.

    The task that  faces planners in  air  pollution control in  rela-
tion to the gasoline engine seems to be formidable, but I do believe
that it can be mounted.

    The problem of technology  keeping up with rising population, be
it human or  automotive, may be new to the engineer and  scientist,
but it is old hat to to the developmental economist,  who  long has
had to contend with Malthusian equations. Perhaps we might borrow
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from the economic developer one of the most useful tools at his com-
mand — that of developmental capital, or seed money.

    If the automotive and gasoline  industries who  have a stake in
finding viable solutions to the problem of automotive pollution con-
trol would voluntarily  pool  5 percent  of  their advertising budgets,
which would amount to about 12 million dollars based on  1965 data,
toward a  joint  effort at new and better controls, I  believe progress
would indeed be hastened.

                        GAS TURBINE

    Following  World  War  II, the gas turbine  engine  became  the
dominant  source of power for the aircraft industry.  The gas turbine
engine for land-vehicle use had to be much smaller, however.

    Such  an engine has now been developed by the automotive in-
dustry, but fuel consumption is extremely high and must be reduced
especially at less than peak load.

    The  turbine  blades must be subjected to the  maximum cycle
temperatures, thereby necessitating a great amount of excess  air to
cool the hot gas temperatures.

    Another deterrent to widespread  utilization of the gas turbine
engine in  automobiles is the very high cost of needed regenerators
or heat exchangers.  If ways can be  found to raise  the  maximum
cycle  temperatures and reduce engine  cost, there is no reason why
the turbine engine cannot  become competitive for automotive use.

    The  cost  of  manufacture is likely  to  remain high  for  many
years, and should the cost go down, there is still the consideration
of extensive retooling on the part of the automotive industry to meet
any changeover from piston engines.

    From a pollution control standpoint, exhaust emissions from gas
turbine engines are very low. Tests indicate that emissions of  un-
burned hydrocarbons and carbon monoxide from a turbine-powered
vehicle are approximately  one-tenth  those from a  piston-engine-
powered vehicle,  based on  emissions per pound of fuel burned. Un-
fortunately, emissions of oxides of nitrogen do not compare favorably
with those from the present gasoline engine.

    Considering  the  stage   of  development  of  turbine-powered
vehicles,  we should point out that even for heavy trucks,  which are
considered the most likely  outlet for first application  of the  gas
turbine, production is well  beyond 1970.

    Through our efforts, New York City  is to become the test  site
for the first thorough evaluation of a  gas turbine bus. The bus  is
expected  to be delivered  before  the end  of this  year and,  through
the cooperation of  the Department  of Air Pollution Control  and
The New York  City Transit Authority,  will be given  its first practical
emission  and performance tests.
                              Alternatives to  the  Gasoline  Engine

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                   ELECTRIC AUTOMOBILE

    Between 1959 and 1961 there was a great flurry of activity when
several  newly  designed versions of  the  electric automobile  were
placed on the market.

    The various  batteries  considered for  the light trucks and pas-
senger vehicles represented a  considerable improvement  over those
that were tested  during the first quarter  of this  century.  Nonethe-
less, advances in  technology  have  not  yet provided  a  satisfactory
battery.

    The storage-capacity-to-weight  ratios for  the relatively inex-
pensive  lead-acid type  of  battery were too low,  limiting the speed
and  range  of the vehicles.  The  nickel-cadmium  and  silver-zinc
batteries were too expensive.

    The production and sales of battery-powered, material-handling
transport devices  for industrial use have gained great  acceptance.
Today, more than 100,000 are used inside plants in the United States
where  air  pollution  from internal  combustion   engines  is  either
dangerous or undesirable.

    Despite this positive start, electric vehicles for street and high-
way utilization have not fared well  commercially.

    After several years of testing  on the part of commercial cor-
porations and governmental agencies a few facts have become ap-
parent.  We have found that the energy  storage  capacities of con-
ventional batteries are  too limited  or too expensive to  provide an
acceptable energy source for electric passenger cars, or any  short-
distance electric vehicle.

    A substantially superior  method of  storing electrical  energy
that will provide  much greater  storage  capacity per unit  weight
and volume will  have to be developed to meet the needs.  A great
deal of  progress  needs  to be  made on electric  motors,  controllers,
and chargers.  Further,  we have seen that research and development
must  explore the entire electric automobile, not  merely a few  in-
dividual components.

    Significant improvements in the energy density of storage bat-
teries have  been  made  in  recent  years.  Further  improvement may
prove to be difficult, and there exists doubt that  they can meet  the
requirements of  electric vehicles.  Because  of the physics of  the
problem,  we know that frequent  acceleration,  gradiant climbing,
and high-speed driving place a heavy burden on  batteries, reducing
the range of the vehicle.

    Because of the basic limitations  of existing  battery  systems, a
number  of  companies   are  conducting research  on  new  systems.
Several  of these  designs show considerable  promise,  but as yet it
is  not clear whether or not they  would be desirable  for  electric
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automobiles. All  of  these  new systems  are  in the developmental
stage, and will  require  between  5 and  10 years of additional de-
velopmental work and testing before they can be shaped into an ac-
ceptable energy source for electric vehicles.  The most essential  com-
ponent  of an  electrically powered vehicle is  the battery,  and it  is
confronted  with  serious  developmental  problems.   Consequently,
until  a  battery  with suitable  characteristics  is developed,  there  is
little  incentive to  attempt development of a practical electrical car.
    Until now,  most of the road testing for electric vehicles has
taken place in converted gasoline-powered cars. These internal  com-
bustion  cars, stripped of their engines and adapted to operate with
rechargeable batteries,  are  not an ideal  medium for testing electric
car performance. A specially designed "electric car" should eliminate
all  components  not specifically needed,  reduce the weight  of  other
parts, and allocate a much  greater share of the weight to the motor,
the batteries, and  other  essential electrical equipment.

    Certain steps  must be  taken  if electric powered vehicles should
become  a reality,  and here  I am not referring to that old  saw about
a new market for  long extension cords.  Nationally, it would require
retooling by tens  of thousands  of small service stations to meet the
energy  needs of the vehicles and to adapt to the radically  different
type of  engines.

    The market potential  of an  electric car is probably  one-third
of the automotive  market, based on utilization of the car as  a second
car or one used primarily for short-distance urban driving.  I should
like to point out that  we in  air pollution control have a great interest
in even one-third  reduction of  automotive pollution.

    The use of the electric car as soon as one becomes feasible would
have  immediate effects  on  the carbon monoxide  and hydrocarbon
emission problems of our major cities.  I am particularly interested
in the adaptation  of  the electric  car for use as passenger  taxicabs.
In New York City, taxis  account for about 50 percent of all mileage
driven,  and most  of this driving  is done in highly congested areas.
The introduction of this vehicle would therefore result in a 50 per-
cent reduction of automotive pollution.

                         FUEL CELLS

    The development of fuel cells for energy is now new.  Like all
inventions,  the spirit of the age dictates  whether or not the inven-
tion is  to  be used.  For example, the  telephone  was invented  in
Austria in 1867, but  the need  for it was  not seen until it was in-
vented  a second time, in 1876  by Bell.  Movable type,  was  invented
by  Pi-Cheng  in China  in  1041, but  it remained for Gutenberg  to
re-invent and  utilize movable type  in  the  mid-Fifteenth century
before it took hold.

    The fuel cell  was invented in England in  1839, but it waited for
the development  of the  NASA space  program to  provide  the first
10                             Alternatives to  the Gasoline Engine

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practical application. Fuel  cells  have a number of advantages: high
theoretical efficiency,  relatively noiseless  operation,  and most im-
portant from my standpoint, they are relatively free of pollution.

    Several  major  manufacturers  have  built  and  tested  vehicles
powered by  fuel cells  and have demonstrated that fuel cell  tech-
nology has progressed to a  point where a high-output vehicle power
plant is technically  feasible.  As with  most  good  things,  though,
there are problems  that must be conquered. At present,  fuel cells
have  a  heavy weight, large volume, and a short lifetime,  and they
utilize costly components.  They  depend  on a complicated  start-up
and  shutdown  procedure, and there are  safety  problems  involving
high voltages and electrolytic leaks.

    The costs of the fuel cells today  are certainly not  competitive
with the costs of gasoline-powered engines. However, should it ever
come to pass, the economics of mass production is expected  to result
in a sharp reduction in  overall  cost. The maintenance costs for fuel
cells are completely unknown, and very little indeed is known  about
the longevity and reliability of complete  fuel cell systems.

    The commercial  possibilities for  fuel  cells being  utilized  in
vehicle  propulsion are good. How quickly and how completely they
will be  realized depends on the  speed  and ingenuity with which we
can  overcome  major  problems  that now  prevent fuel cells  from
competing with conventional power plants.

    I question whether the public will pay exhorbitant prices  for
air pollution attachments or pollution-free cars.  If we can  develop
a pollution-free car  that is  also a better car and can be economically
produced so  as  not  to be priced  out of its market, this  car will  be
a prototype that can enter  mass production immediately.

    I encourage the research  and  development  of  such cars,  but I
also ask that you give consideration to  the marketing factors as well,
for if we cannot sell it to the public, it is all for naught.

    It is evident to me, as I imagine  it is to you, that it is safe to
assume that full-scale  application  of  alternatives  to the  gasoline-
powered automobile are between 5 and  10 years away, depending
upon the direction we finally take.  What  do we in air pollution con-
trol do in this interim?  It is necessary to take positive action, because
to do nothing is not merely to stand still, but  to  double and  triple
the problem  for the next generation of planners.

    I suggest that  we  concentrate  in  these next few years on two
key  programs:  alteration of the urban traffic  pattern,  and an  ac-
celerated  program  to reduce emissions  from  certain critically im-
portant segments of the traffic  load —  such segments  as  taxicabs
and buses, for example.

    To  give  you just one  idea  of  how altering  the traffic pattern
can result  in a decrease of pollution, I  would like to cite some data
from  the New York City Department of Traffic.
HELLER                                                        11

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    During peak hours of traffic, we know that there is concomitant
traffic  congestion.   Increased  traffic  congestion  means  increased
carbon monoxide and hydrocarbon emissions.

    Several years  ago,  when  Fifth  Avenue and  Madison  Avenue
were two-way thoroughfares, the City Department of Traffic calcu-
lated  that during  peak hours of traffic,  the average  automobile
traveled  at 3.5 miles an hour.  The changeover  of these two traffic
arteries  to one-way streets resulted  in an  increase to nearly  18
miles per hour.

     An  increased emphasis on the development of  rapid, convenient,
and attractive mass transit systems, similar to  those  now  being
operated in Japan, may result in a decrease in  the anticipated rise
of automobile congestion in  the  metropolitan  area, and therefore a
reduction in the anticipated rise in automotive pollution.

    Similarly,  serious study should  be  given to  the possibility  of
using mini-cabs, because of their lower exhaust volumes; or of using
lead-free gasoline for cabs so that they may be  re-equipped with
catalytic  mufflers  without  fear  that the catalyst will be ruined  by
lead deposits.  Catalytic mufflers  are  presently  being  tested on  10
new Transit Authority  diesel buses.

    I  take heart  from  the  progress  and  achievements we report
in the following  pages.  Knowing  the  problems  and having  seen
limited  success, I hope that your  inborn  scientific inquisitiveness
asks you, as do I, for an immediate acceleration into the research and
development  of battery systems, fuel cells, and gas turbines.

    When John Kennedy was  President of  the United States, I had
the good fortune to be associated with the  Federal  Government.
During a meeting that took place at  the time,  a  task  force report
was submitted to the President on a vital  subject.  The Chairman
paused to direct a question to the Chief  Executive: "Mr. President,"
the Chairman said,  "Do you believe in the power  of an idea whose
time has  come?"  The President rose and answered, "Indeed I do."

    I  submit  that air pollution control  is  an idea whose time has
come, and the next few years will demonstrate the power of that
idea.  We in  air pollution  control cannot wait  for the development
of the  pollution-free car;  we  must reduce  pollution and we must
reduce it now.
12                            Alternatives  to the Gasoline Engine

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           IMPACT  OF ELECTRIC VEHICLES
                  ON  URBAN PROBLEMS


                        Clark  Henderson

                  Stanford Research Institute
                       Menlo Park,  Calif.

                        BACKGROUND

    Electric vehicles have  already had  a major  impact on  urban
development.  Electric  rail  cars  and electric elevators, both  intro-
duced  in the late 1880s, were the most important factors in  urban
transportation for at least 40 years.  Their influence on the pattern
of urban development is clear. For example, central business districts,
such as the Chicago  Loop, developed rapidly as old six-story  build-
ings were torn down and replaced by taller buildings with elevators.
Much of the growth  in  urban population was accommodated in sub-
urban  communities,  which  developed in  radial  patterns  along the
rail lines extending  from the central business districts.

    The elevator, of  course,  has continued its important role.  Wilfred
Owen  reports that there are 45,000 elevators in New York City and
that the total length of  elevator shafts is equal to the total length of
subway tracks. In fact,  some people ride  greater distances in  eleva-
tors each day than they  travel on the ground.*

    The electric rail  car has not fared as well. Streetcar systems have
almost disappeared from U.S. cities. Rail  mass transit systems con-
tinue to play an important part in some large cities;  and a few new
systems, such as BART in the San Francisco area, are  either being
constructed or planned.

    Electrically  powered  trolley buses are  attractive  because they
are quiet and produce no exhaust,  but they  have  never been exten-
sively  used because  of their need for an overhead power supply and
because of  the high labor costs associated  with their operation.  Elec-
tric automobiles, which were introduced  somewhat  later than rail
cars and elevators, had  a  relatively small  impact on urban develop-
ment.

    Gasoline-powered  automobiles  and  buses  began  to dominate
urban  development  in the late 1920s.  The influence  of the  bus has
declined, but  that  of the  automobile  has  increased tremendously
through the years.  Today  the  automobile  is  the most  important
mode of transportation in almost  all  urban areas and is  certainly
the dominant influence  in urban  development.
* See Wilfred Owen,  The Metropolitan Transportation Problem,  Anchor
  Books edition, 1966.
HENDERSON                                                  13

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                 NEED FOR IMPROVEMENTS

    At present, we have many reasons to be  discontented with the
transportation services available in urban areas and with the systems
that are used.  Public  transportation services  are declining  even
though urban populations are growing, and many people who  do not
have  access  to an automobile suffer  inconvenience and  hardship.
Emissions from buses, automobiles, and service  stations add greatly
to air  pollution problems.  Automobiles not only  create noise  and
traffic congestion,  but they also  require unsightly  facilities and are
costly and unsafe.  Automobiles  are also charged with  encouraging
the unattractive pattern of development called "urban sprawl."

    A number of different courses can be followed  to improve urban
transportation  services.  Continued development of new rail systems
and new highways will undoubtedly provide some relief, but we can-
not expect these systems, even on  a much larger scale,  to correct all
present deficiencies while meeting growing  needs.  It has  also  been
suggested that much of the  problem  might  be solved by improving
the design of cities:  old cities could be reconstructed and new cities
could be built with purpose of  reducing the need for automobiles
and emphasizing pedestrian  travel and public transportation.


                         NEW SYSTEMS

    A third  approach,  which interests me  greatly,  would  be to
develop entirely new transportation systems for use in  both existing
and future cities.  The need  for new systems has been recognized in
many  quarters, and considerable research is  being  sponsored by
federal  agencies with the hope that new transportation systems can
be developed.  An especially  noteworthy program,  sponsored  by the
Department  of Housing and  Urban Development, seeks to plan re-
search, development,  and demonstration programs for breakthroughs
in urban transportation.  We at SRI have recently  begun one of the
research projects in that program.

    We have been impressed with the number and variety of trans-
portation concepts that have been put forward  in  recent years.  We
have encountered several dozen  different suggestions and  proposals.
However, only a few of  the  inventors and promoters have actually
constructed and demonstrated their systems or even their key com-
ponents.  Apparently, most  of the concepts  have yet  to  be  fully
worked out on paper.

    Considerable work must be done  before any  new  urban trans-
portation systems are completely  developed  and ready for service.
We have little doubt that a  number of new systems are technically
feasible, but it is not yet clear whether they can be made  attractive
on economic, social, and political grounds.  However, if all goes well
a variety of new systems may be in service within  5 to  15 years

    As it happens, most of the new system concepts call  for electrical
14                                     Impact  on Urban Problems

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power rather than for internal combustion engines.  Consequently,
if new systems are developed from current research efforts, we may
enter a second "golden era" of electric vehicles.

    Let  us  consider  several of these  electric  vehicles and some of
their  possible effects  on urban problems.


                 LARGE  ELECTRIC VEHICLES

    First, assume that it  is possible to replace conventional  auto-
mobiles, trucks,  and  buses  with  battery-powered  vehicles  capable
of providing the  same services at the same costs. It  seems likely that
the most important result  of this change would be the elimination of
air pollution caused by internal combustion engines and  fuel evapo-
ration.  This gain might be partially  offset by the emissions from
electrical power-generating plants, but that problem can be  avoided
by  locating steam plants  outside  urban  areas or  by using  nuclear
power.

    Electric vehicles  may  also be somewhat  quieter than conven-
tional vehicles because engine noises will be reduced; however, other
disadvantages  of the  automobile  will  not necessarily  be  overcome.
Large electric vehicles will still cause  congestion; they will continue
to be involved in accidents; and they will use unsightly roads,  bridges,
parking  lots, and other facilities.

    The function and characteristics of service stations might change.
Batteries would  ordinarily be  recharged at home, and  visits  to local
service stations  would therefore  be less frequent.  However,  when
batteries had to  be  charged at a service  station, the traveler would
be  delayed  long  enough  that he  might want  to use the  time for a
meal, entertainment or shopping.  Thus, service stations could become
less numerous, but they might  compensate by offering  more  services
and they might be located according to new criteria.

    The use of thousands of large-capacity battery chargers in resi-
dential  districts  might  require additional distribution  capacity in
excess of the off-peak capacity that is already available  during the
night. If so, these requirements may help to  accelerate programs to
replace  unsightly overhead distribution lines with  underground
facilities.

    The use of  battery-powered  vehicles might tend to  encourage
the use  of  tunnels,  underground  garages and stations,   and  other
enclosed  spaces  where  conventional  vehicles   cause   ventilation
problems.

    One can also visualize reasonably simple schemes  for  low-speed
movements  of empty vehicles.  Thus,  the adoption of large electric
vehicles would  probably  encourage the  development of  automatic
or remotely controlled parking facilities in central  business  districts
and at other congested areas, such as  airports.
HENDERSON                                                   15

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    These advantages — except for reduced air pollution —  do not
appear to be compelling.  Consequently, if  we want car owners to
replace conventional  vehicles with battery-powered vehicles  volun-
tarily, the new  vehicles should be attractive in terms of  improved
service to the owner  and lower costs. It may be many years before
such vehicles are available.

                   SMALL ELECTRIC  CARS

    In the meantime, there are other near-term possibilities for  elec-
tric automobiles. One of these  is to  find new ways to use  the  low-
performance vehicles that can  be produced  now.  I am thinking of
vehicles  with speed  and range characteristics more like golf  carts
than like automobiles. I am also thinking of their use in low-density
residential  areas where public transportation is  now almost  non-
existent.  Vehicles of this kind could be used to carry commuters to
and from their  stations and for  other  services entailing less than,
say, 3 to 5 miles of travel.
    The  small electric cars could be privately owned.  I'm  told that
several  thousand  such  vehicles are in  use today  in  Long  Beach,
California,  primarily by elderly people.  It  may be more  desirable
for a public agency  or  corporation  to furnish vehicles as  a public
service to an entire community.  If this were done, the agency would
own, maintain, and service the  vehicles;  collect fares or rentals; and
attend to the storage and redistribution of idle vehicles.
    Systems of this kind  have not been developed,  so comments
about their value are somewhat speculative.  It appears,  however,
that such systems would offer a number of advantages.
    Small electric cars would be hired by users on a variety of terms
—by the month, by the day, or by the  ride.  The  vehicles would be
managed as a common  pool rather than  on individual  assignments,
i.e., a commuter would turn in his vehicle each morning and would
receive a different one at night.  Vehicles would be redistributed and
reused to reduce the requirement for cars, to minimize the need for
parking  facilities, and to make cars readily accessible to all qualified
users.  Thus, many  travelers who do not have regular access  to a
private  automobile could be given prompt  and convenient service.
    The  vehicles would  be small and highly standardized, and there-
fore would probably  be less  expensive than conventional automobiles
to purchase and  operate.   If a  high  rate  of utilization  could  be
achieved, the cost per ride should also be low.

    The  vehicle would  have simple controls and would operate at
speeds up to about 25 mph.  With additional speed restrictions to, say,
15 mph,  the vehicles might also be used safely by children and handi-
capped people who  are  not qualified to operate conventional auto-
mobiles.

    The  problems of using  small  electric cars  are currently being
investigated.  It appears that  storage, redistribution, and  manage-
16                                     Impact on Urban Problems

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ment present the greatest  difficulties.  Vehicle design would  not  be
a serious obstacle, but special efforts would be needed  to minimize
costs.

                      AUTOMATIC  CARS

    Now let me turn to another family of electric vehicles that may
also have a major impact  on urban problems.  I will use the  term
"automatic cars" as the name for a group of systems that call  for the
operation of relatively small  vehicles  on exclusive rights-of-way
under automatic controls.  Examples of such systems are the Westing-
house Transit Expressway and the Stevens-Adamson Carveyor.  At
least a dozen such systems have been proposed within the last decade.
     These  systems would  have  fixed routes and would require ex-
clusive rights-of-way similar to those of modern rail  transit systems,
but  the structures would  be much less ponderous.   Automatic cars
would be much smaller than rail  cars and would not, in most cases,
operate in trains.  Automatic car systems of many kinds can  be en-
visioned.  The systems could vary greatly in features such as speed,
frequency  of service, capacity, network configurations, and stations.
One of the simplest automatic car systems was the automated  shuttle
train considered some years ago for  service between Times  Square
and Grand Central  Station. Automatic cars in that service would
require low speed, frequent departures, and  high capacity.  Service
would be provided on a  single,  short  route with a  station  at each
end.  Another group  of systems  has  been proposed  to link  airports
with central business districts.   These systems require high speed,
low frequency service, and low capacity.  A trunk line would connect
the two  areas,  and two or more stations could be provided at each
end of the route.  A third group of automatic car systems has been
proposed for circulation in central business districts. Such  systems
would have  low speed, frequent  service, and high capacity.  The
network of routes would  be complex, with many links  and stations.
High standards of  safety  should be  attained,  and  the  noise and
aesthetic problems of  rail  systems would be partly avoided.
     Automatic  car  systems would be  permanent installations but
would provide considerable flexibility in design and planning.  Sys-
tems could be  installed piecemeal; they could  be tailored to match
varying  requirements; and they could  evolve  to satisfy  changing
needs.
     Such systems have one major limitation — they cannot provide
door-to-door  service  throughout  the  entire  urban  complex.  The
stations  would  have  to  be widely  separated in residential  areas
where transportation demands  are  low and  irregular.  However,
other schemes, such as the small electric cars described above,  could
be used  to supply this service.

         DUAL-MODE  TRANSPORTATION SYSTEMS

     Dual-mode transportation  systems represent still  another ap-
proach to the exploitation of electric vehicles.  In recent years, several
 HENDERSON                                                 17

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proposals have been advanced for the development of such systems.
The  proposals  call  for  small electric  vehicles capable of operating
on two different types of roadway.  In one mode, they operate under
the driver's control on city streets with battery power (in the same
manner as  the  small electric cars described above) at about  25 mph.
In the second mode, they  operate under automatic control on an ex-
clusive right-of-way  at about 60 mph, using power  drawn  from an
electrical distribution system in the roadway.  The cars would change
from one  mode to  the  other at entry and exit ramps in much the
same way as automobiles enter and leave freeways.

     Again  it must  be emphasized that these  systems have not been
developed  and cannot be evaluated at present.  It appears  that the
dual-mode  system  would combine  most  of  the  advantages  of the
small electric  cars and the  automatic car systems previously de-
scribed. It would be somewhat less flexible in installation than the
automatic  systems  but would  eliminate  the need for some  of the
transfers that  passengers would have to make  with automatic car
systems.

     High standards of safety can be provided on the  exclusive right-
of-way. The roadways for automatic operation would ordinarily be
elevated or underground. Roadways would  require  less land than
freeways for equal volumes of traffic. Driverless operation on the
exclusive right-of-way  would be used to  redistribute empty  vehicles.
Automatic  parking and the pooling of vehicles might eliminate most
of the parking problems in congested areas.

     The dual-mode systems are relatively complex. They  will be
more difficult to develop than small electric cars  and automatic cars
and  may be more costly as well.


                          SUMMARY

     Large  electric vehicles would  reduce air  pollution  but would
not  necessarily make other  contributions  to the solution of urban
problems.

     Small  electric  cars suitable for use  in low-density traffic areas
could provide one essential stage of an area-wide public transporta-
tion service, and automatic car systems could  extend  the public serv-
ice throughout the urban area.  Technically, these two systems appear
to have the potential for improving transportation services  to most
of the urban population within a relatively short time.

     Dual-mode systems combine most of  the advantages of the small
car  systems and  automatic car systems  but,  because of their com-
plexity, may  not  be available for  many years  and may be more
costly than the other two alternatives.

     Economic,  social, and political questions  have not yet been re-
solved for  any of these advanced systems.
18                                     Impact on  Urban  Problems

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      IMPACT OF ELECTRIC POWER  SYSTEMS
       ON URBAN  TRAFFIC FLOW, CONTROL,
                     AND FACILITIES


                          Walter Helly

             The Polytechnic Institute  of Brooklyn
                         Brooklyn, N. Y.

    The  transition  to electric propulsion for automobiles is viewed
primarily as  a  means to achieve significant  reductions in air pollu-
tion  and other urban irritants.  Though these  environmental  con-
siderations are paramount, some attention  should be given to the
perhaps  less  dramatic  effects  on  the  transportation system  itself.
It  will be  argued here that these  are fairly complicated  and that
some are not  altogether  beneficial.


             AUTOMOTIVE TRANSPORT TODAY

    The  vehicles  used include trucks for  local delivery  and for
longer trips,  taxis  and  buses for  transit,  and private  cars for
commuting, shopping, personal travel,  and business. All  vehicles
have a range of 200 to 300 miles between  quick refuelings. However,
they differ significantly  in performance. The normal full-size Ameri-
can car can  accelerate  from 0 to  60 mph  in less than  15  seconds,
and  from  30 to  50  mph in about  5  seconds.   It  can  climb a  5
percent  grade  (about  the  steepest experienced  often  on  streets
designed for heavy traffic)  at a  speed  greater than any present
or contemplated  speed limit.  In  contrast,  a  Volkswagen  acceler-
ates  from 0 to 60 mph in about 27 seconds, from 30 to 50 mph in
9 seconds.  Its top speed  on a 5  percent  grade is  about 55  mph.
A  heavily  laden  trailer truck  may take  more than  100 seconds to
accelerate  from 0 to 60  mph, and may be unable  to go at  more
than 10  to 15  mph on  a  5 percent grade.

    Such a  wide  disparity in performance is  harmful  to  traffic
flow  capacity  and  to  safety.  Capacity  is lowered  by  vehicles
that  cannot  maintain  optimum flow speeds.  For example, in the
Lincoln and  Holland Tunnels under the Hudson River,  the  peak
flows occur at  about 20 miles per hour.  Some trucks cannot main-
tain  this speed on the upgrades and so effect  a serious  reduction
in  the number of  vehicles these  tunnels can serve.

    Safety is affected adversely when vehicles  of  widely different
acceleration capabilities are fairly  closely  spaced at high  speed  on
expressways.  These vehicles with  low  maximum  acceleration are
forced to oscillate  through  a  relatively dangerous  wide  range of
velocities if  they  consistently attempt  to achieve and  maintain
HELLY                                                        19

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"optimally close" headways  in a  stream where  the  majority  of
vehicles  are very powerful performers  (Helly, 1959).  Further,  the
underpowered vehicles face difficulties in merging with high-speed
expressway traffic. It may be argued that safety  considerations for
high-speed  roads are  not important  in congested  urban  centers
where average  effective speeds may  be below 10 miles per  hour.
However, one  must  remain  aware of the fact that today  a very
high  proportion  of urban  trips  take place partially  on sections of
expressways with free flow  and speeds of 50 mph  or more.

    Because of  the wide range  in size  and performance of  present
vehicles, our road system  is  generally designed in a very generous
manner  to provide for everyone.  Lanes are wide, and where  high
speeds are possible and legal, every effort is made to bank curves
for such speeds and  to provide  long acceleration  lanes for merging
by relatively low-powered vehicles. In signalized grids,  the timing
of  light cycles  is geared   to  the  capabilities  of  all but  the most
sluggish participants.

    There is  one important  property  of present day automotive
traffic that is present for  every type of vehicle and  on every road
or  street.  That is the very  high  probability of propulsion  failure.
A typical  vehicle may experience about one  unexpected stoppage
per 10,000-mile-year as a  result of running out of fuel, mechanical
malfunction, or tire failure.  This  may not appear to be very large
until  one considers that a  three-lane flow on a 5-mile-long section
of  expressway  produces  about 25,000  vehicle-miles  in  a  1-hour
peak  period.  This  would correspond  to  an  expected average  of
about 21/2  stoppages.  Because a high proportion of stoppages occur
in the main traffic  lanes  before the affected  vehicles can  get  off,
the effect on flow capacity is disastrous:  it is part of  our common
experience that  the  typical commuter inches  his way past such a
bottleneck at  least once daily!

    To provide  succor to  the stranded  and to refuel all vehicles,
the present  transport system includes  a tremendous  network  of
service stations.  In  1963   the United States  contained  211,000  of
these, employing  730,000  persons  including  proprietors, with gross
annual sales of  17.8 billion  dollars.  These  figures are for service
stations  only; they do not include dealers  or repair  garages.

    Because range limitations are a leading obstacle to acceptance
of electric vehicles at today's  stage of development, it  would be most
desirable to obtain   the distribution  of  daily  travel  distances  for
various  classes  of vehicles.  Unfortunately, there  is little data  at
hand.  One would suppose—hopefully—that the urban vehicle needs
a  smaller  range than the  national  average.  Unfortunately,   the
evidence does not support this premise. A Regional Plan Association
of New York  study  showed that 72 percent  of Manhattan vehicles
travel more  than 50  miles per day.  This  is  definitely above  the
national  average,  which must be based on  about 10,000 miles per
20                                       Impact on Urban Traffic

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vehicle per year.  Manhattan, like other city centers, has an unusually
high proportion of traffic in the form  of high-mileage  buses, taxis,
and  commercial  vehicles.  Available estimates show that,  in New
York, the  average taxi  goes about  100  miles per nominal 8-hour
shift  (a  little over  200  miles  per day)  and  the  average  bus goes
about 100  miles per day.

    Direct fuel costs  may be  very important in the  selection of
power plants  for  commercial vehicles. There are  at present about
40,000 electric bread and  milk trucks  for  local deliveries in Great
Britain.  These  are used,  despite the inconvenience of  a  30-mile
range  and a  20-mph top  speed, because they  save money in a
country where off-peak electric power is especially cheap and where
gasoline  is taxed  much  more highly than  in the United States.
                 THE TRANSITIONAL PHASE

    The English experience with electric delivery vehicles suggests
that the present state  of development is  marginally sufficient  for
such vehicles in urban  areas.  However, a somewhat higher per-
formance will be required for passenger vehicles. In the transitional
phase,   where  electric  cars must  survive  in  an  environment of
high-powered internal  combustion  competition on expressways as
well as  on congested city  streets,  the  minimum  acceptable per-
formance specifications  might be:

1.  Acceleration from 30 to 50 mph in 10 seconds.  To achieve this,
    a  3,000-pound  vehicle requires  about  25 horsepower more
    than needed to cruise at a steady 50 mph.

2.  A top speed of 50 mph on a 5  percent grade.  To achieve this,
    a 3,000-pound vehicle requires  about 20 horsepower above that
    needed to cruise at  a  steady 50  mph  on a level road.

3.  A range  of  50 to 75  miles.

    Though these specifications  are offered rather  arbitrarily, they
represent about the  minimum  performance for safe operation  on
expressways, for minimum degradation of flow, and for a reasonably
significant  fraction of the range  demand distribution.  They  would
satisfy many commuters  and shoppers.  However, unless very rapid
recharges or battery exchanges are developed, taxis would necessarily
continue to use internal  combustion engines.

    To  summarize,  early and  relatively primitive  electric vehicles
would be acceptable for local delivery trucks and to some commuters.
These vehicles must offer performances at  the lower  end  of  the
present  day spectrum, or better.   Because roads and control systems
have generally been designed for present vehicles of  all types, such
an  introduction of electric cars  would not raise new problems in
traffic management.
HELLY                                                        21

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               THE FULLY ELECTRIFIED ERA

     When reasonably  priced  batteries or fuel cells  are developed
to  a stage  matching  present  automobile  capabilities, there should
be  a fairly rapid and widespread  transition to  electric propulsion.
The transition may well be accelerated by governmental incentives
or  selective  taxation, in view of the environmental advantages to
be  gained.

     From a traffic viewpoint, the advantages of such a transition are:

1.  The flow capacity of the street  network  will be improved. A
    small improvement may be  expected from greater uniformity in
    vehicle  responses to driver inputs.  The major  gain will come
    from a  significant  reduction in  unexpected  vehicle  stoppages
    that delay heavy traffic.   The simple electric power plant,  with
    very few moving parts, is very unlikely to expire unexpectedly.
    Further, there should be  no sudden equivalent to an empty gas
    tank. A fuel cell  or battery at  the end of its  range  will  still
    give some power,  enough for  a vehicle to  remove itself  from
    interference  with the traffic stream.

2.  Safety will be improved.  It will be possible to give all vehicles
    flexible and  smooth performance characteristics within a  fairly
    close  range,  thus minimizing the buildup of  irregularities  and
    shock waves in traffic. Braking,  if in part by motor induction,
    will be simpler  and more  reliable.  There will be  less danger
    of fire and no danger of  carbon monoxide poisoning from  leaky
    exhaust systems.

3.  External controls, such as automatic roadways, will  require  less
    instrumentation than for  internal combustion  power plants.

4.  The cost  of  underground roadways will be  reduced by up to
    50 percent because of smaller  ventilation requirements.

     Some  aspects of  the transportation  system  will  be  largely
unaffected by the transition because  there will still  be old vehicles
and because  there  will  still be a wide variation in vehicle  size and
in driver performance.  These aspects include  the  geometric design,
construction,  surfacing, lighting, signing,  and control  of  the road
network.  Parking  will  be affected only insomuch as there may be
reduced requirements  for garage  ventilation  and  for fireproofing.

    One facet of the transition is  likely to raise  serious problems.
It certainly is most attractive to the motorist to  experience fewer
mechanical  failures and to be  able  to refuel at night  by tapping
any electric  outlet.  The  gasoline station  operator is  not  likely to
be  as favorably  impressed.   One  may anticipate that a  general
transition to  electric  power would ultimately force the closing  of a
great majority of the country's  211,000 service stations.  The direct
economic  and social  consequences  to these businesses and  their
employees can be weathered, just as  with other major technological
22                                        Impact  on Urban Traffic

-------
dislocations in  the past  (but one must be prepared for substantial
political  difficulties and  a certain amount of government  spending
in relief  of this  declining  industry).  There  is  another  problem,
more important in the long run.  The  many service  stations today
get their  primary  income from fuel  sales and  from  routine  main-
tenance.   Yet, from the  motorists' viewpoint, the stations' ubiquity
and  long  open  hours are at  least as  important for emergency assis-
tance, for rest rooms, and for communications.  If  the  great majority
of service stations were  to close, the government would have to
assume  a major new responsibility for the nation's 3 million miles
of roadway. A precedent for  government-organized  service exists
on some toll and  interstate  roads. Experience with these leads one
to suspect  that  vast  improvements  would be  demanded  if such
arrangements become more  widespread.

     A possible amelioration of  this  problem is to  continue  to  fuel
vehicles  at  service stations by  using  interchangeable  fuel  cells and
specially  designed hoists.  There  are  other advantages to  such a
system.  The problem of  the long-distance motorist  would be solved
completely. A  very large proportion  of urban cars  today are stored
on the streets, not in garages.  If this were to be the  case  in  the
future, these vehicles could readily  be fueled with interchangeable
cells; it  would  be most awkward  for  them to  require  lengthy
overnight  curbside access  to  electric power  outlets.   Further,  if
the  fuel  cells  are very  expensive and  have a  useful life  longer
than that of the  typical vehicle, the  motorists would  find it  advan-
tageous  to  rent rather than own them.

                           REFERENCE
Helly, W.,  1959,  Dynamics  of single lane  vehicular traffic flow.
     Research Report No.  2.  Center for Operations Research.   M.I.T.,
     Cambridge, Mass. pp. 45-49.
 HELLY                                                         23

-------
 TYPES OF POWER SOURCES:  reviews

 of  system developments, including

 several kinds of hybrids.


    Electric power -for automobiles came long before piston engines.
 The first electrically propelled vehicle on record apparently was that
 of Davenport, a Vermont blacksmith who constructed an electrically
 powered car in 1834 and ran it on a short stretch of track.  Davidson,
 a Scotsman living in Aberdeen, built a more sophisticated electrically
 propelled vehicle in 1837.  This was only 44 years after Volta's first
 primary battery, and but 7 years after the principles  of the first elec-
 tric motor had  been  demonstrated by Negro  at  the  University  of
 Padua; it is evident that engineers then were as alert as they are
 today in picking up new  ideas and in doing something about them.

    Davidson's vehicle used primary batteries of  iron and amalga-
 mated zinc plates  immersed in sulfuric acid.  His  motor was crude,
 with the rotor a wooden  cylinder carrying copper-wire-wound iron
 bars  between the  poles of two  electromagnets, with commutating
 switches mounted on the axle. Basically, it was the same as traction
 motors used today. His system developed 2 horsepower and was able
 to pull a 6-ton coach at 4 mph on wooden rails.

    In 1851,  a  similar, but larger, vehicle was built in the United
States by Page. His vehicle developed 16 horsepower and ran  at
speeds up to 19 mph, but the severe jolting over track joints in short
order ruined the Grove primary cells he used.
                                                          25

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    The rapid development of steam during this period diverted  at-
tention  from battery-powered vehicles, and not until  1888 did  the
first real  electric "automobile" make its appearance, almost simul-
taneously in England and in the United States.  By 1903, the electric
"Torpedo" built by Walter Baker had  achieved a speed of 120  mph.
The trend though was largely to luxury cars for wealthy old ladies,
each  automobile complete  with velvet upholstery  and  a cut-glass
vase to  hold fresh flowers. Over the next 25 years, many versions of
electric automobiles were built.  But with the great developments in
piston engines, including invention of the self starter, the electric  car
was gradually replaced and few were built after about 1930.

    Now, the pendulum swings back. Once more electric automobiles
are in the public eye, thanks mainly to the fact that they do not emit
air pollutants.  Electric automobiles offer other advantages for urban
transportation:  they  can be  small  for crowded city streets, nearly
noiseless  for residential  areas,  and extraordinarily convenient  for
stop-and-go  driving.  It  is  unlikely  that  electric automobiles will
ever compete  performance-wise with piston-engined cars, and their
range is always likely to be limited  to 100 miles or so before recharg-
ing or refueling is required. Hence,  in the future, electric automobiles
seem most likely to move us  about  within cities, with high-powered,
high-speed, massive piston-engined cars still  being used between
cities and for general-purpose driving.

                                    William T. Reid
                                    Battelle Memorial Institute
26

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       HYBRID  POWER SYSTEMS  FOR VEHICLES



                      George A.  Hoffman

                    University of California
                       Los Angeles, Calif.

                       INTRODUCTION

    Air  pollution has  reached  catastrophic proportions  in  many
metropolitan areas of the  United States. Much of the contamination
in the urban air originates from our essential travel by automobile,
bus,  and truck.  Engine exhausts account for over half of the be-
fouling of the atmosphere in New York City and for over three-
quarters  of the smog plaguing Los  Angeles.

    It  is becoming alarmingly clear that present attempts at con-
trolling and abating the noxious exhausts of the piston engine are
too feeble and inadequate.  In his message to Congress Jan. 30,  1967,
President Johnson said:

        The sheer number  of  motor  vehicles  may, within  a
    decade or two, defy the best pollution control  methods we
    can  develop.  If  this proves  true, surely we  cannot  con-
    tinue to use the type of internal combustion  engine now in
    service.  New types of internal combustion  engines — or
    indeed new propulsion systems —  may  be required.

        I recommend an  increase of  50 percent  in  funds to
    expand our research  efforts.

    A  steep escalation of the war on air pollution must be under-
taken soon if urban America is to avoid inundation and suffocation
by the effluvium from  our transportation.   Significant reduction of
smog, possibly leading to  its elimination, can be envisioned through
two distinct approaches to automotive  design.

    The  first approach, illustrated in Figure 1,  hypothetically con-
sists  of an elaborate array of chemical reactants and  scrubbing equip-
ment, occupying  most of  the space in  the trunk compartment of a
family car  and estimated  to  cost upward of $500 per vehicle.  Pure
and  breathable  air could flow from the final exhaust  pipe of this
imaginary  apparatus.  But the  accumulated  tankage  of  absorbed
products of combustion  would  require emptying and  replenishing
every time one pulls into  the corner gas station to fill up the empty
tank,  and probably  at a  cost comparable to that of the fuel pur-
chased.  The logistics and  diseconomies of this design approach for
pollution abatement by total  exhaust suppression appear  enormous.
The costs and intricacies of full  exhaust absorption will undoubtedly
cause the American public to resist strongly the mass adoption of
this scheme for air purification.
HOFFMAN                                                    27

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         A:  UNIT  TO CONVERT CO AND  HYDROCARBONS TO C02
            AND H,O

         B:  AQUEOUS SCRUBBER AND  NOX, C0.2 ABSORBER

         E:  EMPTYING OUTLET

         F:  FILLING INLET

Figure  1.   Total  exhaust  controls for  piston-engine  cars.

    The  other widely  discussed alternative  for  eliminating  auto-
motive air pollution on a  national scale is the early and compre-
hensive  substitution  of electric-battery-operated automobiles  for
conventional cars  (Hoffman, 1966).  But this  candidate for cleaning
up the urban air also must  surmount some formidable obstacles. The
concept  of phasing out, scrapping,  or outlawing a hundred million
vehicles powered  by internal combustion engines in the United States,
and making the transition to a comparable number  of electric vehicles
in a  dozen years  or two could easily dismay the hardiest proponent.
The appalling obstacles  yet to be surmounted in the design of a viable
all-electric vehicle are  also not to  be dismissed too lightly: to this
day we lack even small fleets of demonstration prototypes, let  alone
a single vehicle (as in  Figure 2)  at  reasonable cost, range  or per-
formance.  Batteries exceeding the  critical level  of 50 watt-hours
per pound are still in the laboratory  stage.
      C: CONTROLS                                  M:  MOTORS

    Figure  2.   All-electric  battery-operated automobile.
28
Hybrid  Power Systems

-------
    Therefore comes our pessimism concerning near-term solutions
for enhancing the quality of urban air through radical automotive re-
design.  In spite of the stated willingness  of many to  switch im-
mediately to  battery-operated cars, or  of  the  certainty  that  com-
plete exhaust chemoabsorption is technically feasible, neither of these
re-engineered vehicles  could  arrive  cheaply enough upon the  auto-
motive  scene  by 1980 to offer  a  modicum of relief in air pollution
levels.

    A third  possibility  for significantly reducing smog is reviewed
in this  paper: hybrid power  systems for passenger cars,  buses, and
trucks.  A hybrid is defined  as the enhanced offspring of the  union
and cross-breeding  of the mature form of  a male plant species (in
this case  the  internal combustion engine) with  the equally  mature
form  of the female of another species (the electric motor  generator).
The power package proposed for consideration here is  a  transitional
intermediate between the all-electric and the all-combustive power
supply. as shown  in  Figure  3.  The hybrid system  consists  of an
internal combustion  engine  of rating much reduced from the  con-
ventional motor that it supplants driving at  its optimal speed a gen-
erator.  The generated  electric power  goes to the traction  motors
 (integral with all  the  wheels) and  to  a sizeable secondary  battery,
also connected with the four electric motors.  (The suggestion of  a
traction motor in each  wheel  of the vehicle is only illustrative. Early
designers of hybrids might find it expeditious and simplest to use  a
single motor  driving two wheels, rear  and  front, through a differ-
ential and axle.  This would obviate the  problems of greatly increased
unsprung weight  that  will eventually  arise  from  installing  motors
within  the wheel rims.)  Solid-state controls divert  power from both
the generator and the battery to the electric motors when the  driver's
power  demand  exceeds the  capability  of the constant-speed engine.
When the accelerator  pedal  demands  less  power than the  internal
combustion engine  delivers  continuously, the controls divert some
power to the wheels and some to recharge the battery.  If the battery
is topped-off, a  progressively lesser amount of fuel  is metered  out to
the internal combustion engine.

    Replacement  of the  piston-engine under  the hood of   today's
vehicle by hybrid  power sources is the topic of  this paper,  and its
objective is to show the advantages of  this substitution  in terms of
performance, economy, volumetrics.   planning,  and  environment.
These  advantages  have  led  most Detroit manufacturers to  become
actively interested in the hybrid  concept.

     The idea of hybrids occurred to automotive designers a  genera-
tion ago, though the earliest literature  dates back  only  to the mid-
 1950's.  More recently. Prof.  J. L. Shapiro of the  California Institute
of Technology and Dr. A. L. Stanly of TRW Systems, Inc..  studied
this concept and brought it vividly to the author's attention  in 1966.
Prof. Shapiro dubbed  it the  "gasoline-electric" automobile,  whereas
Dr. Stanly called  it the "quasi-electric" economy  car,  certainly as
appropriate  an  appellative as  our "hybrid" terminology.  Dr. G. R.
 HOFFMAN                                                      29

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   B: BATTERY                         C: CONTROLS

   E: INTERNAL COMBUSTION ENGINE    M: TRACTION MOTOR(S)

   G: GENERATOR

   Figure 3.   Schematic  of  hybrid  power  systems  for
                   cars,  trucks,  and buses.

Frysinger of  the U. S. Army has also aptly used the noun "hybrid"
in connection with a power system analogous to the one in this study,
but with the internal combustion engine replaced by a non-regenera-
tive hydrocarbon fuel  cell (Frysinger,  1966). Not  to be outdone by
all this activity in the  United States, A. P. Zobov in the U.S.S.R. has
also engineered a hybrid system by modifying a Moskvich sedan.  In
England, Jack Brabham,  of Grand Prix  fame,  proposed a battery-
powered passenger car  with  a gasoline  engine for  charging and
occasional peak power.

              WHY HYBRID POWER  SYSTEMS?

    The negative or detractive reasons urging us toward the design
of hybrids stem from  two sources. First, vehicles  operated entirely
by battery will not exist in  large numbers  for dozen of years  to
come, and even then another decade or two must pass  before a dent
can be made in the soaring pollution rate.  Things look pretty  grim
for all-electrics until  the end  of this century.  On the other hand,
tacking thorough  exhaust purifiers  onto  present-day engines and
vehicles is probably an insufferably expensive complexity that might
be shunned by most of the motoring public.
    The contributive  or positive reasons for developing hybrids are
threefold: first, they present an early capability for reducing exhaust
pollution  substantially by use  of  existing  automotive technology;
second,  hybrids promise  a perceptible lowering of operating and
fuel costs;  third,  many beneficial  attributes  emerge when planning
the transition to an all-electric  21st-century America.
    The hybrid's  exhaust would  be proportionately less  polluting
than its conventional  counterpart, for these  reasons:
1.  In the first-generation hybrid the power  output would  be about
   one-half that  of the engine  it replaces.  (It could  be even less
30
Hybrid  Power  Systems

-------
   in later designs.) Expelled contaminants  therefore should also be
   half of those found  in conventional exhaust, if contaminant rate
   may be  assumed proportional to energy-rate  as  a  first approxi-
   mation.
2. The engine-generator set  could  be run at  fairly constant speed,
   near  the rpm  at  which  minimum  specific fuel  consumption  is
   achieved and  with fixed-setting  carburetion.  With the patterns
   of fuel consumption, engine rpm, and time at rpm stipulated  in
   Figure 4, a further pollutant reduction of one-third can be calcu-
   lated from  just running engines at constant optimum speed  with
   non-variable carburetion.  For example,  Figure 4 shows that  an
   engine dwells only 40 percent of the  operating time at its level
   of least  specific consumption, which occurs  at  0.3 to 0.6 of maxi-
   mum rpm.
3. Fixed-speed internal combustion engines allow most easily the in-
   corporation  of regenerative  heating  of  inlet air  by  heat  ex-
   changers and  recirculation of exhausted  gases.   The chilled  ex-
   haust  from the exchanger swept turbulently over large catalytic
   surfaces, and its partial readmission into  the inlet, should lead  to
   an additional reduction of the unburned  hydrocarbons  and nitric
   oxide produced earlier in the combustion chamber. This reduction
   of  smog  agents,  with  a  well-designed   regenerative  exchanger,
   could amount to another one-half.
     A well-engineered   hybrid  power pack  could be  one-fourth  to
one-eighth  as emissive  of smog products as its  equivalent piston en-
gine  if the three  effects just  cited  are  properly utilized  and com-
bined.  Moreover  the  heat-exchanger surfaces  offer  a  fine  oppor-
tunity and  base  for  chemical  activation  (perhaps  in the form  of
expanded nickel or graphite coatings) and might also be an excellent
suppressor of most contaminants except CO2.*
     The second class of beneficial contributions from  hybrid power
systems  is  lowered operating  costs.  Without  changing the driver's
 '•"It is a matter  of conjecture how long mankind will consider the massive
 and rapidly rising effluvium of COj as innocuous.  In the first  century after
 the birth of  industrial  civilization, the  CO.. content  of  the atmosphere
 rose imperceptibly by a  few percent.  Since  the turn of this  century, it
 has risen about another  10  percent.  It  is now increasing at the  rate  of
 about 0.5 to  1  percent per  annum.  At this  rate  of accumulation,  some
 meteorologists claim  the  re-radiated heat from earth is decreased notice-
 ably, and by  the end of  the  21st century the average surface temperature
 of this planet will register a dozen or so degrees  higher than it does now.
 The polar icecaps will then  partially melt, inundating most  coastal terri-
 tories less than  100 feet above sea level.
 I do not necessarily hold  to such cataclysmic predictions: methods of power
 generation alternative to  combustion will be more  widely used: and  vast
 expansion of reforestation,  landscaping, and  agricultural activities  will
 absorb much  of the added CO..  Fixation  of carbon dioxide from exhausts
into  disposable  carbonates  or  by manipulated  photosynthesis will  un-
doubtedly be investigated in the next  century, and a  workable solution
to the suppression of CO- emissions might be adopted.
HOFFMAN                                                       31

-------
  2.0
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~ rpm EQUIVALENT OF  120-mph  ROAD SPEED
      c FRACTION OF ENGINE TIME AT rpm IN AN URBAN TRIP
       COMPENSATED FOR IDLING TIME AND BRAKING BY
       ENGINE DRAG


      Figure 4.   Fuel  consumption,  engine  speed,  and  time

                 at speed  for  a 3-year-old  engine.


    power demand  for  performance,  speed,  acceleration,  and  grade
    climbing, fuel consumption would be slashed one-third just  by the
    constant-speed operation  of the engine (note the patterns in Figure
    4).  Cheaper and less-refined  fuels than those  presently required
    for our variable-speed  engines can be fed into fixed-speed engines.
    32
                       Hybrid Power Systems

-------
In sum, the fuel costs  of  hybrids  might well be  one-half to  two-
thirds of those of gasoline for conventional  engines for equal auto-
motive missions.
    Maintenance costs  of  hybrids  also may be perceptibly lower.
The on-board diagnostics of constant-speed engines can be readily
visualized  as  a welcome  simplification of  today's complexities of
dashboard  gages,  warning lights, and other puzzlers.  Compressor,
gasifier, and power vanes are all on the same shaft  as the generator's
rotor  and at the same rpm.  The single rotating part implies much
savings in  upkeep. Finally the hard-mounted engine-generator  unit
and the nonmechanical power transmission  to the wheels  allow for
easy powerplant plug-in and replacement, less destructive vibration,
and freer interchange of parts.
    The last  category  of  advantages  for hybrids  is less  technical
and more an ease-of-planning benefit.  Hybridizing the power systems
of the automobile, the truck,  and the bus  buys a few decades of
breathing time for the more orderly research  and development of
individual  travel means. These few decades of respite could permit
a more unhurried evolution of advanced batteries for the all-electric
car and a more gradual  introduction of the  driving  populace to
electric propulsion. The industrial  complex would  be less dislocated
by the smooth transition of automotive manufacturers from produc-
ing all-combustive power  components to the mass-production of
battery-motor  systems. Public utilities would have a more gradual
time-table  for national rewiring and up-rating of electric distribution
to home garages, parking lots, and service stations and for the electri-
fication of  our  networks of federal highways and limited-access ex-
pressways.

    The future motorist driving a hybrid vehicle might also avoid
for a few  more  decades the  logistics  of battery recharging or  re-
placement, and might cling  sentimentally for a while to  the habit
of "filling-her-up-with-gas" every 300 or 400 miles, aside from the
cleaner air and  the  smaller  burden  on the pocketbook.  And  the
quiet hum of  the turbine-generator-motor  might yet prove  a  less
offensive sound than the muffled roar of the V8.

    Essentially, the hybrids might prove the least traumatic sequen-
tial conversion of the internal combustion engine species of vehicles
dominating the 20th century into the unavoidably electric mainstays
of the 21st. A transition scheme is given in Figure 5.

     COMPOSITION  OF FIRST-GENERATION HYBRID
           POWER SYSTEMS FOR AUTOMOBILES

    This section examines a specific family of ground-transporta-
tion vehicles, the family passenger car, as an example of analogous
studies regarding buses and trucks.

    I believe  that the future electrically propelled vehicle should
be a look-alike, act-alike,  simple counterpart of the piston-engined
HOFFMAN                                                    33

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                            YEAR




1960-1970     1970-1980    1980-1990    1990-2000      2000
                                                                    2050
N

H
ON-ELECTRIC

ENGINE _ i
POWER
BATTERY = Q
POWER
O
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ELECTRIC
REPLENI:
OUTLETS

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HYBRIDS
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> 	 . LEGEND
1 I AUTOMOBILE, TRUCK,
ID 	 9 OR BUS
cm BATTERY
0 ENGINE/GENERATOR

W PISTON ENGINE







Figure  5.   Scheme  for  a transition from  non-electric  to  all-electric  vehicles via  hybrids.

-------
vehicle with comparable dimensions, performance, and speeds (Hoff-
man, 1967).  Apart from changes under  the hood, which tend to be
of least concern to most outside observers  or to the passenger,  I am
firmly convinced  that  hybrid vehicles must conform to the major
characteristics of conventional cars of today as  regards configuration,
power,  and spectrum of  sizes offered to the public  (from small or
compact cars up to large luxury automobiles).  This  premise defines
the  basic composition and  design criteria  of the first generation of
hybrid-powered automobiles.
     The •weight compostion  of family  passenger  cars  of the  late
1960's, ranging  in curb weight from  1,500 pounds  (a small car) to
over 5,000 pounds (a large, luxurious one), is  uniform in the  pro-
portions of weight of components and in the linearity of subsystem
weight  with curb weight  (Hoffman, 1962). Table  1  lists  the ratios
of subgrouping weights to overall weight in this decade's automobiles;
these ratios are the starting point of  this synthesis of hybrid power
vehicles.
     The next step is  elimination or transformation of  the car's build-
ing blocks that  are altered by the substitution  of the hybrid power-
plant. From the parametric analysis in Table 1 one can forecast that
future hybrid vehicles that are  identical twins  to conventional  ones
in shape, size, and performance would still call for two-thirds of the
vehicle weight  to be  conventional  subsystems, and one-third in-
novated power systems. In this  section I will discuss this innovative
third of the vehicle  system weight,  and its subdivision into engine
(denoted in Table 1  by A), generator (B), motors (also amounting
to B as a first approximation)  and X, the battery weight.

Engine
     Having fulfilled  the "look-alike" requirement,  one  must  next
choose engines  to satisfy the  "act-alike" requirement. Providing  a
constant level of power comparable to that available  in conventional
cars traveling at 50 mph gives three results (see Figure 5, Hoffman,
1967):
1. Accelerative performance  from 0  to 30 mph  superior  to  that
   given by piston-engine  cars,  even  with  constant torque provision
    (rather than power) up to 15 mph.
2. Equivalent performance from standstill  to 60 mph, (that is, equal
   time to accelerate from  0 to 60).
3. Somewhat inferior  performance  beyond 60 mph, but boostable
   in hybrids by injection of battery-supplied spurts of power.

     The actual  power available to  the  driving wheels  of  modern
passenger cars at 50 mph is shown in Figure 6 for standard and inter-
mediate-performance engine options.  An apparent satisfaction  with
0.025 to  0.035 horsepower per pound  seems to emerge as the urban
public's demand level for automotive power, the lower  value being
for "standard" and the upper  for the next-in-line  ("intermediate")
consumer option of engines.
HOFFMAN                                                     35

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        Table 1.  WEIGHT APPORTIONMENT IN CONVENTIONAL
                      AND  HYBRID VEHICLES
«£
o OD
Ic'SJ
gs
Component _~
"j s
5 c
S. o
*- 0.
Se
> o
C 0
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.c
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'£
* Redesign possibilities from substitution
•S of a hybrid powerplant
o




Body 0.33 Elimination of transmission hump; fewer vi-

Trlm 0.14
Engine 0.15
bratlon mounts; redistribution of weights
Simplification of dashboard furnishings, controls
See text
Starter 0.005 Becomes traction motors in the wheels
o"£ 2
^ M no
2'S '3
„* *
5 = e
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o> c u
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Q.
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Is


0.32
0.14
A
B
Transmission 0.040 Eliminated
Suspensions 0.060 Better balanced front-rear springing; low

center of gravity
Glass 0.032 No alterations
Wheels 0.025 Incorporation of traction motors
Tires 0.032 No significant change
Brakes 0.038 Decelerating function partially taken over by motors
Steering unit 0.016 More equitable weight distribution

0.056
0.032
0.030
0.034
0.020
0.016
Rear axle, drive line 0.043 Not needed
Exhaust, smog system 0.014 Heat recuperator at engine controls exhaust
Battery 0.012 Size increased to meet high-power peaks
X
Radiator, full 0.014 Eliminated
Fuel tank, full 0.044 More modestly sized for lowered fuel consumption
Generator, controls 0.005 Growth into full-power generator on turbine shaft
0.022
B
                                            Sum = A+2B+X + 0.67 = 1.00

    If we assume that the electrochemical conversion efficiency of the
hybrid's  electric  motors and  generator  is  93 percent,  the  engine
power requirement is then

              (0.03 ± 0.005)
        hp =
                            W
                                                             (1)
                   0.932
and the least horsepower required of the engine is about

        hpmln,i.c.E. = 0.029 W

where W is the curb weight of the car in pounds.

    The maximum speed of hybrid autos on level grade and without
battery  augmentation is calculated by equating the actual propulsive
power at the wheels

        hpwt,eels = 0.025 W                                    (2)

with  the  power  needed  to overcome  aerodynamic  drag and tire
rolling resistance.

    Assume  that  the  tire  rolling  tractive  force  (SAE,  1967)  of
modern tires is

        0.015 W, Ib                                          (3)

and that the aerodynamic drag of a well-streamlined family car is
        7 x ID-6 W v2, Ib                                     (4)
36
                                          Hybrid Power Systems

-------
    0.05
     0.04
Q.
.C


jf
Q.
  H-
   - 0.03
OL
LU
O
Q.
 O

 <
     0.02
     0.01
                         SMALL
                          O
      COMPACT     FULL-SIZE
         O           O
          INTERMEDIATE
               O
                                                         LARGE
                                                           -0
                               INTERMEDIATE PERFORMANCE OPTION
                                    Q^        O
                                              6
                       STANDARD
                                                 PERFORMANCE OPTION
                            1
                                                1
                          2,000
                                               4,000
                                        6,000
                                CURB WEIGHT, Ib

      Figure  6.   The  actual  mean  power available at  the
       driving wheels  of modern passenger  cars traveling
       at 50 mph with  standard option  and intermediate
                       performance engines.

        The total force resisting automotion, i.e., expressions  (3)  plus
    (4), when multiplied by the speed, v (mph), and  the appropriate
    conversion factor, is close to the total automotive drag power that is
    required of the motors. This tractive power requirement (hp)  is then
            0.00267  (0.015 — 7 x lQ-« v2) W v                     (5)
    where
                 0.00267 =
1.467 (ft/sec) /mph
  550 (ft-lb/sec)/hp
       At the top speed of the hybrid not utilizing batteries for power,
    the horsepower in expression (5) balances the motor-delivered power
    HOFFMAN
                                                                37

-------
in (2).  Equating expressions (5)  and (2) yields the maximum speed,
v, to be 103.5 mph.  This speed is without resort to battery augmenta-
tion, which presumably  will  be employed mostly for upgrading,
during short periods, the poor passing performance of hybrids beyond
60 mph.
    The characteristics  of some conventional  automotive  engines
that could drive the generator in a hybrid are listed  in Table 2.
They were derived for a unit of 50- to 100-horsepower output by
updating  material  presented  earlier   (Table  2,  Hoffman,  1967).
Observe that the relative characteristics of these engines do not differ
by  amounts  significant enough to indicate a clear preference  for
hybrid  vehicles.  The  selection of the  gas turbine for this study,
therefore, is not to be construed as definitive or  final, but rather is
only illustrative. The  piston engine  (rotary, diesel, or  Otto cycle)
certainly remains a strong candidate for powering the generator in
hybrids.

       Table 2.   PROJECTED CHARACTERISTICS OF  PRESENT-DAY
        AUTOMOTIVE POWERPLANTS UNDER 100 HORSEPOWER
                            Gasoline      Diesel    Rotary piston  Gas turbine
                          piston engine  piston engine    engine
Engine weight per horsepower, Ib/hp
Best thermomechanical efficiency,
installed under the hood
Least fuel consumption at optimum
speed, Ib/hp-hr
Relative fuel costs
Lowest number of reciprocating and/or
rotating parts between combustion
chambers and power pick-off
Mass production cost, dollars/hp
3 to 4

0.2 to 0.25

0.4
highest

13
(6 cyl)
2 to 3
4 to 5

0.3 to 0.35

0.4
intermediate

13
(6 cyl)
2 to 3
2 to 3

0.3 to 0.4

0.4
highest

3
(2 rotors)
2 to 3
1.5 to 2.5

0.25

0.35 to 0.45
lowest


1
3 to 4
    The properties of the gas turbine in Table 2 vary slightly from
the data on automotive gas turbines usually found in the literature
(Turenen and Collman, 1965). This difference comes from calculating
the entries in Table 2 for a new, simpler, and smaller breed of auto-
motive  turbine  engine  with  carburetion  fixed  for  constant power
output,  no reduction gears  to the output shaft, no power  transfer
clutch, and omission of the  many parts  required for the  mechanical
transmission  of power to the wheels.

    From the gas turbine's  mean value  of 2 pounds per horsepower
in Table 2, we may conclude that the engine weight ratio in hybrids
will be about

         A = (2  Ib of eng/hp) x (0.029 hp 'lb of W)

or about A = 0.058, nearly  6 percent of the  vehicle weight.

    With typical power  densities of 10  to  12 horsepower per cubic
foot for  turbine  and rotary piston  machines, the engine in  a  full-
sized  hybrid  car  would occupy 8 or 9 cubic  feet, half of the volume
now taken by the engine-transmission  assembly.
38
Hybrid Power Systems

-------
Generator and Motors
    Alternating-current generators in aircraft today operate  at top
speeds of 8,000 to  10,000  rpm, half to one-third  of  the turbine's
shaft  speeds of 20,000 to  30,000 rpm.  But reduction gears should be
avoided in hybrid systems to achieve  quietness and higher efficiency,
and to  reduce manufacturing costs,  it also would be  desirable to
mount the generator's  rotor  directly  on the power shaft.  This ar-
rangement would require a sharp  upward  revision  of  the  ratio of
axial  length to diameter of the stator and rotor. The presently favored
configurations with  length-to-diameter  ratios near  unity  can prob-
ably be slimmed down to ratios of  1.5 to 2.5 or even higher  for the
hybrid  turbine-generator  sets without  incurring a weight  penalty
and still avoiding  gear  reduction.

    The rated outputs  of aircraft generators and of some  advanced-
design oil-cooled motors are plotted in Figure 7 against their weight.
The mean ratio of weight to power of  these generators and  motors
is about 1 pound per horsepower. Then the fraction of vehicle weight
to be  allocated first to the generator, B,  and then  again to the motors
in the wheels  is

        B.ng = (1 Ib of gen-mot  hp)  x  (0.029  hp Ib  of  W)  x 2 x
                 x (0.932  + 0.93)-1 =  0.032

    In other words, about 6.5 percent (= 200 x 0.032) of the  vehicle
weight will be in  generator and in  traction motor(s).

Battery and Controls

    At  the  bottom  of  Table 1 we see  that the sum of component
weight apportionments  is

        1.00 = A + 2B + X + 0.67

from  which the weight ratio that  can be allocated to  batteries and
controls in first-generation hybrids becomes

        X =  1 — (0.67 + 0.058 + 2 x 0.032)
or about X =  0.21.

    The variable-frequency stepless  and continuous controls regu-
lating a 200-horsepower  motor in a truck wheel  weigh about 80
pounds  (SAE, 1966).  Assuming the weight of  well-designed  electric
controls to be proportional to the controlled motor's output,  we can
deduce  that controls will  take up about  0.01 of  the  curb  weight,
leaving one-fifth of the vehicle weight for battery.

    At least two distinct design possibilities for charging this sizable
battery pack are available:

1.  Using a fraction of the power generated by the turbine-generator.
   The constant power  level from the generator can be selected so as to
   exceed by  a carefully preset amount the road-driver demands for
   most  driving  situations.  That portion of electrical energy from
HOFFMAN                                                     39

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       LEGEND:                              ( O SUNDSTRAND
        AIRCRAFT A-C GENERATORS, OIL-COOLED j  + BENmx


        fj COMMUTER TRAIN TRACTION MOTOR, GARRETT

        A ARMY TRUCK IN-THE-WHEEL MOTOR, LEAR-SIEGLER

       /S PROTOTYPE ELECTRIC CAR  MOTOR,  GM
1,000

100
cc
UJ
§
UJ
1
I
10



1
= ' o/:
: / '
; /'•
*% i
I Of1" :

0


— 1 Ib/hp^ :


^ _
i i i i i 1 1 1 1 i i i I I i 1 1 1 I I I I I I II


100

5
^
of
UJ
g
10 p
0.
Q
UJ
1-
<
cr
1
                       10                100              1,000

                   MOTOR OR GENERATOR WEIGHT, Ib

    Figure 7.   Weight  and  power  of selected electric
                  motors  and  generators.

   the power-plant that is over and above the energy requirement
   for the trip can then be metered out at preset rates to the battery.
   An accurate  allocation of power of this type should be based  on
   a predictive  catalog of vehicle usage,  in the form of speed-time
   plots for a variety of trips,  driver behaviors, locations, grades,
   and weather conditions.
40                                       Hybrid Power  Systems

-------
 2.  Regenerative braking.  An urban electric vehicle  could recover
    about half of the kinetic energy  of deceleration, presently  dissi-
    pated in friction heating of brakes and engine linings (Hoffman,
    1963).  With a third of the urban trip time spent in deceleration,
    perhaps one-sixth of the energy now  required for automotive
    travel could be recaptured into the battery.  Traction motors are
    easily and instantly  operable  as  generators,  braking the vehicle
    down to 5 mph, below which speed conventional brakes and  park-
    ing locks could take over.  A simplified alternative design of first-
    generation hybrids  might thus consist  of the turbine-generator
    connected  only  to  the driving  wheels,  and  with regenerative
    braking as the sole  battery energizer.
     To explore the potentialities of battery installation amounting
 to  one-fifth of  the  curb weight,  consider  a conventional lead-acid
 battery,  capable of storing 10 watt-hours per pound, and delivering
 20  watts per pound within a  half-hour discharge time.

     The short-time power boost derivable from the 0.20 W in bat-
 teries is  then
     0.20 W x  (20 w/lb) x  (0.001341 hp/w) or 0.0054 W, hp
 namely,  a  20 percent increase in power pulses.

     This  power boost  can raise  the accelerative and passing  per-
 formance  and  the grade-climbing  ability  of hybrid-power-system
 vehicles  to that of conventional piston-engine  cars over  all   con-
 ceivable urban and highway driving conditions (see Figure  8).  The
 other effect of battery power augmentation is to  increase the maxi-
 mum speed of this vehicle to 110 mph.

     The patterns in Figure 8  indicate that this first system design of
 hybrid power for  automobiles provides  too much driving power at
 speeds below 50 mph and not enough beyond  80 mph, even with bat-
 tery boost. Follow-on parametric studies should explore power match-
 ing at 30 mph as a starting point (rather than  the 50-mph base of this
 preliminary study),  with  occasional battery-power  augmentation
 beyond 30 mph  on demand.  With this better balanced arrangement,
 we  forecast that a hybrid-power passenger car will:

 1.  Pollute our air only one-eighth to one-fourth  as much as today's
    conventional car.
 2.  Consume only half as much fuel.
 3.  Compare well in size, performance, and top speed.
 4.  Disrupt industry less than any other system in the eventual transi-
    tion to  all-electric cars.

                          REFERENCES

Frysinger,  G. R., 1966.  Fuel  cell  — energy storage hybrid  systems
    for vehicles.  Paper No.  66-975,  3d  Annual  Meeting, AIAA,
    Boston, Mass.  (Dec. 2).
HOFFMAN                                                    41

-------
o
o:
o
<
    1.0 r-
    0.8
    0.6
   0-4
    0.2
                               INDUCTION MOTOR
                                             BATTERY BOOST
        INTERNAL COMBUSTION  '
        ENGINE WITH AUTOMATIC
        TRANSMISSION
               20        40        60       80

                           VEHICLE SPEED, mph
                                                       100
120
  Figure  8.   Torque-speed characteristics  of conventional
             cars and  hybrid  power automobiles.

 Hoffman, G. A.,  1962. Automobiles today  and tomorrow. RM-2922-
     FF, the RAND Corp. (Nov.) ($3.00).
 Hoffman, G. A.,  1963. Electric motor cars. RM-3298-FF, The RAND
     Corp. (Mar.) ($3.00).
 Hoffman,  G.  A., 1966.  The electric  automobile.  Sci. American.
     215:34-40 (Oct.).
 Hoffman,  G. A.,  1967.  Systems design of electric automobiles.  J.
     Transportation Res. 1(1): 3-19.
 Society of Automotive Engineers, 1966. W.  Slabiak. An AC individual
     wheel drive  system  for  land  vehicles. SAE  Paper No. 660134.
      (Jan.).
 Society of Automotive Engineers, 1967. D. M. Tenniswood and H. A.
     Graetzel.  Minimum  road load for electric cars. SAE Paper No.
     670177.  (Jan. 13).
 Turunen,  W. A.,  and J.  S. Collman, 1965.  The General Motors re-
     search GT-309 gas turbine engine.  Res. Publ.  GMR-495, General
     Motors Corp. (Oct.).
  42
                                             Hybrid Power Systems

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      NASA WORK  ON  HIGH-ENERGY-DENSITY
        ELECTROCHEMICAL POWER  DEVICES

                         Ernst M. Cohn

        National Aeronautics and Space Administration
                        Washington, D.C.

    To  ensure  crew safety  during manned  space flights  and to
maximize the probability  of  success  of  unmanned  space missions,
all spacecraft subsystems must have extraordinarily  high  reliability.
In addition,  each subsystem  should  be  as small  and as  light as
possible, to make available a maximum of space  and  weight  for
payloads.  These are  the general goals of the electrochemical research
and  development  program that aims  at providing reliable, high-
energy,  and  high-power-density  subsystems for  space.  Since  the
same type of criteria, together with  other  considerations,  must be
applied  to automotive  power plants,  a  number  of space-oriented
electrochemical  projects  are  of  terrestrial interest as  well.  The
methods used and results  obtained in  these studies may find more
or less  direct  commercial  use.  And  even if a  given  space-type
device is not  practical under everyday conditions, the lessons learned
from its development are often helpful in adapting it to meet other
physical and economic  requirements.

                          BATTERIES

Organic Electrolyte Systems
    Among pertinent battery  tasks is the search for high-energy-
density  electrochemical couples, i.e., fuel-oxidant combinations, with
compatible electrolytes.  For 6 or more years, the Army,  Navy,  Air
Force, and NASA have  sponsored  in-house, grant, and contract work
on the  use of organic  solvents with  inorganic  solutes as  battery
electrolytes.  All of  these  efforts  have shown how  difficult  it is to
obtain highly pure  cell components;  and purity appears  to be a
requisite for  compatibility.  Even  if this  problem is  solved, the fact
remains that all organic electrolytes investigated to date  have ionic
conductivities so low  that they  are  unsuitable  for high  rates of
discharge.  Thus, although high energy  density  may be  achieved,
high power density  has yet to  be shown.  We can  go even further
and say that an operable,  compact, high-power cell would have an
inherent difficulty:   Because no electrochemical reaction  is  100 per-
cent  efficient, the rate  at  which heat  is  produced  per unit volume
in such  a system   must be  higher  than in  a  conventional one;
hence, special  engineering  skill is necessary to  maintain thermal
control.   The negative  results  of  these efforts  are valuable lessons
in themselves.  In addition, a potentially  positive  result  has come
from  one  of  the  contracts in  this  area.

    Since mid-1963, Monsanto Research Corporation has been inves-
tigating their dry-tape  battery or fuel cell (US  Pat.  3,260,620 and
COHN                                                         43

-------
3,293,080)  under  various  NASA contracts  (currently NAS3-7624).
One might have a prolonged semantic discussion as to whether this
is a battery or a fuel cell.  Suffice it to say that the device employs
a multiple-reserve construction,  i.e., the active components are pack-
aged separately and combined only immediately before use.  Because
of  the  bulk  and   weight  of  its inevitable  non-active components
(packaging, drive, controls,  housing),  the dry  tape does not appear
to be applicable for  4-  or  5-hour missions,  the maximum  duration
of driving a conventional car  before refueling.  One of the  cathodic
materials studied under  this task does,  though, have some interesting
properties that make it,  as well  as related substances, worth further
consideration. Trichlorotriazinetrione (also called trichloroisocyanuric
acid) is  a solid, organic bleach  that contains 85 percent equivalent
chlorine  on a weight basis.   In combination with magnesium,  for
example, the theoretical  energy density of the electrochemical couple
alone is  750 watt-hours  per pound. An electrolyte more compatible
than those now available remains to  be found;  further, the weight
of a battery would obviously be much more than that of the active
materials themselves.  But this bleach offers  the  energetic advantages
of chlorine without the tankage weight penalties and the  toxicity
hazards  entailed by the use of  that gas.

    I should like  to  suggest, therefore, that bleaches be considered
as oxidants in batteries or battery/fuel-cell hybrids. If an acceptable
solid electrolyte can  be found,  a  flow-through cathode might be
combined with  it,  through which  a liquid  bleach  or a bleach  dis-
solved  in  an inert  solvent  is  pumped.   The  lightweight  storage
tank for the oxidizer might contain a flexible bladder so  that the
spent liquid can be stored in the  same container  before re-processing.
The solid electrolyte  must prevent diffusion of materials  into the
anode.  The flow-through cathode  would permit continuous  flushing
of the cell, and  thus undesirable build-up  of products  could be
avoided.

Alkaline Batteries
    Let  me  now  switch from  a  futuristic to  a  more immediate
electrochemical  system,  the zinc-oxygen cell.  A number of projects
aimed at improving the silver oxide-zinc space  battery have direct
bearing on that system,  particularly on a rechargeable zinc-oxygen
or zinc-air battery.  When the  zinc anode  is  recharged,  i.e., when
zinc is electroplated from the electrolyte back on the anode, it becomes
covered  with  uneven  zinc deposits.  Zinc dendrites or needles tend
to penetrate  the cell  separator  and eventually to short-circuit the
cell by contacting  the cathode.
    In   a   contract   with  the  Goddard   Space  Flight   Center
(NAS5-3908),  scientists at  Leesona  Moos Laboratories  observed
three distinctive types of zinc dendrites.  Mossy,  pine-tree-shaped,
or acicular deposits were formed,  depending on the overpotential.
The mossy kind, deposited at up  to 0.1-volt overpotential,  is least
objectionable; but this means  that zinc plates have to be recharged
very slowly.   Small hydrogen  bubbles  and  local density differences
44                         NASA:  Electrochemical Power Devices

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between zincate-rich and zincate-depleted electrolytes caused local-
ized convection at dendrite tips and thus contributed to  undesirable
needle growth. Once started,  needles grew more easily than smooth
deposits, because zincate ions diffused slowly; the needles "reached
out" for more  zinc.  Needle  growth was  worst at  the  edges  of
electrodes.   Masking the  edges  with  non-porous  polyethylene  or
other plastic was proposed as  a solution to edge growth.  Unsymmet-
rical pulse  charging was suggested to the contractor, who did indeed
find that 30 percent on—60 percent off  resulted in lower  dendrite
growth than continuous charging. Thus a "half-wave" or other type
of discontinuous  charge may  overcome  some  of the  rate limitation
set by the  low overvoltage requirement for continuous charge.

    A parallel effort at  Yardney Electric  Company  (NAS5-3873)
confirmed  a number of these findings.  In  addition, examination  of
zinc deposits  in  membranes  established  that  they  penetrate  by
deposition  within the separator rather than by mechanical puncture.
High overpotential and low zincate concentration in solution are the
chief causes for such harmful growth.  Furthermore, the overpoten-
tial at which  penetration  takes  place  was  found to be a  function
of the  partition  of  zincate ions between the  adsorbed state  (on
separator fibers) and the free state  (in solution,  held within the
separator). The lower the partition ratio of adsorbed  to free zincate,
the more resistant is the  membrane to zinc penetration. Although
cellophane soaked  in 44 percent KOH gave a ratio of only 0.03, it
is not  stable enough to be a  good separator.

    The best  organic separator  found  thus far, for  both  stability
and low zinc penetration, was  prepared by  the  Borden  Chemical
Company.  (NAS5-9107).  A 10 percent aqueous  solution of methyl
cellulose (700g)  and a 10 percent aqueous solution  of (polyvinyl
methyl/maleic anhydride)  (300g)  were mixed at 0°C.  The solution
was poured on a glass plate, leveled  with a doctor blade, and water
was allowed to  evaporate before the film was  stripped from the
glass.  Even so, the 60 or so  cycles obtained  with  silver oxide-zinc
cells would obviously be  far from commercially acceptable.  Relief
may come  from projects that started for completely different reasons.

    An inorganic separator was developed by Astropower Laboratory
to operate  silver-zinc cells at much  higher temperatures than the
normal range of about  0° to 40°C.   It  has been incorporated  into
test cells  (NAS3-7639)  and sustained well over 1,000 cycles at  35
percent depth  of discharge and  25°C; even at 50 percent  depth  of
discharge and 100°C, it has sustained more than 250 cycles.  Another
inorganic  separator, electrodeposited calcium hydroxide, has been
studied for us by  General Electric  Company  (NAS5-9168)  and is
now  being further  evaluated.   A  separator made  by Radiation
Applications,  Inc.,  specifically for sterilizable batteries  (JPL con-
tract 951015)  still  remains to be tested for resistance to zinc pene-
tration. In principle, however, inorganic or organic high-temperature
or sterilizable  separators  may turn  out  to  be tougher and longer-
lived under ambient conditions than their more traditional precursors.
COHN                                                          45

-------
    We have started work on primary and  secondary zinc-oxygen
cells for space during  the past  fiscal  year.  Of  particular interest
are  preliminary  results  obtained  at  Union Carbide Corporation
(NAS5-10247), where a zinc-oxygen 16-AH secondary cell was dis-
charged about 20 percent in 2 hours and recharged in  6 hours.  This
8-hour  cycle has  been repeated  14 times thus far.  Such charge/
discharge times  approach  those  one  might expect  for  everyday
battery uses.

Auxiliaries and  Test Procedures
    Whereas the cathode  of the  zinc-oxygen (air)  battery  is  only
a partial  product of recent fuel-cell  research, the fuel  cell as a
whole has been incorporated into batteries, not as  a power-producing
but as a gas-consuming device.   The gassing of  zinc  plates,  which
evolve  hydrogen  with  almost any electrolyte  under  almost  all
circumstances, would make a sealed battery  structure impossible if
the gas could not be consumed again.  Miniature fuel  cells inserted
in silver-zinc cells  have operated  satisfactorily  for up  to  1 year
(NAS5-9594) and  are  being further  developed  and  evaluated by
Astropower  and  at NASA's  Goddard  Center.  The same purpose
can  be achieved by fuel-cell  type auxiliary electrodes  that have
been  used  by  General  Electric  Company  (NAS5-3669),   among
others, to remove  both hydrogen and  oxygen from sealed  silver-
zinc  cells.
    The question of charge  control  is not  simply answered;  the
correct  method  depends on the  size  of the  power supply and on
the time available  for  recharging,  according to  a General Electric
Company report  on contract NAS5-9193.  They recommended con-
stant current charge for  small   (up  to 15  watt) nickel-cadmium
power  sources  and  1-hour charge time;  and  constant voltage/
coulometer cut-off  with auxiliary gas-recombination electrodes  for
larger power supplies. A simple electrochemical coulometer made from
commercial cadmium plates was described by E. R. Stroup in  NASA
report  X-716-66-462. It functioned well with nickel-cadmium  bat-
teries at 0°  to  25°C for  at least 1 year. Although these charge-
control devices and procedures were developed specifically for nickel-
cadmium batteries—the space workhorses—I  cite  them because they
indicate what can be done  and  must eventually be adapted to  ensure
safe  and reliable  operation of other  battery power plants.
    Like all  battery manufacturers and many other battery users,
we have our own test  programs  and procedures. An  original con-
tribution to  this  type of activity arose from a brief  contract with
Radio  Corporation  of America  (NASw-1001) to develop  statistical
methods for  correlating  the  voluminous  test  data.   It  is a non-
destructive  procedure  for  determining the  quality of  a battery.
Though perhaps  not an original  discovery of Mr. J.  H.  Waite, (it
appears to have  been used on  relays  in  WW  II), it  is potentially
applicable to any mass-produced  item and looks particularly valu-
able  as a deterministic, instead of the  usual  probabilistic,  statistical
approach.
46                         NASA:  Electrochemical Power Devices

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     Briefly, the procedure is as follows:  A  statistically  meaningful
sample of a population is tested to destruction under normal operating
conditions,  while significant data  are being recorded,  particularly
frequently during the initial test period.  The data  are manipulated
to show differences,  for the initial  portion  of  the life  test  only,
among  samples that  passed  and those that  failed for a variety  of
reasons. One can then take another member  of the same population,
obtain initial life data only, and match the results to those previously
obtained, in  order  to  predict  whether  this specific member  will
complete its mission or, if not, what  will cause  it to fail.

     It  is not  yet known whether a general mathematical  basis,
similar to  conventional statistics, can  be evolved  for this approach.
Nor  are the physical details for  meaningful battery  testing  fully
explored as  yet. Preliminary indications from nickel-cadmium bat-
tery tests are that the method may be made fail-safe; i.e.,  although
tests showed likely premature failure, some battery  packs completed
their mission;  but  no  "sound"  batteries, according  to  prediction,
failed.

                          FUEL CELLS

     For the present,  at least,  NASA is  concentrating on one type
of fuel  cell only, the hydrogen-oxygen cell with alkaline  electrolyte.
Although the Bacon-type intermediate-temperature (250°C)  fuel cell
for the Apollo  spacecraft needs  no added catalyst (the  nickel  elec-
trodes  are catalytic enough  at  that temperature), low-temperature
fuel  cells,  operating  at  temperatures up to about  150°C,   do  need
catalysts on  both  anode  and  cathode.   The  greatest  problem  of
inefficiency  consists   of  the  voltage  loss at the  cathode   of  low-
temperature systems,  where  0.2 to  0.3 volt per cell is lost as soon  as
any  power is  drawn.  This  is true even for the best platinum  or
silver  electrodes.

     To overcome this loss, I started a program at Tyco Laboratories
in mid-1965 (NASw-1233)  on preparation and screening of a series
of alloys  that  are  potential  cathodic electrocatalysts.  Thus  far,
osmium and certain titanium alloys have been identified as promising
materials.  They are perhaps of dubious commercial value.  On the
other hand,  nickel  carbide  was found to be  about 90  percent  as
good as platinum.  That is not  good enough for  space, but  in  view
of its price  and availability it may attain  commercial  importance.
I hasten to add that,  thus far,  it has been too unstable to be useful
for any length of time.  Similar preparations are  being made for
us by the Bureau of Mines (Contract W 12,300) and being evaluated
for  possible  ground  applications  by  six  firms.  We  furnish free
catalyst samples to them, in return  for  which we obtain  the  test
results.  Since this  mutual  aid  program  has just begun, it is too
early to speculate  on the results.

    Another problem of gas-fed fuel-cell electrodes has been  with
us for a long time.  In 1839,  Sir William  (later Lord Justice) Grove
COHN                                                           47

-------
mentioned, in describing the very first hydrogen-oxygen  fuel  cell,
that the seat  of the electrochemical reaction  is at the three-phase
interface.  He  thought  that  power  production  occurs  where  the
gaseous  reactant,  liquid  electrolyte,  and  solid  electrode  meet.
Though  he was  almost right,  modern work has  shown that  the
locus of reaction  is just below this  boundary,  in  a thin film  of
electrolyte above  the  visible meniscus. Gas does not react at  the
solid  surface  until after it  has been  dissolved  in  the  electrolyte.

    On a grant to Professor Bockris at the University of Pennsyl-
vania  (NsG-325),  a graduate  student has  been working  on  the
behavior  of the  pore  of a  gas-fed fuel-cell electrode,  deepening
the insight gained into this problem by Professor Meissner's students
at Massachusetts Institute of  Technology, Dr. Will at General Electric
Company,  and others.   Mr. Cahan  observed boiling of the meniscus
in a model pore.  Further work showed  that about 90 percent of
the current was produced in a  meniscus  ring  about 10~s  centimeter
thick.  In other words,  only about 5  percent of the catalyst  now
used  in  fuel-cell  electrodes appears  to  perform its  function;  the
rest is wasted. This study points out that extremely thin electrodes
would suffice  for  the  electrochemical reaction.

    On the other  hand,  the thinness of the active layer may simply
be  the  result  of the way we  operate fuel cells today.   They  are
still being built according to Grove's  recipe, maximizing  the  three-
phase  interface.   If the active layer  is  so  thin only because all
of the sparsely soluble gas is  used up in that region, then it  may
be possible to  improve the power density  of a fuel cell by separating
the two operations, gas saturation of electrolyte  and electrochemical
reaction, that  are  now so  closely  coupled in the  electrode.   This
decoupling does not make  sense for a  single cell, but it may result
in advantages for a stack of 30,  60,  or  even more cells.  We  now
have  three contractors taking a look  at  the  engineering  problems
of  novel  types of  fuel cells  that would  break with the  Grove
tradition. Furthermore, new work  on optimization  of porous elec-
trodes is underway. In general, fuel cell  power plants of today
are not much  more than assemblies of slightly scaled-up  laboratory
cells.  A  good deal of  imaginative  chemical engineering remains
to be done.

    But,  though the core of a fuel-cell  plant  represents a fairly
loose coalition  of  individual  cells thus far, their  combined behavior
is far from that  of the same  number of single cells.  Something
always gets lost in the  stacking of them, and it doesn't much matter
which kind of basic building block  is being  used.  Whereas single
cells might perform well for a year or even several years, the  very
best stacks have  only  lasted for hundreds (say  1,800)  instead of
thousands  of hours  so  far.   The reasons  for failure depend on the
type of cell, on the method of operation,  and on the control devices
to name only the most obvious.  Not  enough full-size stacks  have
yet been built to  know details  about  the behavior, reasons for  and
mechanisms of failure of  any  fuel-cell system in existence  today
48                         NASA:   Electrochemical  Power Devices

-------
    The  first extensive  fuel-cell stack  test is being  carried out
by Allis-Chalmers Manufacturing Company (NAS8-2696).  We are
doing here what has been done  with batteries routinely  for  years.
However, in  view  of  the much  higher cost  of these stacks, the
program now comprises  only  eight  of  them. The stacks  are being
built  as  much alike as possible,  though we will take advantage of
improvements that  become apparent  as we go along.  Each  stack
will  be  run  under  standard conditions for the first 200 hours to
ensure uniformity.  After this check-out procedure, each  stack will
be tortured  in a  different manner  until  failure:  repeated  starts
and stops, simulated external short circuit,  unbalanced gas pressure,
improper water  removal,  excessive  temperature,  etc.  The results
will permit a rather modest statistical assessment of full-size stacks,
their  uniformity, their  capability to withstand abuse,  their  mode of
failure  under  different  stresses,  their  safety,  and their  reliability.
Though this is the first  such systematic  evaluation of fuel-cell stacks,
it will have to be repeated, and on a much larger scale, if commer-
cial use of  them is ever to become widespread.  I  hope that this
exercise will  set a  helpful precedent  and that many of the results
and conclusions will be applicable to other than the specific system
with  which they  will have been obtained.

    Although the  Allis-Chalmers  Manufacturing  Company system
still  uses ordinary  asbestos to contain  the electrolyte, we already
know that a  considerably improved material must take its  place, if
long-term operation of matrix-type cells is to be achieved  at mini-
mum rates of degradation.  Several contractors, among them Electro-
Optical  Systems   (NAS3-2781),   are  studying  composite  asbestos
matrices  or   completely  different substances  for  this purpose. In
addition, Union Carbide Corporation is upgrading its free-electrolyte
fuel cell for the high power and energy densities  required  in  space
 (NAS3-9430). It will be interesting and instructive to compare the
performance  and  longevity  of  this  modified  equipment  with  that
using an electrolyte matrix, since both will be tested under  very
similar load  conditions.

                          CONCLUSION

    This summary of space-oriented  electrochemical research and
 development, aimed at producing compact, lightweight reliable power
 sources, clearly  shows  that we  have  no ready-made,  50- to  100-
 kilowatt product directly applicable to consumer uses.  Yet, I  hope
 you will agree that these ideas,  approaches, data, and devices can
 contribute to our  obtaining  considerably  improved batteries and
 fuel  cells, be they upgraded conventional ones  or  radically new
 ones.  This program should help  solve  some long-standing problems,
 lead  to  simplified  controls, and  perhaps result in easier  operability
 and  maintainability of such power plants.  We do,  of  course,  hope
 that  some of the  concepts will  end up as practical  hardware that
 can  be  applied where  and when  electric vehicles  may  prove to
 be feasible.
 COHN                                                          49

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            POTENTIAL  BATTERY SYSTEMS
                IN  VEHICLE PROPULSION


                        Robert C. Osthoff

                    General  Electric  Company
                        Sclienectady, N.Y.

    In the past most efforts to study the potential opportunities  for
electric vehicles have centered on the lead-acid battery as the energy
source.  This choice  was based primarily upon the low cost and ready
availability of the  lead-acid battery. However, the relatively low
energy  content of  the  lead-acid system resulted  in  vehicles with
very  limited ranges; further, the weights of  the batteries  were ex-
tremely  great, compared to the weight of the very  high-capability,
gasoline-powered, internal combustion engine. During the  period of
1958 to 1962, at least three such converted vehicles  powered by lead-
acid batteries  were built  by the General Electric  Company.  These
vehicles  were  plagued by  limited range, although acceleration and
top speed were adequate for ordinary  city driving.  Nonetheless,
their  unpredictable range  made  these test  vehicles  highly unsatis-
factory.  At that time, no other  battery candidate  systems were avail-
able to consider as alternative power sources. Little  or no analytical
work was done to predict  vehicle properties  in advance of building
such vehicles.  As  a  consequence, interest in battery-powered vehicles
declined  at General Electric  and also at other organizations that
had shown early interest.

    In England, where  other  economic considerations are  involved,
engineering development  and  manufacture of electric  vehicles has
proceeded with considerable success.  Delivery  trucks  powered  by
lead-acid batteries have had broad acceptance in Great Britain.

    As  research  and devedopment  on fuel  cells  increased  in the
early part of this  decade, there came an awareness of the very great
desirability of this  power  source for  vehicle propulsion.   The suc-
cessful application of fuel  cells to the Gemini space flights  increased
the public interest  in  the fuel cell.  Nonetheless,  the  questions  of
cost, life, simplicity, and reliability of fuel cells have precluded their
use in vehicles during the next  few  years  on a  large commercial
scale.

    Within the past  2 years the development (to the point of feasi-
bility demonstration)  of   the  zinc-air battery,  the sodium-sulfur
battery,  and  the  other existing high-energy-content  systems has
established a new technological base for a variety  of concepts of an
electric-powered vehicle. Additionally, the widespread concern over
pollution  of  the air by gasoline-powered internal combustion en-
gine  systems   has  considerably increased  the  interest  in electric
vehicles.
OSTHOFF                                                      51

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    It is natural that analyses of vehicle systems at General Electric
involved the transportation, battery, and systems competence of the
Company.  The analyses presented here are based on studies of the
zinc-air  battery,  because a large  amount  of  background informa-
tion  existed at General Electric.  The  techniques  are applicable  to
any battery system, however, provided the investigators have suffi-
cient technical information concerning the battery.

    For  initial  consideration, Figure  1  shows the forces required  to
accelerate a 2-ton vehicle as a function of its speed.  The linear por-
tion just below 1,200 pounds of  force is established by an initial ac-
celeration requirement (in this  case,  9  mph per second)  and the
current  limit for the two direct-current traction  motors that were
assumed to  power the vehicle. Also plotted in Figure 1 is the drag
force. The  accelerating force is chosen so that it crosses the drag
force  curve at 80 mph. The so-called balancing speed of 80 mph is
chosen so  that some  acceleration will be available at the  design
cruising speed of 50 mph.
   1,200
   1,000
     800
 o
     600
     400
     200
CURRENT
  LIMIT
                         -CONSTANT ACCELERATION
                   \
                                                  CRUISE  SPEED
                              40          60

                                SPEED, mph
                                            80
100
Figure  1.   Acceleration force  vs.  speed for  2-ton vehicle.

    In Figure 2, the information of Figure 1 is replotted as power
against speed. About 50 kilowatts of power is required to reach the
balancing speed of 80 mph.  To proceed further in this analysis, let
52
                               Potential  Battery  Systems

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us examine the data of Figure 3.  At the top is plotted the accelera-
tion  to  50 mph,  followed by  a period of constant (level-terrain)
cruising at 50 mph, and then by braking at a constant rate.  Braking
deceleration at 5  mph per second  was assumed, but the actual value
is  not  important to the  analysis.  The  middle section  of Figure 3
represents the motor current divided into both armature and field
currents,  assumed to be  controlled separately.  In this scheme the
armature  current remains constant  throughout the acceleration and
then drops to that  current level  required to maintain  the  constant
speed.  On the other  hand, the field current is  constant through the
constant initial acceleration  period, then  drops until the  constant-
speed portion of the cycle is reached, and  then increases slightly for
the constant-speed part of the mission.  In the analysis no regenera-
tive  braking  was assumed, and hence the  current in the two motors
in the  vehicle will drop  to zero  when  braking commences. In the
lower section of Figure  3, the power  delivered by each motor  is
shown  through the cycle.  The top power  level does not necessarily
represent  motor  sizes.  Traction  motors  can  withstand  prolonged
periods  of overload.  The sizing of the motors requires  sophisticated
engineering judgments that need not be discussed here.
    100
 o
 CM
 ro
 CTl
 CD
 cc
 LJ

 o
 CL
     40
20
                             40          60

                               SPEED, mph
                                                80
100
Figure 2.   Acceleration  power vs. speed for 2-ton vehicle.

    Mathematical  models  were  established  for  these  types  of
vehicles based  upon the considerations just discussed, and computer
programs  were established.  For a typical  analysis,  we selected a
2-ton  vehicle  with a  1,000-pound  zinc-air battery as its  power
OSTHOFF
                                                                53

-------
source. Some properties of the battery must be known to complete
the  analysis.  These data  include  polarization curves,  power-rate
data, and voltage cut-off level.
Figure 3.
              O.
              E
              o.
              co
              Q.
              E
              LU
              tr
              ce
              Z)
              o
              o
              D-
ou
40
20
0
60
40
20
0
60 '
40
20
0

/
/


~\


/
50 mph








AF

vl
"53.2 hp
I

1




25







WATUF

FIELD


.8 hp


\




iE








\
\




|



                         20
                 40     60
                  TIME, sec
80    100
Motor  current  and  power requirements for  a
          specified  cycle.
    The analytical techniques are  illustrated in  Figures  4 and  5.
Figure 4 shows an acceleration to 50 mph, followed by  immediate
braking; in Figure 5  the acceleration is followed by  a period  of
constant-speed level  driving  and then  by braking.  The  constant-
speed range value may be conveniently varied (a geometric progres-
sion is convenient in computer programming). For all of  these runs
the initial constant acceleration rate, A0, is 9 mph per second. Table
1 summarizes  the typical vehicle properties  that were  commonly
employed, the input data, and computed  results  for the vehicles.

    Of greater significance for the battery problems are the data  in
Table 2. In this table the miles  per cycle, that is,  the distance  as
represented by the ordinate  for  the cycles of Figures 4 and 5  are
54
                                        Potential  Battery  Systems

-------
.c
Q.
E
LU
>
VELOCITY, 50 mph
      ACCELERATION = 9 mph/sec
                                  BRAKING AT 5 mph/sec
                       RANGE, miles

Figure 4.   Acceleration of a 2-ton  vehicle  with  a 1,000-
   Ib  zinc-air  battery  to 50  mph followed  by braking.
 o
 o
                   CONSTANT SPEED
                                                 BRAKING AT
                                                 5 mph/sec
       ACCELERATION = 9 mph/sec
                        RANGE, miles

Figure 5.   Acceleration of a 2-ton vehicle with  a 1,000-
Ib zinc-air  battery to 50  mph followed by constant speed
                driving and  then braking.
OSTHOFF
                                                         55

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               Table  1.  TYPICAL VEHICLE  PROPERTIES
  Program constants
      Balancing speed on level load, mph                       80
      Retardation (braking rate), mph/sec                        5

  Input Parameters
      Gross weight of car, tons                                  2
      Initial acceleration, mph/sec                              9
      Weight of Zn-air battery, Ib                             1000
      Cruising speed, mph                                    50
      Propulsion system  potential, volts                         72

  Computed Results
      Max. power/motor at wheel rim, hp                       26.6
      Specific load at full power, w/lb                         49.6
      Speed to reach full power, mph                          11.2
      Acceleration on reaching  full power,  mph/sec             8.98
      Current drain at full power, amp                         689
      Weight of control,  Ib                                    44
      Volume of control, in.3                                 1096
      Acceleration on reaching  cruise speed, mph/sec            1.4
      Power/motor to maintain  cruise speed, hp                8.45
      Current drain at cruise speed, amp                      218.7
      Specific load at cruise speed, w/lb                      15.7

tabulated, as is the average  speed,  the  range attainable  for  that
particular cycle,  and  the computed  weight of  motors  and  gears.
Note  that as the  number of  miles per cycle increases the range at-
tainable with the fixed weight of batteries also increases.

    Since the  power  requirements of the  motors  are  accurately
known  as the  vehicle  is accelerated and run at the top speed, from
the computer   program results  one   can  calculate the  amount  of
energy  required for any specific mission within the framework de-
scribed.   One can also obtain the  fraction  of  total battery energy
(or  capacity)   required for each  accelerate/brake  or  accelerate/
cruise brake situation. These energy  requirements as fractions  of
battery capacity for a given  distance are easily summed to synthesize
range values for  any mission. Obviously,  for a given size,  the mis-
sions  that involve more stops and  starts  give  shorter  range  values
than  do those  missions in  which most  of the total distance traveled
is at  the  cruising speed. The utility of such a system of  calculations
is that  one can calculate  vehicle properties  in  terms of range for a
desired mission, rather than for average missions, which are generally
unrealistic.
56                                        Potential Battery Systems

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 Table  2.  SAMPLE VEHICLE PROPERTIES FROM COMPUTER PROGRAM
Miles
per cycle
0.21
0.25
0.32
0.4
0.5
0.63
0.8
1
1.6
2
2.5
4
5
10
16
20
25
40
50
Avg speed,
mph
29
32
34
37
39
40
42
43
45
46
47
48
48
49
49
49
49
49
49
Range,
miles
67
77
91
105
120
135
151
166
193
205
215
232
239
252
258
260
262
264
265
Weight of gears and
motors, Ib"

436
417
400
383
366
350
335
308
297
287
270
264
249
243
241
239
237
236
     ° This weight is for continuous duty at the specified duty cycle for
      a direct-current, two-motor traction system.

    The effect of top speed  on range is illustrated in Figure 6.  The
ranges for 50-mph and 70-mph cruise speeds are given as a function
of miles per cycle. Other calculations show that the range  is further
decreased by  increased  cruising speed  as the  vehicle  weight is in-
creased. This  appears to be the  case  even if the total weight  of
batteries is  proportionately  increased.

    The properties of the zinc-air cell systems of most interest in this
analysis are represented graphically  in Figure 7, in which are plotte'd
both the polarization curve for  a General Electric zinc-air battery
and the energy content  curve for  the same battery.

    These  properties  may  be combined  as illustrated  in  Figure 8,
in which the  energy content in  watt-hours  per pound is plotted
against  the power density expressed as watts per pound.  The portions
of the curve of interest  for acceleration power and for range energy
are indicated.   Since a combination of these properties is clearly re-
quired  for  vehicle propulsion,  a  hybrid  power-source system  is
suggested.  Because  high  energy  content and high  power density
generally are  not compatible  in  battery systems,  a dual  battery
system  may be required. These properties are illustrated  in  Figure
9, in which current is plotted as a positive quantity in  both  directions
OSTHOFF                                                       57

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   300
.2  200
'E
   100
         ACCELERATION = 9 mph/sec
        	I    I    i	I
                                            50-mph CRUISE
                                                i-mph CRUISE
I
     0.2      0.5  0.8 1.2    2       5     10

                        DISTANCE OF  RUN, miles
       20
50
  Figure 6.   Variation of  range  of  a 2-ton  vehicle  with a
      1,000-lb  zinc-air battery over various run  (miles
                       per  cycle)  ranges.
                                                            125
                                                            100
                                                                a
                                                                oc.
                                                                UJ
           50       100      150        200

                     CURRENT, amp/1,000 cm"
      250
300
    Figure  7.   Polarization curve and energy  content  of
                         zinc-air  cell.
  58
                                       Potential Battery Systems

-------
from the voltage axis for  a  high-energy-content battery  and for a
high-power-density battery.

    In such a system the  high-energy-content power source could
be a battery or a fuel cell,  and the other power source could  be any
battery  (or other system of  high power capability)  capable  of de-
livering high currents to supply acceleration power. The high-energy
power sources can then be  used to recharge the high-current  (high-
power-density)  source  at  the  stop  condition  if the  latter  power
source  is a battery.  This will be done at relatively high efficiency
because of the operation  of the high-energy-content system near the
open-circuit voltage.
                       POWER DENSITY, w/lb
  Figure  8.    Watt-hours  per pound vs.  watts  per  pound
                    for  zinc-air  batteries.
    In summary,  a computer program has been established with
which  the properties  of  electric  vehicles can  be estimated.  Pre-
liminary studies based on zinc-air  battery systems have  been  made
in which the vehicle  range  for any mission  can be calculated. The
utility  of  hybrid battery  systems or battery and  fuel cell  systems
has been shown.
OSTHOFF                                                     59

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                       VOLTS (E)
I                              REGION FOR HIGH-POWER-DENSITY
                                   BATTERY RECHARGING
    REGION OF ENERGY   /
   FOR EXTENDED RANGE /
                I  I   I   I
           CURRENT OF
     HIGH-ENERGY-CONTENT
           BATTERY, amp
    CURRENT OF
HIGH-POWER-DENSITY
    BATTERY, amp
Figure  9.   Two-battery  hybrid system  polarization  curves.
                    ACKNOWLEDGEMENT
    This paper is based upon the work of Mr. C. E. Kent, Dr. J. L.
Manganaro, and  Dr. H. A. Christopher of the General Electric Re-
search  and Development  Center  in Schenectady, N.Y.,  and on the
work of Mr. J. E. Wallace and Mr. H.  G. Moore of General Electric's
Transportation Systems Division  in Erie,  Pa. The  efforts  of  these
gentlemen are gratefully  acknowledged.
60
      Potential Battery Systems

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      BATTERY-POWERED  ELECTRIC VEHICLES
                     D. Thomas Ferrell, Jr.,
                      and Alvin J. Salkind

            The Electric Storage  Battery Company
                        Philadelphia  Pa.


    The Electric Storage Battery Company (ESB) has gained years
of practical experience with various types of battery-powered vehicles
now operating  and now is engaged  in research and development on
new power sources for electric vehicles.

    We  have supplied  power systems  for  three  types  of electric
vehicles  now in operation. In the first category are battery-powered
fork-lift trucks and golf carts. About 100,000 to 200,000 units of each
type are in use in the United States, an indication that quiet, clean
operation combined  with low maintenance and low  operating  costs
makes battery power  attractive  to  many users.  Battery-powered
vehicles  have  proved  themselves in many other applications in-
cluding mining equipment and in-plant utility vehicles. The principal
battery used  for  these types  of applications is  lead-acid.

    ESB increased by 18 percent the energy output per unit volume
of its  Exide-Ironclad  cell construction with  improvements intro-
duced between  1952 and 1954; we further increased the energy output
by another 43 percent with improvements introduced between  1954
and  1966.  At present, this long-life, deep-cycle type of lead-acid
battery delivers  approximately  1.4  watt-hours per  cubic  inch at
the 6-hour rate.

    The second  category of  electric vehicles  for which ESB  can
provide operating data is the delivery  truck.  Vehicles of this  type
have  used Exide-Ironclad batteries since 1910.  Our most recent
experience is  with route trucks  manufactured by Battronic Truck
Corp.,  an ESB  affiliate.  Some of these trucks  have been in use for
more  than 3 years.  The power system  is an 84-volt  Exide-Ironclad
battery of either  425  ampere-hours  (42TSC11) or 340 ampere-hours
(42TSC9). The  smaller battery delivers approximately 11 watt-
hours per pound.

    In typical multi-stop delivery service, such as on milk or bread
routes, the present Battronic  trucks  have a loaded  range  of about
40 miles and a top speed of about 25  miles  per hour (Figure  1).  The
maximum gross weight  is 9,500  pounds,  including the load. Com-
bined load and battery weight is 5,000 pounds;  route requirements
determine the size of the battery,  which  weighs  2,000 to 3,000 pounds.
Data on these vehicles are summarized  in Table 1.
FERRELL, SALKIND                                           61

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             Battronic
           Electric Truck
         Figure  1.   Truck  powered  by an 84-volt
                   Exide-lronclad  battery.
  Table 1.  OPERATING CAPABILITIES OF A DELIVERY TRUCK POWERED
                    BY  LEAD-ACID BATTERY
Load capacity:
Gross maximum weight

Top speed on level road (loaded)
Acceleration
Hill climbing speed (10% grade)
2,000 to 3,000 pounds
(vehicle and load): 9,500
Present
25 mph
1.5 mph/sec
12 mph
Maximum range on one charge of
the battery (loaded, 8 stops per mile) 40 miles
Time required for full charge of the
battery (after complete discharge)
Type of motor
Type of controller
up to 10 hours
series traction
contractor
pounds
Presently
possible
35 to 40 mph
1.5 mph/sec
14 mph
60 miles
up to 10 hours
compound traction
solid state
62
Battery-Powered Vehicles

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 TRUCK  IN USE AT MAPLEHURST FARMS DAIRY, LINCOLN, R.I.
    Operating experience  has shown  over-all  costs  (depreciation
included) of $4.76 to  $6.00 per day for  an electric  truck, compared
with  $7.00 to $9.00 per day for a  gasoline truck on similar routes.
Thus, the possible savings are $1.00 to $4.25 per day.  Projected im-
provements in the  lead-acid batteries,  the  controller, the motor, and
the chassis are expected  to yield speeds up to  35 to 40  mph  and a
maximum loaded range of about 60 miles.  Many delivery routes and
other functions could be handled by the existing or improved trucks.
Benefits  that  would be realized are lower operating costs  and re-
duced noise and air pollution.

    The  third type of  electric vehicle for which we have operational
data is the small  personal car, such as the ESB-Exide  Electric Car
(Figure 2). This vehicle operates  with twelve  6-volt golf-cart-type
batteries (3LDT-9). which produce a total of  10.1  kilowatt-hours.
Without  sophisticated  electronic controls, aerodynamic  streamlining,
improved motors, or special tires, this vehicle has a range of  35 miles
and maximum speed of 40 mph  (Table  2).  The economy of operation
is shown in Table 3.  Projected improvements are expected to  result
in  a  maximum-load  range of  50  to  60 miles  and  a top  speed of
50  mph (Table 4).
FERRELL, SALKIND
63

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  Figure  2.   Electric  car powered  by  twelve  6-volt  golf-
                      cart-type batteries.
  Table  2.  PERFORMANCE CHARACTERISTICS OF  PRESENT  ESB-EXIDE
                           ELECTRIC CAR

             Maximum speed: 40 mph on a level road
             Range: 25 to 35 miles per battery charge
             Acceleration: from  stop to 20 mph in 3 seconds
             Hill-climbing rate:  10 percent grade at 20 mph


    Our total experience  with the three types of electric vehicles
so far discussed  is summarized  in  Figure  3.  This figure, a plot of
range versus the ratio of available power  to  total vehicle weight,
shows the  effect  of weight and  acceleration losses on the  range of
vehicles at a speed of 30 mph. Other charts at other speeds show that
at a ratio of  4 watt-hours per pound, with a vehicle traveling at 15
mph,  the range without stops would be 60 miles; at 30 mph,  50 miles;
and at 45 mph,  42 miles.  Then  range is reduced  as the number of
stops  increases. This ratio of 4 watt-hours per pound of total vehicle
weight is approximately the ratio for existing  vehicles.
64
Battery-Powered Vehicles

-------
Table  3.  ECONOMY OF OPERATION OF PRESENT ESB-EXIDE ELECTRIC CAR

     Estimated cost of operation for 5 years driving 5,000 miles per year
Electricity
Battery replacement
Licenses
Greasing
Repairs with labor
Contactor tips
Motor brushes
Total
$375
450
50
12

35
17
$939
               Estimated cost per mile:       3.50
     *The  ESB-Exide Electric Car uses 0.75 kilowatt-hour of  alternating
     current for each mile of driving. Based on a household rate of 20
     per kw-h, the cost of electricity for recharging the battery is  1.5C
     per mile.
   Table 4.   PROJECTED  PERFORMANCE  CHARACTERISTICS  OF SMALL
     "URBMOBILE"  POWERED  BY EXISTING LEAD-ACID  BATTERIES

             Maximum speed: 50 mph on a level road
             Range: 50 to 60 miles per battery charge
             Acceleration: from stop to 20 mph in 3 seconds
             Hill-climbing rate:  10 percent grade at  30  mph

    With present technology, the speed and range of electric vehicles
are limited  by the energy  available in the power source (as  shown
in Figure 3).  With the power sources  now available on a production
basis, economics pretty well limit the choice to the lead-acid battery
system  with the limitations of speed and range  indicated.
    Although ESB is continuing research  and  development  on the
lead-acid,   nickel-iron,  nickel-cadmium,   silver-zinc,  and   silver-
cadmium systems, it  is likely  that improvements in the performance
and economics of these  systems will be incremental. It appears that
large increases in range  or  speed of an electric vehicle will come only
with the introduction of a new power source  that  can be produced
cheaply enough to provide energy at about the same cost per kilowatt-
hour as  the lead-acid battery, i.e., in the range of  $50  to $100 per
kilowatt-hour  initial  cost.  A  number of other requirements  must
be considered, such as power density,  convenience  of use, start up,
and life.
    ESB  is  investigating,  in  research  and development stages,  a
number of systems that  show some  promise for application to electric
vehicles.  These  include  fuel  cells,  metal-air  cells,  non-aqueous
systems, and  cells  with organic active materials. At present, all of
these systems show some limitations for vehicle applications.
FERRELL,  SALKIND                                            65

-------
   80

   70

   GO
(/)

1  50
uj
z  40
<
   30

   20

   10

    o
                                                STOPS  PER MILE
                                                             0
                      I
                                 I
I
I
   0123         456
     RATIO OF  ENERGY  TO TOTAL WEIGHT OF LOADED  VEHICLE,  w-hr/lb


Figure 3.    Effect of vehicle weight and acceleration  loss
            on  range (30-mph  cruising speed).

    Fuel  cells are currently unattractive  in terms of cost, life,  con-
venience,  and power  density. Since  fuel cells have  received  con-
siderable  attention generally, we will  briefly,  describe the work of
ESB on other systems, with comments about their future possibilities.

    ESB has been investigating metal-air cells for more than 10 years
by several approaches involving both static and  dynamic systems.
Most  of our efforts  have been concentrated  on the  zinc-air system,
which seems to offer the best combination of characteristics.

    Our most recent zinc-air projects have been in static systems in-
corporating very thin air  electrodes with a third electrode for re-
charging  the zinc electrode.  A typical seven-cell  secondary battery
of this type is shown in Figure 4.  The  output performance, power
density as a function of current density, is shown in Figure 5, which
indicates  an average  peak power for the secondary  battery  of 88
milliwatts per square  centimeter.  This  figure also  gives  the  data
for a primary zinc-air cell  of similiar design  and shows that  even
greater output is possible  with the present secondary  design. As an
example of the progress that has been made, the lowest  curve  indi-
cates the  performance  of an  earlier cell.

    The effect of temperature on performance  is shown in  Figure  6.
These data  were obtained at close to isothermal conditions, i.e., the
battery was not  permitted  to heat up as  a result of chemical ineffi-
 66
                                         Battery-fowl-roil Voliii-Ics

-------
ciencies. Even under those very severe conditions, useable power was
obtained at low temperatures.
          Figure 4.
ESB  research  metal-air  cell.
    Figure .  shows the cycle life performance of zinc-air cells of the
present design, indicating  good performance  for over 50 cycles.  We
believe that the loss of performance  is associated with the  zinc elec-
trode.  In half-cell tests, the air electrode has given continuous per-
formance equivalent  to over  120.000  miles  at 30  mph.  Indicated
energy  density for the zinc-air system is in the range of 50  watt-
hours per pound.  Although recent discoveries show promise  for  im-
proving the cycle life of the zinc electrode, many more improvements
in  separators and  zinc  electrode reehargeabihty will be required to
make this system practical.
FERRELL. SALKIXD
                                        67

-------
  120
1100
o
^

>  80
05
Z
UJ
   60
   40
  20
                                                    PRIMARY BATTERY
                                                         l-ZAP-94
            SECONDARY  BATTERY
                 7-ZAS-266
EARLY DESIGN BATTERY
      l-ZAS-292
                50         100        150        200         250
                          CURRENT DENSITY, ma/cm2

          Figure  5.   Power Output  of  Zinc-Air Cells.

      Non-aqueous systems that use lithium or other alkali metals are
  intriguing because of the possibility of energy densities of over 100
  watt-hours per  pound.   ESB  Research has built  cells  with  lithium
  anodes that delivered more than 100  watt-hours per pound at low
  discharge rates.  Although  these systems are capable of high energy
  densities,  the low  conductivity of the  electrolytes makes the power
  densities rather  low.  Considerable improvements in rate capability
  will be required  to make these systems attractive for vehicle applica-
  tions.

      Systems that use organic compounds as active materials have in-
  trigued  battery investigators for a number of years.  Our recent in-
  vestigation of certain organic compounds indicates good  recharge-
  ability and an energy density of over  50 watt-hours per pound of
  cathode in small laboratory  cells. These systems show promise for
  high-rate rechargeable batteries, but will require more  development.
  At present, the economics are uncertain.
      Let me summarize our experiences. We believe it  is feasible to
  construct delivery and small personal electric vehicles that will elimi-
  nate  air pollution and satisfy  a need for transportation  over a range
  of approximately 50 miles. This can be done with existing  commer-
  cial batteries.  For much greater ranges,  newer power systems will
  be required.
                                          Battery-Powered Vehicles

-------
                        CELL OUTPUT, amp-hr
Figure 6.   Effect of temperature  on performance of  zinc-
            air cell  (l-ZAP-97, 4-hour  rate).
                               FINAL CYCLE
                            (APPROXIMATELY 100)
                        CELL OUTPUT, amp-hr
    Figure  7.   Typical cycling performance of zinc-air
              secondary cells (4-hour rate).
FERRELL, SALKIND
                                                        69

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    POWER SYSTEMS FOR  ELECTRIC  VEHICLES
       FOR MILITARY AND  COMMERCIAL  USE


                        Edward A. Gillis

  U. S. Army Engineer Research and Development Laboratories
                        Fort Belvoir, Va.

                       INTRODUCTION

    Many power sources  and many combinations of power sources
have been proposed as  the power plant for electric  vehicular pro-
pulsion. In  a recent report to the CTAB Panel of the  U.S.  Depart-
ment of Commerce on Electrically Propelled Vehicles,  the U. S. Army
Engineering Research  and  Development  Laboratories  (USAERDL)
reported for the U. S. Department of Defense (DOD)  on the DOD
program in  electrical propulsion. It was pointed  out that the types
and  severity of  problems  and the areas  of  emphasis for  military
vehicles were  quite divergent from those for private  vehicles,  but
that the basic  technology  being  developed would, in  most instances,
be  applicable  to all electric propulsion programs.
    The following  are  some  of  the  conclusions  presented  in  that
report1
1.  An all-battery power plant  is not feasible for military  vehicles
    because  the charging facilities cannot be provisioned in a  military
    environment.
2.  The most promising power plants were gas turbines,  fuel cells,
    and hybrid systems. State of the art and improvement potentials
    were considered when determining the  applicability  of  these
    power plants.
3.  The prime mover portion of a hybrid power plant where batteries
    are  a part of the  hybrid system  should  have the peak power
    capability. For  operational  characteristics required by  military
    vehicles, it appears that  dependence  upon energy storage  for
    peak power  is not practical whereas  it may be for commercial
    or private vehicles.
4.  The three  primary  hybrid systems that can  be  considered  are
    (1)  gas  turbine and fuel cell, (2) gas turbine and battery, and
    (3)  fuel cell and battery.
    Battery  and  fuel cell hybrids have been proposed and prototypes
constructed  for continuous duty  power plants to  meet the following
objectives:  (1) relatively low weight,  (2) fuel economy, (3) silence,
and (4) low  pollution.
    In the   analysis of  this hybrid,  however, the most  important
considerations  are weight  and fuel consumption.  For instance, if
weight alone were  the  only consideration, turboalternators in  the
capacity of  prime movers or peaking devices  can be  installed  at
GILLIS                                                       71

-------
2.5  to 4.0 pounds per  kilowatt. Batteries or fuel cells  either alone
or hybrided cannot approach this weight, but in noise or pollution
or part load fuel consumption, the turboalternator may fail to meet
requirements.  If fuel  consumption  alone is  important,  a fuel eel]
is the most efficient energy conversion device available, but heavy.
Because  of the  interest  in air pollution  reduction, the gas turbine
is deleted from  this discussion, although  for military purposes the
gas turbine or gas  turbine hybrids  look  extremely attractive. This
discussion, therefore,  will be concerned  with  the  two  remaining
power sources:  (1) fuel cells and (2) fuel cell  and battery hybrids.

              FUEL  CELL SYSTEM ANALYSIS

    There are nearly  as many different types  of fuel  cell systems
as batteries.  In  fact, a fuel cell system itself may be a hybrid with
more  than one fuel conditioner or with hydrogen storage capabilities
for peak  power demands. To meet  military requirements the fuel
cell systems  must  use  a logistically available  liquid  hydrocarbon
fuel such as  Compression  Ignition—Turbine Engine  (CITE)  fuel
or JP-4.  This fuel is  converted  to  a hydrogen  rich stream for use
in the fuel  cell. Ambient  air is the oxident  in all  cases.
    Fuel cell systems operating on logistic fuels have been researched
at USAERDL  for more than a decade, and continue to be the most
attractive energy conversion device for future  general  purpose sta-
tionary  power plant use. A  fuel cell system that is attractive  for
ground  power may not, however, be attractive for  vehicular use,
since  it would have been optimized for  silence,  fuel economy, and
ruggedness,  whereas for vehicular  use  it  must  be optimized  for
weight  as well.  As an analytical  tool to aid  in the  optimization
of fuel  cell  and hybrid systems,  a  Figure of Merit equal  to:

             _,      ,,   x   Power  plant weight  (Ib)
             Power (kw)	—	;—-	
                        '           100  Ib/kw
                    Fuel consumption  (kw/hr)

was used as measure of efficiency  to  indicate the power available
to  move  the  vehicle  and  payload,  minus  the  power required  to
move the  power  plant.  The  100-pounds-per-kilowatt  constant  is
representative  of the  power-to-weight  ratio  of  military vehicles
now being designed.
    The type of hydrocarbon-air fuel  cell system  with  the highest
Figure  of  Merit at the 40- to  100-kilowatt  power  level  required
by  most  military  vehicles was  an acid electrolyte, hydrogen-air
fuel cell.  Three types  of fuel converters to change  the liquid fuel
to hydrogen were  analyzed:
1.  A steam reformer with the unpurified reformate  passed directly
    to  the fuel  cell.
2.  A  partial oxidation unit  with  product gas  passed  directly  to
    the cell.
72                    Power for  Military and Commercial Vehicles

-------
3.  A steam reformer—partial oxidizer combination with the partial
   oxidizer used for peak loads and transient operation.  Schematics
   for each of these systems are shown in  Figure 1. The weights
   for 40-kilowatt output, with modest state of the art improvements
   are shown in Figure 2 as a  function of the fuel  cell current
   density.  (No  frame or structural weight was charged to the
   power plant, however,  since it was assumed the fuel cell would
   be  built into the vehicle  either using  or contributing to  its
   structural frame). Also shown  in Figure 2 is the  specific fuel
   consumption for  the power  plants  with a spent fuel exhaust
   containing  10  percent hydrogen by  volume.
 FUEL-
  AIR-
PARTIA
OXIDIZE
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                                    CONDENSER
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         Figure 1.   Fuel  cell system  schematics
GILLIS
                                                              73

-------
I
C3
O
Q.
   2,500
   2,000
   1,500
   1,000
    500
              O  REFORMER SYSTEM

              D  PARTIAL  OXIDIZER SYSTEM
              O  REFORMER PLUS PARTIAL  OXIDIZER
                                         1.0

                                         0.8  3
                                         0.6
                                            o~
                                            u_
                                         0.4 <"

                                         0.2
                         50               100
                          CURRENT DENSITY, amp/ft2
                                   150
    Figure  2.   Forty-kilowatt  indirect  fuel cell  power  plant
            weights  and specific  fuel  consumptions.
       It can be see in Figure 2  that the  reformer system  is nearly
   twice the  weight of the partial oxidation system, but  uses  only
   three-quarters of the fuel.  When the Figure of Merit is  applied to
   the systems as shown in Figure 3, the reformer and partial oxidizer
   systems are nearly equal, 0.2.   By comparison, the Figure of Merit
   for the 94-horsepower spark  ignition engine of  an M37 truck  is
   0.095 at maximum power.  For most commercial or private vehicles,
   100  pounds per  kilowatt will  not  give  adequate  performance.  If
   the weight-to-power ratio  of  modern compact automobile  (25 to
   40 Ib/kw) is substituted, the partial  oxidizer and  fuel cell  combi-
   nation is  far superior to the other two  systems.

       In Figure 3, the systems all show  a maximum at 85  amperes
   per  square foot, but  the  fuel  cell at  this current density  is  far
   from its peak power, and additional ancillary devices can be installed
   74
Power for  Military and  Commercial Vehicles

-------
to allow  the cell to operate continuously at peak power.  Figure 4
shows the Figure of Merit over the full range of power, with average
or most  economical  power  still  at  40 kilowatts, but  peak power
between  64 and 70 kilowatts.  For  the  partial oxidation system,
the maximum specific  power density of 66  watts per pound occurs
close to the peak power point.
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              ©  REFORMER SYSTEM
              D  PARTIAL OXIDIZER SYSTEM

              O  REFORMER PLUS PARTIAL OXIDIZER
                        50              100
                          CURRENT DENSITY,  amp/ft2
                                           150
 Figure 3.
Forty-kilowatt  fuel  cell  power plant  figure of
  merit versus  current  density.
                 POWER SYSTEM ANALYSIS

    Two  battery  systems were analyzed  for  use  in  the hybrid
system. The first is an idealized  100-watt-hour-per-pound battery
with unlimited charge or  discharge  rates and a 75 percent wattage
efficiency  over one cycle.  This represents  the  goals for  vehicular
batteries needed for  the  hybrid  system calculations.   The second
battery analyzed is an  idealized metal-air  type, limited on charge
and discharge rates by  air electrode performance only  and limited
on total charge  by a maximum active metal weight.  This battery
discharges  between 1.27 and 1.0 volt and charges  between  1.9 and
GILLIS
                                                              75

-------
  2.23  volts,  depending on  ampere  rate.  Other goals for vehicular
  batteries that are important but do not enter into the calculations are
  (1) charge rates equal to discharge rates,  (2) cycle life of over 10,000
  cycles, (3)  minimum of  50 percent of energy delivered at 80 percent
  of open-circuit voltage or higher,  (4)  self-discharge of less than 5
  percent per day, and (5) 18-month activated life.
o:
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       0.3
       0.2
       0.1
©  REFORMER SYSTEM

D  PARTIAL  OXIDATON SYSTEM

O  REFORMER PLUS PARTIAL OXIDIZER
                      40
              80

              % POWER
120
                                                              160









16 32 48 64
POWER, kw
      Figure  4.   Fuel  cell  power  plant  figure  of  merit
           for  10  to 170  percent of  rated  power.
                  HYBRID SYSTEM ANALYSIS

      A fixed-weight  power plant was used for  the  hybrid analysis
  with the battery comprising  0 to 100 percent of the weight. Figure
  5  shows the peak power  per pound of  power plant capability as a
  function of  time for  various  fuel  cell and  battery  combinations
  with the ideal  100-watt-hour-per-pound  battery.  Also plotted  is
  76
 Power for Military and Commercial Vehicles

-------
the recharge time of the battery  when the power plant is providing
less than  peak power.  For example,  200 watts per  pound can  be
provided for 4 minutes  by a 10 percent battery hybrid system. The
recharge time with  no  net power out (all  of the fuel cell power
recharging the battery)  is about  14 minutes.  But if  40 watts con-
tinuous power is used by the vehicle (i.e. cruise power), it requires
40 minutes to recharge  the battery, since there  is little  excess fuel
cell power for charging.  If the  battery proportion increases  to  50
percent, 200 watts per  pound  is  available for a longer time,  about
18  minutes,  but  since   the fuel cell  is much smaller, 33  watts
capability, the recharge time at idle is over  2  hours and the system
cannot sustain 40 watts per pound  continuously.
 ;
of
O
Q.
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Q.
                                       RECHARGE TIME WITH
                                  CONTINUOUS  POWER OUTPUT OF
                                        Q NONE
                                        <3> 20 watts

                                    °0   A 40 watts
                                    10"
                               TIME, seconds
10*
  Figure 5.   Ideal  battery  and fuel  cell  hybrid system
     peak  power,  discharge  time,  and  recharge  time.

    Figure  6 shows much the same peak-power-versus-time  capa-
bility for the  metal-air  battery, but anode and  cathode limitations
are apparent.  Figure  7 shows the ratio of charge  to discharge
times as  a  function of  continuous  power  required in watts  per
pound.

    The minimum-weight  hybrid system  was  calculated for  two
types of duty cycles. All of the duty  cycles assume a  peak power
period,  a continuous power period, and  an  idle  period, v> ith  the
battery  fully recharged  at the end of the cycle. Duty cycles  1  and
2 are  short-term  "milk-route" types   of cycles,  characterized by
short  peak power times.  Duty  cycle number  3 is a  military battle-
GILLIS
                                                               77

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field power profile recently reported, and duty cycle  number 4 is
a USAERDL estimate of an 8-hour military mission based on proving
ground  tests on the  fuel-cell-powered M37 truck. Table 1 shows
the characteristics  of the duty cycles and the operating characteristics
of a hybrid system containing the idealized 100-watt-hour-per-pound
battery. The hybrids listed under each duty cycle have the maximum
performance possible under the  peak-to-average-power ratios and
time ratios dictated by the duty  cycles. As would be expected, the
"milk-route" duty cycles, 1 and 2, have superior power plant char-
acteristics, both in  peak power density and in continuous power capa-
bilities.  The minimum-weight hybrid for the military  vehicle  duty
cycles has much poorer performance,  especially  in continuous power
capability,  which  may be  considered  as  the  reserve or emergency
power. Figure 8 shows the horsepower requirements for three classes
of military vehicles, with the peak power requirement occurring over
a wide range of conditions. It is not inconceivable that the peak power
       	    100%  FUEL CELL
      10"
              103
         TIME, seconds
                                                                 104
    Figure  6.   Metal-air  fuel cell  hybrid  system  peak
               power versus peak  power  time.
78
Power for  Military and  Commercial  Vehicles

-------
may be demanded for more than  1  hour continuously, especially
since  these are  rough terrain  vehicles with  up  to  a 60 percent
grade requirement.  If  the  power plant is  designed  for duty  cycle
number 3, once  the  peak power demand has exceeded 1.2 hours,
or if a series  of  short peak  power bursts total this time without a
substantial idle time, the  available power drops to about 20 percent
of peak.  This is not sufficient  power to maintain  convoy speeds
on level ground, much less  on  3 percent grades.
               10
     20         30

CONTINUOUS POWER, w/lb
                                                 40
    Figure  7.   Metal-air  battery and fuel  cell  hybrid
 charge-to-discharge-time ratio  versus  continuous  power
GILLIS
                                        79

-------
 Table  1.  DUTY CYCLES AND OPERATING CHARACTERISTICS  OF  HYBRID
          SYSTEM CONTAINING  IDEALIZED BATTERY (battery,  100  w-hr/lb)

    Hybrid power plants                       Duty cycle number
      characteristics                    1       2        3       -b
Duty cycle characteristics
Peak power (Pt)
Peak power time (tp)
Average power (Pa)
Average power time (ta)
Idle time (ti)
Hybrid operating characteristics
Peak power density, w/lb
Continuous power, as % Pt
Continuous power, w/lb
Figure of Merit

1
Vz min
0.5 Pt
3 min
3 min

187
35
65
0.178

1
Vz min.
0.25 Pt
3 min
3 min

300
22
65
0.185

1
1.2 hr
0.2 Pt
15.6 hr
7.2 hr

80
19
15.5
0.176

1
1 hr
0.4 Pt
4 hr
3 hr

85
35
30
0.179
     Table 2 shows the same duty cycles and power plant perform-
ance as  above.  However, it augments the first in that the hybrid
characteristics have been calculated for  both  types of batteries, and
a  comparison of an all-fuel-cell  power  plant with a hybrid power
plant has been added. The specific fuel consumptions and Figures of
Merit  shown are better for the  fuel  cell power  plants  than the
hybrids  in all cases.  The higher fuel consumption for hybrid sys-
tems and its consequent effect on  the Figure of  Merit due to the
inefficiency  of the battery  in  that  from 35  to  100  percent more
energy has to be put into  a  battery than can  be taken out.  Also, in
a  hybrid system a  relatively small fuel cell works  at full power
continuously, either  helping power  the  vehicle  or  charging  the
battery.  Little  advantage  can  be  taken  of  the fuel  cell's ability
to operate with higher efficiency  at  part load.

     For  duty cycles 1 and 2,  substantial  savings of power plant
weight are  possible with the hybrid  systems.   The  all-fuel-cell
power plant  weighs from 2 to 4.5 times  the hybrid systems weight.
For  military duty cycles this weight savings  is not substantial.  An
increase  of less than  25 percent  in  power plant weight  for either
duty cycle 3 or 4 and all fuel  cell power, the vehicle  will not  be
restricted by peak  power  times.  If the  weight  of  fuel required
for the  mission  is added,  the  weight  differential  drops to under
12 percent. The continuous peak power capability seems well worth
the extra weight.

                          SUMMARY

    Battery and fuel cell hybrid  power plants do not offer appreciable
savings in  weight over fuel  cell  power  plants for use in military
vehicles.  All-fuel-cell power plants offer the advantages  of much
80
                      Power for Military and  Commercial Vehicles

-------
  lower fuel consumption, and more important, continuous peak power
  capability. Conversely, fuel cell and battery hybrid systems do offer
  the potential of a lightweight power plant for electrically powered
  commercial vehicles.  For the  military vehicle  that may require
  extended periods  of  operation at  high  power  levels and where
  noise or air  pollution are not  handicaps,  hybrid systems utilizing
  engines as well as electrochemical power plants may be more suitable.
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          GROSS  VEHICLE  WEIGHT
          16,000  Ib
           8,000 Ib
           4,000  Ib
         UJ
         Q
         Q:
         o
                        I
I
I
A
                                  T
                                  I
                                                           UJ
                                                           Q
                                             I
              10        20       30         40
                          VEHICLE SPEED, mph
                                                      50
                             60
      Figure 8.   Vehicle horsepower  requirements  as  a
                 function  of speed  and slope.
  GILLIS
                             81

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   Table 2.   COMPARISON  OF  ALL-FUEL-CELL  POWER  PLANT AND  HYBRID
             POWER PLANT
Hybrid power plants
characteristics
Ideal battery (100 w-hr/lb)
Duty Cycle Number
1234
Advanced metal-air battery
(107 w-hr/lb at 1-hr rate)
Duty Cycle Number
1234
 Duty cycle characteristics
   Peak power, (Pt)
   Peak power time,  (tp)
   Average  Power, (Pa)
   Average  power time, (ta)
   Idle time, (ti)
  1111
1/2 mln  1/2 min   1.2 hr  1 hr
 0.5 Pt 0.25 Pt  0.2 Pt 0.4 Pt
 3 min   3 min  15.6 hr  4 hr
 3 min   3 min   7.2 hr  3 hr
  1111
1/2 min  1/2 min   1.2 hr   1 hr
 0.5 Pt 0.25 Pt   0.2 Pt  0.4 Pt
 3 min   3 min   15.6 hr  4 hr
 3 min   3 min   7.2 hr   3 hr
 Hybrid operating characteristics
   Peak power density, w/lb               187    300.    80     85    133     162     83     80
   Continuous power, as % Pt             35     22     19     35     36    24.5     22     43
   Continuous power, w/lb                65     65    15.5    30     48     40     18     34.5
   Battery only time at Pa              1.5 min   1 min  4.8 hr  1.6 hr 1.2 min  1.8 min  4.7 hr  1.7 hr
   Specific fuel consumption,  Ib/kw-h     0.874  0.860   0.820   0.812  0.914   0.982   0.813   0.840
   Figue of Merit                      0.178  0.185   0.176   0.179  0.166   0.157   0.178   0.171

 All-fuel-cell power plant
   Relative wt, fuel cell/hybrid
   Specific fuel consumption,  Ib/kw-h
   Figure of merit
 2.76    4.5    1.19    1.27   1.99
 0.625   0.622   0.534   0.640  0.625
 0.224   0.225   0.262   0.218  0.224
        2.43    1.24    1.19
        0.622   0.534   0.640
        0.225   0.262   0.218
82
                              Power for Military and Commercial Vehicles

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            FUEL  CELL —BATTERY  POWER
            SOURCES FOR  ELECTRIC  CARS


                       Galen R. Frysinger

         U. S. Army Electronic Components Laboratory
                      Fort Monmouth, N. J.

    In recent  approaches to  the electric automobile,  attempts have
been made to  redesign vehicles to make them  more  appropriate  to
electric-drive  concepts;  to  rethink the  way in  which  people use
vehicles so that an electric car may fit into a new type of transpor-
tation mode. All of  the thinking is dominated  by the fact  that the
electrical  automobile cannot have all  the versatility,  range,  speed,
and other characteristics associated with present  internal-combustion-
driven vehicles.  These  considerations  come back to basic limitations
of the  battery,  which must contain  the  stored  electrical  energy
required for the  complete duty period.

                     BATTERY PROBLEM

    The basic limitations  a  power source places  on  a vehicle are
(1) the limited range or the number of miles the vehicle  can travel
without refueling, (2)  the  acceleration characteristics of the vehicle,
and  (3) the  percentage of time the vehicle  is  available  for  its
prescribed duty.  For  the  conventional internal combustion engine
the range  depends  upon the amount of gasoline  carried,  which  is
commonly  adequate for about  300  miles, and the acceleration  is
dependent  upon  the design horsepower of  the engine,  which  in
most American cars is adequate  to allow high-speed  passing.  The
off-duty time  for a  conventional petroleum refueled vehicle  is the
5- to 10-minute  period required every  250 to 300  miles  to  refuel
the gasoline tank.

    For  a vehicle   battery,  the  range  is limited  by the  energy
density  (kw-h/lb)   of  the battery;  the  acceleration  is limited  by
the power  density (maximum kw) of the battery; and the  off-duty
time is, of  course,  the time required to recharge the battery for
the next discharge period.  Conventional batteries that have been
used,  such  as the lead-acid, nickel-iron,  or  nickel-cadmium,  and
in some experimental  cases  silver-zinc, all have distinct limitations
in these three areas  and  also  have  the additional  limitation  of
higher cost than  those presently associated with the  power  source
in a conventional vehicle.

    Several new battery  systems under investigation would  sig-
nificantly  increase the energy  density  of  future  vehicle  batteries.
Based on  the  recent development of highly  advanced fuel cell  air
cathodes, new zinc-air  systems  have  become possible  with conven-
tional alkaline electrolytes.  They are,  however,  limited  to about
80 watt-hours per pound.  There are some difficulties in achieving
FRYSINGER                                                   83

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very  high rates without  drastically  affecting  the  energy  density,
and long life recharge capability is still highly uncertain.  Investi-
gators have  explored  two types of  nonaqueous  electrolytes.  The
first consists  of salts  dissolved in organic  electrolytes  used  with
alkali  metal  anodes and  halogen  cathode materials.  These  have
been  extensively  investigated by  National Aeronautics  and Space
Administration  for  satellite  communication batteries, but do not
appear  attractive for vehicle propulsion  because of the very low
rates  that are obtained and the many  problems involved  with the
dissipation of heat  generated by the inefficiency of the reactions.
The second  major  category  of  non-aqueous systems  includes the
molten  electrode  or molten  electrolyte types.  The sodium-sulfur
battery announced to the public by Ford Motor Company  only last
month is an example  of this type  of  cell.  The lithium-chlorine
batteries  being  developed  by General Motors use a molten lithium
anode, lithium  chloride electrolyte, and  a porous  carbon  cathode
in which chlorine gas is either evolved during recharge or consumed
during the discharge.  These systems based on sodium  or lithium
anodes  and  sulfur-, chlorine-,  or  possible  fluorine-based  cathode
materials have  theoretical energy  densities  sufficiently  high  that
practical  devices in the range of 150 to 200 watt-hours  per pound
are within the realm of feasibility.  Together with  Ford and General
Motors, several  other investigators are trying to tackle the problems
associated with  the  containment of  these reactive  materials in  con-
figurations that can make  them attractive as  high-power-density,
high-energy-density batteries. The concept of using a  molten elec-
trolyte battery  operating at  elevated temperatures  introduces  new
types of  operational patterns for  vehicle  propulsion.  The whole
question of start up and how one  maintains  the  system in molten
condition ready for  operation  over extended  periods  must be
considered.

    If one requires equivalent performance from any new electrically
propelled vehicle, as is now obtained from conventional vehicles using
internal  combustion  engines, the  present  performance parameters
must be determined. The conventional power plant weight associated
with typical  vehicles is shown in column 2  of Table 1.

This includes just the engine weight. The weight of the transmission
and the  power train  for  this  calculation were  assumed to be
equivalent to that required in the future  for  the  electrical drive
train  system. Column  3 shows  the  fuel weight  normally carried
in these  vehicles immediately after refueling.   The  total weight  of
the power plant, the fuel,  and the tankage is shown in column 4.
The amount  of  energy  that can  be generated from this fuel in the
internal  combustion  engine converter is, of course, a function  of
the conversion  and utilization efficiency.  Based on detailed calcu-
lations,  the specific fuel consumption  for these vehicles during their
normal duty cycle,  which includes  periods of idle, traveling across
country,  on secondary  roads,  on highways, and  at peak power, has
been calculated  in terms of pounds of petroleum fuel per kilowatt-
84
                               Fuel  Cell —Battery Power Sources

-------
     Table 1.  WEIGHT  AND  FUEL CONSUMPTION SUMMARY  FOR
       CONVENTIONAL INTERNAL COMBUSTION POWER  PLANTS


Vehicle
Type
% ton
% ton
2V2 ton
5 ton
10 ton
Tank
Conven-
tional
power-
plant
weight,
Ib
418
590
1,550
1,675
2,200
4,870

Fuel
weight,
Ib
108
146
305
476
1,036
2,741
Total wt
(PP, fuel,
and tank),
Ib
555
773
1,932
2,270
3,447
8,068

Duty cycle
SFC,»
Ib/kw-h
2.10(11%)
1.53(12%)
1.02(18%)
0.97(19%)
1.02 (18%)
1.41(13%)


kw-h
Equiv
51
95
299
490
1,015
1,940



w-hr/lb
97
129
161
229
314
254
a Specific fuel consumption.

hour and is shown in column 5. From these data the kilowatt-hour
equivalent  of the fuel, and the  watt-hours per pound of total engine
and  fuel can be  readily  calculated.  This  represents  the  energy
density  of  the  power source  in conventional  vehicles.  The watt-
hours per pound range from approximately 100 for the one-quarter-
ton truck to over 300 for the 10-ton cargo carrier.  From this com-
parison  it is obvious that no aqueous electrolyte battery, not even
the 80 watt-hours per pound estimated for the zinc-air system, can
directly  replace the  engine and fuel tank in conventional  vehicles
and  give equivalent performance.  If the molten  battery  systems
could be developed to store 150 watt-hours per pound,  they could
be used  as  direct replacement for conventional engine power sources
in all but the very heavy and long-range vehicles.  Improved versions
with  energy densities  of up to 300  watt-hours  per pound would
be required for the  larger trucks and combat tanks.
    Table  2  shows the  power  requirements, in  kilowatts  provided
to the drive train, required during idle,  cross  country,  secondary
roads, highways, and at peak power.

         Table  2.  POWER  REQUIREMENTS TO DRIVE TRAIN
                   OF  CONVENTIONAL VEHICLES
                           (in  kilowatts)
Idle
Vehicle (30%)
1/1 tnn
% ton 	
O1A tnn
5 ton 	
10 ton 	
Tan Ir

Cross
country
(20%)
2.4
5.6
11.5
17.4
61.3
153
Secondary
(20%)
4.5
9.4
19.9
29.4
97.5
261
Highway
(25%)
6.3
12.2
24.0
33.4
104.0

Peak
(5%)
37
55
108
130
216
400
FRYSINGER
                                                               85

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     Internal combustion engines have been designed on the basis of
providing  the  peak  power  required  and  in  many  cases  almost
idle during  normal  operating  conditions  for highway transit.  To
give equivalent performance the  battery must of course be capable
of providing the same output. These discharge rates are no problem
for the molten electrolyte batteries because  of the very high con-
ductivity of  the electrolytes  and  because  of  the  fast  electrode
reactions at these elevated temperatures. Most of these peak demands
require  discharge at  about the 1-hour rate. Molten batteries  are
capable  of high  capacities and  efficiencies even at  15- to 20-minute
rates.  The  molten  electrolyte  systems,  therefore, have  sufficient
power density for these vehicle applications.

    The third  major  limitation  of battery systems  is  the high
percentage  of nonduty  time during which the  battery  must be
recharged.  Various  proponents of the family-type  electric car have
suggested the overnight recharge to replace the  electrical  power
consumed during the day's use.   This  immediately limits the type
and extent  of use of the electric automobile because it  must  stay
within its 1-day  range, often mentioned as a maximum of 150 miles,
and can  only be  recharged at home or where  other  suitable charging
equipment may  be  available.  An alternative would  be supplying
energy to the  electrical automobile  by a method analogous  to  that
now  employed  for   refueling  conventional  hydrocarbon-burning
vehicles. This requires  a fast charge capability for the battery so
that its  energy content can be completely renewed in a period of
approximately 10 to  15 minutes, which  is  only  somewhat  longer
than now required for obtaining a full tank of gas at  the gasoline
service station.  The kinetics of the electrode reactions of the molten
electrolyte cells  are  sufficiently rapid  so  that  charging of  a total
system within 15 minutes is a possible feasible  solution.  Special
designs  to minimize resistance  in  the  electrodes  and electrolytes
must, of course, be taken and some loss of efficiency  in  recharge
is inevitable.  If  high-power charging stations were available  across
the country, such  as gasoline  service  stations are now,  the total
energy content for another 200- to 300-mile trip could be transferred
to the molten electric battery in this short period  of time.  One of
the principal problems  is, however, the  large amount of current
that must be conducted  through the cables that  link the  charging
station to the  battery.  This represents a very significant  bus bar
weight on the vehicle.  This extra weight in terms  of cell terminals
and conductor hardware is  so large  that  it drastically reduces the
effective  watt-hours  per  pound  of  the battery.   It is,  therefore,
highly unlikely that  a  15-minute  recharge  battery  can  be achieved
with the watt-hours  per pound required for the vehicles listed in
Table 1.  At  first glance the alternative appears  to  be  either to
reduce the range of the vehicle and to  allow fast  recharge so that
an  additional  increment  of  power  can be  quickly taken  on as
required  or to remain  with the concept of overnight charging and
increase  the  range   of  the vehicle  by developing batteries with
significantly higher watt-hours per pound.
86
Fuel Cell —Battery Power  Sources

-------
                         FUEL CELLS

    Fuel  cells  have also  been proposed  for  vehicle  propulsion.
Except for the cases where very  special  fuels  and oxidants  such
as tank hydrogen and tank oxygen  have  been utilized,  very little
progress has  been made.  The  economics of electric vehicle  propul-
sion  does  not lend  any  attractiveness to the utilization of special
fuels such as hydrogen or hydrazine in fuel cells  for vehicle  propul-
sion. The cost of hydrocarbon fuels  for  utilization in hydrocarbon-
air fuel cells for vehicle propulsion is, of course, extremely attractive,
but the present day complexity  and weight of hydrocarbon air  systems
make them infeasible for vehicle mounting.  One principal problem
is that a  fuel cell  is much like an  internal  combustion engine  in
that  it must be sized to deliver the peak power demands.  The peak
requirements for  the military vehicles shown in Table 2 would have
to be used  as the  design point for  the rated performance  of  the
hydrocarbon-air  fuel cells.  At  the  present power  density  of  the
fuel  cell  (50 to  100 Ib/kw), it is evident  that the hydrocarbon-air
fuel  cell weight  would  be in  excess  of the total  vehicle  weight.
Even though  a   fuel cell  would have  a  high  energy  conversion
efficiency  (40 to 50%) at its rated power,  which is  the peak power
requirement, as  listed in Table 2, its energy conversion efficiency
at normal cross  country power requirements  could  be less  than  10
percent and not  much  better than  internal   combustion   engine
efficiencies.


   FUEL CELL —ENERGY STORAGE HYBRID SYSTEM

    Molten  electrolyte batteries have the  advantage of  high power
density, easily providing  the peak currents required for  fast accel-
eration  and  for  heavy  service, but  have  limitations  in the  total
amount of energy that  can be stored in a given amount of  weight
They also have  the disadvantage of often requiring longer  periods
for  recharge or  for  short charge periods having significantly lower
energy storage capacities.  Fuel  cells on the other  hand have the
advantage that they can  convert a hydrocarbon  fuel, which has  an
extremely high  watt-hours per pound of theoretical energy,  very
efficiently into  electrical  energy, but have the difficulty of having
very low  overload capabilities, and  therefore, have  to be designed
for  the peak power requirements  that are only  utilized  5  percent
of the total time  during  a day's operation.  In the design of a future
power  source that is  to be strictly  limited  to  the weight  of the
existing engine   (transmission  and  drive  train  excluded)  and  its
normal amount of fuel, and that  is to be optimized for lowest specific
fuel  consumption over its average daily duty cycle  (optimum  high
efficiency)  it is  logical  to  choose a fuel  cell and  battery  hybrid
system. A hybrid power source system would  consist of approxi-
mately  an  equal weight  of  hydrocarbon fuel,  fuel  to electrical
converter, and battery.  The one-third of the  weight that is battery
would  store electrical power for use during  peak requirements  or
FRYSINGER                                                    87

-------
 where the power required is above  the  average.  The one-third of
 the  weight in the fuel to electrical converter could  be a  highly
 simplified  liquid hydrocarbon fuel  cell used  as a battery charger
 running  at an average power level for the entire daily duty cycle,
 with power  being  stored  during idle or  below-average  demand
 periods for use during periods of above  average drain.

     The exact proportion of weight in the fuel  cell battery charger
 and  that in the battery must, of course, be dependent on the particu-
 lar duty cycle of the vehicle, with the peak-to-average power ratio
 being the  most important design parameter.  Table  3 indicates  the
 rated kilowatt capacity  of  the  fuel cell  and  the kilowatt-hours of
 battery storage for  the  vehicles previously described.
        Table 3.   FUEL CELL CAPACITY AND BATTERY STORAGE
          REQUIRED FOR VARIOUS  CONVENTIONAL VEHICLES
Vehicle
% ton
%ton
2Vz ton
5 ton
10 ton
Tank
Rating, kw
2.4/4.5/6.3/37
5.6/9.4/12.2/55
11.5/19.9/24.0/108
17.4/29.4/33.4/130
61.3/97.5/104.0/216
153.0/261.0/ 	 /400
Rating of
fuel cell," kw
4.5
9
20
30
100
175
Max. power
from fuel
cell, kw
6.75
13.5
30
45
150
263
Energy
storage, kw-h
37
50
94
102
78
164
a Based on 0.8-volt single cell.
    The fuel cell  battery charger is given a nominal power  rating
corresponding to 0.8 volt per single  cell and is capable of overrated
operation up to the maximum kilowatts listed in the  fourth column
of Table 3.  In each case,  the  secondary road and highway steady
power demands  can be satisfied by the fuel cell, with the battery
being used  only  during peak  power  demands.

    A typical system may use the molten electrolyte lithium-chlorine
battery, which operates at 450° to 600°C  together  with  a reformer
and a molten carbonate matrix electrolyte fuel cell  operating  at the
same  temperature. Since excellent  electrical  transient response  is
provided by the storage battery  energy, the lag time of the reformer
and  fuel  cell  can  be  rather  lengthy, thus allowing  very simple,
largely  self-regulating controls.
88
                               Fuel Cell —Battery Power Sources

-------
      FUEL CELL AND BATTERY  VEHICLE POWER
                  SOURCE PERFORMANCE

    In Table 4 the distribution of  weight between fuel cell compo-
nent,  battery component,  fuel, and  fuel  tankage is  given for the
vehicles.

Table 4.  WEIGHT  DISTRIBUTION OF  FUEL  CELL AND BATTERY VEHICLE
        POWER  SOURCE

JD
ll
'3 ~v
52
155(4.5kw)
297(9kw)
630(20kw)
900(30kw)
l,785(70kw)
3,675(175kw)






*"" "^
> U
ii
!5 §1
/ \ ^ c: ^ J-i
^ (ii .— o a) ^3 — +^
'o —
£ f
'5 *j
§ -O
246
334
626
680
855
1,094


.£?— -

5.2
139
128
609
621
1,051
2,969


"5^
-C ~_
'5 c
S ™
15
14
67
69
117
330


JD
	 ^
"o 'S
K 5
555
773
1,932
2,270
3,808
8,068


o a>
^ o
•tj 3
Q S
52
52
54
54
51
48


^£ !=J
'~ C S F"
0^ O Q. — i

36
36
38
38
36
34


' co K
0.51
0.51
0.49
0.49
0.51
0.54
(2,000
w-hr/lb)
c
"ra
CT 4
LU ^
278
256
1,218
1,242
2,102
5,938


CO
ro
Q
o
4
C\J
2.4
1.2
2.9
2.1
1.8
2.0




JD
-=
5
500
332
630
550
560
735


    Each hybrid system meets  the  duty cycle  power requirements
shown in Table 2 and has the equivalent weight of the conventional
engine as given in Table 1. This means that the hybrid fuel cell and
battery system postulated for each of these vehicles will be equiva-
lent in every respect to the conventional internal combustion engine
in performing the specific duty cycle.  The calculations were made
on the basis of sizing the fuel cell and  battery according to Table 3
requirements and using all excess allowable weight for fuel.  The
power source  efficiency  was calculated during  performance of the
actual duty cycle  and is shown in column 7 of Table 4.  Columns
8 and 9 indicate  the allover utilization efficiency and  the  specific
fuel consumption  based on  an  assumed 70 percent efficient drive
train.  Based  on  these efficiency  calculations,  2,000  watt-hours
are obtained from every pound  of  fuel  consumed.  This gives a
hybrid fuel cell  and battery system for these vehicles an energy
density of  from  500 to 700 watt-hours per pound.

    Table  5 summarizes the performances of the conventional  in-
ternal combustion engine and the battery and fuel cell system.
FRYSINGER                                                  89

-------
  Table 5.  PERFORMANCE  COMPARISON OF THE CONVENTIONAL INTERNAL
          COMBUSTION ENGINE AND THE BATTERY AND FUEL CELL HYBRID
          SYSTEM
                      Conventional
Fi>el cell — battery
Vehicle
Type
% ton
% ton
2Vz ton
5 ton
Combat tank
Efficiency,
11
12
18
19
13
Days
before
refueling
0.44
0.45
0.71
0.84
0.64
W-hr/lb
97
129
161
229
254
Efficiency,
36
36
38
38
34
Days
before
refueling
2.4
1.2
2.9
2.1
2.0
W-hr/lb
500
332
630
550
735
     Efficiencies of the battery and fuel cell system can be improved by
 a factor  of 2 to 3,  giving energy densities that would allow these
 vehicles to go three to five times as far before refuelings.
                         CONCLUSIONS

     Through the use of a fuel cell and battery hybrid power source,
 all of the  so-called vehicle  "battery"  problems  can be overcome.
 This  power  source  allows an  electric vehicle to have:

 1.  Full-range capability.
 2.  Excellent acceleration characteristics.
 3.  Very fast energy refuel.

    Achieving the  performance  outlined  for  the vehicle  requires
 the successful development of a  150-watt-hour-per-pound molten
 electrolyte battery and a 20- to 35-pound-per kilowatt hydrocarbon
 fuel  cell.  Research progress  indicates  that  these goals  should be
 achieved in  operational  hardware within  the  next 5  to 10  years.
90
                               Fuel Cell —Battery Power Sources

-------
            ELECTRIC VEHICLE RESEARCH
                       Howard A.  Wilcox

                  General Motors  Corporation
                       Warren,  Michigan

    Among  the  several  types of  automobiles  presently  being con-
sidered for electrification  are  small  urban cars of limited range and
acceleration performance, larger  cars  intended to  be  competitive
with today's general  purpose passenger vehicles, and  special auto-
motive vehicles  such as taxi-cabs.*  Hence  considerable  research
and development effort is going into electrochemical energy  systems.

    Our  effort in  this area is focussed on two  principal  objectives:
(1) to conduct exploratory research into a -wide variety of promising
electrochemical couples such  as lithium-sulfur,  lithium-air,  sodium-
chlorine,  and  sodium-sulfur  and   (2)  to  carry  out research  and
development work on high-performance energy conversion systems
based on the lithium-chlorine couple.

    This latter  objective is  pinpointed here because  our  work  to
date under  the  first  objective indicates that  the  lithium-chlorine
couple holds the best promise for satisfying most of the  applications
of greatest interest to us.  Table 1  explains one of the reasons why
this is true. It gives  the  energy storage density of various  reactant
pairs  in  watt-hours  per  pound of  reactant—that  is, per pound  of
reactants that have to be carried  in the automobile either before  or
after  the battery  has been discharged.

Table  1.  COMPARISON  OF  THEORETICALLY AVAILABLE  ENERGY FROM A
                   VARIETY OF REACTANT PAIRS

  Reactant pairs  Li/CI     Li/S   Na/CI    Na/S    Zn/Air  Li/Air    H202


              '  ll050   U3°   60°   30°-650    50°   2'000   i'600

    From the energy storage  density standpoint, the lithium-chlorine
couple looks good; the lithium-sulfur couple  looks slightly  better,
the sodium-chlorine  couple looks  pretty good; and the  lithium-air
couple looks best  of  all.  However,  the presently achievable electro-
chemical reaction  rates at the air electrode are not  good even with
the most expensive catalysts, and the  direct lithium-air couple still
suffers from that obstacle, so  it remains at present  an item of  purely
potential interest to us. In  fact, our study of electrode reaction rates
  Other types  of  vehicles  that  are  already electrically powered or are
  being  considered for electrification include  light, medium, and  heavy
  trucks; locomotives; and  off-road vehicles  such  as  dump trucks  and
  scrapers.
WILCOX                                                        91

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for these couples has caused us to look most favorably, as of now, on
the lithium-chlorine couple.  Figure 1 depicts a research-type electro-
chemical cell  we have used to explore  the  performance  potential
and operating features  of this couple.
                CHLORINE  INLET!

              GAS OUTLET
J CHLORINE

I LITHIUM

  LITHIUM  CHLORIDE
                                         CHLORINE SEPARATOR
                                               SCREEN
                     v^^i\  A^mm-^ts i
  LITHIUM CHLORIDE-
        LEVEL        MINI
                     "   '   ---—   •     LITHIUM  ELECTRODE
                                           CHLORINE  ELECTRODE
   Figure  1.   Vertical  experimental  lithium-chlorine cell.

    The chlorine electrode, which is  the positive pole of the cell,
utilizes  a porous carbon frit to separate the  molten lithium chloride
electrolyte  on the  one side from the hot chlorine  gas  on the  other.
The  molten lithium  chloride does  not wet the  carbon frit. The
gaseous chlorine molecules are forced through the pores of the frit
to the interface between  the carbon  and the  lithium chloride.  There
they go into solution, at which time  most of  them dissociate, gain an
electron from  the carbon, and become  negative ions in  the melt. We
have devoted considerable attention to  the basic physical mechanisms
underlying the  operation  of  this electrode, and  believe  we have
achieved an excellent understanding of its electrochemical  behavior.
Moreover, we have rather extensively studied its operating features
from an engineering point of view, and believe that it poses  no  insur-
mountable  problem to the  future  development  of  a very  high-
92
Electric Vehicle Research

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performance battery. Our tests have shown the feasibility of achiev-
ing chlorine electrode current  densities  up  to  4,000 amperes  per
square foot without  significant  polarization  losses,  and  still  higher
current densities are possible.

    Similar studies have been accomplished on the lithium electrode,
which is  the negative  pole of  the cell.  Here  we  use  a  porous,
stainless steel structure to bring  molten lithium  from the one side
to the molten lithium  chloride  on the other.  The  stainless steel is
completely  wetted by at  least  a thin film  of  molten  lithium,  so
lithium chloride is excluded from touching it  as long  as some excess
of lithium  remains.  Thus, the  electrochemical  reaction occurs  on
the surface  of the thin  film  of  molten  lithium  facing  the lithium
chloride.  Our tests  show that  current densities achieved at this
electrode  can exceed 40,000 amperes per square foot without notice-
able polarization losses. Hence,  we  believe that the lithium-chlorine
electrochemical  cell  is  potentially  capable  of  very high-power-
handling capacity, and, further,  we  suspect that this power-handling
capacity is ultimately going  to  be limited  more  by the chlorine
electrode  than by the  lithium  electrode.

    Most of our current  research problems  in  connection with this
system involve  trying to find  materials capable  of long  life  while
handling  the highly  corrosive  hot chlorine gas, the  molten lithium
chloride, the molten  lithium, and the corrosive impurities that may
creep  into the system.  Our research is  still  in an  early stage,  and
potential  life  data  for   a  lithium-chlorine  electrochemical  power
system cannot yet be presented.

    On the basis  of  our work to date, we believe that development
of a rechargeable electrochemical power system is technically feasible.
In  the 100 hp class  with an  energy storage capacity of  about 100
hp-hours,  we believe  we can probably achieve  a lithium-chlorine
electrochemical  power   system  with  the   characteristics   listed
in Table  2.

   Table 2.  CHARACTERISTICS OF  LITHIUM-CHLORINE  POWER SYSTEM

       Open circuit voltage            3.5 volts per cell
       Average operating voltage       3.2 volts per cell
       Power capacity                 0.2 hp per pound of
                                    electrochemical  power system
       Energy storage  capacity         0.13 hp-hour  per  pound of
                                    electrochemical  power system


    As yet, however, we are far from being assured  that we can solve
our  problems of  long  operating  life,  operating  hazards,  and  a
favorable first-cost picture.

    Recently General Motors described  and demonstrated two full-
scale   electric  vehicles  and showed that  there are currently  no
 WILCOX                                                         93

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 absolute technological barriers to such developments (Rishavy, Bond,
 and Zechin, 1967; Marks,  Rishavy, and  Wyczalek,  1967;  Agarwal,
 1967;  Wyczalek, Frank, and Smith, 1967; and Winters and Morgan,
 1967).  Let me tell you briefly  about these research vehicles.

     One (Figure 2) was a battery-powered car we called Electrovair
 II. This car used a 530-volt silver-zinc battery as its basic energy
 storage unit. The silver-zinc battery has about five times the energy
 storage  capacity, and also about five times  the power-handling
 capacity,  as the  same weight of  typical lead-acid batteries  with
 which we  are all rather familiar.  Since they contain a lot of silver,
 they are fearfully expensive—much too expensive ever to be practical
 for use in  mass-produced automobiles.  However,  they represent the
 most advanced  type of battery system available today  for vehicle
 propulsion. Even so,  they  fall  far short  of  the energy  storage  and
 power capabilities of  an  engine fueled with gasoline.  The  Electro-
 vair II therefore weighed  3,400  pounds,  which is  800  pounds  (or
 about  30 rr) more than its counterpart., the  standard 1966  Corvair.
 It also had an operating range of only 40  to  80  miles (depending on
 how it was driven), as compared to  the  250- to  300-mile range of
 the standard 1966 Corvair  with  a full tank of gasoline.  A weight
 and performance comparison is given in Table 3.
                  Figure  2.    Electrovair  II.
94
                                         Electric Vehicle Research

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                             Table 3.

WEIGHT AND PERFORMANCE COMPARISON OF ELECTROVAIR II AND CORVAIR

                                Electrovair  II             Corvair
Weight, Ib 3400
Acceleration (0 to 60 mph) sec 16
Top speed, mph 80
Range, miles 40-80
Power train weight, Ib 1,230
2,600
16
86
250-300
610
    The silver-zinc battery pack for the Electrovair II was composed
of 286 cells, and it did not represent a serious development problem.
It was quite otherwise,  however, with the electric motor system (see
Figure 3) that took the power from the  batteries and  converted it
to torque at the wheels of the Electrovair II.  In fact, this  car was
intended  to  be a  test-bed  to  evaluate  the  electric motor  drive
system. This propulsion unit was newly developed for this  applica-
tion, as well as for others, and it used  a set of high-power electronic
switches  called thyristors  (or silicon  controlled  rectifiers—SCR's)
to control its  torque output. The more conventional direct-current
electric motor  utilizes a commutator instead of  electronic switches,
the commutator  being in  effect  a  set of mechanical switches  for
accomplishing  much the  same function.   However, a  mechanical
commutator is  limited to moderately low switching rates by mechan-
ical and  inductive sparking problems;  on  the contrary, however,  the
electronic switches  are able  to  function  at relatively  high  rates.
Consequently, it is possible, using the high-power electronic  switches
in what  we call  the "modulating inverter assembly" (Figure  4)  to
design the motor to operate at greatly increased rotational speeds—
about  13,000  rpm—the conventional  direct-current  electric motor
operates  at about  3,500 to  4,000  rpm in  this horsepower  range.
These high speeds  (at  the same  torque levels) imply, in  turn,  a
correspondingly  increased  power-handling  capacity for the  same
weight of motor.  Table 4  gives a weight  analysis for this motor
system.

        Table 4.  WEIGHT ANALYSIS OF ELECTROVAIR II MOTOR
                  AND RELATED CONTROL SYSTEM
                             (in pounds)
Motor
Gear box
Modulating inverter assembly
Control electronics
Cooling system
Cables, etc.
TOTAL
130
25
235
24
80
56
550
WILCOX                                                        95

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                 Figure  3.   Electrovair  II.
96
Figure  4.   Modulating inverter.






                         Electric Vehicle Research

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    Using such a high-speed motor  system, we found it possible to
deliver approximately  100 peak horsepower to the  Electrovair II
from  a motor weighing  only  130 pounds. The conventional type of
direct-current motor in this same application would have required an
estimated 500 to 800 pounds to yield the same number of horsepower.
This extra motor weight would then  have required further structural
material and weight  in  the  body of the  vehicle, and all  this extra
weight would  have produced  correspondingly  increased  power  and
acceleration  losses.   By  using  the  lightweight  high-power  motor
controlled  by electronic  switches, it was possible to achieve  accel-
eration performance in the Electrovair II comparable to  the  accel-
eration performance of the standard 1966 Corvair, despite the greater
weight of  the  Electrovair II.

    The electric car  was  simple to  operate, but complicated  in its
control circuitry.  The driver  was required to manipulate only the
steering wheel, brake, an on-off switch,  a  forward-neutral-reverse
lever,  and an  accelerator pedal that  provided  smooth,  "step-free"
acceleration  and  speed  control  over  the whole  operating  range.
Figure 5 shows (schematically) the  car's control circuitry. The low-
power logic  circuits  were required to  shut  off the main battery
power if  anything went seriously  wrong, to prevent over-speeding
or over-accelerating,  to  prevent sudden reversals  of  output  torque
under any conceivable  malfunction condition, and so forth.   It is
very  important,  of  course, that adequate safety features be  built
into such  a  car, because  the  hazards  are otherwise  significant; at
the same time and for  the same reason, it is very  important that
the operating procedures required of the driver be extremely simple,
smooth, and  similar in  character and  effect  to  what he  is already
accustomed to.
DRIVER POWER__
VROLS' DEMAND

LOW-
POWER
LOGIC
CIRCUITS
SPEED SIGNAL



1 CONTROL
fsiGNAL


LOW-
POWER
TRIGGER
CIRCUITS



j TRIGGER
D-C POWER YPULSESA-C POWER
SILVER-ZINC
BATTERY PACK


SOLID-STAT
INVERTER A
POWER CONTF
E
\|p _ ._
ROL
3-PHASE
A-C
' INDUCTION
MOTOR
SHAFT
•*-
POWER
      Figure  5.    Control  circuitry for  Electrovair  II.
WILCOX
97

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    Our second experimental vehicle powered by electricity (Figure
6) was called  the Electrovan;  it  was  produced mainly for study,
on an  experimental basis,  of the problems of powering a passenger
vehicle with an  electric fuel battery.   The fuel cell  modules  were
developed by Union Carbide, and we developed the means of putting
them  together  into  a  successful fuel battery.
                     Figure  6.   Electrovan.

     Figure 7 shows  a  phantom  view of  the Electrovan  with its
electric  drive train  displayed  rather  completely.  In  this  van you
will note that we  used  a battery  composed of 32  fuel  cell modules
connected in series to produce an open circuit voltage  of  520  volts.
This battery had a power capacity of 32 kilowatts  continuous and
160  kilowatts for short  time periods.  Almost  the  same drive motor
system was  used in the  van as  was used in the Electrovair, but
in the van it was able to produce 125 horsepower,  instead  of the
90  or 100 that it  developed  for  the  Electrovair,  because the fuel
battery  voltage in the van  did  not sag  as  much under load  as did
the  voltage of the  silver-zinc  battery in Electrovair.

     The  van's  fuel  battery uses  pure  hydrogen  as  the  fuel and
pure oxygen  as the oxidizer;  these  can be stored  either  in  high-
pressure containers or in liquid form at  very low temperatures.  A
little study—summarized in  Table 5—shows that  cryogenic storage
is best.
 98
                                          Electric Vehicle Research

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WATER
CONDENSER
                                               LIQUID HYDROGEN TANK
                                                     LIQUID OXYGEN TANK
 ELECTROLYTE
 RADIATOR
A-C
INDUCTION  MOTOR
        GEARBOX
      ELECTROLYTE
      RESERVOIR  "
     32 FUEL CELL
     MODULES
              Figure  7.   Phantom view of  Electrovan.
     Table 5.  COMPARISON OF WEIGHT, VOLUME, AND RANGE CHARACTERISTICS
             OF CRYOGENIC AND COMPRESSED  GAS  FUEL SYSTEMS
Item
Total volume, ft3
Total weight,
(incl. vaporizers), Ib
Total weight of product,
Ib of H2 and 02
Total specific volume
ft" per Ib H, and 02
Total specific weight,
Ib/lb H2 and 02
Range, miles
Cryogenic
13

389

108

0.12

3.6
100 to 140
Compressed
gas
at 5000 psi
6

358

47

0.13

7.6
45 to 65
Ratio
2.2

1.1

2.3

0.9

0.5
2.3
         I want to point out most emphatically, however, that stored hydro-
     gen and oxygen gases, whether at high pressure or at low temperature,
     would not be satisfactory or practical as an energy source for pas-
     senger  vehicle  transportation.
     WILCOX
                                                                 99

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     Figure 8 shows the four loops of plumbing used in our Electro-
 van.  These  loops  contained hydrogen,  oxygen, liquid potassium
 hydroxide in aqueous  solution, and  cooling air.  Keeping  leaks out
 of all this plumbing was  of course  a major headache during the
 debugging of the van.
   VENT



 £>-^- SOLENOID

          VACUUM LINE
       RESERVOIR
         BURST
LIQUID H2
               I
               L-LJ
                                          REGULATOR
                                              AND
                                           JET PUMP
CONDENSER/
                      EXHAUST
                      WATER
                                 	COOLER KM
                                                              AIR
      Figure 8.   Schematic  of  Electrovan  fluid system.

      Figure 9 shows the electrical diagram of the fuel battery system
 of the van.  Since  the potassium  hydroxide electrolyte  had to be
 circulated to cool the modules, there was an electrical shunt across
 the fuel battery through this electrolyte circulation loop. Our plumb-
 ing  design  was aimed at minimizing this  electrical  leakage, but
 even so it  amounted to 2.4 kilowatts.

      Table  6  shows the  weight  analysis and  performance levels
 achieved with the  Electrovan  compared  with those of a  standard
 production van.

      At this point I should mention that we are interested  not  only
 in the purely  technical problems involved, but also in all aspects  of
 potential markets  for  our electrochemical power  systems and their
  100
                       Electric Vehicle Research

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associated  electric drives.  Some  possible  applications under  study
are listed below:

              Small cars
              Full-size  cars
              Taxis and busses
              Light, medium, and heavy trucks
              Locomotives
              Off-road  trucks and scrapers
              Industrial variable-speed drives
              Load levelers for  utilities
                  FRONT OF VEHICLE
   ROOF   MODULE
   FANS   DUCT FANS
 «i—OO
Jt
  GROUND
OCURRENT
  MONITOR
OIL
PUMP
      KOH
      PUMPS
                                + DC RIGHT SIDE
                               .GAS SOL
                                                 BLOWER OIL FAN
                                                CONDENSER-
                                                COOLER FAN
 Figure  9.   Schematic  of  Electrovan  fuel  cell  electrical
                           system.

 Table 6.  COMPARISON OF PERFORMANCE AND WEIGHTS OF ELECTROVAN
                   AND CMC PRODUCTION VAN

Total vehicle weight, Ib
Fuel cell powerplant weight, Ib
Electric drive weight, Ib
Powertrain total weight, Ib
Acceleration (0 to 60 mph), sec
Top speed, mph
Range, miles
Electrovan
7,100
3,380
550
3,930
30
70
100 to 150
CMC van
3,250


870
23
71
200 to 250
WILCOX
                                   101

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     Many of these markets are highly dynamic and are influenced not
only by economic, but also by political and psychological, pressures.

In summary:
1.   Potential advantages of electric vehicles include quiet operation,
    efficiency not limited by heat engine cycle,  reduction of emis-
    sions, and use of low-cost electricity generated by nuclear reactors
    when fossil fuels become more scarce.

2.   Research on  electric vehicles  offers  potential  for  commercial
    payoff in many other fields.

3.   Any power system,  considered in  the whole, presents  possible
    pollution problems.

4.   It is still too early  to  state definitely that any  kind of electric
    automobile will soon be  able to win  an economically significant
    and  viable place for itself  in  the total  transportation  picture.

    Returning  to comment briefly  on  the first of these  points, the
single most important  reason for the  current  strong resurgence of
interest in electric motor cars is the  growing problem of air pollu-
tion; however, we  are  also  interested in electric  vehicles  because
the  development of efficient and  constantly improved  systems of
energy  conversion is vital to the  automotive transportation industry.
For this reason, we  •will continue to pursue aggressively any method
of energy conversion that offers potential  for  improving our vehicles.

     I should like to mention at  this point that if one is willing to
accept  the relatively low  performance  levels  currently promised
by  the  all-electric automobile, then  we  should also take a  careful
look at how much  emissions can be reduced  from  a oar powered
by  a small internal combustion engine that  features the same per-
formance level as the  all-electric.  Emission level comparisons can
only be validly made on the  basis of  comparable  performance levels.

     Concerning  the  second  point,  greatly improved batteries  and
also improved electric  motors are going to be  needed  if  millions
of electric  cars  on the  highways  are ever  to become  a practical
reality.   As far  as  energy storage and power-handling  capacity  is
concerned, passenger cars with internal combustion  engines  perform
very well  indeed.  Consequently,  much  improvement  in batteries
and electric motors  is  needed  if they are  to be  able  to  perform
approximately  as well  as  the  internal combustion  engine.  Even  if
we are  not able, in the near future, to  achieve the  high levels of
performance required for a truly practical electric passenger vehicle,
improved batteries and  motors will undoubtedly produce  commercial
payoffs  in other applications.  We  are interested in  improving the
electric  power  train  of diesel  locomotives,  for example.  We are
interested in  improving  our starter  batteries.   So we  believe  we
have justification for pushing ahead with  our research and develop-
ment in all these fields.
102                                       Electric  Vehicle Research

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    Turning to the third point, the fact is often overlooked  that
any power system creates  pollution problems. Suppose, for example,
one has  a  completely  sealed battery that draws and  stores energy
from  an  electric wall  plug and delivers  it on demand  to the wheels
of the car.  This would appear  to be  a power system  wholly free of
pollution problems.  However, power drawn  from the  wall plug  has
to be  generated somehow,  and presently it is generated by a central
power-generating  plant that uses  oil or  coal  as fuel.  This  plant
has an exhaust stack, of  course,  and at all times emits  oxides of
sulfur, nitrogen, and carbon, because these  are  combustion products
when coal  or fuel  oil is burned  in air. Oxides of sulfur and nitrogen
are, of course,  some of the major offenders  in air pollution.  Carbon
monoxide  is another  undesirable pollutant  if present.  However, it
usually is not found  in significant amounts in  power plant stack gases.

    Of course,  many technologists  believe that most of our  energy in
the future  will be  generated by  large  nuclear  reactors.  However,
these  reactors  have  pollution problems  too,  since  radioactive waste
products are generated and have  to be disposed of  appropriately.

    Consequently, we  see  that  any power system, considered in  the
whole, generates some sort  of pollution  problems.

    With  respect  to  the  fourth  point,  it is believed  that  electric
vehicle propulsion is technically feasible. However, our research  has
not indicated when  it  would be economically feasible or acceptable
to customers in terms of  safety,  utility, and convenience.

    In some applications, such as diesel-powered  locomotives, electric
drives have thus far  demonstrated  their  capacity  to  do the  job
better than mechanical power  trains.  However, the  personal pas-
senger vehicle  imposes its own very stringent  and special  require-
ments on  its  power  train. Many  American   passenger  cars  are
required to have  a heated  cabin  when it  is cold  outside,  an  air-
conditioned cabin  when  it   is  not  cold outside,  several  powerful
headlights,  electric window  lifts, a  radio, a  record player, and other
convenience items.  All these take power—in some cases as much
power as is required  to propel the car  along the  road at  moderate
speed. The modern American  passenger car requires peak  power
levels  five  to  seven  times   larger  than it  uses  at   urban speeds
Moreover,  it is frequently  driven  hundreds of miles  with  only a
few brief  stops for  "re-energizing."  Hence, the major obstacle to
the early mass use  of an all-electric car  is the  present  day lack
of an  adequately  high-power plus high-energy-capacity storage or
fuel  battery at reasonable  cost.  Some  batteries have good  power
but poor energy storage capacity,  some  have the reverse,  but none
is  adequate in  both areas at once.

    We know  that  any vehicular  power plant  must  be developed
first for  technical feasibility, next  for  producibility and cost, then
for durability under engineering test, and  finally for safety, relia-
bility,  and  convenience in  the hands of the public.
WILCOX                                                       103

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     At this time not all the answers to attaining these goals with
 electric power are known.   Consequently, we believe that our ex-
 tensive research and development  work must be continued if  we
 are  to continue to make necessary progress in energy  conversion.

                         REFERENCES

 Society of Automotive  Engineers,  1967 (Jan. 13).

     E. A.  Rishavy, W.  D. Bond, and T. A. Zechin.  Electrovair—a
        battery electric car. SAE Paper No. 670175;

     C. Marks, E.  A.  Rishavy, and  F.  A.  Wyczalek.  Electrovan—a
        fuel cell powered vehicle.  SAE Paper No. 670176;

     P. D. Agarwal and  T. M. Levy.  A high performance AC  electric
        drive system.  SAE Paper No. 670178;

     F. A. Wyczalek, D. L. Frank, and  G.  E. Smith.  A vehicle fuel
        cell system. SAE Paper No. 670181;

     C. E. Winters and W. L. Morgan. The hydrogen-oxygen thin fuel
        cell module. SAE Paper No. 670182.
104                                     Electric Vehicle Research

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 EUROPEAN  DEVELOPMENTS OF  POWER  SOURCES

                FOR ELECTRIC  VEHICLES



                            M. Barak

            Chloride Electrical Storage Company Ltd.
                        London, England

                        INTRODUCTION

    The immediate availability of conventional storage  batteries has
 stimulated in Europe the building of  a  number of small  electric
 vehicles for testing. At the same time  many companies have initiated
 programs on the research and  development of novel devices  such  as
 fuel cells.  The progress  of this work  on passenger-carrying vehicles
 and power systems is reported  here.
    The use of  electric power  to  drive  automobiles  is by no means
 new.  In 1899 M. Jenatzy, a Belgian racing driver, momentarily won
 the world speed record at 65.8 mph with  his electric car La Jamais
 Contente  when  he defeated a fellow racing driver, the  Comte de
 Chasseloup-Laubat, also  driving an electric car (Electricity Council,
 1966).  Unfortunately, shortly  afterwards, Jenatzy forsook his  first
 love and turned to the gasoline internal-combustion-engine vehicles,
 which at the turn  of the century, because  of their  greater range and
 speed, were rapidly ousting the electrics from popular favor in many
 cities in the United States as well as in  Europe.  With the prolifera-
 tion of the internal-combustion engine we now  face the menace  of
 chronic traffic congestion in the cities, as  well as the acute discom-
 fort and hazards to health caused by  noise and  noxious fumes. On
 the latter point, it has been estimated that  about 5 million  tons  of
 carbon  monoxide belch forth from the exhaust pipes of the  world's
 internal-combustion-engine vehicles each year. This is equivalent  to
 a daily output of this  lethal gas  of about  400 million cubic feet;  in
 addition the vehicles emit quantities  of partly  oxidized  hydro-
 carbons, some of which are believed to be carcinogenic.
    It is worth  noting that the internal-combustion  engine  is con-
 suming its fuel and pouring out noxious fumes even when the vehicle
 is stationary  and idling in traffic.  This does  not apply to an  electric
 vehicle.
    The wheel  has now  turned full  circle. Interest in electric auto-
 mobiles has been re-kindled in many  of the highly developed coun-
 tries of the world.   What factors led to the demise of these vehicles,
 and how can they  be resuscitated?

                      THE POWER UNIT

    The obvious deficiency lay in the  power unit.   Lead-acid  and
nickel-iron alkaline storage batteries have to date  provided the only
BARAK                                                       105

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source of power sufficiently  reliable and durable to meet industrial
and commercial requirements.  But these systems have relatively low
power densities, in the range of 10 to 15 watt-hours per pound for a
running  time of 2 to 5 hours,  so that a large weight of battery has
to be carried  to  provide horsepower equivalent to that of even  a
small automobile.  For 10 horsepower,  for example, this amounts to
between  1,000 and 1,500 pounds.

    A few years ago the silver oxide-zinc couple  made a  meteoric
appearance on the battery scene, offering a four- to  five-fold increase
in the energy  density  of  the conventional  storage  batteries.  Un-
fortunately, it proved to have poor reversibility and a low cycle life
in multicell systems and this,  together with  the high material  cost,
has restricted its commercial use.

    More recently still, fuel  cells have  received  much  publicity.
Theoretically and in fact on  the laboratory scale, these systems offer
a considerable  reduction in weight, although not in overall volume,
and they offer the added advantage that the  fuel can be replenished
in about  the same time as would be taken to refill the gasoline tank
of a  conventional automobile.  Fuel cells are  therefore attractive for
this purpose, but they are  complex systems and rather expensive to
make, and at present, the most effective fuels are expensive or diffi-
cult  to  handle. Hybrid systems  sometimes  called  semi-fuel  cells,
having a metal anode, such as zinc — as in storage batteries — and
a fuel-cell-type cathode consuming oxygen or air such  systems  are
under development both in primary and reversible forms and show
some promise. Reversible semi-fuel cells, like storage batteries, how-
ever,  have the  disadvantage  that several hours are required for re-
charging.

    Within the past few months disclosures have been made of new
electrochemical couples,  in  particular sodium-sulphur and  lithium-
chlorine.  These show,  on paper at least, the highest energy  densities
attainable so far,  but  for various reasons,  they have  to be worked
in the temperature ranges 300° to 500°C and 500°  to 650°C, respec-
tively. A preheating source is therefore necessary, and these systems
would probably have to carry a considerable amount of insulation for
intermittent use.  Also, the active materials would present dangerous
hazards in the event of an accident.
      ENERGY DENSITIES OF DIFFERENT  SYSTEMS

    Figure  1  shows the energy  densities in watt-hours  per pound
for different durations  of  discharge  for  various systems  mentioned
(Barak, 1965). The values given for  the Bacon hydrox cell, consum-
ing hydrogen and oxygen and working at temperatures around 200°C
and pressures of 600 psig,  include the  estimated  weight of all  the
ancillary equipment and are still  the  most favorable for  fuel  cell
systems.
106                                       European Developments

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 150

 100
  80
  60
  50
'  40
:  30

-  20
  15

  10
   8
   6
   5
   4
   3

   2
  1.5

   1
                                 'X LITHIUM-CHLORIDE

                                 X SODIUM-SULFUR
                                 X ZINC-AIR
                                                LEAD-ACID
                                           NICKEL-CADMIUM  (IRON)
               J	L
_LJ	I	L
                _L
                   30
                         60
 346
10
 hr
                                                 20
40  60 100
                               LOG TIME
     Figure 1.   Energy  densities at  different  rates of
            discharge for  various  battery  systems.

     These curves indicate that for continuous durations  of discharge
 of less than about 1 hour, storage batteries have a higher  density than
 fuel cells.  This becomes  more and more pronounced  as the current
 approaches starter battery currents.  It  is  unlikely, therefore, that
 any of these other systems will displace conventional storage batteries
 for this service in internal-combustion-engine vehicles. On the other
 hand, for periods of discharge of  about 2 hours and longer, common
 to traction service, fuel cells show a continuing superiority over stor-
 age  batteries.  The position of the  semi-fuel cells and  the new high-
 temperature storage batteries should  be  noted.

         DEVELOPMENTS IN  ELECTRIC TRACTION

     Work  on  electric passenger  vehicles is being  actively carried
 out in  Great Britain.  The climate is  particularly favorable  because
 electric vehicles for industrial and commercial uses have been popular
 for a longtime.  Hender  (1965) has shown (Figure  2)  how the num-
 ber of  battery-electric vehicles registered for road use increased  be-
tween  1953  and 1964.  'nhese now number over 40,000, and  with  the
70,000  battery-operatt   electric industrial trucks, make a total popu-
lation of about  110,000.
BARAK
                            107

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                                                                - 150
                                                                      CO
                                                                      o
                                                                      _
                                                                      -2
                                                   > in
                                                   P CTl
                                                   < d
                                                   cc
                                                                       o
                                                                       o
1952
1956
                                       1960
                                                           1964
                                                                  100
                             YEAR
     Figure  2.    Increase  in  the  number of  battery-electric
      vehicles  registered  for  road  use  (excluding  p.c.v.s.)
       with  comparative  fuel  costs  of oil and  electricity.

       Experience over many  years has  proved that, in Great  Britain
   at least, the fuel and maintenance costs  are less for an electric than
   for an internal-combustion-engine  truck; the life expectancy is ap-
   preciably greater, and there are other benefits, such as freedom from
   noise  and fume.  The favorable cost of electricity compared with fuel
   oil is  indicated by curves  a  and b in Figure  2. Some comprehensive
   figures for economies in depreciation, maintenance, and running costs
   achieved by the use of electric fork-lift trucks are given in The Elec-
   tric Industrial Truck, published by the Australian Lead Development
   Association, 95 Collins  Street,  Melbourne.   The annual figures  for
   depreciation and maintenance of an electric vehicle are  estimated to
   be only 51 percent of  those for  a  diesel truck and the economy in
   fuel,  67 percent.  Within recent years  also,  considerable  improve-
   ments have been made  in the energy  density of storage batteries of
   both  the tubular type and  the flat plate-glass retainer types.  For
   example, at the  5-hour rate, the gains in watt-hours per pound and
   watt-hours per cubic inch have been about 35 percent, and at the
   30-minute rate, about 40 percent (Barak, 1965).

       The advent of new materials,  e.g., lighter and stronger  plastics
   suitable for battery cases,  and of improved designs  to reduce the
   proportion of inert metal  in the battery  will undoubtedly  allow still
   further gains. Unfortunately, though significant,  these gains  will be
   marginal and it is unlikely that spectacular improvements  will be
   achieved again.
   108
                          European Developments

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     Several electric passenger vehicles with storage batteries as the
 power unit have been produced  during the past few  years.  Four of
 these were recently demonstrated by the  Electricity Council and de-
 scribed by K. W. C.  Jeremy (1966).  Three were conversions of in-
 ternal-combustion-engine cars,  but the fourth,  the  Scamp,  made by
 Scottish Aviation Ltd.,  was specially designed for the purpose.  The
 objective  was a  "town-about"  car,  small enough  to  avoid  traffic
 congestion, easy  to  maneuver  and  park, quiet  and fumeless,  and
 therefore a noncontributor to the smog problem, with a  fairly lively
 performance, and a range of about 20 to 30 miles.

     The characteristics  of one of the converted Mini-travellers made
 by the British Motor Corporation and the Scamp are given in Table 1.

         Table 1.  CHARACTERISTICS OF THE MINI-TRAVELLER
                          AND THE  SCAMP

                         Mini-traveller                 Scamp

 Curb weight, Ib               2,499                     1,000
 Motor              V67 type made by AEI, Ltd.,   Twin, made by CAV, Ltd.,
                   with  chain drive to original driving onto each rear wheel
                          differential.
 Rating                   96 v, 110 amp         24 v, 150 amp  (each)
                        equiv to 12 hp            equiv to  2.7 hp
 Weight, Ib                     178
 Battery               96 v, 66 amp-hr (1 hr)     45 v, 105 amp-hr (5 hr)
    Power, kw                  6.3                        1
    Energy, kw-h               6.3 (1 hr)                5 (5 hr)
    Weight, Ib                  830                      400

 Controls            Thermistor pulse unit with
                      regenerative braking
Weight, Ib
Maximum speed, mph
Range, miles
110
41
30

35
15-20
    The range of these cars  is generally regarded  as  being too  low.
Range should be nearer  100  miles on one charge,  and this  calls for
a system with higher energy density.

    Table 2 lists some of the salient features of the storage battery on
the Mini-traveller and also the minimum specification for an energy
source to meet this requirement.

    I will mention various other  custom-built cars under  construc-
tion and present  photos of some  of  these.
BARAK                                                         109

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     The Carter Coaster is made by Carter Engineering Co., of Tarn-
 worth,  Staffordshire.  This vehicle is  expected to  have a  top speed
 of about 30 mph and a range of 40 to 50 miles.

     The Winn  car  is made  by the  Telearchics Ltd. of  Lechlade,
 Gloucestershire, who  are  also developing battery-propelled motor-
 cycles.

      •
110
                                          European Developments

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  Table 2.   STORAGE  BATTERY CHARACTERISTICS  AND SPECIFICATIONS

Power

Weight, Ib
Watt-hr/lb
Volume, ft3
Watt-hr/ft3
Range at 30 mph,
miles
Life, cycles
years
Costs, capital
£/kw
recharging
or refueling
Storage battery
96 v, 66 amp-hr (1 hr)
6.3 kw-h or kw
830
7.6
5
1,300
30
1,500 to 2,000
5 to 6
£150 ($420)
£23 ($64)
0.8d/kw-h (0.930
0.33d/mile (0.380
Minimum specifications
25 kw-h (2 hr)

< 1,000
25 to 30
6
2,000
50 to 100
> 1,000
4
< £250 ($700)
£20 ($56)


Note: The cost of petrol (gasoline) in Great Britain is about 5s  3d (73 cents)
per gallon; for a medium-sized car consuming about 1 gallon each 30 miles
this is equivalent to a cost of about 2 d (2.3 cents) per mile.


    Tube Investments Ltd., has built a small-two seater city car with
an all-in curb weight of about 1,000 pounds. It is powered by lead-
acid storage batteries of 48 volts and 350 pounds weight.  This vehicle
is  fitted with  a  semiconductor-controlled  rectifier  (SCR)  pulse-
controller system of novel design,  developed by Lansing-Bagnall Ltd.
Tests  have been made  over several hundred miles  and the range  in
open country at a speed of about  25 mph is 50 to 60 miles. On tests
in commuter traffic  this car has traveled 27  miles with  117 stops on
one charge.

    Ford Company of Great  Britain  is building  two models ulti-
mately  to be fitted with the sodium-sulfur  batteries under develop-
ment at the Research and Development center in Detroit. It is under-
stood  that the  initial trials will be made with  conventional  storage
batteries.

    An interesting development in France is a battery-powered bus
made by Sovel for operation in the airport of Marseilles. In Italy the
Fiat Company  is understood to be experimenting with electric cars.
The Urbanina, made by Bargagli  Cristiani of  Santa Groce,  a small
car for  town use, of very novel design, was  recently demonstrated at
the Italian Motor Show.
112
                                           European Developments

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    All  of these vehicles are powered by the well-proved lead-acid
storage batteries. Recognizing the limitation imposed by the weight
of these batteries, engineers are examining all  aspects of the vehicle
to obtain the best performance possible, e.g., the use of SCR pulse-
control  systems  to  ensure  the  maximum efficiency  of  use of the
battery, design of chassis and body to keep the weight to a minimum
and provision of regenerative braking, which is estimated to  increase
economy of power by 15 to 30 percent.


           FUEL CELLS  AND METAL-AIR CELLS

    Three  industrial  companies  in  Great Britain are  actively en-
gaged in developing fuel cells, some of which could be used to power
electric  vehicles.  Shell Research Ltd., who has  demonstrated  units
of about 1-kilowatt capacity with an alkaline  electrolyte consuming
hydrazine and hydrogen and a 5-kilowatt hydrogen-oxygen battery
linked to a methanol reforming unit,  has lately  turned attention to
cells with  acid  electrolyte, breathing  air.  Figure  3 shows a  300-
watt battery of this  type  with a sulfuric acid electrolyte  (private
communication with  K. R.  Williams,  Shell  Research  Ltd.).  Two
marked advances have been made recently.  The first concerns the
use of porous plastic substrates with higher temperature stability than
materials used earlier; the  second concerns the hydrogen and oxygen
electrodes,  which are now capable of working at current densities as
high  as  500  milliamperes  per  square  centimeter  in sulfuric acid
at a cell voltage of 0.6 volt.

    Energy Conversion Ltd., who is associated with Pratt and Whit-
ney Co.  and  is  working on a  variety  of systems, has  recently de-
veloped a methanol-air battery with internal reforming and hydro-
gen diffusion membranes of palladium-silver  alloy.   A 4-"bi-cell" is
shown in Figure 4  (private communication with J. C. Hart, Energy
Conversion Ltd.). This works at 200° to 250°C and has an output
of about 170  watts at 2.7 volts overall.  By virtue of  their agreement
with Leesona Moos, Energy Conversion Ltd. is also engaged in  work
on the zinc-air system.

    Electric Power Storage Ltd.,  a member of the  Chloride Group
of Companies, has been working primarily with hydrogen-oxygen or
air  and hydrazine-oxygen  or air cells (Barak, 1963). Many 60-watt
cell modules of each type have been built and have given satisfactory
lives up to 10,000 hours on test (Gillibrand and Gray, 1966).  Typical
cells are shown in Figures  5 and 6.  Batteries of 1 to 2 kilowatts have
also been built. Figure 7 shows a 2-kilowatt hydrogen-oxygen battery
of 63 cells, having  an overall voltage on load  of about  36  volts
mounted on a small industrial  truck.

    Joseph Lucas and  Co.  has  recently announced  association with
General Dynamics in the development of semi-fuel cells of the zinc-
air  type; experimental  work on these systems is also being  done by
Energy  Conversion  Ltd., and by Electric Power  Storage Ltd.
BARAK                                                       n3

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 Figure 3.   300-watt  methanol-air battery  with  sulfuric
          acid  electrolyte  (Shell  Research,  Ltd.).


           OTHER DEVELOPMENTS IN EUROPE

    In Germany, the Varta Company  has been engaged in fuel cell
development for some years and  recently demonstrated  a fork-lift
truck powered by a hydrogen-oxygen fuel battery of about  2  kilo-
watts with an overload factor of about 3. This battery has electrodes
of  the sintered nickel, DSK type developed by Justi (1962), giving
energy densities  of about 10 watts per pound and  about  1 kilowatt
per cubic foot (Justi and Winsel, 1962).
114
European  Developments

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   Figure  4.   120-watt  methanol-air battery  operating
          at 200°C  (Energy  Conversion,  Ltd.).
BARAK
                                                      115

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     Figure 5.   60-watt,  low-temperature, H2-02 cell
               (Electric  Power  Storage,  Ltd.).
    Siemens-Schuckertwerke has also experimented with hydrogen-
oxygen fuel batteries as a means of propulsion.  Using electrodes of
the Justi type, Siemens has built a 24-volt assembly  with an output
of about 400 watts to power a small boat. (Sturm, Nischik and Weid-
lick, 1966).  Siemens has  stated however, that "predictions of fuel
cells entering  into the fields of automobiles  and large-scale power
generation are purely speculative and must be considered unrealistic
in the light of  present knowldge"  (Sturm, 1966).

    In France, the  Office  National Industrial de 1'Azote  (O.N.I.A.)
has experimented with cells of the  Bacon  type working at  about
200°C and  at both high and atmospheric pressures (Laroche, 1965).
Units up to 2  kilowatts have been constructed, and  a battery of 20
kilowatts is under development.  To  avoid the problem of carrying
heavy bottles  of  gas, O.N.I.A. is developing  batteries with built-in
units such as ammonia-crackers to produce on-site hydrogen.

    Compagnie Generale  d'Electricite  (C.G.E.) is  engaged in work
on low-temperature hydrogen-oxygen cells  and has produced units
with outputs up to  1 kilowatt (24 volts)  (C.G.E., 1966).

    In Sweden, Allmana Svenska Elektricka Aktiebolaget  (A.S.E.A.)
is carrying out a considerable program of work in the development of
116
European  Developments

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low-temperature hydrogen-oxygen fuel batteries (Lindstrom,  1966).
Using sintered nickel electrodes of their "quadrus" type with  nickel
boride catalyst, A.S.E.A. has  made  a number  of  5-kilowatt units,
some of which have been tested on fork-lift trucks and also on other
large industrial trucks. A.S.E.A. is also building a 200-kilowatt  unit
that consumes hydrogen from an ammonia cracker to power a coastal
submarine.
       Figure  6.   60-watt, low-temperature,  N2H4-02
        oxygen  cell  (Electric  Power  Storage,  Ltd.).

    In Switzerland,  Brown, Boveri Co., Ltd.  is experimenting with
low- and high-temperature systems that consume a variety of fuels,
particularly methanol and hydrogen (Plust, 1966). Though primarily
looking at  low-output applications such as harbour buoys,  TV  re-
peater stations,  and so  on,  the  company  has  a high-performance
H2~O2 unit of several hundred watts output.  In  Italy, the Fiat Com-
pany  is also known to  be experimenting with low-wattage units
that consume hydrogen and to be looking at possible developments
of electric automobiles.

                          SUMMARY

    Several European Companies are exploring  possible uses  of fuel
batteries for electric  traction with  the  system  generally  chosen
being the low-temperature hydrogen-oxygen (or air) cell. Although
none of these developments has yet reached the  stage where it could
BARAK                                                       117

-------
be adopted for passenger vehicles, they should supply data for proper
feasibility studies in the near future.
    Some of these systems could meet many  of  the  requirements
in the specifications in  Table 2, but none could be  made at a cost
anywhere near the limit  of £20  ($56)  per kilowatt.  Much of the
capital cost of  fuel  cells  is absorbed in the noble metal catalysts.
Some progress is  being  made in reducing the amount necessary, but
this is slow and the search for cheap alternatives that could be used
with cheap low-grade fuels has not so far achieved a breakthrough.
The materials of  construction and other components also appear to
make the cost prohibitive. Whether  these problems can be solved
will depend on the progress made during the next few years.
  Figure 7.   2-kilowatt,  hydrogen-oxygen  low-temperature
      battery  on  an  industrial  truck  (Electric Power
                        Storage,  Ltd.).

                          REFERENCES
Barak, M.,  1963.  Some developments in fuel cells.  In:  Fuel cells.
    Chemical  Engineering Progress Technical  Manual.  American
    Institute of Chemical Engineers, New York, N. Y. p. 74.
Barak, M., 1965.  Developments in electrochemical energy-conversion
    devices, batteries and fuel  cells.  Proc. Inst. Elec. Engrs  112-1439
    (July).
118
                                         European Developments

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Compagnie, Generale d'Electricite, 1966.  Les piles a combustibles on
    centre de  recherches de  la  Compagnie  Generale d'Electricite.
    Marcoussis, France (Oct.).
Electricity Council, 1966.  British electric passenger cars.  An interim
    report.  Electricity Council, London  SW1, England. (Mar.).
Gillibrand, M. I., and  J. Gray, 1966.  A  Ikw  hydrogen fuel battery.
    Presented at 5th International Power Sources Symposium, Sept.
    1966, Brighton, England.  Publication pending in:  Power sources
    1966.  Collins, ed.  Pergamon Press,  Ltd., London, England.
Hender, B. S., 1965.  Recent developments in battery electric vehicles.
    Proc.  Inst.  Elec. Engrs. 112:2297-308 (Dec.).
Jeremy, K. W.  C., 1966. The electric car.  Report by  the Electricity
    Council's Appliance  and Method  Research  Panel.  Reproduced
    from  the March/April edition  of  Electricity, published by the
    Electricity  Council, London SW1, England.
Justi, E., and  A. Winsel,  1962. Kalte Verbrennung.  Franz Steiner
    Verlag G. m. b. H., Wiesbaden, Germany.
Laroche, J., 1965.  Les  piles a combustible a  moyenne temperature.
    Revue Generale de 1'Energie. 74: 63-66.
Lindstrom, O., 1966. Fuel  cells for traction purposes.  Electrical Rev.
    pp. 243-46  (Aug. 12).
Plust, H. G., 1966. Aussichten der Brennstoffzelle als Automobilantrieb.
    Automobil  Rev. No.  25.   Special  publication by  A.  G. Brown,
    Bovin and  Cie., Baden, Switzerland.
Sturm, F. v., 1966.  Electrodes in fuel cells.  Siemens Rev. 33:118-23
    (Mar.).
Sturm, F. v., H. Nischik,  and E. Weidlich,  1966.  Fortschrifte  in der
    Brennstoffzellen-Entwicklung. Ingenieur  Dig. Vol. 2, issue 5.
BARAK

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 AUXILIARY SYSTEMS:  component

 development; other aspects of  the total

 vehicle system.


    Having worked with  energy conversion and batteries since 1934,
 I am gratified to see the progress made in new and promising systems,
 either in  production or in advanced stages of  development.  Before
 World War 17 the only secondary batteries were  the lead-acid and
 nickel-iron  in  this  country  and lead-acid,  nickel-cadmium,  and
 nickel-iron in Europe.

    At a time when a  new urgent requirement for  high-energy
 systems arises, many candidates are available thanks to the foresight
 of DOD and NASA in promoting  very  effective and far-reaching
 investigations of  energy conversion systems from the beginning of
 World War II to the present time.

    If similar efforts had been made on the rest of the components
 needed for the  complete electric vehicle design, we  would be much
 nearer to a matched power source and electric vehicle system.

    We will go through a period of overdesign (larger power require-
 ments) for the power source until a more efficient  motor and control
system are available. Thus, I strongly recommend that concentrated
efforts be  made to stimulate work in these other areas to bring them
abreast of the power source effort.
                                                         121

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     I do not subscribe  to the continuous complaint that the electric
vehicle is impractical because of the lack of a suitable power source.
This is true  only  because  of the lack of development work on  the
rest of the components and systems required.  A practical  electric
vehicle must be developed from the ground up as a system and  not
as individual components.   We  should not  blame  the power source
for inefficiencies of the remainder of the  system.

     Although the power sources under development are not yet a
final product, toe  can feel  proud of the advances to date  and  the
number  of candidates  available for  design  into  the  proper  end
product. With  a little  down-to-earth planning  there  is  no reason
why a successful system cannot be developed in the next 5 to 10 years.

    Along with this  development another  major problem arises —
educating the public to accept a practical electric  vehicle regardless
of appearance and limited  performance. This  effort  may  require as
much time as developing the vehicle.

                                   Paul L. Howard
                                   Consultant
                                   Centreville,  Md.
122

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          ELECTRONIC CIRCUITS FOR  SPEED
                CONTROL  AND  BRAKING


                          Victor Wouk

                      Gulton Industries, Inc.
                         Neio York., N.Y.

                           SUMMARY

    Modern high-power semiconductors in comparatively simple cir-
 cuits, controlling power from batteries that  are capable of being re-
 charged rapidly, make  a battery-powered bus technologically practical
 for some urban  applications. Regenerative braking can substantially
 extend  the  range between charges, in  stop-and-go  traffic, besides
 being a necessity for safety.

    Some basic  concepts of electronic circuitry incorporate  "off-the-
 shelf"  high-power  semiconductors  and  100-ampere-hour  cells that
 can be charged  at rates up to 1,000 amperes, for  an operational bus.

                        INTRODUCTION

    Experimental electric  vehicles,  operated with both batteries and
 fuel cells have  been developed utilizing modern high-power  semi-
 conductors and  power sources  (SAE,  1967).  David  Ash  (1967),  a
 car-performance analyst, stated that the performance of some experi-
 mental  cars compares favorably with  that  of conventional automo-
 biles.  An electric bus with electronic controls would give similar ac-
 ceptable performance.  High speed  and long range between charges
 are not mandatory  for a  bus  in  urban  traffic.   A battery-operated
 delivery van would also be satisfactory in urban applications, because
 a van  does not need  high speed  and  long range.  Hender (1965)
 reported that in Great Britain approximately  40,000  vehicles  are
 battery-operated.  The high cost of gasoline in Great Britain makes
 this particular factor of great importance, in addition to air  pollution
 reduction.  Since at  present no  major  economic  drive  in the United
 States would encourage the use  of battery-powered delivery vans, an
 initial political solution is  probably most acceptable.  For the intro-
 duction of battery-powered  vehicles for reduction of air pollution,
 I suggest that we start  with the battery-powered bus for the following
 reasons:

 1.  The  bus  is a much  more obvious offender than a delivery van as
   contributor to air pollution because it is  much larger and creates
   such obvious clouds of  exhaust.

 2.  There are fewer  buses  than  delivery  vehicles.

 3.  The  bus is  generally public-owned,  so  the problem of initially
   higher cost should not be a major deterring factor.
WOUK                                                         123

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4.  The sense of community participation  would  be much greater
   with a bus, since so many people ride buses.  Large numbers of
   citizens could experience pollution-free transportation,  thus  en-
   couraging further expansion of battery-powered vehicles as better
   power sources are developed.

                       SPEED CONTROLS

    The major objectives of electronic circuits for  speed control  and
braking, in comparison with "conventional controls", are these:

1.  Maximum utilization of stored  energy for driving the  vehicle,
   i.e., minimum power dissipation  in the speed controls  (for maxi-
   mum range between battery charges).

2.  Stepless speed control to simulate as closely as  possible operation
   of the accelerator of a conventional vehicle (for  acceptable vehicle
   performance).

3.  Regenerative  braking  controls  that  will return  energy to  the
   batteries  during the slowing-down of the  vehicle  (for further
   extension of vehicle range).

    The objectives can be met by means  of modern solid-state elec-
tronic circuitry. The degrees to which the objectives can be met are
essentially governed by economics. Although the developmental costs
of some automatic controls  may be high, with advances  in integrated
and etched circuits  techniques, the  actual electronic  logic  circuitry
can be cheap.

                 CONVENTIONAL CONTROLS

    Figure 1 is a typical example of conventional controls, as used in
the Henney Kilowatt.  The .batteries are switched from  parallel to
series-parallel  to series arrangement by  means of heavy-duty  con-
tractors.  Also,  the  field  winding  of the  motor  is  switched with
paralleled and  series resistance.

    The electric motor in  the "first  generation" of electric vehicles
can be a direct-current motor, "series" connected.  The direct-current
motor requires considerably fewer components and much simpler con-
trols than an alternating current  (SAE, 1967), and  since this paper is
confined to  vehicles for urban  use,  which  means short hauls  and
stop-and-go traffic, the increase in flexibility of performance possible
with alternating current is not discussed.  Further, the series direct-
current motor is recognized as ideal for vehicles, because  at low speeds
its high torque can be used for rapid acceleration.

    The control  method of Figure  1 is  a "lossless" speed control,
(except for the lowest speed), because essentially all of the power
coming from the battery goes into the motor. No power is dissipated
in loss elements to control  the speed.  This system is  not completely
satisfactory, however. Besides the operational disadvantage of contac-
124                            Speed Control and Braking  Circuits

-------
tors switching heavy currents (currents above 500 amperes have been
measured  in  performance of this  car),  which  can result  in rapid
deterioration  of  the contacts in heavy stop-and-go traffic,  the per-
formance is jerky.  Each time the system switches, the motor power
changes rapidly,  producing a  discontinuous  change of acceleration,
or a jerk.

    When  being interrupted  by a contactor, the  currents  develop
microscopic amounts of ozone.  The quantity is so small, that  even if
all internal combustion vehicles were  changed overnight to electric
vehicles with contactor controls, the  increase  in ozone  concentration
in urban  areas  would  be scarcely detectable.  Further,  the  use  of
electronic controls in any practical  electric vehicle (see next section)
would  eliminate all ozone.


                   ELECTRONIC CONTROL

    Figure 2 shows the basic circuit  that can  provide stepless power
control. This circuit is known variously as  ''variable  width  pulse,"
"pulse width modulation", or  "time  ratio control."  It  is  referred  to
herein as variable width pulse, or VWP

    In Figure 2, the source of power, assumed to be a battery,  is
permanently connected for maximum  voltage output.   A  switch (S)
is opened and closed rapidly to produce pulses of  controlled width
at the terminals (T) of the motor.  Across the terminals of the motor
is a diode (CR1),  connected so that it does  not  conduct when the
switch is closed.  The series motor field is (F), the armature (A).

    It can be shown (Wouk,  1962)  that if the  switching frequency
of the switch (S)  is high enough, then the motor will operate  as
though a steady direct-current voltage were applied to  the terminals,
the direct-current value being the average value  of the voltage ap-
plied.  This average is given  by the equation:
where
        tli2 = time on (See Figure 3)
        T = time between start of successive pulses.

    With the switch closed for a short percentage of the total period,
tj (Figure 3a), the equivalent  voltage Eollt,  applied to the motor is
low and ihe resulting speed is low.  The current that is drawn depends
upon  the load on the motor. If the switch is closed for a longer portion
of the period,  t2  (Figure 3b),  the effective voltage applied  to  the
motor terminals," is  higher, and  hence a greater speed is  called for.
The ratio of t/T is the "duty cycle."

    If the switch  (S) of Figure 2 is an electronic solid-state device,
such as a thyristor  (the generic term  for an SCR or semiconductor-
controlled rectifier), then it can  be  turned on and off with  great
WOUK
                                                                125

-------
                 POWER CIRCUIT
                                      50 mv
        KEY SWTCH
                 FORWARD-
                 REVERSE  -1-
         12V.  "SWITCH-DASH
NOTE:
     D DENOTES CONTACTOR
        AUXILIARY SWITCH.

        CONTROL CIRCUIT SWITCHES
        MARKED RS, FS, HI, FR, LO
        ARE CAM-ACTUATED.
             CONTROL CIRCUIT


  KEY SWITCH OFF
          Figure  1.   Diagram of conventional  controls.
   126
Speed Control and Braking  Circuits

-------
rapidity, in the order of microseconds. (With a solid-state control, the
current is  interrupted and started with no arcing whatsover, and ac-
cordingly  no ozone is generated. Thus the ozone problem discussed
earlier is completely academic.)
        u
   i-;
                                      CRI
                                    MOTOR
Figure  2.   Basic variable-width  pulse circuit  for stepless,
           "lossless" direct-current motor control.

    The function of the diode CRI of Figure 2  is to bypass the motor
current from the battery during the "switch off" interval.  Without
this diode, often called a free-wheeling diode, if the switch were to
attempt to interrupt the current in the inductive circuit of the motor,
high voltages would be generated that would vitiate the simplifying
assumptions.

    The circuit shown in Figure 2 can effect  motor voltage control
with no inherent power loss  (except  for unavoidable  dissipation in
the bypass diode  CRI, and in the switch itself). Also,  the following
additional performance  characteristics are readily obtainable with
simple feedback controls.

Smooth Acceleration
    Even if the accelerator were to be "floorboarded," i.e., depressed
so as to demand virtually continuous  conduction through the switch
(S), the  pulse width could be  increased  comparatively slowly to
ensure gradual increase of voltage application to the motor.

    This  "gradual" could be over a period as  short or as long as  is
desired,  depending upon acceptable  acceleration characteristics.  It
WOUK
                                                              127

-------
 could be adjustable from the dashboard to give the vehicle a "jack-
 rabbit" getaway characteristic, or a "little old lady" slow-acceleration
 characteristic  (presently  associated  with  electric-vehicle perform-
 ance).

(a)








F
'-





n





\

F









F ft m





—
L
j


                                                              LOW
                                                              SPEED
  (b)
                                    Eln (t2/T)
HIGH
SPEED
    Figure 3.   Waveforms of  voltage  applied to motor,
                     low and high  speeds.

Battery Current Limitation
    Circuitry can be incorporated  to  limit the battery  current, both
for automobile  performance control and for battery protection.
    Thus, with a stalled motor (starting against locked wheels, etc.)
the VWP could be maintained at a low value by circuits that would
override the position of the accelerator and thus prevent damage to
the control elements, the rectifiers, the motor  brushes, or possibly
the battery.
128
                               Speed  Control and Braking  Circuits

-------
"Wild-Eyed Automation"
    In principle,  such an electronic control  can be readily  adopted
to the "highway of the future" dream of completely automated  and
guided vehicles. Where starting  or stopping a car or controlling a
speed is a simple matter of electronic circuitry  (not  further linked
to mechanical systems in the control), then a true over-all electronic
control system can  be effected with all its attendant  possibilities of
accurate response, automatic control, and  other advantages.

    Figure 4 shows the relative  simplicity of the over-all controls.
The speed-control circuits develop signals determined by the position
of the tap on the potentiometer (Rl), which represents the  position
of the accelerator pedal. The signal developed from this block deter-
mines when the power SCR will be turned off  in the cycle shown
in Figure 3.
                              CR2
                                                          	1
      ACCELERATOR PEDAL
                  CONTROL
        DASHBOARD PICKUP CONTROL
      TO REGENERATIVE BRAKING
      CIRCUITS CONTROL
     Figure 4.    Block  diagram of control  circuitry  for
                       full  performance.

    If the current becomes too great the current detection could over-
ride the  speed-control circuit to limit  the current.  Further, if the
pulse width has been reduced to minimum and the current is still
excessive, then these circuits  could decrease the pulse repetition rate.

                      POWER CIRCUITS

    A feasible electronic power circuit  is discussed here to  illustrate
basic cost considerations.

    Data recorded on the Henney Kilowatt indicate that for accept-
able performance under maximum load, such as going up a long steep
WOUK
                                                              129

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hill,  500  amperes might be drawn from the battery  (Private com-
munication with C. Gold, Yardney Electric Corp, New York, N.Y.).
Hence, the electronic controls would have  to be  designed for  this
"worst case."  The 500 amperes  are not delivered  at  full battery
voltage, however, but at a lower  voltage, 25 volts, corresponding to
lower speed.  Therefore, the duty  cycle  would be, let us say, 25
percent. Figure 5a shows the required motor current of 500 amperes.
Figure 5b shows the applied motor voltage, assuming  100 volts from
the battery, with 25 percent  duty cycle.  The average of this is 25
volts, which we are assuming corresponds  to the voltage required
to provide the needed current and hence power for  the particular
mode of  operation.
   (a)
                    T
500 amp
MOTOR CURRENT

(b)

n 	




T
100 volts
1
T






25-volt average
T

MOTOR
VOLTAGE

(c)

0 	



~T
500 amp
1
T




125-amp average
T
BATTERY
CURRENT

        Figure 5.   Voltage and current waveforms to
               illustrate 25 percent  duty cycle.

    Figure 5c shows the current through the  power control switch.
Although the average current flowing is 125 amperes, unfortunately,
from an economic point of view, the heating and current ratings in
these semiconductors depend to a large  degree on root-mean-square
(rms) values of current.  In a pulse of this nature
                J-rms = Ipeak V
So, the rms of this waveform is 500/\/ 4, or 250 amperes. For reliable
design this is too close  to the maximum rating available  at present
from a single inverter type of SCR.  Hence, two SCR's would have to
be paralleled.

    If it were possible simply to parallel two SCR's, then each  would
handle approximately half the peak current,  or  250 amperes, with
each handling the rms current of 125 amperes, a safe value. Parallel-
ing SCR's simply and reliably usually is done by dissipative methods
130
           Speed Control and  Braking Circuits

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(Gutzwiller et al.,  1964).  A method of avoiding dissipation is to in-
corporate several SCR's, but operate them sequentially,  as indicated
in Figure 6, which shows  a possible complete power control circuit.
The rms currents would be 500 '\/ 8, or  178 amperes, a safe value.
The explanation of the mode of operation is shown in Table 1.  This
is a "dissipationless'' SCR  turn-off method in that the energy in the
capacitor is supplied to the load. Any losses are incidental,  i.e., not
inherent in the mode  of  operation.  As  components are improved,
efficiencies will be  improved.

    Figure  7  illustrates some of the more important waveforms of
voltage and current in  such a circuit. The relationships are complex.










	 E
















-k
CR2
CR3
^j
1
CR4 CR5



r—
E -
\I
CR6


M
^J^

be

CR7
fcl
*k




CR1 '




















M
0
T
0
F


\


  Figure 6.   Circuit  with sequential  conduction  of power
               SCR's for proper current rating.


  Table 1.  SCR's FIRING SEQUENCE and POWER CONTROL FUNCTIONS
Time
to
tn
t3
t6
SCR(s) Firing
CR2
CR5.6
NONE
CR3
CR4,7
NONE
CR2
FUNCTION
Start application of power to motor.
Apply reverse voltage E to CR2. This blocks
CR2, and commutates motor current to ca-
pacitor C.
C voltage reversed to E. All SCRs blocking.
Motor current flowing through CR1.
Per CR2.
Per t,, except CR3 blocked.
Per t,,.
Repeat cycle.
WOUK
                                                              131

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    All waveforms are idealized.  The motor current increases during
the power pulse and decreases during a portion of the turn-off pulse
and during  the free-wheeling interval.  Also,  substantial switching
transients of voltage and current  usually occur.  These  are neglected
for ease of understanding of the basic concepts.

    All designations in Figure 7 are in accordance with IEEE stand-
ards.  Lower-case letters  denote  instantaneous values.  Upper-case
letters denote average values, or  rms values, as would  be read by a
meter. We will examine Figure 7 in detail, part by part.
(a) The voltage -applied to the motor.  During the horizontal portion
parallel to the zero axis, voltage  is applied through CR2 or 3.  This
persists for  the interval t,, which  is adjustable for speed  control.  At
the end of the interval, when the appropriate turn-off thyristors are
fired (in this case CR5 and 6), initially the capacitor voltage adds to
the battery  voltage, so that the  motor voltage is doubled. Since it is
assumed that the  motor current remains essentially constant  during
the entire interval, the voltage across the capacitor reverses at a con-
stant  rate, so that the voltage  applied to  the  motor  drops to zero
linearly. It is this triangular position of the waveform that represents
the "dissipationless" turn-off, in that the energy in the capacitor is
supplied to the load.
(b) The motor current.  The motor current is assumed  constant.
(c) The battery  current.  Note that this current flows while either
power thyristor is conducting and also  during  the  interval that the
turn-off-capacitor, voltage-applying SCR's  are still conducting.

(d) The current  through one of the switching thyristors,  in this case
CR2.  Note that the current that flows is equal to the motor current,
and it is assumed that  the current turns off  instantaneously when the
turn-off  thyristors are fired.  Further note that the pulses  occur Vz
as frequently in (d) as they do in  (c), because of the sequential firing
previously discussed.

(e) The current  through  the second power thyristor, CR3  in  this
case.  Note  that the current is  displaced one period of motor pulse
frequency, T, but is otherwise identical.

(f) The current  through  the turn-off  thyristors  CR6  and 5.  This
current flows only during the interval following the turn-off of CR2.
Its magnitude is equal to the motor current.

(g) The current through the turn-off SCR's, CR4  and 7. This cur-
rent flows only after the turn-off of CR 3.  Its magnitude is equal to
the motor  current, and it  flows  only during the  capacitor voltage
reversal  interval.  It is identical to (f), displaced by T.

(h) The bypass diode current.  The current in  CR1  flows only when
all of the thyristors are extinguished and the voltage applied to the
motor  is essentially zero.  The magnitude of current is equal to the
motor  current. The shorter the interval tj, the greater  will be the
interval  that CR1 conducts.  It is further  evident  that the interval
132                            Speed  Control and Braking Circuits

-------
     (k)
    Figure  7.   Basic waveform for circuit  in  Figure  6.
WOUK
133

-------
depends on the interval that the capacitor is conducting.  These re-
lationships are examined at length in Wouk (1962).

(i)  The voltage across the turn-off capacitor C.  Note the trapezoidal
waveform, with the  voltage essentially  constant, either positive or
negative,  during the  power interval  and the free-wheeling interval.
It changes linearly from one polarity to  the other during the power
thyristor turn-off interval.

(j)  The power thyristors CR2 and 3. During conduction the voltage
across both thyristors is essentially  zero,  even though  only  one of
them is conducting.  At turn-off, the voltage goes negative, because
of the voltage across the capacitor,  which initially is equal to the
battery voltage.  The voltage rises linearly from —E to +E, as the
polarity of the capacitor is reversed.  The interval between the time
that the voltage initially goes negative and  the time  that it  rises
linearly again to zero, is known as  the  turn-off interval (t0).  The
capacitance must be large enough to ensure that this interval is greater
than  some specified minimum (currently as low as 20 microseconds
for inverter-type high-power thyristors). This interval  of 20 micro-
seconds, in conjunction  with the maximum current that ever has to
be  turned off, determines the size of capacitor required by the re-
lationship:

                 C — — x t
                 u - Y   °

This implies that with a light load, the "tail-off" will be longer. Since
tj is usually correspondingly reduced, for an application such as this,
it probably would never be necessary to modify the pulse repetition
rate  (T).  This is analyzed at great  length  in Wouk  (1962). During
the free-wheeling  interval, the voltage  across the power thyristors
is constant, equal  to the battery  voltage.  Note  that there  are no
rapid rises, or high rates of de/dt, in this circuit, which simplifies one
of the design  problems  of employing thyristors, since no thyristor is
subject to a rapid forward increase of voltage that might cause it to
turn  on spontaneously.

 (k) The  current  through  the turn-off  capacitor.   This  current  is
alternating, with the rectagular  peaks  equal  to  the motor current
and lasting during the  turn-off interval of the power thyristors.

     We emphasize that this circuit is only typical of many that may
be  developed; undoubtedly properly applied ingenuity  will reduce
the number of costly components without introducing other energy-
dissipating elements.  None of the  engineering subtleties of circuitry,
such as "softening" circuits or saturating reactors, are  included in the
 circuit to reduce the di/dt through semiconductors.

     At present such semiconductors are expensive.  Using General
 Electric's type C185C for the power, type C55C for the  commutating
 SCR's, and type A295B for the bypass diode would  cost about  $400
 in  large quantities.
 134                            Speed Control and Braking  Circuits

-------
                  REGENERATIVE BRAKING

    In an urban vehicle, subject to frequent start-and-stop operation,
with the  slowing  down time equalling an appreciable part of the
accelerating time,  a significant amount of power  can  be regained by
the battery  if the kinetic  energy of the moving  vehicle  is returned
by some reasonably efficient system into the batteries.  Calculations
of the watt-hours  that  could  be returned to the  battery  in  a bus
slowing down from 30 mph to a halt are given at the end of this paper.

    One of  the reasons  for  the  disfavor of regenerative braking in
the past,  as  applied to  battery-powered  vehicles,  undoubtedly has
been  the  enormous regenerative  braking currents.   Batteries  that
normally  could have  accepted  such rates of recharge would  have
required  substantial overdesign  for  normal  operations.  With the
availability  of  high-speed recharge nickel-cadmium  cells, regenera-
tive braking now  becomes practical for a  battery-operated  bus.

    The calculations are completely theoretical and assume no losses
whatsover.  Even  if the losses  in the regenerative braking process
reduce the actual range  of extension, regenerative braking offers im-
portant advantages above  and beyond range  extension.

    One of  the advantages is safety of operation.  Existing  battery-
powered  vehicles  give  the  driver  free-wheeling on straightaways,
which may  not be  undesirable, except for  the uneasy feeling it  may
give the  driver that he has no  control over the  car.  Down  steep
grades, however, the problem of brake failure is a serious one, and
the braking action  of regenerative braking  adds an  important dimen-
sion to driving safety. It acts  as a safety device in  slowing down the
car, and  in  addition to the incidental  advantage of recharging the
batteries, it also lessens wear and tear on the brakes.

    Figure  8 shows the basic connections required for regenerative
braking.  An additional component is required,  in this  case  shown
as CR2, to conduct the  power from the armature of  the motor back
to the battery.

    As indicated  briefly before, the circuit of Figure 6 is  indeed  in
free-wheeling  through CR1, when all SCR's  are  open,  corresponding
to the foot off  the  accelerator.  The current that may  have existed
when  the foot  was removed  from the  accelerator  would decay  to
zero,  because of circuit  losses in the circuit that consists  of the three
basic elements — the armature, the field coil, and the diode. A very
slight braking action  is not even possible, because without the field
being reversed, the motor  could not act as a generator. To be a  gener-
ator,  the  current would have to flow out of  the  terminals  as shown,
rather than into them, and the current could not flow in this direction
through the diode.

    Figure  8 shows how motor braking can be introduced, under the
assumption that to minimize maintenance problems the design ob-
jective prohibits the  use  of contactors. For the motor to act as a
 WOUK                                                         135

-------
 generator, the series field would  have to be reversed. Since this is
 assumed undesirable, an additional field coil, which could be a shunt
 field, would  be employed.  Current could then flow as shown  from
 the armature through CR2 into the battery, recharging the battery.
                       CR2
                                           SERIES
                                            FIELD
                          CR1
                             CR3
                                      SEPARATE
                                       CONTROL
                                        FIELD
  Figure  8.   Basic connections for regenerative braking.
    The amount of current flowing back into the battery is given by

                     Eg — ECR2 — Eb                          (2)
                I =.
                            R
where

Eg = the voltage generated by the motor, now acting as a generator.

ECR2 = the voltage across CR2.

Eh = the battery voltage.

R = the sum of all circuit resistance, including internal resistance of
    the battery, the generator, and the wiring.
(3)
    The generated voltage is shown by
                Eg = k$w
where

k = a constant.

4> = the flux density in the control field.

w = angular velocity of the armature, which is directly proportional
    to car speed. Therefore equation (3) can be rewritten
                   = k$v
(4)
136
                              Speed  Control  and Braking Circuits

-------
    As  the vehicle slows  down,  if all  other parameters are held
constant, the  generated voltage will drop and the feedback  power
will  drop,  causing the braking effect to be  reduced.  This action is
contrary to present operating experience.  Because mechanical brakes
are usually Coulomb  braking, i.e.,  constant  braking force (within
limits),  the field strength  (4>) must  be  increased as the speed  de-
creases, until  it is  impractical to increase the field strength further
to compensate for the  lower velocity.

    The foregoing implies indirectly, and it should be  stated here
directly, that  regenerative  braking cannot bring the vehicle to rest.
The  function  of  regenerative braking is  to  return as  much energy
as possible to  the battery, not to  stop the car. The brake pedal will
therefore be somewhat more complicated in  overall function than at
present. For the start of brake travel, the regenerative braking will
take place, but as the car reaches some minimum  speed  the braking
force will be eliminated by the motor and the operator will have to
depress the pedal farther to put mechanical braking into effect.  Since
the kinetic energy is proportional to the  square of the velocity,  re-
ducing  the speed to  Vi initial value will absorb  90 percent  of  the
initial energy.

     Here again the electronics will lend themselves readily to auto-
matic control.  Depending  upon  pedal pressure,  the  field  strength
could be controlled automatically to maintain constant current into
the  battery  independent  of  speed,  with  mechanical  feedback  to
simulate present operation of the foot pedal.

     Figure 9  shows  a  possible  implementation of such  a  circuit.
CR1 and CR2  are the power control SCR and the bypass diode,  re-
spectively, for normal-drive operation; these are assumed inoperative
when the  driver's  foot is off  the accelerator.  If the brake pedal is
depressed, the rheostat shown will be activated by  hydraulic pressure
and will turn on the transistor through the transistor control circuits.
These in turn will apply current to the shunt field, which generates a
voltage at armature  terminals  1  and  2.  Simultaneously  CR3 is
turned  on  as the voltage is generated at the armature terminals,  de-
veloping a voltage higher  than the  battery voltage. When  the SCR
fires, current  flows  into  the battery  at  a  rate determined   by
equation  (2).

     The current can be detected by the same or a different current
detecting circuit mentioned with respect to Figure 4. In all  events
this current can be maintained constant  by automatic circuits, which
will control the current  through  Ql  and hence  the current into the
shunt field coil, which in  turn determines the  battery current that
will flow.  As the motor  slows down,  the transistor can be  driven
further into conduction.

     As a  final example of the  value  of regenerative braking  and
the  magnitudes  of current involved,  Figure 10  shows some  of  the
parameters of a 3,000-pound vehicle being  held to a  10-mph speed
on a 10 percent grade, with  100 volts of batteries being recharged
 WOUK                                                        137

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A A A
I vVV
N CR3
p '
j /^r^~\
CRl^
CR2'
SERIES +
C
1
°vl

BP
cor

2 J
t


AKING
^JTROLS- —
1
'1 R1 1
LWW
— " ^
BRAKE
PEDAL
RHEOSTAT 	 |
to MOTOR
CURRENT
DETECTION
CIRCUITS
        Figure 9.   Circuit  diagram  for controlled
                   regenerative  braking.
                               POWER = MGV(SIN$)
          M = 3,000 Ib
          V= 10 mph
          $ = 10% GRADE
   P = 6 kilowatts
   I = amperes at 100 volts
    Figure 10.   Regenerative  braking requirements of
                 automobile on downgrade.
138
Speed Control and Braking Circuits

-------
through  regenerative braking.  The recharging  current would  be
approximately 60 amperes.

    For  a 30,000-pound  bus under  similar circumstances, with  300
volts worth of battery, the recharging current would be 200 amperes.

    These figures indicate why, for practical applications in a battery-
powered vehicle, "dynamic braking," where the power is sent into a
resistor  (which  would allow braking  action down  to  much lower
speeds),  is impractical.  On  a :l-mile grade, for example, where the
resistors  would  be  absorbing power  for 6 minutes, the resistor bank
would have-to  be  disproportionately large to absorb and dissipate
the energy properly.

                         CONCLUSION

    In a battery-powered vehicle, electronic circuits can  perform the
functions of electric motor control for maximum utilization of battery
power and can  provide performance similar to that  of conventional
fuel engines.  In addition, electronic controls  can  allow  regenerative
braking,  which  will provide performance similar in most respects to
conventional braking on  conventional automobiles. The circuits that
will obviously work at present, even in quantities of thousands, will
be substantially more expensive than the simple mechanical controls
for a conventional automobile. However, if we apply the lower prices
of low-power semiconductors, the outlook  is  much more attractive.
In an application such as a bus,  where the complete elimination of
the contribution to  air pollution is invaluable to the  community, the
added initial  cost of the  battery-powered bus is negligible.

    The  possibility  of polluting the air  with ozone, discussed earlier,
is purely academic  when  semiconductors are used. Some  people have
also shown concern  about the strain on the electric-power-generating
capacity  of the  United States  if battery-powered vehicles were  used
widely.  This  concern is  completely unnecessary, because  if all in-
ternal combustion engines were converted to battery-powered vehicles
overnight, the load requirements  on the electric utilities  would  be
approximately doubled.  Calculations of  power-generation are also
given at the end of this paper.

    All  facets of the air pollution  problem  point to the  great  de-
sirability of putting into  operation at once, with today's technology,
a  battery-powered  bus.   When  tomorrow's  technology eliminates
the problems of range,  speed, and  initial  cost of  battery-powered
buses, we will all be able to enjoy the benefits of this pollution-free
type of transportation.
     CALCULATIONS OF POSSIBLE EXTENSION OF RANGE
     BETWEEN CHARGES WITH REGENERATIVE BRAKING

    Data recorded on the Henney Kilowatt indicate that  a  car with
four passengers running  on a level at 30 mph draws approximately
WOUK                                                         139

-------
60 amperes at 40 volts (Private communication with C. Gold, Yardney
Electric Corp,  New York,  N. Y.).   (100 volts  of  100-ampere-hour
cells are  used.)  This  represents a  drain of 2.5 kilowatts, with a
load of 2,600 pounds, car and passengers.

    For a bus with 10 times the number of passengers, assume 10
times the  total weight, and  10 times the "road load", or 25 kilowatts;
to keep   the  ''steady" current  below  100  amperes,  use 300-volt
batteries.

    Then

        Mass of bus = m =	:	~— = 11.8 x 103 kg
                            2.205 Ib/kg

At 30 mph,
        v = 30   x    1.4667         x   0.3048      =  13.4 mps
           (mph)     (ft/sec/mph)     (meters/ft)

    From National Safety Council charts, the safe stopping distance
at 30 mph is 90 feet.

        90 feet = 90 x 0.3048 = 27.43 meters

    Assuming  constant braking effect,  so  speed reduces linearly to
zero,
                            13 4
        average velocity = —— = 6.7 mps

                                 27  43
        time to come to stop T = 	— = 4.1 seconds
                                  6.7

        Initial bus kinetic energy =  0.5 mv2
        = 0.5 x (11.8 x 103) x  (13.4)2 = 1.05 x 10fi joules

    If all of this  energy were  fed back to the battery by bringing
bus to a halt, then
                         1.05 x 106 = EIT
where
        E = battery voltage, assumed  300 volts for a large bus
        T = 4.1 seconds
              1.05 x 10"
        1 =  4.1 x 300 ^ 85° ampereS

    Thus, the required value of  current  for successful  regenerative
braking is well within the range that some nickel-cadmium batteries
can absorb.

    The energy absorbed during  stopping, approximately 106 joules,
will drive the  bus, at the assumed 25-kilowatt drain,  for a time

             106
 140                            Speed Control and Braking Circuits

-------
a distance of
        40   1X
        ~X ^ =  ^ mile- at 30
    The  assumed battery capacity of 300 volts, 100 ampere-hours,
will run  the bus continuously for approximately
        300 x 100
    In an urban area such as congested midtown  Manhattan, this
distance  (30  miles)  is more than adequate.  Regenerative braking,
which may extend the range by 25 to 50 percent, renders the battery
bus concept even more practical.

   CALCULATIONS OF  ELECTRICAL-POWER-GEJVERATIWG
 CAPACITY  REQUIRED  FOR INSTANT CONVERSION  OF ALL
      CONVENTIONAL  VEHICLES TO  ELECTRIC  DRIVE

    The  following figures are based on approximate  parameters  in
a region such as New York State and are  rounded off for ease  of
calculations.

(1) Assume number of vehicles = 10,000,000 = 107
    This value is the correct order of magnitude for New York State.
(2)  Assume horsepower per vehicle  =  250.
    A reasonable assumption; horsepower  of buses and  trucks,  is
    higher, and of many small cars, lower.
(3) From (2), kilowatts per vehicle = 250  x 0.746  = 200 kilowatts
(4) Assume  present electrical-power-generating capacity in New
    York State = 20,000,000 = 20 x 10" kilowatts.

    This value is fairly close to the actual figure.

    At first glance, it might appear as though the additional power
required is  indeed formidable.  From  (1)  and  (2),  the  additional
capacity needed =

(5) 200 (kilowatts per vehicle) x 107 (vehicles) = 200 x 107 kilowatts

    From (4) and (5) the additional power required is

(6)       (5)/(4) = 200 x 107/  20  x 10fi = 100
    i.e., the generating capacity would have to be increased 100-fold.

    This figure looks formidable and has been quoted in newspapers;
however, this reasoning incorporates two  major fallacies.

FALLACY 1:
    The 200-kilowatt power figure  of  equation  (3)  is peak power,
used only infrequently, when the vehicle accelerates rapidly or moves
up steep inclines. The average power  required is substantially less.
WOUK

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    Taking into account the lower average power requirement, plus
the acknowledged greater  efficiency  of a  battery-electric  motor
system, one might estimate the average power requirement  at  20
kilowatts. So, from (6):

         (7)  100 x - = 10, or a tenfold increase.
           '        200 kw

    The tenfold increase is still substantial.

FALLACY  2:
    Vehicles are NOT used 24 hours a day.  Considering values from
24 hours a day for some taxis to 2 hours a week for some suburban
cars, we can reasonably estimate an average use of 2.4 hours  a day.
Using  (6) and  (7) and 2.4 hours, we get

                   20 kw   2.4 hr
     i.e.,  the order of magnitude of increased electrical power re-
quired is a doubling, not a  100-fold, multiplication.

     The recharging process for batteries is not distributed uniformly
during the day. If we assume the worst, that all vehicles are plugged
in at the same time  and recharged in  8  hours,  then the value in
equation (8) would be tripled.

     Nobody expects  electric vehicles to  replace internal combustion
engines  overnight. More probably, where battery-powered vehicles
are brought into use, the changeover will take place in 10 to 20 years.
The electric utilities can readily absorb, with their anticipated normal
expansion,  the  additional  capacity  needed  for  battery-powered
vehicles.

                           REFERENCES

Ash, D.,  1967.  On a clear day you will  see the electric car.  New York
     Times,  Magazine  Section.  (Jan. 29).
Gutzwiller, F.  W., (editor), 1964. Silicon controlled rectifier manual.
     3d  ed.   Rectifier  Components  Dept.,  General  Electric  Co.,
     Auburn, N. Y.
Render, B.  S.,  1965. Recent developments in battery electric vehicles.
     Proc. Inst. Elec. Engrs. (London), 112:2297-308 (Dec.).

Society  of Automotive Engineers, 1967 (Jan.  13).
     E. A. Rishay, W.  D. Bond and T. A. Zechin.
         Electrovair — a battery electric car.  SAE Paper No. 670175.
     A. Kusko and  I. T. Magnuson.  Vehicle electric drive systems.
         SAE Paper No. 660761.

Wouk, V., 1962. VWP:  a new approach to  small, light,  efficient high
     power  regulated power  supplies.  1962  Institute of  Radio En-
     gineers International Convention Record, Part 6.
 142                            Speed Control  and Braking  Circuits

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             THE MECHANICAL  DESIGN  OF
                ELECTRIC  AUTOMOBILES


                         Carl A. Vansant

                Operations Research Incorporated
                        Silver Spring, Md.

    It is not necessary  that  the  mechanical design of electric cars
differ from  that of conventional  automobiles.  Indeed, many of the
electric cars that have been built have  substituted  an electric prime
mover for  the  gasoline  power plant in an  otherwise conventional
vehicle. There is the feeling, however, that totally new designs might
provide better  electric  vehicles than can  modifications of standard
vehicular designs.

    One difficulty of  the electric  vehicle is that  batteries plus  elec-
tric motors  are costly and heavy  in comparison  to the gasoline en-
gines that can do similar jobs. There has been no competition. In its
technical performance as a torque  producer,  the gasoline engine  is
far ahead of any prospective challengers. If, however, a valid reason
exists for considering electric  motive sources, we have no good reason
not to exploit  any mechanical design  possibilities inherent in the
new power source.

    For vehicular elements other  than the power source,  there  is no
need  for complete redesigning. An electric  automobile  would em-
body the same components,  except for the propulsive elements, found
in conventional  cars  —  but they  may look different,  be  made  from
different materials,  and  such.  We are fortunate that  automotive
technology endows us with  a  rich  art from which to draw know-how
appropriate to our purpose.

    Somewhat  aside  from  the  internal  engineering  aspects are
mechanical  design factors relating to the marketing and use of elec-
tric cars.  At the  present stage it is well  to take  these  factors into
account,  since  they  have a  quite  significant  part in the  decision
whether or  not to design and build electric cars at all.  Part of our
purpose here is to construct  images of clearly desirable and useful
automotive  transportation  systems that  are  consistent  with  tech-
nological capabilities  and economic  realities.

        ELECTRIC VERSUS CONVENTIONAL CARS

    Electric vehicles  can be  superb machines. The persistent prob-
lem that must be reconciled in all electromotive  designs,  however —
that of storing sufficient  energy in a less-than-enormous package and
at a cost that can be afforded — is the battery problem. It dominates
even  the  mechanical design of  electric vehicles.  Except  for this
problem, wholly  satisfactory electric  vehicles  could be made  by
VANSANT                                                     143

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merely replacing the engines of conventional cars with electric motors
and batteries.
    The conventional  gasoline-powered car is  the standard against
which electric vehicles will inevitably be compared. Modern  auto-
mobiles typically  have weight-to-power ratios  on the order  of 20
pounds  per road horsepower.  Reid  (1966) shows,  on  the basis of
published  figures,  that  contemporary  cars  have  weight-to-power
ratios of about 10.9 pounds per horsepower. This  figure is degraded
to around 20 when "road" horsepower is considered.
    These  numbers  are  significant in  assessing the broad potential
of electric cars.  For example, 20 pounds per horsepower is a typical
weight for  electric motors of standard design and construction.  Thus,
it is  practically  obvious that, barring radically  improved motors, an
electric  car even without batteries could not match the  performance
of a conventional automobile.  The energy-to-weight ratio of modern
cars, 80 watt-hours per pound  — and that is  for the entire car — is
better than the  energy density of even the superior silver-zinc bat-
teries.  If,  then, by  some miracle  one could  effect propulsion  from
a battery alone, sans car, the machine still would not  be attractive
on the basis  of  energy density.  Because of the  low energy density,
the range of  electric vehicles will necessarily be limited.

                  AUTOMOTIVE ENERGIES

    Power must be provided in an  automobile  for  both  propulsion
and accessories. In general, propulsion power is applied to raise the
kinetic and potential energies of the car and to overcome frictional
and  drag forces.  The stored  energies are potentially  recoverable,
but energy applied to overcome  frictional and drag  forces  or to
operate accessories is not. The distribution  of automotive  energies is
considered in the following paragraphs.
    Modern low-profile,  low-pressure tires allow a comfortable ride
and good handling, but they consume a significant  amount of energy.
Tire rolling resistance is a function of a number of parameters, in-
cluding specific  tire  design, materials of construction, tire diameter,
car weight, and vehicle speed.

                 Table 1.  ENERGY LOSS IN TIRES"

                                       WEIGHT, Ib
kw-h/mile
0.008
0.010
0.012
0.014
0.016
0.016
0.020
0.024
0.028
0.032
0.032
0.040
0.048
0.056
0.064
0.048
0.060
0.072
0.084
0.092
0.064
0.080
0.096
0.112
0.128
    "From Campbell and Hunsberger, 1962.


144                                             Mechanical Design

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    Table 1 shows the approximate energy requirement, in kilowatt-
hours per  mile, to overcome  tire rolling resistance for variations in
car weight and in the tire  rolling resistance coefficient.  The  typical
modern car requires nearly 0.1 kilowatt-hour per mile  to overcome
tire rolling resistance.


        Table  2.   ENERGY LOSS DUE TO AERODYNAMIC  DRAG"
                        (at constant 35 mph)
Air resistance
coefficient,
Ib-hr2/
(ft-mile)2
0.0006
0.0008
0.0010
0.0012
0.0014

15

0.022
0.029
0.037
0.044
0.051
FRONTAL AREA, ft2
20 25
kw-h/mile
0.029 0.035
0.039 0.047
0.049 0.059
0.059 0.071
0.069 0.082

30

0.046
0.059
0.074
0.088
0.103
    "From Campbell and Hunsberger, 1962.

    Energy is also  consumed by  aerodynamic resistance.  Table 2
shows these energy losses for variations in drag coefficient and in the
frontal area of the car.  Of course, aerodynamic drag is strongly de-
pendent on speed.  Table  3  shows the  effect  of speed  on the aero-
dynamic losses of the typical modern car. For the typical car, aero-
dynamic losses predominate over other losses at speeds of  about 45
mph and greater.


         Table  3.  ENERGY  LOSS DUE  TO AERODYNAMIC DRAG*

        Speed, mph                       Energy Loss, kw-h/mileb
10
20
30
40
50
60
70
80
0.005
0.019
0.048
0.077
0.120
0.173
0.235
0.307
        aFrom Campbell and Hunsberger, 1962.
        ''Aerodynamic drag coefficient  of 0.0012 and frontal  area
         of 20 ft2 are assumed.
 VANSANT                                                    145

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     The energy required for acceleration increases the kinetic energy
 of the vehicle so that,  in  principle at least, some fraction  of that
 energy could be recovered. Table  4 shows the energy amounts re-
 quired to  accelerate vehicles  of  various  weights to certain  speeds.

           Table 4.  ENERGY REQUIRED FOR ACCELERATON
VEHICLE WEIGHT, Ib
Vehicle
speed, mph
1,000
2,000 3,000
4,000
kw-h/mile
20
40
60
80
0.010
0.040
0.090
0.160
0.020
0.080
0.180
0.320
0.030
0.120
0.270
0.480
0.040
0.160
0.360
0.640
     Energy is  also required for  hill-climbing.  Although in the long
run the car  will  descend as many hills as it climbs,  the  potential
energy gained  during an ascent  may be partly lost through braking
when  descending.  Table 5 illustrates the effect of grade on energy
expenditure.

          Table 5.  ENERGY REQUIREMENTS DUE TO GRADE
                                VEHICLE WEIGHT, Ib
    Grade, %
1,000
2,000
3,000
4,000
                                       kw-h
—2
0
+ 2
+4
+6
—0.040

+0.040
+0.080
+0.012
—0.080

+0.080
+0.160
+0.240
—0.120

+0.120
+0.240
+0.360
—0.160

+0.160
+0.320
+0.480
    Requirements for accessory power can vary widely, from a few
watts to several kilowatts.  On the basis  of current practice, heating
and cooling are the major items in the energy budget for accessories.
Accessories such as lighting or convenience features normally require
only small amounts of energy.

    It is not unusual for automobile heaters to have outputs of 20,000
or 30,000 Btu per hour, the equivalent of about 6 or 8 kilowatts of
electrical resistance heating.  Automotive air conditioners  often  can
pump about 20,000 Btu per hour.  In line with electrical air condi-
146
                                                Mechanical Design

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tioning practice this output would require about 3 kilowatts of power.
It is easy to see that even a low-powered electric air conditioner can
consume considerable  energy.

    The requirements for heating would  perhaps best be  met by
using a non-battery-powered source, e.g., a phase-change system that
could be  "recharged"  by  resistance heating  when  the  batteries are
being charged. One of the best phase-change systems, although some-
what exotic, is the lithium hydride system. Lithium hydride  releases
about 1000 Btu per pound upon freezing.  A practical lithium  hydride
"heat cell" might easily  produce more than  350 Btu per pound, or
approximately 100 thermal watt-hours per  pound.  Chemically fueled
heaters could  provide  even more heat per  unit weight,  although the
air pollution  problem  would  have to be  reckoned with.  Catalytic
heaters that "burn" fuel at low temperatures  are, however, reputedly
free of noxious effluents.

              TOTAL ENERGY  REQUIREMENTS

    Total energy requirements  for  various  driving modes  are  ex-
amined in Table 6.  Three types of driving are considered.

    Urban    — average speed 15 mph; 5 stops per mile
    Suburban — average speed 30 mph; 1 stop per mile
    Turnpike  — average speed 60 mph; 0.01 stop per mile.

    Table 6.   ENERGY  REQUIREMENTS  OF A  TYPICAL  MEDIUM-SIZE
          AMERICAN CAR  FOR  VARIOUS TYPES OF DRIVING
                            (kw-h/mile)

       Energy  use          Urban        Suburban       Turnpike
Tires
Aerodynamic losses
Acceleration
0.092
0.011
0.086
0.092
0.048
0.053
0.092
0.173
0.003
        Total              0.189          0.193          0.268

    The totals in Table 6 are approximations of the energy require-
ments for propulsion. The requirements may be somewhat understated
in that they exclude allowances  for system inefficiences and for power-
ing accessories.  A  "worst-case" accessory load might include an air
conditioner  operating at  10,000 Btu per  hour and  requiring about
1,700  watts; with other small loads, the total accessory load could be
2 kilowatts.  In the case  considered, then, the energy requirements
would be  as shown in Table  7.  Reid (1966) determined that modern
cars expend energy at a rate of  about 0.3  kilowatt-hour per ton-mile.
For a 3,000-pound car,  0.45 kilowatt-hour per mile would be the
corresponding expenditure rate. This figure seems to agree well with
the numbers derived here for idealized situations.
VANSANT                                                     14V

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    Table 7   TOTAL ENERGY REQUIREMENTS  OF ELECTRIC VEHICLE
                 DURING VARIOUS  DRIVING  MODES
                            (kw-h/mile)

       Load totals          Urban         Suburban        Turnpike
Propulsion
Accessories
Propulsion plus
accessories
0.189
0.133
0.322
0.193
0.067
0.260
0.268
0.033
0.301
    What were the energy requirements of early electric cars?  J. E.
Homan  (1911) wrote:  "The current consumption of electric vehicles
operated by storage batteries varies more or less with different makes,
but some idea of the same may be obtained from the results of a test
run of 62 miles over dirty and slippery roads recently made in France.
In this run a number of electric vehicles  each carrying four passen-
gers and weighing, complete, over 2 tons, covered the  entire distance
at an average speed of 15 miles per hour with an energy consumption
of about 160 watt-hours per ton mile. The best performance was that
of a Vedrine, which required  155 watt-hours per  ton mile. Under
ordinary conditions, this vehicle consumes 110 to 120 watt-hours per
ton mile."

    Although many changes have taken  place since that early  day,
it appears that the 0.180 kilowatt-hour per mile that would have been
required by  a  3,000-pound vehicle is  slightly less than  would be
required by a present-day vehicle  operating under similar conditions.

    Consideration of data in Tables 6 and 7 in light of current  bat-
tery art tells us  plainly  that  practical  battery-powered  turnpike
vehicles are not in the immediate offing.  For urban-suburban driving,
where long range  is not required,  strong technical  promise for prac-
tical electric vehicles is implied — even for off-the-shelf components.
However, since the power system in a vehicle built  with available
elements falls far  short of the standard  to which we are accustomed,
promising directions for further development  should  be  examined.


           INCENTIVES FOR IMPROVED DESIGN

    The power source is the only  part of the conventional automo-
bile that is inherently  different from an electric car. The motor  and,
in particular, the  ponderous batteries of  electric  vehicles have led
many to expound  the need for  lighter weight, more powerful motors
and batteries. Better  batteries and motors are, of course,  much to
be desired. However, other directions for development that lie within
the area of mechanical design could be at least as rewarding and per-
haps more immediately productive.

    Other approaches  can be illustrated  by analogy in the  aphorism,
"One can either make more than  he spends or spend less than he
148                                             Mechanical Design

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makes."  That is, improving the efficiency  of propulsion may  be as
fruitful a course to pursue as that of developing batteries that have
higher energy density.

     For example,  we have considerable incentive for seeking tires
with lower rolling resistance coefficients. Tire rolling resistance is a
major energy loss  during  propulsion.  For the  automotive  racing
world,  tire  manufacturers  have recently  performed  some  minor
miracles in designing and constructing high-performance racing tires.
Perhaps,  if given the challenge,  tire  manufacturers could develop a
tire with very low rolling resistance for electric vehicle service.  Also,
light weight is desirable to reduce tire rolling drag losses and energy
requirements for  acceleration and hill-climbing.  Although there is
a  large  incentive  for a  lightweight  vehicle, we  are cautioned   by
Homan, who  wrote, 56 years ago:  "There  may be some advantages
in light constructions, formerly supposed to  be essential, but present-
day practice recognizes the evident fact that strength and durability
are  more important considerations."

     Nevertheless, light weight does afford a technically more efficient
machine.   Eliminating  a pound  of structure  produces far  greater
benefit in an  electric than in a gasoline-powered car  because of  the
greater cost and weight  of the power system.  The best examples of
lightweight vehicular structures  are found  in racing  machines. Al-
though  racing cars  are  highly  specialized,  they  embody techniques
that may  be useful in  the design of  lightweight  electric  vehicles
(Costin and Phipps, 1962).

     Fiberglass has proved to be a practical body material for limited-
production  cars. Since this material provides for a  lighter weight
shell than steel, it  is probably a  good  choice for electric cars.  (One
likely candidate for a near-term electric car  is the  Meyers  Manx,
produced  by B. F.  Meyers and  Company and sold  in  kit form only.
This handsome car is essentially  a fiberglass bathtub on a shortened
Volkswagen chassis.  The total  weight,  without prime mover,  is less
than 1,000 pounds.)

     Particularly in urban use we have incentive for developing a  re-
generative  braking  system.  There has  been much talk about this
possibility, but little activity of practical merit.

     Vehicles for urban-suburban use have little need for aerodynam-
ically clean design,  since they are seldom driven  at high speeds.

     If we  assume no  further technical development of components,
about the only things that  can be done for an electric car designed
for urban use are to choose efficient tires, to design for lightweight
structure, and to design a regenerative braking system.  Because of
large heating-cooling  loads  imposed by accessories, it is reasonable
to  consider even insulated walls and  double glass windows.  Some
efficiency  in design over  conventional practice may  be gained  by
appropriately packaging the components in  ways that are impossible
with a gasoline  engine.
VANSANT                                                    149

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    These, then, are  the  general directions  in  which  engineering
attention  can be expected  to  produce advances in electric vehicle
design.  Drawing our attention to  just one of the potentially reward-
ing areas, let us consider the effect on cost of reducing the weight of
a 3,000-pound electric car, of which 1,000 pounds is lead-acid battery,
to 2,000 pounds.  If an energy density of 15  watt-hours per pound is
assumed, the battery will contain  15  kilowatt-hours. The cost of the
battery will be about $300.  (Price estimates for batteries vary con-
siderably, but the U.S. Government procures lead-acid SLI batteries
at prices of about $20 per kilowatt-hour (private communication from
J. Reinman,  U.  S.  Army Tank Center, Warren,  Mich.).  Reputable
retail establishments sometimes sell  batteries for $15 per kilowatt-
hour, based on nameplate rating.) If the weight  of the car is only
2,000 pounds, the energy requirement for the same range will drop
by about one-fourth  (see Table 8) for urban-suburban driving. The
battery goes from  33  percent  to  37  percent of vehicle  weight, and
propulsion power  requirements  decrease  by approximately  one-
third; this means that if a  15-horsepower motor had  been used for
the 3,000-pound  machine,  a 10-horsepower  motor  would  suffice for
the 2,000-pound vehicle. At 20 pounds  per  horsepower  and $15 per
horsepower this represents  a reduction  of $75.  The motor accounts
for about 10  percent of the vehicle weight in either case.

    Exclusive of the power plant, then,  a 2,000-pound machine can
cost as  much as  $150 more than  a 3,000-pound machine before the
heavier vehicle  becomes more attractive in  terms of first cost.

     Table 8.  EFFECT ON ENERGY REQUIREMENTS OF REDUCING
           VEHICLE WEIGHT FROM  3,000  TO 2,000  POUNDS

                           Energy requirements of
     Driving mode      3,000-lb vehicle, 2,000-lb vehicle,  Change, %
                         kw-h/mile       kw-h/mile
Propulsion only
Urban
Suburban
Turnpike
Propulsion plus
accessories
Urban
Suburban
Turnpike

0.189
0.193
0.268

0.322
0.260
0.301

0.135
0.130
0.239

0.268
0.197
0.272

—29
-33
—11

—17
—24
—10
    Many similar comparisons could be  made; the important point,
however, is that the careful weighing of alternatives is a worthy pre-
requisite to actual design.
150                                             Mechanical Design

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    So  far, the  energy requirements of electric  automobiles have
been a principal subject. The whole of automotive  mechanical design
obviously involves much more.  We are the beneficiaries of long years
of significant  progress  in automotive technology.  To appreciate  our
technological  inheritance,  we need  list  but a  few of  the  dramatic
early engineering accomplishments:
         The  differential,  which  allowed  the  rear  wheels  to
    negotiate corners  without  scrubbing;  the  pneumatic  tire,
    which made motoring less wearing for both vehicle and pas-
    senger; and steering mechanisms able  to  accommodate the
    different  turning radii  of front wheels.
    Now that we are in a technically sophisticated and less romantic
era of transportation technology than our  forebears, it may  be  ap-
propriate to view a vehicle as  a  box on four  wheels. We need no
longer view as  a problem the  development of,  e.g.,  a satisfactory
braking  system.  Today, by contrast, the "problems"  affecting even
mechanical design appear  to  spring  from economic as  much as from
engineering considerations. For example, who  would  have foreseen,
even 20 years ago, the impact of loan credit on  the whole  automotive
industry, including the mechanical design of vehicles.
    Technically, it  appears that  a completely satisfactory  electric
car can be built today.  This is no news;  it has been true for  at least a
decade.  Even from a  cost standpoint,  satisfactory  electric vehicles
that are  not  prohibitively expensive can  be  built.  From a solely
economic viewpoint, however,  the  competition of the conventional
car is  overwhelming.

                THE MODERN  ELECTRIC  CAR

    The various prognosticates of electric automobile developments
are correct in suggesting the small "runabout,"  particularly the com-
muter vehicle, as the first  reincarnation  of the electric car.  Such a
machine  can  most comfortably exploit the values placed on light
weight, low speed, and  small size.  The technology is certainly  at hand
for the production of electric vehicles satisfactory for commuter serv-
ice, mainly because great  range is unnecessary.
    More important, since  the  air pollution problem is most serious
in the city core,  attention  should first be directed  to urban-suburban
commuters; they are, collectively, perhaps most responsible  for and
affected  by airborne contaminants.
    Although the air  pollution problem provides  the most recent
mandate  for an electric car,  I believe that a number  of automobile-
associated urban  problems could  be alleviated by the electric auto-
mobile.  Some of these crucial  problems are air  pollution, parking,
and road space.  Electric cars have the  potential,  through  design, of
providing relief  in each of these problem areas.  Electric  vehicles, of
themselves, can meet only the  air pollution problem;  however, more
useful solutions  may be found by a composite problem-solution ap-
proach than by attacks on  individual problems.
 VANSANT                                                      151

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    Perhaps as great as the  engineering problems associated  with
electric automobiles  is  the acceptance  problem.   Individuals  have
little  natural  incentive  to  possess  electric vehicles, since gasoline-
powered cars  can, now  and in the  future, outperform electric cars
on almost every score except that of holding down  air pollution.

    Even on this  point,  it is not  clear that the electric power plant
is  the best of the alternative propulsion systems.  Steam  engines,
turbines, and  even improved  spark-ignition engines have consider-
able potential for very low  pollutant emission under the impress of
an air pollution criterion. Nor  are all electric systems necessarily free
of emissions.

    In addition, it is practically  certain  that electric  cars will cost
considerably more than  equivalent gasoline-powered ones.   People
will not, then, gladly abandon  their gasoline cars to  buy electric cars.
The incentives will have to be created.  The  banishment of gasoline-
powered vehicles by legislation does not appear to me to be a practical
possibility.

    One incentive would  strongly encourage  the use of  electric
vehicles and, at the same time, take advantage  of an inherent char-
acteristic of the electric car.  That incentive?  A place to park. Public
parking structures limited  to  electric  vehicles  would  surely be in-
centive enough in most urban business  districts. Such a scheme is
favored,  again, by the zero-emission characteristic of electric  cars.
Parking  structures could be built  underground or anywhere,  with
relatively little concern for ventilation.  It seems reasonable  to insist
also that cars  meet  such requirements as maximum  dimensions  or
certain  construction  features,  so  that they are  compatible with the
parking facilities.

    Another proposal is to put commuter vehicles on rails.  The steel
wheel on the  steel rail is, in  a practical  sense,  unsurpassed  for low
rolling resistance.  In many cities  a number of railroad  lines run
from  surrounding residential areas  into the core areas. Perhaps ar-
rangements could  be  made to use  these tracks as rush-hour commuter
lanes for electric vehicles  capable  of both  on-track  (steel wheel)
and off-track  (pneumatic tire)  service.  A  speculative  design  of a
vehicle for such dual service is shown in Figure 1.

    There  is room for a great deal of variety  in  design of electric
cars;  however, it may be in the public interest to place limits on the
designs of  electric commuter  vehicles  in consideration of the prob-
lems  of air pollution, parking  space, and  road space and to  establish
special incentives  for the use of these commuter vehicles.


                  TOWARD A TOTAL  DESIGN

    If one wishes to build an electric vehicle today,  it can  be  done
by assembling off-the-shelf  components.  Companies as well  as  indi-
viduals have done exactly that. Naturally — particularly in view of
152                                              Mechanical Design

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the markedly superior performance of gasoline-powered machines —
it would be desirable to produce a better car than can be assembled
from presently available components.
Figure  1.   Two-passenger  electric  commuter  vehicle  for
both  road and  rail service has rubber tires and steel wheels.
The single traction motor is in the rear compartment; bat-
teries are in the fenders. For entrance and exit, the wind-
              shield slides back into the roof.

    We recognize that financial resources for progress toward  the
better electric vehicle will not be unlimited.  It is therefore, worth-
while to inquire  where research and development payoffs  should be
sought. Some possibilities are mentioned in the following paragraphs.

    Most  proponents  of electric  cars recognize  the need  for less-
expensive, lighter weight batteries and motors. These technical areas
probably call for some straightforward  inventing — or at least  for
rediscovery of some dormant concepts.

    The tires appear to have potential for considerable improvement
in relation to the  large amount of power they require  on contemporary
vehicles.  Light weight is desirable, particularly in urban use. A good
regenerative braking system would likewise improve propulsive effi-
ciency for urban  driving. For urban-suburban vehicles, we probably
have little incentive for aerodynamically "clean"  design.
VANSANT
                                                             153

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    The power requirement total for accessories, it was shown earlier,
can be nearly as great as the requirement for propulsion. I believe we
should expect commuters  to demand the level of  comfort  afforded
by year-round air conditioning.  For the electric vehicle, this  require-
ment  will introduce a new direction for design, i.e., thermal design.
Previously, we have been able to overpower the weather with heaters
and air conditioners that  have  been merely  added  to the  car.  In
electric automobiles, for climate control as well as for other accessory
functions, the cost of providing extra power is incentive for the use
of relatively efficient systems.
    Electric  cars  may, at last,  provide the long-lived automobile.
Commercial vehicles often have service lives  of 20 years.   What if
the life of private electric  cars were 20 years  rather than the 7 or 8
years now typical for automobiles?  From the viewpoint of mechanical
design, 20-year vehicle life is a practical possibility.

    Although a number of engineering alternatives for  electric vehi-
cle design are well known  and are  found throughout the spectrum of
modern technology, I  conclude  that  electric cars are really favored
only by entirely new designs —  designs that are inherently suited to
electric propulsion.  In addition, we  should  view the electric car as
an evolving vehicle. It has been proposed as a solution to air pollution
problems, but we should not expect  it to appear, miraculously, as a
panacea.

    Especially  for the  near future,  the electric  automobile holds
somewhat limited promise. It will not be able to match,  in either per-
formance or  range, the fire-breathing machines that are familiar to
us. This is not to say  that the promise it does hold is not worthy of
aggressive pursuit — for if  the  electric car  is viewed in the context
of a  responsibility toward  improving  our  transportation  systems
rather than as merely  another  automotive alternative,  we can hope
to develop imaginative  approaches that are  genuine improvements
over conventional schemes.

                           REFERENCES
Campbell,  R. W., and J. R.  Hunsberger, 1962. Energy recovery  in-
    centive for regenerative braking.  SAE Paper  No.  498A. Tables
    1, 2, and 3 are derived from the GM road  load  horsepower equa-
    tion in this reference.  The equation is attributed to Administra-
    tive Engineering  Department, Research  Laboratories,  General
    Motors Corporation, Warren,  Michigan,  General  Motors auto-
    motive engine test code.  5th ed.
Costin, M., and D. Phipps,  1962.  Racing and sports  car chassis design.
    Robert Bentley, Inc.,  Cambridge, Mass.
Homan, J. E., 1911. Self-propelled vehicles.  Bobbs-Merrill Co.,  Inc.,
    New York, N.  Y.  pp.  562-63.
Reid, W. T., 1966. Kilowatts for cars — a comparison of energy costs
    for electric automobiles. AIAA Third Annual Meeting, Boston,
    Mass.  Paper No. 66-978.
154                                              Mechanical Design

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              ELECTROCHEMICAL  SYSTEMS
                     Andre J. de Bethune*
                         Boston College
                      Chestnut Hill, Mass.

     The search for more powerful and lighter weight electrochemical
 systems  for electric  vehicles can be facilitated by applying to the
 whole chemical gamut of  the periodic  chart certain basic principles
 of thermodynamics and kinetics.  The fundamental thermodynamic
 relations  governing  an electrochemical  cell or  battery  were  first
 derived by Gibbs (1878) and may be expressed in the forms
     En. < E = -AG/nF                                      (1)
     dE/dT = AS/nF                                         (2)
     AH = Q  - We                                          (3a)
        = heat absorbed  — electrical energy delivered        (3b)
        = TdWe dT- W,,                                   (3c)
        = TAS- (-AG)                                     (3d)
        = nFT(dE/dT) - nFE                               (3e)
     Heat developed = (-AH-nFEw                           (4a)
        = enthalpy  drop  — Electrical energy delivered        (4b)
 where
     E,T = working voltage  under load
     E = theoretical maximum reversible, or  open circuit, voltage
     T  = temperature  (Kelvin  scale)
     F = the Faraday, 96,487.3 ampere-seconds, or 26.802 ampere-
           hours
     n   = 1,2,3 ... as the case  may  be
     Q = heat absorbed  by the  battery
     Wp = electrical  energy delivered  by the  battery
     H = enthalpy  of the battery (its total energy plus the pres-
           sure-volume product)
    S  = entropy of the battery  (measured by  J  dQrtn-/T)
    G = Gibbs  function  ("free enthalpy")  of the  battery  (its
           enthalpy  minus  the temperature entropy product).
"Theoretical electrochemistry editor, Journal of the Electrochemical Society.

de BETHUNE                                                 155

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 The maximum voltage is given by the Gibbs function drop  ("free
 enthalpy,"  "Gibbs  free  energy"  drop)  of  the  battery  per unit
 charge  delivered.  The temperature coefficient of the maximum vol-
 tage  is given by  the entropy gain of the  battery  per unit  charge
 delivered.  The enthalpy gain  of  the  battery is equal to  the heat
 absorbed from the surroundings less the electrical  energy  delivered
 (nFEw). Equations  (3a)  and (3b)  express  the  first law  of thermo-
 dynamics in its  electrochemical  form. Equations   (3c), (3d), and
 (3e)  are forms  of  the Gibbs-Helmholtz equation.  The transition
 from (3a)  to  (3c)  involves Carnot's theorem in  the form dWe  =
 QdT/T  under  reversible  conditions.   The  heat developed by  the
 battery  is  given  by the enthalpy drop less the  electrical  energy
 delivered.  Therefore, maximization of the  electrical energy  output
 (e.g., low internal resistance) has  the beneficial effect of  lowering
 the concurrent development of heat.

    Thermodynamic information permits a  calculation  of the maxi-
 mum or reversible   voltage E  of an  electrochemical  combination.
 For example, take  the classic zinc-copper  cell, a battery  that was
 popular a century ago,  before electricity became commercially avail-
 able,  when  researchers had to  assemble  their own  batteries  out  of
 inexpensive and readily available materials.  The schematic diagram
 of the zinc-copper cell is

     (-)Zn/Zn+ + , SO,=,aq,"  SO1==, Cu+ + , aq..'Cu( + )        (A)
    V°            - 0.7628       +0.337   volts
     (dV° dT)lso   + 0.091         +0.008   mv/°C

 The standard electrode potential V°, and its isothermal temperature
 coefficient  (dV°/dT)(BO  (both referred to  the standard  hydrogen
 electrode SHE as zero at all  temperatures)  are  taken  from the
 compilation of  de  Bethune  and  Loud (1964).  The Gibbs-Stockholm
 sign convention is followed, i.e.,  the electrode  potential  is positive
 if the electrode is  the ( + )  terminal of  a cell whose second electrode
 is  the SHE.  The  familiar  Latimer "oxidation potential"  (Latimer,
 1952) has the opposite sign and is not used here.  The cell voltage
 E,   following the  Lewis-Stockholm  sign  convention  (Christiansen
 and  Pourbaix,  1954; Christiansen, 1960;  Lewis and  Randall,  1961;
 and  Licht  and  de  Bethune, 1957), is computed  from

    E(Cell) = V  (Right) — V(Left)                           (5)

 Note  that the  "Zellspannung" or  "Cell Tension"  recommended by
 C.I.T.C.E. is  V(Left)  - V(Right)  (de Bethune, 1964), and  is not
used here.

    For  the zinc-copper cell (A), there  results

        E°(25°C) = (+0.337)  - ( -0.763) = +1.100 volts
        dE°/dT   = ( + 0.008)  - ( + 0.091) =  -0.083 mv/°C
        E°(100°C)= +1.094 volts
156                                       Electrochemical Systems

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 The  cell  reaction

         Zn  -f-  Cu++ + S04- = Cu + Zn++ + SO,-        (B)

 yields  2  faradays  or 192,974.6  ampere-seconds of electricity  at  a
 maximum voltage  of 1.100 volts.  The maximum energy yielded as
 electrical work at 25°C is

         2.200 volt-faradays =  212,272 watt-seconds
                            =  58.964 watt-hours                (6)

     The volt-faraday is a convenient energy unit in electrochemical
 work.  Its conversion factors  are

         1 volt-faraday  =  6.023 x 10-3 electron volts           (7a)

                        =  23.061 kilocalories                   (7b)

                        =  91.51 Btu                           (7c)

                        =  71,165 foot-pounds                  (7d)

                        =  96,487.3 watt-seconds               (7e)

                        =  26.802 watt-hours                   (7f)

 At its  23-kilocalories equivalent, the volt-faraday represents,  for
 example,  92 percent of the heat of combustion of a  25  (large) calorie
 "Metrecal" cookie.

    In  the zinc-copper  cell,  it  takes a  minimum  of  112.50  grams
 of chemicals (if sulfate  is used  as the counter ion required by the
 law of electroneutrality) to  yield  1 faraday of  electricity.   This
 comes out to 102.27 grams per volt-faraday. Division of this number
 into the conversion factor 26.802 watt-hours per volt-faraday yields
 the theoretical  maximum energy  density  as   0.2621  kilowatt-hour
 per kilogram at 25°C.  At 100°C,  the corresponding figures  would
 be  102.92 grams per volt-Faraday  or  0.2604 kilowatt-hour  per
 kilogram.

    In  Table 1, similar values are  assembled  for  a  number  of
 well-known  batteries.  The  numbers  are based   on the  data  of
 chemical  thermodynamics  (de  Bethune and   Loud, 1964; Latimer,
 1952;  Pourbaix,  1966; and  Rossini et al.,  1951) for the  substances
 in their standard  states and may differ  from actual  engineering
 performance  data.   For  the  lead  storage  battery,  the  theoretical
 maximum energy density is about 0.17 kilowatt-hour per kilogram.
 For the zinc-silver,  zinc-copper,  and cadmium-nickel  batteries, it
 is  about  50  percent  higher.  For  the hydrogen-oxygen fuel  cell,
 the theoretical maximum energy density jumps spectacularly to 3.5
 kilowatt-hours per  kilogram,  i.e., to 20-fold that of the lead  storage
 cell.  This figure gives the order of magnitude  of the optimum that
can be  reached  in energy densities by going  to light-weight  active
materials.
de BETHUNE                                                  157

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  Table 1.  STANDARD VOLTAGES  AND MAXIMUM ENERGY DENSITIES
              FOR A  NUMBER OF COMMON  BATTERIES*

                                           Maximum energy density,
         E°, volts           Weight/charge,            kw-h/kg
    at 25°C     at 100°C          g/F          at 25°C     at 100°C

(— )Pb/PbS04, H2S04, PbS04/Pb02(+)
2.0408 2.1528 321.296
(— )Zn/ZnS04,aq.//CuS04,aq./Cu(+)
1.100 1.094 112.50
(-)Zn/Zn(OH)2,KOH,Ag20/Ag(+)
1.590 1.563 157.578
(— )Cd/Cd(OH)2,KOH, Ni(OH)2/Ni02(+)
1.299 1.284 119.566
(-)H2/H+,H20/02(+)
1.229 1.167 9.008
0.1702
0.2651
0.2704
0.2912
3.656
0.1796
0.2604
0.2658
0.2878
3.472
a Based on standard data of chemical thermodynamics (de  Bethune and Loud,
  1964; Latimer, 1952; National Bureau of Standards, 1952).

    Theoretical  maximum  energy  densities may  be  expected  to
exceed  operational energy densities  by a factor ranging  from  3:1
to 10:1 or greater.  The theoretical maximum  energy  density does
not take into account three operational factors  that  drastically  cut
down  the  ratio  of  energy  to  weight:  (1)  voltage  losses  due  to
polarization  and/or internal resistance,  (2) the necessary  weight
of electrolyte, separator, box, and connectors, (3) the limited depth
of discharge (50 to 75%) per  cycle  permissible if  cycle life is  not
to be sacrificed.

    In  the  lead  storage cell,  for example,  a good quality  12- volt
automobile  battery,  sold by Sears-Roebuck, is rated  at 70 ampere-
hours  (20  hours rate)  and  weighs  46  pounds  (21  kilograms).  On
slow  discharge,  this  battery yields  840  watt-hours,  or 18.2 watt-
hours  per  pound, which is  40.2  watt-hours per kilogram, or 1:4.2
of the theoretical maximum energy density of 0.17 kilowatt-hour
per kilogram.  On fast discharges, of the type needed in automobile
propulsion,  this  battery might  yield only  8 to 12  watt-hours  per
pound, or 18 to  26 watt-hours  per kilogram, i.e., between 1:10 and
1:6.5  of the  theoretical maximum.

    Dalin, in another  part of this book, quotes the  following  opera-
tional  energy  densities, in  watt-hours  per  pound.  They are here
converted to watt-hours per kilogram and compared with theoretical
figures  from Table 1.
158                                        Electrochemical Systems

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                        Operational       Theor.        Ratio
                   w-hr/lb     w-hr/kg  w-hr/kg     Oper:theor
Zinc-silver
Cadmium-nickel
40 to 50
18 to 20
88 to 110
40 to 44
270
290
1:3 to
1:7
1:2.5
    The present theoretical study of novel anode and cathode mate-
rials is based  extensively on  the de Bethune-Loud  (1964) compila-
tion  of electrode potentials and isothermal temperature coefficients.
These are all  referred  to the  SHE as zero.  However, the standard
hydrogen  electrode is an inconvenient reference point for the study
of cathodes  and anodes of  potential  usefulness to electric vehicles.
Therefore, other reference  electrodes have been chosen  as  a  basis
for comparison.  They  include two reference anodes:  lithium  and
zinc-zinc hydroxide, and two  reference cathodes: fluorine and sulfur.
These reference electrodes are  much closer  to the  types of half-
cells being developed  in actual engineering studies.  Two of them,
the lithium  anode and  the  fluorine cathode, represent the extremes
attainable  in   electrode  potential  and  lightness  of  weight.   The
characteristics of these four reference electrodes are given in Table 2.
        Table 2.  CHARACTERISTICS OF  THE FOUR REFERENCE
                 ELECTRODES USED IN  THIS STUDY"

           (referred to the SHE as zero  at all temperatures)

                          Reference anodes

                                 Zn/Zn (OH).,,OH-

V° = —3.045v                    v°=— 1.245v

(dV°/dT) .so = _0.534mv/°C         (dV°/dT)iso= —1.002 mv/°C

6.94 g/F                          {d2V°/dT2).go= -5.978 ^v/(°C)

                                 49.698 g/F


                         Reference cathodes

F-/F2                             S=/S

V" = +2.87 v                      V° = —0.447 v

(dV°/dT)i80= _1.83 mv/°C           (dV°/dT)lgo= -0.93  mv/°C

19.00 g/F                         16.033 g/F

a Data from de Bethune and Loud, 1964.
de BETHUNE                                                   159

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    In Table 3,  chemical thermodynamic data have been  assembled
for 28 possible  anodes of 15 chemical  elements. In the  table, the
anodes are listed in alphabetical order  of chemical symbols of the
major  element.  In the periodic chart,  the  elements considered are
arrayed in the groupings
                         Anode elements
H
Li  Be
Na Mg
K  Ca  Sc °   °   °    °   Fe
o   o   \T   ooooo

    0  (15 °) °
    For each anode, the tables lists the following information:

    The  weight-to-charge ratio  (grams per  faraday) of the  elec-
        trode reaction, including the weight of any necessary counter
        ions indicated as  (Li+) or (H+).

    The electrode potential V°  at 25°C, and the isothermal tempera-
        ture coefficient (dV°/dT)iso at 25°C, both referred to SHE
        as zero at all temperatures.

    The anode potential E° versus the fluorine cathode  and or the
        sulfur cathode,  calculated at  25°  and  100°C.  The  anode
        potentials are all  given  the negative sign, to correspond to
        their observed  (—)  polarity in the cells; the cell voltages
        are given by the  same number without the negative sign.

    The maximum energy density, in kilowatt-hours per kilogram,
        for the given anode when coupled with the fluorine cathode
        and/or the sulfur cathode, at 25° and 100°C.

    The optimum thermodynamic performance is that of the lithium-
fluorine cell  with a maximum voltage of 5.9 volts  and an energy
density of 6.1 kilowatt-hours per kilogram.  The aluminum hydroxide,
aluminum sulfide, calcium, magnesium, sodium, potassium, yttrium,
hydride, and hydrazoic acid anodes are close seconds, when coupled
with a fluorine cathode, with voltages ranging between 5.1  and 6.2
volts and  energy densities between 5.1  and 2.7  kilowatt-hours per
kilogram.  The beryllium, acid  hydrogen, alkaline hydrogen, hydra-
zine, and  scandium anodes give voltages between 2.9 and 4.9  volts,
versus  fluorine, and energy densities  between  2.2 and  5.4 kilowatt-
hours  per  kilogram.  The aluminum fluoride, cadmium, iron, am-
monium hydroxide,  and  zinc anodes give voltages between  3.3  and
4.9  volts,  versus  fluorine,  and energy densities between 1.2  and 1.9
kilowatt-hours per kilogram.
160                                       Electrochemical Systems

-------
              Table 3.  CHARACTERISTICS OF  ANODES"
       (V° and (dV°/dT)lso referred to SHE as zero at all temperatures)

(—) Anodes, g/F             versus F~/F.n(+)           versus S=/S(+)
     V°(25°),v         E°(v) and kw-h/kgat  25°C  E°(v) and kw-h/kgat 25°C
      (dV0/dT)lso,mv/°C E°(v) and kw-h/kgat 100°C E°(v)and kw-h/kgat 100°C

AI/AI+++; 899
      -1.662          —4.532      4.337         	        	
          +0.504          —4.357      4.174      	        	
AI/AI(OH)3,OH-(Li+); 32.938
      —2.30           —5.17       2.668      —1.853      1.0142
          —0.93           —5.10       2.632      —1.853      1.0142
AIF6-s,F-(Li+); 60.873
      -2.069          —4.939      1.657      —1.622      0.5653
          —0.20           —4.816      1.616      —1.577      0.5496
AI/AI2S3, S=(Li+); 31.966
      —2.595          —5.465      2.874      —2.148      1.1966
          —1.66           —5.452      2.867      —2.203      1.2273
Be/Be++; 451
      -1.847           —4.72       5.38          	        	
          +0.565          —4.54       5.17       	        —
Ca/Ca++; 20.04
      -2.866           —5.736      3.938      -2.419      1.797
          —0.175          —5.612      3.853      -2.363      1.756
Ca/Ca(OH)2,OH-(Li+); 43.99
      —3.02              	         	      —2.57       1.148
          —0.965          	         	        —2.57       1.148

Cd/Cd++; 56.20
      —0.4029          —3.27       1.243        	        	
          —0.093          —3.14       1.194      	        	
Cd/Cd(OH)2, OH-(Li+); 80.153
      —0.809           —3.68       0.9947    —0.362      0.1009
          —1.014          —3.62       0.9785     —0.368      0.1025

Fe/Fe++; 27.93
      —0.4402          —3.31       1.890        	        	
          +0.052          —3.17       1.810      	        	
de BETHUNE                                                     161

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                           Table 3.   (continued)
 (—) Anodes, g/F             versus F-/F2(+)          versus S=/S(+)
      V(25°),v         E°(v)andkw-h/kgat  25°C E°(v) and kw-h/kgat  25°C
       (dV°/dT).so,mv/°C E°(v) and kw-h/kgat 100°C E°(v) and kw-h/kgat 100°C
 Fe/Fe(OH)2, OH-(Li+); 51.873
       —0.877          —3.75      1.418
           —1.06          —3.69       1.395
 H2/H+, H20; 1.008
       0.0000           —2.87      3.845
           0.000           —2.73       3.657
 H2/H20,OH-(Li+);  24.956
       —0.82806        —3.698     2.255—
           —0.8342        —3.623      2.209
 H2/H-(Li+); 7.948
       —2.25            —5.12       5.092
           —1.57          —5.10       5.072
 K/K+; 39.100
       —2.925          —5.795     2.673
           —1.080         —5.739     2.647
 Li/Li+; 6.94
       —3.045          —5.915      6.111
           —0.534         —5.818     6.011
 Mg/Mg++; 12.16
       —2.363          —5.23       4.50
         +0.103           —5.09       4.38
 Mg/Mg(OH)2,OH-(Li+); 36.11
       —2.69              	        	
          —0.945         	        	
 Na/Na+; 22.997
      —2.714           —5.584      3.563
          —0.772         —5.505      3.513
 NH4OH/N2,OH-(Li+); 36.630
      —0.736           —3.61       1.74
  -0.430      0.1697
   —0.440     0.1737
  -0.381      0.2491
   —0.373      0.2439
 -2.478      1.205
   —2.591      1.260

 -2.598      3.031
   —2.568      2.996

 -1.916      1.821
   —1.839      1.748

 -2.24       1.151
   —2.24       1.151

 -2.267      1.557
   —2.255      1.548
—0.289
                                                          0.147
N2H5+/N2,H+(F-); 13.0135
      -0.23           -3.10      2.595
          —0.84          —3.03      2.537
162
                                            Electrochemical  Systems

-------
                          Table  3.  (continued)
(—) Anodes, g/F             versus F~/F.,(+)           versus S=/S(+)
     V°(25°),v         E°(v)and kw-h/kgat 25°C  E°(v) and kw-h/kgat  25°C
      (dV°/dT)Kolmv/°C E°(v) and kw-h/kg at 100°C E°{v) and kw-h/kgat 100°C
HN,(g)/N2,H+; 43.032
—3.40
—1.193
Pb/PbS04,S04=(H +
—0.3588
—1.015
Sc/Sc+++; 14.97
-2.077
+0.25
Y/Y+ ++; 29.64
2 37?
£- .O / £.
+0.18
Zn/Zn ->"»-; 32.69
-0.7628
+0.091
Zn/Zn(OH)2,OKHLi +
—1.245
—1.002
Zn/ZnS,S=(Li+); 55
1 405
—0.85
—6.27
—6.22
); 152.646
	 3 23
—3.17

—4.947
	 4.791

R ?4?
	 -J .£-'+£.
—5.091

—3.63
—3.49
); 56.638
—4.115
—4.053
.663

	
2.71 	
2.69 	

0 5671
0.5566 	

3.903 	
3 780

"} RRff
iC.OOO 	
2.805 	

1.882 	
1.810 	

1.458 —0.798
1.436 —0.803

0 958
0 952

	



	

	



	






0.2943
0.2962

0.4613
0.4584
"Data from de Bethune and Loud, 1964.

     Table 4 gives  similar information  for 21 possible cathodes of 13
chemical  elements, listed in alphabetical  order of chemical symbols
of the major element.  In the periodic chart,  the  elements considered
are arrayed in the groupings

                          Cathode elements
                    Cr  Mn Fe
                                    Ni
                                       Ag
      (15°)
                                                       N
                                                  Pb
O  F
S   Cl
    Br
                                                                 Xe
de BETHUNE
                                                                 163

-------
               Table 4.   CHARACTERISTICS OF  CATHODES"
        (V and (dV°/dT)leo referred to SHE as zero at all temperatures)

 Cathodes (+), g/F           versus (—)Li/Li+        versus (—)Zn/Zn(OH),
      V°(25°),v         E°(v)andkw-h/kgat  25°C  E°(v) and kw-h/kg at  25°~C
       (dV°/dT)i,(l,mv/ °C E°(v) and kw-h/kg at 100°C E°(v) and kw-h/kg at 100°C
 OH-,Ag20/Ag; 124.881
        +0.345
           —1.337
 OH-,Ag203/Ag; 52.97
        +0.564
 Br-/Br2; 79.916
        + 1.0652
           —0.629
 OH-,Br-/Br03-; 30.327
        +0.61
           —1.287
 CI-/CI,; 35.457
        + 1.3595
           —1.260
 Cr+++/Cr207=; 29.69
        + 1.33
           —1.263
 Cr(OH)3/Cr04-; 62.69
       —0.13
          —1.675
 F-/F2; 19.00
       + 2.87
          —1.83
 F-/F20;  14.004
       +2.15
          —1.184
(Li+)OH—,Fe(OH)3/Fe04=;
       +0.72
          —1.62
 +3.390     0.6839     +1.590      0.2704
   +3.330      0.6771     +1.563      0.2658

 +3.609     1.615      +1.809      0.4723
 +4.110      1.268      +1.310      0.2709
   +4.103       1.266      +1.338     0.2767

 +3.655      2.628      +1.855      0.6213
   +3.599      2.588      +1.834     0.6142

 +4.404      2.784      +2.604      0.7580
   +4.350      2.750      +2.585     0.7523

 +4.375      3.201        	         	
   +4.320      3.161      	         	
+2.915      1.122       +1.115      0.2659
   +2.837      1.092      +1.065      0.2540

+ 5.915      6.111       +4.115      1.713
   + 5.818      6.011      +4.053      1.687
+ 5.195      6.648
  + 5.146      6.585
66.285
+3.765      1.378      +1.965      0.4284
  +3.684      1.348      +1.918      0.4182
164
                                             Electrochemical Systems

-------
                            Table 4.  (continued)
  Cathodes (+), g/F            versus (—)Li/Li+        versus (—)Zn/Zn(OH).,
      V°(25°),v         E°(v)andkw-h/kgat  25°C  E°(\i) and kw-h/kgat  25°C
        (dV°/dT\0,mv/°C E°(v) and kw-h/kg at 100°C £°(v) and kw-h/kgat 100°C
Mn++/Mn04-; 32.341
+ 1.51
_nfifi
OH-


NH4
(F-),
OH-


,Mn02/Mn04-; 51.654
+0.588
—1.778
+, N2/HN,; 23.028
+ 1.96
-0.14
+4.555
+4.545
+3.633
+3.540
+ 5.005
+ 5.035
H+, N,/H2N,0,; 51.023
+2.65 +5.695
-0.09 +5.662
Ni(OH)2/Ni02; 63.371
+0.490
-1.19(?)
H+, H20/02; 9.008
+ 1.229
_n RAF,
OH-,

S04=

S=/S;


H20/0.,; 17.008
+0.401
-1.680

+3.535
+3.485
+4.274
+4.251
+3.446
+ 3.360
=, PbS04/Pb02; 169.666
+ 1.682 +4.727
+0.326
; 16.033
—0.447
—0.93
+4.792

+2.598
+2.568
Q 77R
O. / / vJ 	
3 767

1.662 +1.833
1.619 +1.775
4.476
4.503 	
9 fi^
^_.uoo 	
2.618

1.348 +1.735
1.328 +1.721
6.379 	
fi ^AR
O.OHO 	
3.857 +1.646
3.760 +1.595
0.7174 	
0.7272 	

3.031 +0.798
2.996 +0.803


0.4847
0.4694



	

0.4113
0.4079
	
0.7058
0.6839



0.3254
0.3274
S04=/S208- 48.033


+2.01
—1.26
+ 5.055
+4.999
2.188 +3.265
2.164 +3.245
0.8954
0.8899
H+,H20,Xe/Xe03; 30.891
      + 1.8             +4.8
                                     3 4
a Data from de Bethune and Loud, 1964.
de BETHUNE
                                                                   165

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     In Table 4, the weight-to-charge ratio in grams per faraday gen-
erally does not include the weight of any counter ions required by the
law of electroneutrality.  The maximum energy density in kilowatt-
hours per kilogram then represents a ceiling that one would not ex-
pect to attain even under the most idealized conditions. For example,
the maximum energy density of the fluorine cathode is listed in Table
4 at 1.713 kilowatt-hours per kilogram versus the Zn/Zn(OH)2 anode
at 25°C.  The inclusion of one mole of lithium ion Li+ as a necessary
counter ion would drop this maximum figure to  1.458 kilowatt-hours
per kilogram, before any further losses are taken into account.  Simi-
larly, the maximum energy  density of the  sulfur cathode, listed as
0.3254 kilowatt-hour per  kilogram versus the  Zn/Zn(OH)2 anode,
is  dropped to  a  maximum of 0.2934  kilowatt-hour per kilogram  by
inclusion  of one mole of Li+ as  a counter  ion. Where  the counter
ion is explicitly  mentioned, as  (Li+) or (F~), its weight is included
in the calculations.
    The  cathode potentials E°  are given versus the lithium  anode
and/or  zinc-zinc  hydroxide anode,  calculated  at 25°  and  100°C.
They are listed with the positive sign, to correspond to their observed
(-]-)  polarity in  the  cells.  These potentials  equal, as  given,  the
standard voltages  of the cells:  (—)anode/cathode( + ).
    The optimum  thermodynamic performance is that of the fluorine,
oxygen  fluoride,  and acid oxygen  cathodes when  coupled with  a
lithium  anode, with maximum energy densities of over  6  kilowatt-
hours per kilogram.  Other cathodes whose maximum  energy den-
sities exceed  2  kilowatt-hours  per  kilogram,  when  coupled with
lithium, include the bromate-bromide, chlorine, acid dichromate, acid
permanganate,  hydrazoic  acid,  hyponitrous acid,  alkaline  oxygen,
sulfur, peroxydisulfate,  and xenic acid cathodes. Cathodes  of silver-
Ill oxide,  bromine, alkaline chromate, alkaline ferrate, alkaline per-
manganate,  and nickel-IV oxide give energy densities between  1
and  2 kilowatt-hours per kilogram  when  coupled  with  a  lithium
anode.
    Under actual  conditions, the reversible, or open circuit, voltage
E would differ from the standard voltage E°  by a small term, usually
of the order of ± 100 to 200 millivolts, calculable from the  Nernst
Equation,  which  has also been  called  the  Electrochemical  Law  of
Mass Action. As applied to  a  single electrode potential,  where  the
electrode  reaction  can be written in the generalized form:
        Ox + ne- = Red                                     (8a)
        (written in either direction)
the Nernst  equation  (with the  Gibbs-Stockholm sign convention)
takes the form

                  +  (RT/nF) In (Ox)/(Red)                 (8b)
                  +  (0.05916 volt/n) log  (Ox)/Red at 25°C    (8c)

where (Ox) and  (Red) denote  the  activities,  or  activity  products,
of the electromotively active chemical  substances, in their oxidized
166                                       Electrochemical Systems

-------
and  reduced forms, that appear in  the  electrochemically balanced
expression for the half-cell reaction.
                    KINETIC FACTORS —
              INTERNAL AND POLARIZATION
                        RESISTANCES

    The  kinetics of the electrode reactions  become of  paramount
importance  in  dealing  with an  operating  battery.  The inequality
contained in  equation   (1)  was originally  formulated by  Gibbs
(1878) in the form

         (V"-V) ^ -d£ /de                                     (9)

where V and V" are, in Gibbs'  words, "the electrical  potentials in
pieces of the  same  kind of metal  connected  with the  anode and
cathode,  respectively," and d£ and de become AG and nF in modern
notation.  Gibbs' inequality  (equation 9)  is more  useful  than its
modern counterpart  (equation 1)  since it applies equally to the dis-
charge cycle (V">V)  and to the charge cycle  (V>V"). It is  well
known that the anode on discharge becomes the cathode on recharge,
and vice-versa.

    The  inequality  in equations  (1)  and (9) can also  be expressed,
for a  discharging battery, by

         V" —V' = Ew = iRx = E —iRj                       (10)

where
         i  = total current in amperes
         Rx = external or load resistance
         R; = internal resistance, including electrode
              polarization "resistances,"  if any.

The maximum  current  yielded by a  cell is its  short-circuit current
(Rx=0)  equal  to E/Rj.  The power  output  is zero at short circuit.

    A battery yields its maximum power, equal to E2/4R)7 at a  cur-
rent output  equal to one-half the short-circuit current.  In general,
the power output is given by the  parabolic function

         P = Ewi = Ei — i2Rj                                  (11)

This result shows the manifest importance of minimizing  Rt to obtain
an operational battery.

    The  internal resistance can be broken up into the ohmic resist-
ance Rs of the electrolyte, equal to pL/A, where

         p = resistivity
        L = electrode spacing,
        A = projected  (geometrical) electrode area,
                                                              167

-------
plus the polarization "resistances" RA and Rc of anode and cathode.
The polarization resistances  are  not constants; they vary with the
current  density  I.  For  activation  polarization  (overvoltage),  the
resistance has the limiting value

         RAct(ohms) = b/2-2.303 I0A                          (12a)

at zero current density and decreases with increasing  current ac-
cording to

         RAct(ohms) = (b/IA) log I/I0                        (12b)

where b and I0  are the  Tafel parameters of  the  activation  over-
potential  (Vetter,  1961).  For  concentration  or transport polariza-
tion, the resistance has the limiting value

        Rconc(ohms) =RT/nFIdA                             (13a)

at zero current density and increases with increasing  current  ac-
cording to

        Rconc(ohms) = (RT/nFIA) lnld/(ld-l)                (13b)

going to infinity  as I  approaches the  limiting diffusion  (transport)
current Id.

    In an operational battery,  the  electrolyte resistivity should  not
exceed 10 ohm-centimeters (e.g.,  the resistivity  of a  1  molar sodium
chloride brine).   Consider  an  electrode  spacing of  1  millimeter
(0.03937 inch).  The unit area resistance A-RS is then  equal to

         1 ohm-cm2 (or 0.00108 ohm-ft2)

This value probably represents a reasonable norm, and at the same
time,  an operational upper limit, for the  internal  resistance of a
battery.  At  an A-R value of 1 ohm-square  centimeter,  an output
current of 600 milliamperes per square centimeter (557 amperes  per
square foot)  means a  voltage loss of 600 millivolts,  e.g., about half
of the open-circuit voltage of the hydrogen-oxygen  fuel cell.

    To the  electrolyte resistance must be  added  the polarization
"resistances" arising from the kinetics of the electrode reactions, as
given by equations (12)  and (13).  Since activation and  transport
polarizations act  in series, and since RAct  decreases  while Rcnnc in-
creases  with  increasing current, their  combined effects can often  be
approximated by a linear  polarization up to about 99 percent  of  the
limiting transport  current  (de  Bethune, 1960).  Numerical calcula-
tions, based  on equations  (12)  and  (13), lead to Table  5, in  which
are given the combined activation and polarization unit  area resist-
ances of electrodes having the  following kinetic parameters.

        Tafel constants:  b = 0.120  volt

                         I0 = 10, 1, 0.1, and 0.01 a/cm2

        Transport  constants: n = 1, Id =  10, 1  a/cm2
168                                        Electrochemical  Systems

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         Table 5.  COMBINED ACTIVATION AND CONCENTRATION
       (TRANSPORT) POLARIZATION RESISTANCES OF ELECTRODES
               AS A FUNCTION OF CURRENT  DENSITY"

       Tafel constants: b=0.120 volt, l(1=10,  1, 0.1, and 0.01  a/cm2
       Transport constants: n=l, ld = 10, 1 a/cm2

Current
density
(a/cm2)
0
0.1
0.2
0.5
0.8
0.9
0.99
1.00
ld=10 a/cm2
I0=10 a/cm2

A'R
(ohm-cm2)
0.0052
0.0052
0.0052
0.0052
0.0052
0.0052
0.0052
0.0052
ld=10 a/cm2
I0=l a/cm2

A.R
(ohm-cm2)
0.028
0.028
0.028
0.028
0.028
0.028
0.028
0.028
ld=10 a/cm2
I0=0.1 a/cm2

A'R
(ohm-cm2)
0.26
0.25
0.18
0.17
0.14
0.13
0.12
0.12
Id=10a/cm2
I0=0.01 a/cm2

A'R
(ohm-cm2)
2.6
1.2
0.78
0.41
0.29
0.26
0.24
0.24


Current
density
(a/cm2)
0
0.1
0.2
0.5
0.8
0.9
0.99
1.00
ld=l a/cm2
I0=10 a/cm2

A'R
(ohm-cm2)
0.028
0.030
0.033
0.040
0.045
0.069
0.123
QO
ld=l a/cm2
I0=l a/cm2

A.R
(ohm-cm2)
0.052
0.053
0.055
0.063
0.078
0.092
0.146
oo
ld=l a/cm2
l,,=0.1 a/cm2

A'R
(ohm-cm2)
0.28
0.28
0.26
0.21
0.18
0.19
0.24
OO
ld=l a/cm2
L=0.01 a/cm2

A.R
(ohm-cm2)
2.6
1.2
0.81
0.45
0.33
0.33
0.36
OO
lThe body of the Table gives the unit area  resistance A-R of the electrode
 in ohm-cm2 (1 ohm-cm2 = 0.155 ohm-in.2 =  0.001076 ohm-ft2).
de BETHUNE
169

-------
The degree of constancy of the A-R values in Table  5  measures the
reliability of the approximation of linear polarization as a substitute
for the combined  nonlinear  activation and  transport  polarizations.
For the kinetic  parameters  chosen, the polarization  resistance  of
the electrode  is almost everywhere a small fraction of  1 ohm-square
centimeter  (up to  99% of the limiting transport current).  Beyond
99  percent of the  limiting  current, the polarization  voltage goes
rapidly to infinity,  and the current output remains  at its transport
limited value.
    Kinetic parameters I0 and Id  significantly lower than those con-
sidered in Table 5  would tend to make the battery non-operational.
For example,  I0 and Id values of 10~4 amperes per square centimeter
each would correspond to a combined unit area resistance of approxi-
mately 1,000 ohm-square centimeter up to 99 percent  of Id.


              CORROSION —CELL UNIFORMITY

    Batteries  made up of active,  free energy rich  chemicals can be
expected  to suffer from  corrosion problems  in  which these  active
chemicals react through other reaction paths than  those  anticipated
or desired.  This can be illustrated by the role of the cathodic oxygen
reaction

        O, + 4H+  -f 4e~ = 2H,O                            (14)

in corrosion and in  a fuel cell.  For corrosion control, reaction (14)
must  be inhibited,  e.g., by paint  films or chemical inhibitors,  or  it
must  be satisfied by a superimposed cathodic protection current to
supply  the  needed  electrons from another  source than the  metal
under  attack.  In a fuel cell,  reaction  (14) needs  to be  actively
promoted on the fuel cell's catalytic cathodic surfaces.  It must also
be vigorously  controlled and  inhibited elsewhere in the fuel cell to
prevent destructive  corrosion of the cell.

    Cell uniformity, not only mechanical and geometrical,  but also
chemical,  electrochemical, and thermal uniformity, becomes of para-
mount importance when cells are stacked together  in series  to form
a battery (e.g., the voltaic  pile).  Experience has shown that the
weakest cell in a pile can actually reverse its voltage  by polarization
when it is driven by the other cells of the pile generating a current
in excess  of its own intrinsic  short-circuit current.  In  such  a  situa-
tion, the weak cell is  rapidly destroyed by  the  continued operation
of the pile and greatly reduces the effectiveness of the whole  battery.
Stringent control of cell uniformity becomes of paramount importance
in ensuring good battery operating  characateristics and good cycle
life. A battery, like a chain, is no better than its  weakest cell.

                          REFERENCES

de  Bethune, A. J.,  1960.  Fourth report to  the Bureau  of Ships.
    Boston College (Jan.  1).
170                                       Electrochemical Systems

-------
 de Bethune, A. J., 1964.  Tension, cell and electrode.  In: Encyclopedia
     of electrochemistry, C. A. Hampel, ed. Reinhold, New York, N. Y.
     pp. 1102-03.
 de Bethune, A. J.,  and N. A.  Swendeman  Loud,  1964.  Standard
     aqueous electrode potentials and temperature coefficients at 25"C.
     Published by  Clifford A.  Hampel,  8501  Harding  Ave.,  Skokie,
     111. 60076.  20pp.  Also available in:  Encyclopedia of electro-
     chemistry,  C.  A. Hampel, ed.  Reinhold,  New  York, N.  Y.  pp.
     414-26  (1964).

 Christiansen, J. A., and M. Pourbaix, 1954. Compt. rend. conf. union
     intern, chim. pure et appl. (I.U.P.A.C.), 17th Conference,  Stock-
     holm, 1953. Maison de la Chimie, Paris, pp. 82-84.

 Christiansen, J. A., 1960.  Manual of physico-chemical  symbols  and
     terminology.  J.  Am. Chem.  Soc., 82(21): 5517-22  (Nov.  9).

 Gibbs, J. W., 1878.  Trans. Conn. Acad.  Sci. 1875-78.  Available in:
     Collected works, W. R. Longley and R. G. Van Name, eds. Vol.
     1, Thermodynamics. Longmans, Green, New York, N.Y. pp. 332-
     49,  429. 1928.

 Latimer, W. M., 1952.  Oxidation potentials. 2nd ed. Prentice Hall,
     New York, N.  Y.

 Lewis, G. N., and M.  Randall, 1961.  Thermodynamics, 2d ed. Revised
     by K. S. Pitzer and L. Brewer.  McGraw-Hill, New York, N. Y.

 Licht, T. S., and A. J. de  Bethune,  1957.  Recent developments con-
     cerning the signs of electrode potentials. J. Chem. Educ., 34:433-
     40 (Sept.).

 Pourbaix, M., 1966. Atlas of electrochemical equilibrium in aqueous
     solutions.  Pergamon,  London,  Eng;  Cebelcor, Brussels, Belg.

 Rossini, F. D., et al., 1952.  Selected values of chemical thermodynamic
    properties.  National Bureau  of Standards Circular 500.

 Vetter,  K.  J.,  1961.  Elektrochemische   kinetik.  Springer  Verlag,
    Berlin, Ger.
de BETHUNE                                                  171

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                  SEPARATOR SYSTEMS



                        Harry P. Gregor

                Polytechnic Institute of Brooklyn
                         Brooklyn, N. Y


                        INTRODUCTION

    The science and technology of synthetic membrane systems has
been developed, particularly in the past  decade,  to  the point  where
new materials with a wide variety of  useful properties are available
for use as battery  separators. Some of  these  new materials are
beginning to find  their  way into  battery  separators, and with the
current development of  new battery  systems,  particularly  those  of
the type required  for  the electric  vehicle, many new  developments
may ensue.

    For many of the new battery systems now under development,
the availability of  new separator systems is an  absolute requirement.
Even in older systems such as the  lead-acid batteries, the availability
of new separator  materials  has led to improved  performance and
reliability.  The failure of a large fraction of  all  batteries may  be
traced  to the inadequacy or malfunction of the  separator.

    In this contribution I will describe  the  recent advances  in the
physics, chemistry, and  technology of battery  systems that may  be
applied to advantage in  the fabrication of new and superior battery
separators.  I  will  not describe all  of the different materials and
systems that may  be employed,  but  rather will  indicate  some  of
each class.*

    Different  battery  systems require   rather  different kinds  of
separator  systems.  The  separator must,  of  course, allow  for  the
passage of the  ions  that carry the current and,  in  some  cases, they
also must permit the ready  flow  of solvent. In  other systems, it is
desirable to inhibit  or even prevent solvent flow.   In  some  systems
certain ionic  or molecular species  should  be  prevented from moving
across  the separator to the  opposite electrode.  In most batteries the
separators must prevent the movement  of particulate  matter away
from the plates and retard, if  not  inhibit,  dendritic growth, particu-
larly from one  plate toward the other.
* Dr. Gregor's  presentation gives  an extensive  background  of  material
from the literature; these references are cited  directly as he provided
them.  Since he describes various  materials  and systems as examples of
their class,  Dr. Gregor does not regard  the literature citations as an ex-
haustive bibliography on separator systems.
GREGOR                                                       173

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             CLASSIFICATION OF SEPARATORS

    Separator  systems  are best classified on  the basis  of pore di-
ameters and the nature of those chemical groups fixed  to the pore
walls.  Although we tend  to think of films having cylindrical pores
extending through the membrane, each  at right angles to  each face,
real systems are not at all like this with the  possible exception of
some new films wherein holes are ''punched through" the membrane
by  radiation (i;.  Separators usually have pores of varying diameter
that extend in  a highly branched configuration  in all directions from
one membrane face to  the other.  Indeed,  with  many  membranes
one should  think more of a three-dimensional polymeric  gel-like
structure; certain membranes are best viewed  simply  as solid solu-
tions, with no pores, as such.  Table 1 lists pore diameters expressed
both in microns (/j.) and  Angstrom  (A) units; the range  of pore
diameters extends over six orders of magnitude for membranes now
available.

             Table  1.   PORE AND SOLUTE DIAMETERS
Microns (,j)
100
1 mil —
f 10
Millipore -< 1
I o.i

Angstroms



10,000 A
1,000 \
100 /
10
(A)




Colloids
Proteins
Na+. Cl-

1

    The selective transport  of  an ionic and/or molecular specie
across  a membrane is controllable by relatively few parameters:
size; charge (whether negative or positive);  chemical reactivity with
a fixed  (charge) group; solubility.

           MACROPOROUS MEMBRANES (d > 1/x)

    Highly porous membranes, having pore diameters from 1 to 10
microns, are conveniently prepared by mixing a molten polymer with
fine particles of uniform diameter, the particulate matter occupying
approximately three-fourths the volume of the suspension.  One then
extrudes a sheet from this  suspension  and, after the  polymer has
solidified, dissolves the particulate matter, leaving the porous matrix.
Finely divided salt particles  have been used  for this  surface, as  have
starch  granules, the latter because of their rather uniform size.  Such
films are available commercially from several sources, including the
Electric Storage Battery  Company(2). The  polymers used  for  this
174                                             Separator Systems

-------
 purpose include  polyethylene, polyvinylchloride, and certain  of  the
 fluoro-polymers.  A somewhat analogous procedure starts with solid
 particles of the polymer, which are sintered together either by heat
 or by the  use  of an  appropriate solvent to cement the par tides (3).
 The lower limit  of the pore  diameters for these films is about  1
 micron, because this is approximately the size of the smallest particles
 available for providing the voids or for  cementation.

    MICROPOROUS (1 M  >d>100A) AND MOLECULAR PORE
                  (100A >d>lA)  MEMBRANES

     Polymeric membranes of graded porosity are usually prepared by
 dissolving  the  polymer  in one solvent,  casting a  film and allowing
 the solvent to  evaporate partially, then coagulating the film  by im-
 mersion in a non-solvent. Other kinds of polymeric  films, particularly
 the familiar cellophane film, are produced by extruding  a solution
 of a cellulosic  derivitive (viscose) into  a bath that partially coagu-
 lates the film  and simultaneously converts  it back  to the original
 cellulose (4).

     Control of the porosity of films of this type has been the  subject
 of many investigations; the general principles and procedures des-
 cribed by Elford  are still commonly employed(5, 6).  The  higher the
 solvent content of the film at the time of coagulation, the  greater its
 porosity, as  a  general rule.  Elford described films  that  were re-
 markably homoporous, prepared by the use of mixed solvents both
 for dissolution of the polymer and for coagulation.  These general
 procedures  apparently have been  followed  in the  preparation  of
 Millipore membranes, which are usually composed of mixed deriva-
 tives of cellulose; similar membranes have been prepared  from mix-
 tures of cellulose acetate and cellulose nitrate,  as an example.  Table
 1  lists the  stated  pore diameters of Millipore membranes.

     Control of porosity of nitrocellulose membranes has  been de-
 scribed by Sollner and Gregor, among  others, who showed that  by
 drying a coagulated  nitrocellulose  film in  atmospheres of progres-
 sively  lowered relative humidity one obtains membranes of  graded
 porosity(7, 8).  This principle  has been extended  by CarrfS), who
 re-swelled nitrocellulose membranes in  mixtures of  swelling sol-
 vents, in this case alcohol-water mixtures, then coagulated  the film in
 water  and  obtained films  that showed  a  remarkable  degree  of dis-
 crimination between  molecules of low  molecular weight,  with esti-
 mated pore diameters varying from about 5 to 50 Angstrom units.

    Similarly,  Craig (10) has varied the porosity of cellulosic mem-
 branes by using swelling solvents and by stretching membranes uni-
 axially to convert the pores from a spherical to  an elliptical  shape.

    With certain  kinds  of  coagulated,  porous membranes,  drying
of the  film may reduce  its porosity. This  can be  avoided by  use  of
a mixture  of two  polymers, one being  strongly hydrophilic and the
GREGOR                                                      175

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other being an insoluble, hydrophobic matrix  material. Porosity can
be  maintained in a swelling solvent with such  films. An example
of membranes of this  kind has  been described by MindickflJJ, who
cast interpolymer membranes from a mixture of a copolymer of vinyl-
chloride and  acrylonitrile (Dynel,  Union Carbide Company)  and
polyvinylpyrrolidone (PVP), both dissolved in an  appropriate com-
mon solvent.  After casting the film and allowing the solvent to evap-
orate, one obtains a  continuous phase of the water-insoluble polymer
(Dynel) and the macroscopic pores contain the hydrophilic polymer
(PVP).  This  general interpolymer technique,  first  described  by
Gregor(12), is useful because it is very  flexible, it  allows one to use
many different polymer mixtures (although selecting an appropriate
solvent may be rather difficult), and it permits one to  produce films
with high-speed  equipment at  relatively low  cost. Additional sta-
bility can be obtained  by the use of appropriate cross-linking agents,
although their use makes the formulation  somewhat more complex.

          DETERMINATION  OF PORE DIAMETERS

    The determination  of pore  diameters  is relatively  straight-
forward for highly porous materials; it becomes quite difficult with
pore diameters less  than  1,000 Angstrom  units.  With materials  of
larger  pore  diameter  (d  > 0.1  /.i), the mercury  intrusion technique
gives both  the pore  spectrum  and the  total pore  volume.  Un-
fortunately,  mercury intrusion cannot be applied to finer pore sys-
tems, particularly those  composed  of  polymers  that  are pressure-
deformable or those in which the porosity depends on the presence
of a swelling solvent such as water.  Here, the most reliable method
is to measure  the permeation across the membrane of solute mole-
cules of different size,  as  first described by Collander(13).  Unfortu-
nately,  nature has  not  provided us  with  an  adequate  series   of
spherical  molecules  of different sizes, ones  that do not  absorb   or
otherwise fix  themselves  to pore  walls. Further, as the diameter  of
the solute molecule  approaches  that  of the pore, the classical hydro-
dynamic equation of Stokes, as applied  to  spheres  moving  in homo-
geneous media through spherical or rectangular pores  by Fa.xen(14),
may be subject to considerable error.  The same applies to evalua-
tion of the measurement  of air or water permeability, because each
pore contributes  to  the permeability proportional  to the 4th  power
of its radius;  a highly distorted average  pore  diameter may be thus
calculated.

    Staining of molecular pore  membranes by  the  formation  of pre-
cipitates, presumably within the pores, has been tried with indifferent
results.  The  staining  procedure  usually  alters the pore structure,
but by this technique one may observe the  occurrence  of large voids,
which  are difficult to avoid in the formation of many polymeric films
There  is considerable  evidence  that  one  cannot form precipitates  in
molecular pores  (of the  order of 5  to 50 A);  these kinds  of mem-
branes may, when used as a part of separators, prevent the  growth
of dendrites through them.
176                                             Separator  Systems

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              ION-EXCHANGE MEMBRANES

     Ion-exchange membranes have been used in several new battery
 systems.  These are films of insolubilized polyelectrolytes, which can
 contain the sulfonic, carboxylic, phosphinic, phosphonic, sulfate and
 phosphate  acids,  amino,  and   quaternary   amine   fixed-charge
 groupsfJSJ. Polymers containing other fixed-charge groups, includ-
 ing phosphonium, arsonium, and iodonium, have also been described.
 The commercial ion-exchange membranes are  of the sulfonic  acid
 type for  the cation-permeable membranes, and of the quarternary
 ammonium type for the anion-permeable membranes, because these
 groups are strongly ionized, are of reasonable chemical stability, and
 do not form ion-pairs or chelate complexes with  metallic ions(16).

     The most common polymeric matrix for membranes of this kind
 is polystyrene; Figure 1 shows diagramatically a typical cross-linked
 polystyrene sulfonic acid material. The drawing, roughly  to scale,
 indicates  that the pore diameters are approximately  10 Angstrom
 units C17,18).
    '     ©JTWI 0  ^-      ©^S
^e®!    ®   ^^s®      rv
303
  Figure 1.  A typical  cross-linked polystyrene sulfonic
                      acid material.
GREGOR
177

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    Techniques  for the preparation of ion-exchange membranes in-
clude direct polymerization in sheet form; casting from interpolymer
mixtures; and the preparation of heterogenous membranes by sus-
pending ion-exchange resin particles in a matrix polymer and form-
ing a film by extruding or by  casting from a solvent.  Bieber de-
scribes several of the latter procedures(19).
    Whereas the stability  of cation-permeable membranes prepared
from  polystyrene sulfonic  acid has been suitable (these  membranes
can be used  at  temperatures up to 100°C  for long periods without
severe degradation),  the same  is  not true of  the  quaternary am-
monium  anion-permeable  membranes, which usually degrade ap-
preciably  in weeks or months even at  60°C. The recent synthesis  of
a  substituted pyridinium  compound  (2,   6  di-t-butyl  pyridinium
iodide)  of unusual stability  was  reported  by Okamoto  and  Shim-
agawa(20).   These  authors treated 2, 6  di-t-butyl  pyridine with
methyl iodide under  high pressure.  The  compound  could  be sub-
limed at 250°C  under reduced pressure without  decomposition.  Its
unusual stability might be  applied to  the  preparation  of  anion-
exchange  membranes  of  stability  comparable  to  that   of  cation-
exchange  films.

    Ion-exchange  membranes  are selectively permeable either  to
cations or to  anions by virtue of the fixed charges contained therein.
The Donnan  potential gives rise to an equilibrium that may be ex-
pressed in simplified form as follows for a system  of fixed sulfonic
acid  groups  (ReSO^) in equilibrium with  a solution of potassium
chloride:

  [K+]  [CT]y±=  [K+]  [Cl-]y±; [K+]  = [ReSOg] +  [CT],

where [   ] is the concentration  of the  fixed  charges expressed  in
molality or in terms  of the imbibed water within the pore, y^ is the
mean activity coefficient, and the superscript bar  indicates" values
pertaining to the membrane phase.  Recent studies have  shown that
this simple equation predicts the behavior of many membrane systems
rather accurately if one sets y_ =  0.45(21).

    The  Donnan equation predicts that membrane selectivity will
fall with  increasing  concentration  of the ambient electrolytic solu-
tion, and  this is  observed.  For maximum selectivity, the  concentra-
tion or molality of fixed-charge groups within  the  film must be  as
high as possible; commercial films having molalities (m) in the range
of 5 to 8 exhibit a commensurate ionic selectivity. With highly con-
centrated  electrolytes, however, even these membranes will not be
very selective. For example, in 5m potassium hydroxide and a fixed-
charge membrane of concentration 5m, the  transport number  (frac-
tion of current carried by  each ionic species) for the permeable ion
is but 0.73.

    Fixed-charge membranes do not show concentration polarization
within the membrane phase, but do exhibit this phenomenon strongly
in the  adjacent solution  phase.   For  these reasons, fixed-charge
178                                            Separator  Systems

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 membranes are favored for use in fuel cells.  When relatively dilute
 solutions are interposed  between  the  fixed-charge membranes and
 the electrodes,  however,  a marked concentration  polarization en-
 sus, with an increase in the ohmic resistance of the depicted electro-
 lyte layer adjacent to  the membrane  phase;  other undesirable side
 effects also occur(22, 23).

     When a current is passed across a fixed-charge membrane,  the
 selective transport of one species  over another takes place because
 the concentration  of ions  of the  charge opposite the  fixed-charge
 (counter-ions) is very much greater than that of ions of the same
 charge  (co-ions). In these narrow-pore systems considerable hydro-
 dynamic drag is  imposed upon  all ions, particularly those whose di-
 ameters approach that of  the pore. Along with the ionic flux there is
 a flow of solvent, termed electro-osmosis.  The amount of water trans-
 ported by electro-osmosis increases with the size  of the counter-ion
 and the  pore diameter for the "tight" membranes  of high selectivity.
 This solvent transport can be appreciable; for "tight" membranes it
 is about 100 milliliters  per Faraday; in "loose" ones it can be of the
 order of liters  per Faraday.  Recent  studies by  Bagner(24) have
 shown that when the diameters  of  counter-ions  are  approximately
 80  to  90  percent  of the pore  diameter,  "plug  flow"  results, and
 essentially all of the water content of the membrane moves with the
 counter-ions.

    Although this  electro-osmotic flow can be used to advantage  in
 some systems, it  usually  presents a problem to be overcome  in bat-
 teries separators because  the  solvent  flows  with the ionic current.
 The pressures generated by electro-osmosis are considerable. Electro-
 osmotic  flow is particularly troublesome in fuel  cell membranes,  in
 which it acts to dry out one electrode  and flood the others. Wicking
 systems  are used to recirculate water under these circumstances.

    As  mentioned earlier, ions  can be made to show marked  differ-
 ences in permeability in  certain films, on the basis of  differences  in
 their hydrated sizes.  A most interesting film has  been developed by
 Yawataya, Oda, and Nishihara(25),  who  coated the surface of con-
 ventional ion-exchange membranes with a very thin (5 /_/,) layer of a
 co-condensate of  phenol, phenol-sulfonic acid, and formaldehyde, and
 achieved a transport number of 0.01 for Ca++ in  a sodium-calcium
 solution; the latter ion  is about twice  as large as  the former.

    The common inorganic ions, particularly the alkali metal cations,
 demonstrate conductivity in aqueous solution, an indication that they
 are hydrated to an extent that  decreases with the  ionic size.  Values
 for  non-hydrated and approximate hydrated diameters  are given  in
 Table 2.  Because the hydration energies  are  considerable, extensive
 dehydration  of  an  ion on entering  a pore  system  is  not  readily
 achieved.  It  was  observed recently  that  valinomycin, a   cyclic
 dodecadepsipeptide, has such a very fine and rigidly controlled pore
diameter that it can produce a structure more permeable to potassium
than to sodium ions by  a  large factor; this observation shows  at least
GREGOR                                                       179

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that such systems exist, and they may be  the source of the high
level  of  ionic  discrimination  demonstrated  by  biological  mem-
branes C26, 27). The  usual sequence of hydrated volumes is observed
in most  membrane  systems, with  the permeability  series  P°tas-
sium> sodium > lithium.  The markedly higher hydration of the alkali
metal divalent ions  such as  calcium and  magnesium has allowed
the membranes having  very fine  pores to show a  high selective
permeability to univalent over divalent ions(25).

                    Table 2.   IONIC PROPERTIES

H
Li
Na
K
Me4N
Et4N
Pr4N
Bu4N
OH
Cl
Br
1
SCN
pTS
103
NQ3
X° r in A
350
39
50
74 2.1*
45 3.47
33 4.00
23 4.52
20 4.94
195
76 2.3*
76
77
72
34
40 3.7"
71
Crystal
radii, A

0.68
0.98
1.33





1.81
1.96
2.19




      a From distance of approach  in solution  x° is equivalent ionic
       conductance at infinite dilution.
                   MEMBRANE THICKNESS

    The thickness of polymeric membranes can be controlled within
rather wide ranges.  Cast films of a number of common matrix poly-
mers  can be as thin as  5 microns and still demonstrate  reasonable
mechanical  strength  and the absence of pinholes; the conventional
packaging  films  vary in  thickness  from  approximately  10  to  50
microns. Membranes as  thin as 1 micron  have been  prepared and
studied; these  are very  fragile and require support.  One means  of
support is to cast the film directly onto a thin, fine fabric, as is done
180                                             Separator Systems

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with certain commercial ion-exchange membranes. Very thin films
having  a thickness of approximately 0.1  to  1  micron  can be  cast
directly  onto a fine porous matrix  such  as a treated  paper without
the introduction  of holes.  Also, one can apply the techniques  first
described by Loeb and Sourirajanf28/),  who  cast  a film, allowed a
thin skin to form as a result of the rapid evaporation of the solvent
from  the surface  layer, and then  coagulated  the film in a  non-
solvent.  By the  choice  of appropriate materials, solvents,  and con-
ditions,  one can  produce membranes having a highly  porous  and
open substructure with  a very thin film  of the same polymer on one
face.  For example, films having an  effective thickness of approxi-
mately  1 to 2 microns on a substructure of some 50 to  100 microns
have been prepared.

               SOLUTE-BINDING  MEMBRANES

    Membranes that are impermeable to certain ionic or molecular
species can be made by incorporating on  their pore  walls substituents
that react  reversibly  or irreversibly with  the mobile  species.  A
familiar example is the use of cellophane  membranes in the silver-
zinc battery, in which under alkaline conditions the cellulose  reacts
with silver ions  (or colloidal silver)  to form  an insoluble,  immobil-
ized material.  The same type of  irreversible  reaction  may  result
when rubber  membranes vulcanized with sulfur  and  presumably
containing reactive sulfur compounds are used in lead-acid  batteries;
sulfur-antimony  complexes apparently form,  and  the metallic ions,
no longer able to diffuse to the electrode, are "trapped."
    The interactions of ionic species with polymers containing specific
binding  agents have  been  studied  extensively;  the polymers  have
been in solution, in resin, and in membrane form. The original stimu-
lation for this work came from  Skogseid("29), who showed that the
classical chemical  reactions  involving  aromatic structures can be
carried  out with  linear or cross-linked polystyrene.  With systems of
these kinds, byproducts that  are part of  the polymeric structure re-
main  so and cannot be separated; by judicious use of chemical re-
actions  Skogseid  prepared a number  of materials of rather complex
nature.  Figure 2 shows a few of the structures that he prepared and
characterized. Familiar chelate structures  are included.
    Gregor, Taifer, Citarel, and Becker(30) prepared a number of
chelating ion-exchange  resins based upon  familiar condensation re-
actions; extensive studies of  polymers containing groups capable of
specific  interactions with  solutes,  particularly  the  transition  metal
ions, have been reported (31, 32). The general theory  of such  inter-
actions  has been  investigated  by   Wall  (33),   Gregor(34),  Mora-
wetz(35), and others.  The rather  common carboxylic  polymers
form fairly strong complexes with  the alkaline  earth  and transition
metals;  amine polymers form similar complexes with the transition
metals.  Because  of the high  local concentration of ligands or com-
plex-forming groupings in polymeric systems,  one usually encounters
stronger binding  with polymeric ligands than with monomeric ones.
GREGOR                                                      181

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                                                   CH2 —CH-
                                    S03H
                                OH
N02
  Figure  2.   Some of  the  complex structures  prepared
                 by  Skogseid  (reference  29).

    Of  particular interest to  those  concerned  with battery tech-
nology is  the  availability of polymers  containing the SH  grouping,
one capable of rather specific  interactions, particularly with heavy
metals(36, 37).  BayerfSS) has  described an  interesting example  of
a polymeric chelate demonstrating high specificity (Figure 3), with
which the extraction of gold from sea water was claimed.  Preparing
chelate  resins  or  membranes need not entail involved chemical pro-
cedures when the monomeric  ligand is available.  As an example,
Gregor  and  Wa\lace(39)  prepared  thiourea  and  phenylthiourea
polymers  by formation of the condensate (with  formaldehyde) as a
cage about a  hydrophilic polymer to maintain  porosity.   The final
product showed a high capacity of this thiol grouping, one  that forms
particularly strong complexes with heavy metallic ions, particularly
those of silver, mercury, etc. Many other systems are susceptible  to
this kind  of cage polymer formulation.

    The formation  of metal-chelate complex in membranes acts  to
bind metallic  ions and inhibit  their diffusion across the membrane,
and  although  such retardation  can result  in a considerably lower
flux, it is  still finite because the reaction is reversible.  The work  of
Wetstone  and  Gregor(40),  in which they studied the relative trans-
port of  copper and sodium  in  a carboxylic membrane,  is  indicative
182
                                                Separator Systems

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 I
CH
 II
 N
                                         I
                                        CH
                                         II
                                         N
                              N^   ^N^-^N^CH

                             HC - CH

                GLYOXAL  BIS-2-HYDROXYANIL
             or
    Figure  3.   A  polymeric  chelate of  high  specificity
             described by Bayer  (reference  38).

of these phenomena.  For true "trapping" of the undesirable ionic
or molecular species in a membrane, one must use an  irreversible
reaction, of which several are available.  Several oxidation-reduction
polymers  have   been  reported  by   Cassidyf41/),   Manecke(42),
GregorfSS), and  Overberger(37). Strong polymeric reducing  agents
are readily  prepared;  polymeric  oxidizing agents of reasonable sta-
bility and oxidizing power are not known  at  the present time.  A
particularly convenient and simple procedure for preparing strongly
reducing  resins  (or  membranes)  was  described  by  Gregor  and
Beltzer(43), who prepared pyrogallol-formaldahyde co-condensates
of a high degree  of capacity and  porosity.

    Electrically  regenerable  ion-exchange  systems  have  long in-
trigued investigators.  These systems  are electronic  conductors and
contain groups that can be rendered ionic or non-ionic, or at least
have  a  markedly different degree of ionization, as the result  of the
imposition of an  applied electric  potential. Weissf44J reported some
interesting developments.  In principle,  such systems would  attract
anions or cations when polarized (positive or negative), and  would
discharge these ions when the polarity was  removed  or  reversed.
MurphyC45) applied this principle for purposes of desalination. Films
that were conductive  to electrons were  prepared by laying down a
film  of  activated carbon onto a  metallic grid; the film was then
treated  with either cationic or anionic polyelectrolytes.  Imposition  of
the potential onto the  grid caused the accumulation of  either  cations
or anions; these ions were released by reversal  of the potential.  The
exact chemical reactions that  occur  are  not known; apparently they
do not  involve a true oxidation-reduction,  charge-transfer process
but rather a charging  process at  the surface of the charcoal.   Alter-
ation  of the ionic charge  of weakly  acidic groups has been reported
GREGOR
                                                              183

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by  Stillman  and Gregor(46), who prepared polymers of the poly-
acene-radical type with  carboxylic groups as part of the conjugated
ring system and showed  that the acidity of the carboxylic acid group
could be increased or decreased  by the imposition of a potential from
a battery.  Although we  do not know whether any of these electron-
conducting systems  can  be used in  battery separator systems, the
possibilities are  interesting.

                    SOLVENT MEMBRANES

    We now consider membranes that  do  not possess pores in the
usual sense.  These  are  commonly called solvent-type  membranes.
A typical film  of  this type is a  familiar cellulose  acetate reverse-
osmosis membrane first described by Ried(47,) and then improved by
Loeb and Sourirajan(27) for  use in desalination.  These membranes
selectively dissolve  water and  not ions by virtue of the  unusual
hydrogen-bonded  structure   of  water  contained  within  cellulose
acetate.  They  can have low resistance by virtue  of possessing  a
coherent "skin" of extreme thinness, with a porous  substructure for
support.

    The electrical conductivity  of solvent-type membranes,  in  this
case reverse-osmosis membranes of cellulose acetate, has been meas-
ured  by  Saltonstall("48),  who  has also used  the time-dependency of
conductivity  when the membrane is immersed in an  electrolyte solu-
tion to calculate diffusion coefficients in the membrane.  Results indi-
cated that the equivalent conductance of electrolyte in the membrane
did  not  depend on  its   concentration  in  the  film.  Diffusion  co-
efficents of sodium chloride in typical membranes were about  6x10~10
square centimeters per second; distribution coefficients  (in  m) were
about 0.1.  The membrane resistance increased markedly  with heat
treatment; for  example,  resistances  of  membranes heat-treated at
70°C were 3 orders of magnitude lower than those of membranes
heat-treated  at  95°C.  Resistance of membrane  41  microns thick in
equilibrium with 1 M sodium  chloride was approximately  6,000 ohms
for an exposed area of 1.42 square centimeters. Although this  specific
conductivity  is very  low, it is  not an unreasonable value for a mem-
brane having an effective thickness of  1 micron. Further,  since the
concentrations of acids and bases  in membranes of these kinds are
very much greater than those of salts, these  films might prove useful
as battery separators  under special conditions.  The dense  packing
and the strongly hydrogen-bonded water structure in these systems
may allow for much  more rapid  transport of  hydrogen and hydroxide
ions than would be  encountered in ordinary solution.

    The conductivity  of acid and base have more  recently  been
measured in  cellulose  acetate membranes by Saltonstall(48). Under
these conditions, the equivalent  conductivity in the membrane phase
is concentration dependent,  but  not to a very marked extent.  When
comparisons  at the same concentration of all solutes in the solution
phase (on  a  normality basis) were made, it was  observed that the
                                                Separator Systems

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specific conductivity  with potassium  hydroxide was twice that for
sodium chloride,  and for sulfuric acid was 20 times that for sodium
chloride.  These  results,  particularly  with acid electrolytes, appear
very encouraging.


               MISCELLANEOUS MEMBRANES

    Thus far I have  discussed organic polymeric membranes.  Many
inorganic membranes do exist, however,  and they can provide un-
usual advantages in  that they can  be made  of materials that  allow
for a precise and controllable pore structure. Certain ion-exchange
minerals show high  discrimination for ions on the  basis of size,  as
demonstrated  by  Hechter(49) for sodium-potassium exchange.  In-
organic clay membranes were investigated by MarshallfSO,);  mem-
branes of beta alumma(51) provide the basis for the operation  of the
sodium-sulfur  battery described by  DeWitt  in  this volume.  Syn-
thetic  inorganic  membranes  of  a glass-like  nature have  also been
described (5 2).  Membranes made from Vycor glass have been known
for some time(53). Inorganic exchanges  employed  as cracking cata-
lysts may also show a uniform pore structure; the work of Barrerf 54)
and of the group that developed the molecular sieves  is  pertinent
here.  Most investigators have been  unable  to prepare membranes
that demonstrate the highly selective properties of these  inorganic
exchange materials, largely because of the problem of incorporating
these  into  a  structure that allows  permeation  between  properly
aligned particles.

    KrausfSS) has  described inorganic  ion-exchange  resins;  these
and similar systems have been made in membrane form.  An example
is  a  cation-permeable  film  incorporating  zirconium phosphate  in
particulate form; hydrous  thorium oxide  has served in  the anion-
permeable membranes(56).  Transference numbers of these  mem-
branes  were 0.90 to  0.96, whereas under  the  same conditions  trans-
ference numbers  of  organic  materials were  greater than 0.99.  Al-
though not  highly  selective, these  membranes  operated  at high
temperature and adverse polarizing conditions for rather long periods
without showing some of the  defects of the  organic  membranes.
Certain of these  inorganic membranes have  an intrinsic  solubility,
which,  although  very  low,  can  be appreciable under  conditions of
constant current  passage.

     Another interesting development has been the availability of
separator  materials  made  from  polyethylene  and capsulated  fibers
and particlesC57j. Cellulose fibers have been enveloped with sheaths
of polyethylene by the use of transition-metal catalysts, resulting in
materials that can be made in membrane form by paper-making tech-
niques. This process is of considerable interest for battery  separator
applications because  it is simple, because particles that can be con-
verted into membrane form are available in large  amounts at  a low
price,  and particularly because  the porosity of  the final sheet can
be altered by a further pressing technique.
 GREGOR
                                                               185

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    The special requirements of fuel  cells call for development  of
several  different kinds of new separator systems.  The ion-exchange
membrane electrolyte provides several advantages, among which are
ease of  fabrication of cells containing a solid electrolyte in the form
of thin sheets, resistance to concentration polarization,  and the trans-
port of  but a single, ionic species.  However, organic membranes are
susceptible to attack at the  electrodes,  their electro-osmotic water
transport dries out one electrode-membrane interface  and floods the
other, and the commercial  membranes do  not possess semi-perme-
ability for different solutes  (methanol versus water, as an example).
The use of fluorinated polymers,  even as the matrix polymer,  imparts
greatly  increased chemical stability to the membrane.  Further, inter-
polymer systems now available consist of largely fluorinated  materi-
als; these possess even greater chemical stability than  the fluorinated
polymers.  The problem of electro-osmotic water transport  is  cur-
rently handled by various wicking systems; GregorfSSj has shown
that by the use of a mosaic  membrane  one can  re-transport water
electro-osmotically to the  dry membrane side.

    Finally, there  are some new and interesting possibilities for the
preparation of membranes that will  impede one solvent and  not an-
other.  For example,  more polar films not containing aromatic rings,
such as ones prepared from polyvinylsulfonic acid, may be expected
to show much more  sorption of water than less polar solvents  such
as the alcohols.  The recent announcement  that certain helical  anti-
biotic  molecules(26,  27)  can  apparently  form  a channel   through
which only dehydrated ions can  pass suggests that   if  nature can
produce such a highly selective membrane system similar  systems
possibly can be  created in a  synthetic structure.  Finally, the use of
new solvent-type  membranes may prove yet another means for  con-
trolling the transport of solvents.


              HIGH-TEMPERATURE  POLYMERS

    A recent advance in high  polymer chemistry of particular interest
to those concerned with battery separator problems is the preparation
of many  new high-temperature polymers.  For more  information a
collection of papers presented at a recent symposiumfSS) should  be
consulted, particularly  the  papers  by  Atlas  and   MarkffiOj  and
Mark("67, 62). A more recent review by Marvel(63)  describes  later
studies.

    A few of the new  high-temperature polymers deserve mention.
An interesting family  of  linear,  rigid  polyether-methylenesulfonic
materials  (PEMS)  have   been  reported  by  Johnson  et  al.(64),
Karacz(65),  Price(66), and Reich(67).  These materials  are repre-
sented by recurring aromatic  rings connected in the para-position  by
sequences  of —SO2—, —O—, —CH2,  —S—, or —CCCH.,), —bonds.
These  polymers,  particularly the aromatic  poly-ether-methylene-
sulfones have specific gravities of 1.20 to  1.26,  a  tensile modulus of
about 400,000 psi,  a  tensile strength of  about  12,000  psi, and break
186                                              Separator Systems

-------
elongation ranging from 30 to 120 percent. Some of these polymers
melt or soften reversibly at about 440°C without degradation if the
exposure  is short.  Viscosities  are remarkably  constant,  even when
the polymer is stored at  approximately 400°C.  Polymers  of this type
are soluble at high temperatures in certain polar  solvents such as
dimethylformamide (DMF) and dimethylsulfoxide (DMSO),  so they
can be readily prepared  in film and fiber form.

    Another interesting  class of  high-temperature polymers  are the
poly-benzimidazoles  (FBI) prepared  from  pre-polymers  following
the reaction shown in Figure 4, as reported by Gillhamf 68). Proper-
ties  of  these  polymers  show  very little  change  at  approximately
380°C.  Special thermal cures have produced polymers  that maintain
noticeable rigidity  and strength  even  at 500°C for some time. Me-
chanical properties of these polymers  are  unusual;  flexural modulus
and  strength at room temperature are about 4 x  10"  and  0.9 x  10r'
psi, respectively.
                                                     2H20
                                                     2NH,
     Figure 4.    Polybenzimidazoles  (PBI)  as  reported
                  by  Gillham  (reference  68).

     Polyamides containing piperazine are known to be very stable;
 one member of this family has  been studied in  some  detail,  poly
 (isophthaloyl  trans-2,  5-dimethylpiperazine),  ITDMP(69).   This
 polymer has a softening range near 400°C; it is soluble in chloroform
 and formic acid, in which it has high intrinsic viscosities, lending it-
 self to film and fiber formation.

     Another class of high-temperature polymers, the polybenzimida-
 zobenzo-phenanthrolines (BBB) (see Figure  5), have been prepared
 by van  Deusen(70)  and  Marvel(71).  Most  of these polymers are
 soluble  in  sulfuric acid,  benzene sulfonic acid,  and  concentrated
 alkalis.  When tetra-aminobenzene is used  as  the basic reactant, the
 BBL ladder polymers  formed are less soluble than the BBB  poly-
 mers.  These polymers do not show  weight losses of 5 to 10 percent
 until heated in air at 550°C

     Other  high-temperature polymers  have  been  obtained by the
 oxidative coupling of aromatic diamines. These show the structure
 GREGOR
187

-------
        [N = N — Ar — N = N —Ar — O — Ar — N =N]

where Ar is the benzene ring joined in the p-position.  Many of these
aromatic azopolymers are stable at high  temperature; they exhibit no
weight loss up to 325°C and only 10 percent weight loss upon heating
to 425°C.  All of these materials are darkly colored, amorphous,  and
soluble only in concentrated sulfuric acid  at room temperature.  The
work of Kovacic(72),  Preston(73), and  Bach(74) is relevant.

    Finally,  two commercially available, high-temperature  fibers
deserve mention; the first is a poly — 1, 3 — 4 — oxadiazole, and its
thiol-analogue, shown  in Figure  6(75).  This polymer is stable at
250°C and is unaffected by reflux for 48 hours in 10 percent of either
sulfuric acid or sodium hydroxide. The second is a poly (phenylene
triazole) (see Figure 7); this is stable at 300°C and can be spun from
formic acid solutions(76/).
       HOOC-0}

       HOOC-(O
                                              NHr,
     Figure  5.   Polybenzimidazobenzophenanthrolines
       (BBB)  prepared  by  van  Deusen  and  Marvel
                     (references  70, 71).
                                      N —N
       Figure  6.   A  poly-1,  3-4- oxadiazole  and  its
                thiol-analogue  (reference  75).
 188
                                              Separator Systems

-------
    Many  new  polymers of exceptional thermal and chemical  sta-
bility will  find their way into separator applications, particularly in
high-discharge batteries in which the local temperature is high and
in fuel cells operated at high temperatures and under highly adverse
conditions that ordinarily lead to chemical decomposition.
                                        N  —  N
  Figure  7.   A  poly  (phenylene  triazole)  (reference 76).

                            FIBRIDS

    The use of non-woven  fibers as  battery separators  has found
some application.  A new and particularly interesting development in
high polymer technology is the development of "fibrids," a new form
of fibers prepared from a number of commercially available poly-
meric materials.  Fibrids can be made  from many different polymers
in different waysf 77-79 j; in one procedure the polymer is dissolved
under high pressure and temperature in a liquid that is a solvent for
the polymer under these conditions  but is a non-solvent at lower
temperatures and pressures.  This  solution of the polymer is extruded
through the  spinnerets, upon which the solvent  literally  boils away,
leaving a strand that consists  of  a very large  number  of very fine
filaments  having appreciable mechanical strength  but an extremely
fine diameter and a large surface  area. For example, fibers having a
nominal diameter of 25 microns consist of filaments having diameters
of 2 to  4  microns,  but these are ribbons having smaller thicknesses.
Their surface area is of the order of 100  square meters per  gram
compared  to 5 square meters  per gram  for  cotton. Fibrids can be
prepared  directly from the polymer at a cost of about 50 cents  per
pound,  and one can  fabricate  them into screens and sheets having
a  wide range  of  porosities, a range  not  ordinarly attainable with
fibrous  materials.  Many applications of these new polymer  forms to
the battery industry should be forthcoming.

                         CONCLUSIONS

     Battery scientists and  engineers  have been much  too depend-
ent  for  separator  materials  on commercial   films prepared  for
other  purposes,   such   as  packaging  and  water  treatment.   The
amount of material needed  for membranes usually is so  small that
 GREGOR
189

-------
manufacturers and fabricators of plastics have not been encouraged
toward research and development.

    Further, research has  tended  to concentrate separately upon
separator  materials or  upon electrodes  and  their interaction with
electrolytic solutions,  but not upon the combined  system.  A  funda-
mental investigation of electrode reactions in the presence of well-
characterized  separator  materials  should lead to systems  of far-
reaching practical importance.

    We may anticipate the development of several new and vastly
improved  separator systems based  on the new materials  and tech-
nology available today.  The complexity  of battery systems, particu-
larly  for  electric vehicles,  requires  an interdisciplinary  approach,
with close collaboration on the part  of those who synthesize polymers,
prepare them in  membrane form, study their structure, and finally
incorporate  them into practical battery systems.

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                                                                 193

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            NOTES  ON  A CARBON DIOXIDE
                   SCRUBBING  SYSTEM


                        Harry P. Gregor

    Fuel cells that employ alkaline electrolytes and air as one of the
fuels all suffer from one common problem — the carbon dioxide in
the air  converts  the  hydroxide to carbonate  with a loss  in power
output.  The usual remedy  is to pass the air  through a solution of
base, with periodic replacement. This  adds to the volume of the power
unit, and increases its overall chemical requirements.  I would  like,
therefore, to mention some recent studies on a carbon dioxide scrub-
bing system that  may provide a practical answer  to this  problem.

    Traditionally, acidic gases such as  carbon  dioxide have  been re-
moved by chemical scrubbers; those  that use monoethanolamine are
typical.  Here, an  acid base reaction  removes the  acidic gas,  and the
absorbant is regenerated by heating because the equilibrium is shifted
towards  the uncombined reactants  at elevated  temperatures.  The
technology of liquid scrubbers is well advanced;  these systems have
found large-scale  applicability,  as  in the removal of carbon dioxide
from gas streams  of the ammonia process.

    The MEA (monoethanolamine) and analogous scrubber  systems
have certain advantages and some rather serious  disadvantages,  par-
ticularly when applied to  the electric vehicle. The amine is inex-
pensive, but it is  subject  to thermal  decomposition.  Further, amine
odors are noxious and  they can be  somewhat  toxic.   Ethanolamine
scrubbers have substantial heat requirements  for thermal regenera-
tion because for every pound of carbon  dioxide removed a substantial
number of pounds of water must be evaporated. Although this water
can be recovered, the heat  loss involved is large and the water re-
covery system must have  an appreciable volume.

    The use of polymeric amines for removal of  carbon dioxide has
been investigated.  The reactions of  polymeric amines with carbon
dioxide  have also been  investigated   (Gregor  and  Robins,  1959;
Robins,  1959); the applicability of several polymeric amines for the
removal of carbon dioxide from the the air of submarines and space
vehicles  has been  investigated  (Gregor and  Robins,  1959;  Robins,
1959; Weber,  1966; Weber, Miller,  and Gregor, to be published).
Polymeric amines possess  certain  important advantages over MEA
and  its  analogues, and certain relative disadvantages.  First poly-
meric amines are much  more stable than  their  monomeric  ana-
logues,  particularly the ethanolic-substituted  amines  that  are  em-
ployed because of their reduced  volatility compared to the  aliphatic
amines.  Polymeric amines also  show a higher  thermal  stability  and
are more resistant to air oxidation (Gregor and Robins, 1959; Robins,
1959).  The  stability  of polymeric amines varies; the  tertiary alkyl
GREGOR                                                      195

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amines are relatively stable;  for example, poly-N-methylethylenei-
mine is considerably more stable than polyethyleneimine (PEI)  or
polyvinylimidazole.  The  recently  reported  polymeric  amines  of
Gianinni (1967)  promise to  be even more stable.

     Polymeric amines cannot  be employed in  aqueous solution as is
MEA because of the considerably greater viscosity that obtains. How-
ever, there is no  advantage  in employing  liquid scrubbers  in  the
electric car;  it  is, rather,  advantageous  to  use  these polymeric
materials in the solid form.  Under these circumstances,  the amines
absorb relatively small  amounts of water, with  the  amount varying
with the relative humidity of  the ambient air.  On regeneration,  only
a relatively  small  amount of  water must be evaporated; thus,  heat
consumption is drastically reduced.  Further, polymeric amines have
no odor, and thus  their employment  in limited space would not re-
quire an after-scrubber of acid, as is used  to remove  MEA  vapors
under these circumstances.

     The principal disadvantage of polymeric amines in the solid state
is their low  rate of reaction, which is controlled by the diffusion of
carbon dioxide in the solid polymer to the fixed amino groups.  The
reaction has been measured (Gregor, Weber, and Miller,  to be pub-
lished)  and  found  to be approximately  10~s square  centimeters  per
second  for films  in equilibrium with air  at 100  percent relative
humidity.  At lower relative humidities  the  process  is somewhat
slower and equilibrium  not so favorable;  both  the rate of absorption
and  the  capacity are approximately halved at  50 percent relative
humidity.

     Another of the advantages  of polymeric amines is  the fact that
their basicity can  be  controlled, within  appreciable  ranges, by  the
incorporation of salts  within the solid phase.  Table 1  lists data on
the capacity of a PEI-epichlorohydrin condensate for carbon dioxide
as a function of the gas content in  air, its relative humidity, and its
temperature, taken from the dissertation of Weber  (1966).

     Since  the rate of absorption  of acid gases by solid-state polymeric
amme scrubbers is  controlled by diffusion in  the solid, thin film or
fiber absorbers having a maximum area-to-volume ratio are desirable.
The capacity of units designed with different ribbon diameters, based
upon the  work of Gregor, Miller,  and Wolfe (to be published) is
given in Table  2 and emphasizes this point. For particularly rapid
rates of absorption, the  use of solid-state polyamines in the form of
fibrids (Morgan, 1961; Blades  and White,  1963  and  1966) would  offer
special advantages.

     In operation, a polymeric solid-state  scrubber  would consist of
two filter units  operating alternately  to produce  a continuous  stream
of air free of carbon dioxide. The ambient  air would  pass through
the  filter bed and  be  fed to  the fuel  cell, with  its composition  un-
altered except for acidic gases. If appreciable levels of sulfur dioxide
and other  acidic gases were  present, these  would also  be removed.
 196                                             A Scrubber System

-------
Other  acidic gases would interfere with  the  fuel cell  reaction,  and
their removal would be in direct proportion to their acidity.  When
the filter was exhausted, it would be sealed by the closure of a pres-
sure valve and heat would be applied to the unit (probably  employ-
ing the excess heat generated by the  cell);  the acid-base reaction is
reversed and almost pure  carbon  dioxide would be  released to the
atmosphere,  with  an air  condenser  retarding the  evaporation  of
water.

    This is not to say that polymeric  scrubber systems are fully de-
veloped. The capacities  for removal of carbon dioxide listed earlier

       Table  1. REACTION OF PEI RESIN  WTH CARBON  DIOXIDE
Temp,
°C
0

20
20
20
20
20
40
70
C02 in
aim, %
1.0
0.30
1.0
0.65
0.30
1.0
1.0
0.30
0.30
Relative
humidity,
%
100
100
100
100
100
70
55
100
100
Capacity,
m-moles/g
4.1
1.8
2.9
2.2
1.3
1.8
1.0
0.45
1.1
   Table 2.  ABSORPTION OF CARBON  DIOXIDE BY POLYAMINE  FIBERS
                            AND  FILMS
Fiber or film
thickness, M
150
150
75
38
38
% Theoretical
capacity
50
25
25
50
13
Space between
films or fibers,
A
50
25
25
25
25
Bed
vol,
ft3
16
9
5
5
5
Cycle
time,
min.
60
20
10
15
5
% Removed on
one pass
20
30
30
20
40
Conditions:  Air at 25°C, 50 percent  relative humidity,  0.5 percent  Co,,; for
           C02 removal, 15 pounds C02 per hour.
GREGOR                                                      197

-------
are for levels of 0.5 percent, and at 0.05 percent (the usual air level)
the capacities would be lower by a factor of about 10.  This  capacity
could be  increased, however, by  using  more  basic  polymers.  It  is
obvious that several problems must be met,  but the  availability of a
heat-regenerable  scrubber system would make  alkaline fuel  cells
more practical for electric vehicles, particularly for military  vehicles.

    For  the  Union Carbide  (private  communication with  G.  E.
Evans)  alkaline electrolyte fuel cell, air  at a nominal carbon dioxide
content of 0.03 percent is scrubbed to an 80 to 90 percent  removal
level by a caustic solution; without such scrubbing, the cell electrolyte
must  be replenished 5  to 10 times more  often, but this really  trans-
fers the  problem from the cell solution  to the scrubber  solution.  A
100-watt cell employs from  about 500  (4 times  the theoretical)  to
1,250  liters of air per hour.  For  a military vehicle, one needs 1  to
10 kilowatts and even higher level power sources.  Therefore,  a  1-
kilowatt fuel cell would, on  the average, use  5,000  liters of air per
hour  or  require the removal of about 0.1 pound of carbon dioxide
per hour. From Table 2, at a bed volume of 5 cubic feet at a cycle
time of 15  minutes for 15 pounds of  gas removed per hour  at the
0.5 percent  level, this  amounts to  a bed volume  of about 0.3  cubic
foot for the removal of 0.1 pound of gas at  a  concentration level  of
0.05 percent. This  figure may  have  to  be  increased  somewhat  to
reduce exit  carbon dioxide levels to 10 percent of inlet values.

                           REFERENCES

Blades, H., and J. R. White (1963). U. S. Patent 3,081,519 (Mar. 19).

Blades, H.,  and J. R. White (1966).  U. S. Patent  3,277,664  (Jan. 4).

Giannini, U. (1967).  Presented  at I.U.P.A.C. Macromolecular  Sym-
    posium, Brussels,  June 1967.

Gregor,  H.  P., and J. Robins  (1959).  Final  Report,  Contract No.
    nr-839(20).  U. S.  Navy.

Morgan, P.  W. (1961). U. S.  Patent 2,999,788 (Sept. 12).

Robins, J.  (1959).  Dissertation.   Polytechnic  Institute of Brooklyn
     (June).

Weber, O. W. (1966).  Dessertation. Polytechnic Institute  of Brooklyn
     (June).  See also:  NASA  Report,   Contract No. NAS  9-2792
     (Apr. 1966).
 198                                             A Scrubber System

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BATTERIES AND FUEL CELLS: status

of current research on  specific  energy-

storage systems;  how  they perform.


    I have been thinking about the oft-recurring circumstances under
which the  battery industry has responded to the needs for batteries.
This industry  has been at the threshold of the new in science since
1800, when Volta's pile was  announced in England, an event that in-
pired and inaugurated a golden era of  science. Within 30 years came
many discoveries about electric current:  Oersted on magnetic effects,
Ampere on electrodynamics,  the Seebeck effect, Faraday  on con-
version of  electric current and his discovery of induction.

    On the electrochemical side, Davy had isolated the alkali metals
by 1806.  Nicholson and Carlisle demonstrated  the phenomenon of
electrolysis in 1800, and by  1905 Izarn  applied it as a coulometer.
Believe it or not, Grotthus had formulated his theory by 1806.  Elec-
trodeposition  of metals was  demonstrated and an  electrochemical
telegraph was in the process of development.  In all of these events,
the laboratory needed  batteries,  the only known source of current
at that time.  It  was soon found that the Volta pile was most easily
built in fairly  large size by using the inetals, zinc and copper.  Practi-
cal problems were encountered in scaling up, and especially  in the
creation of convenient  and easily handled installations.
                                                         199

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    Within 1 year the people who worked with these larger batteries
had already found that -atmospheric oxygen improved the perform-
ance of this  particular cell.  This observation  has been  discovered
and rediscovered any number of times  in  the  last 170 years. This
period may be said to have culminated in  Faraday's announcement
of the laws of electrolysis.  In all of this, electrochemistry and science
and batteries  were and  are intertwined. Battery technologists find
that their problems in making advances  to meet demands  are always
at the  verge  of the unknown and incompletely  understood.  For ex-
ample, they are pestered by lack of understanding of the structure
of their active materials,  especially  with regard to the  amorphous
materials.  They  constantly watch for  each new  material that may
extend the range of application for practical batteries.

    The same philosophy  applies now  to the people  who enter and
become part of the  battery industry.   We  see a  widening expanse
of the technologists' training, for the   battery  problems encompass
practically every  branch of scientific and  engineering  effort.  I be-
lieve  that the battery industry  welcomes  this  increasing horizon,
this broadening of its views, and the edge that it brings in competi-
tive spirit.

                                   Arthur Fleischer
                                   Consultant
                                    Orange, N.J.
 200

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LEAD-ACID  BATTERIES  AND  ELECTRIC VEHICLES


                        David L. Douglas

                  Gould-National Batteries, Inc.
                     Minneapolis, Minnesota

                        INTRODUCTION

    For the past 50 or 60 years  the lead-acid battery has been pre-
dominant in the field of battery electric motive power.  Today the
span  of  battery propulsion covers conventional submarines, small
submersible vessels, industrial trucks,  railway cars, mine locomotives,
delivery  vans,  and golf carts. In the past the list would also  have
included passenger  cars.  Today  we  are  focusing on electric street
vehicles, which  include the no longer  practical passenger vehicle and
the near marginal delivery van.

    There are literally  dozens of different types and sizes of lead-
acid batteries on the market — each  designed for a specific applica-
tion.  Many  of  these  are  being  used for  electric propulsion.  Four
of the most  important are flat plate  motive power;  tubular  motive
power; golf-cart; and starting, lighting  and ignition  (SLI) batteries.

Flat Plate Motive Power  Cells
    For  many  years  flat  plate  motive  power cells  have been the
standard of the industry for  rugged service  in industrial  truck and
mine  locomotive applications. Figure 1 shows  the  important  elec-
trical characteristics of a typical cell.  A battery  of six  such cells
in a steel  tray  delivers 5.0 kilowatt-hours and  weighs 576  pounds
(8.7 watt-hours per pound).  In average service this battery lasts
for 6  to 7 years, giving about 2,500 cycles before the capacity drops
to 80  percent of its rated value.

Tubular Plate Motive Potoer Cells
    For  certain applications  where volume is  at  a  premium,  e.g.,
narrow-aisle fork-lift  truck,  cells  with tubular  positive  plates are
widely used.  Figure 2 shows  the electrical characteristics of one of
the most  popular sizes. A battery of 18  such cells  in a steel  tray
delivers 20.8 kilowatt-hours and weiphs  1,944 pounds  (10.7 w-hr/lb).
The service life may he somewhat shorter than that  of the flat plate
battery, but still amounts  to 5 to 6  years and  about  1,800 cycles.

SLI Batteries
    These are  familiar to all as  the electrical energy storage device
in the electrical system of all automobiles. Being  relatively low in
cost and readily available, SLI batteries are frequently used  for ex-
perimental electrical vehicles. Important electrical characteristics of
DOUGLAS                                                    201

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a common size are shown in Figure 3.  The ampere-hour  rating of
SLI batteries is specified at the 20-hour rate — quite unrealistic for
motive power applications.  Further, these batteries  are designed to
deliver large currents for engine starting and  to withstand constant
overcharge whenever the engine is  running.  These  factors combine
to make the SLI battery unsuitable for the deep discharges  associated
with motive  power  service.  The  life of a first-quality SLI battery
used to power an electric vehicle  might be less than a year (100 to
200 cycles).
                                                           - 1,300
                                                                   o
                                                           - 1,000  o
   50
100
200         300         400

 DISCHARGE RATE, amperes
                                                           - 700
                                                             400
                                                           500
                                                                   I-  u
                                                                   Z  o
                                                                   LJ  J=
                                                                   8
                                                                   cc.
                                                                   UJ
     Figure  1.    Discharge  characteristics of  flat  plate
   industrial  battery  (GNB  type  72X-13,  1.280  SP. GR.,
                     77°F, 81  Ib per cell).

 Golf-Cart Batteries
     Golf-cart batteries would  seem to be the closest approximation
 to an  electric  street  vehicle lead-acid  battery. Two versions of  such
 batteries are  on the  market.  One is  based on industrial battery
 technology and  has  tubular positive plates.  Presumably it will  give
 service  similar  to that quoted for tubular  plate cells.  By far the
 more  common version  of the golf-cart battery is based on SLI battery
 designs.  The  principal differences  are larger and thicker plates and
 more  effective plate separation.  Figure 4 gives the  electrical char-
 acteristics of this battery.  At  the 5-hour rate the energy density is
 14 watt-hours per pound  and  1.8 kilowatt-hours per cubic foot.  A
 202
                                               Lead-Acid Batteries

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   750-pound  (curb  weight)  golf cart with 180 pounds  of battery has
   a maximum speed of 20 mph and a range of approximately 30 miles.
   Properly  serviced batteries last 1 to  2  years.
 2.00 -
 1.70
  10
o
X
o
—
Q
                                                              1,000
                                                              800
                                             o
                                             u_
                                             o
                                                              600   LU
                                                               400
                                                               200
                                                                    ^ 03
                                                                    O 3
                                                                    O
                                                                    a:
                                                                    UJ
            50
   150            250

DISCHARGE RATE,  amperes
                                                     350
     Figure 2    Discharge characteristics of  Tubular-plate
     industrial  battery (GNB type 85T-15,  1.280  SP.  GR.,
                       77:F,  85  Ib  per cell).


              ELECTRIC STREET VEHICLES TODAY

       The  relatively modest  energy-storage  capability of  the  lead-
   acid battery and  the  resultant "poor"  performance of electric  street
   vehicles incorporating them has  been the subject of much  discussion
   in the technical and public  press in recent months.  It is instructive
   to document this  as  point  of reference.  The two examples that  I
   will discuss  both  incorporate motive power  lead-acid batteries.

       The  first is electric street delivery trucks manufactured and sold
   by  Gould-National Batteries,  inc., 10 to 12 years  ago.  Altogether
   some 50  were made and sold and 10 or more are  still giving  satis-
   factory service in  New  York City.  Table  1 gives  some pertinent
   characteristics and performance figures.
   DOUGLAS

-------
 o
    2.00
     1.75
     1.50
      16
      14
       12
    P  10
    x
    o
                                                         100
                                                         90
                                                          80
                                                              UJ
                                                              O
                                                          70  ° «
             60   £


                 cc
                 LJ
             50   5



             40



             30
                        20             40

                     DISCHARGE RATE, amperes
                                                      60
   Figure  3.   Discharge  characteristics  of SLI  battery
        (1.280 SP  GR.T  77°F, 42  Ib per battery).

    For the second example  I  have chosen one of the many small
passenger  cars  that  have been converted to battery electric pro-
pulsion. This  is the "Mini"  Traveller, converted to  electric drive
by the  Traction Division of A.E.I., Ltd., in  the United  Kingdom
(Jeremy, 1966). Table 2 describes  the characteristics  and perform-
ance of this vehicle.
204
Lead-Acid Batteries

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g  2.00
K  1.80
i  1.60
     16
     14
     12
 I
 o
 CO
 Q
     10
                                                                   400  uj
                                                                        o
                                                                   300
                                                                        UJ
                                                                   200  g
                                                                        o
                                                                   100  g
             20
60          100          140
 DISCHARGE RATE, amperes
                                                              180
          Figure 4.   Discharge  characteristics  of  golf-cart
         battery  (1.280 SP.  GR.,  77°F,  62  Ib  per battery).
           Table  1.  CHARACTERISTICS  OF THE GOULD  "ELECTRUK"
                               (1.5-ton capacity)
               Curb weight, Ib
               Lead-acid  battery  weight,  Ib
               Payload, Ib
               Maximum  speed,  mph
               Range (multiple stops), miles
               Battery capacity (5-hr rate), kw-h
                               9,500
                               2,450
                               3,000
                                  18
                                  20
                                  23
                Controls
             Series — parallel  switching
     DOUGLAS
                                           205

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Table  2.  CHARACTERISTICS OF  THE ELECTRIC  DRIVE "MINI"  TRAVELLER


           Curb weight,  Ib                           2,500

           Lead-acid battery weight,  Ib                  829

           Payload, Ib                                 500

           Maximum speed, mph                        41

           Range  (constant 30  mph), miles              37

           Range  (4 stops per mile), miles               16

           Battery capacity (6-hr rate), kw-h              9.6

           Battery capacity (1-hr  rate),  kw-h              6.4

           Controls                                   SCR
     These examples, and many  more  that could  have been  chosen,
 lead  to the  not-surprising  conclusion  that  electric street  vehicles
 powered by  industrial lead-acid batteries have performance char-
 acteristics much  below  those of gasoline-engine-powered vehicles.
 This leads to the  question of what improvements in  vehicle perform-
 ance might be  expected in  the near future from projected advances
 in the  design of lead-acid batteries.
              IMPROVED LEAD-ACID BATTERIES
                   FOR ELECTRIC VEHICLES

     The  first consideration  here  is simply that  the vehicles just
 described, and all others of which  I am aware, have "made do" with
 available  batteries.  With the  possible  exception of  the golf-cart
 battery, no  battery  has been designed for  this service in terms  of
 electrical characteristics, size and shape of cells, and life.  When the
 battery is designed  as  part  of the total vehicle system,  appreciable
 improvements in performance for the same  weight may be expected.
 Further,  recent  advances in plastic  technology have  made possible
 reductions in weight of containers and connectors amounting  to  10
 percent of the total  weight of a golf-cart battery, for example.  By
 proper plate  design,  making  use of  the   recent  development  in
 ancillary  technology  and designing the battery for the vehicle system,
 it is anticipated  that the energy density (kw-h-lb) may be increased
 by 30 to  40 percent over that in industrial  motive-power batteries.
 Some sacrifice in life will be entailed.

     Gould-National  Batteries is undertaking the design and proto-
 type manufacture of a lead-acid battery optimized for the electric-
 street-vehicle application as we understand it.  The  first  attempt at
 this has given us a battery on paper that will deliver somewhat over
 18 watt-hours per pound at the 5-hour rate. Applied to the  Gould
 206                                            Lead-Acid Batteries

-------
"Electruk" the total capacity of the battery would be over 50 percent
greater.  Similarly,  the "Mini"  Traveller would benefit  from  a  25
percent increase in  battery  capacity. The life of this battery is de-
signed to be  between that  of the  rugged industrial motive-power
battery and the golf-cart battery,  i.e., 3 to 4 years.

    None of  this is particularly  spectacular  when compared  with
battery systems  described  elsewhere in  this  volume; however, this
optimized electric vehicle battery  is characterized  by being  within
reach of present-day  technology — no breakthroughs are required.
One other  consideration deserves  emphasis, the  matter  of cost.
           CONSIDERATIONS OF BATTERY  COST

    I  will  take  it  as  established  that  operating  electric  street
vehicles  will cost substantially less  than operating gasoline-engine-
driven vehicles  (Jeremy, 1966; Hoffman, 1963;  Render, 1965). Here
I want to treat the costs of battery energy sources in a very general-
ized way.  The  price of the most popular  automobiles today falls
between 50 and 75 cents a pound (Hoffman, 1963).  SLI batteries,
which are manufactured in quantities of 40 million or more per year,
are priced to the  consumer at about  50 cents per  pound. Industrial
lead-acid batteries, which are manufactured  on a job-shop basis, are
priced at an average of about 70 cents  per pound.  On this  rough
basis  the price of lead-acid batteries is  at least consistent with that
of automobiles.   Translated into  dollars  of  initial  cost  per  unit of
energy, SLI and industrial motive-power  batteries sell for approxi-
mately S35 and $70 per  kilowatt-hour,  respectively.  Using  Reid's
 (1966) estimate of 20 kilowatt-hours as being required for minimum
acceptable performance we can reasonably project that in mass pro-
duction a lead-acid battery for an electric vehicle will sell for between
S700 and 51,400.  Other types of batteries, some  made on a large scale
today, are priced at from 2  to 20 times the higher of the above values.
One must conclude that the price structure  of  the  lead-acid battery
only  will in the  near future lend  itself to an  attractively  priced
electric passenger vehicle.
                          CONCLUSION

    My conclusion, which does not differ radically from that of many
others who have discussed this subject, is that for  the next 5 to 10
years only the lead-acid battery will be used  in significant numbers
of electric street  vehicles.  Passenger  vehicles will perform  better
than the current "research"  vehicles but their performance will be
marginal compared  to  that of  gasoline-engine-powered automobiles.
Delivery trucks  may  fare  better  if  urbanization  trends continue.
I am  sure  that I speak for  the entire  lead-acid battery industry in
saying that every effort  will be  made  to improve and optimize  this
most useful of battery  systems for  the  electric vehicle.
DOUGLAS                                                     207

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                           REFERENCES
Render, B. S., 1965. Recent developments in battery electric vehicles.
    Proceedings IEE, Volume  112  (Dec.).
Hoffman,  G. A., 1963.  Electric motor cars.  Report No. RM-3298-FF,
    Rand Corporation, Santa Monica, Calif.  (Mar.).
Jeremy, K. W. C.,  1966. The electric car.  Report No. 4062, Australian
    Lead Development Association, 95  Collins  Street, Melbourne,
    Australia.
Reid, W. T., 1966.  Kilowatts for cars — a comparison of energy costs
    for electric automobiles.  Paper No. 66-978, AIAA Third Annual
    Meeting, Boston, Mass.  (Dec.).
 208                                            Lead-Acid  Batteries

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HIGH-ENERGY  NON-AQUEOUS  BATTERY SYSTEMS
                FOR ELECTRIC VEHICLES
                          M. Eisenberg

                   Electrochimica Corporation
                        Menlo Park, Calif.


                        INTRODUCTION

    In the past  decade the desirability of  electric vehicle propulsion
has become increasingly recognized. Although the concept is far from
being new and was somewhat popular after the turn of the century,
it was essentially completely eclipsed in the lata 1920's  and 1930's by
the rapid advances of  the gasoline-powered automotive engine.  The
renewed interest in electrically  driven vehicles can be attributed to
the following  motivations:

1.  The  advances in electrochemical power sources, e.g. high-energy
   batteries,  fuel cells,  metal-air cells, etc., have progressed to a
   point  where  energy densities  required  for reasonable  vehicle
   speed and distances appear to be in sight.

2.  The  large increase  in air  pollution in urban areas throughout the
   world has  placed the long-range  acceptability  of a hydrocarbon
   engine in question.   This is particularly aggravated  by the antici-
   pated growth in the demand for passenger vehicle transportation.

3.  The  consumer prices for gasoline rising proportionately faster than
   the cost of electricity puts greater weight  on the  exploration of
   fuel  cell power supplies  for vehicles  for better fuel  utilization
   efficiency,  and on  the  desirablity of  employing storage  battery
   operated vehicles, recharged overnight with cheap off-peak power.

4.  The  progress in the design and efficiency of electric  motors in re-
   cent years  has resulted in a considerable reduction of their  weight.

5.  Advances in  circuitry and semi-conductor devices offer the oppor-
   tunity for better utilization of the power on changing loads with-
   out appreciable waste of  energy.

    In  order  to  appreciate the  importance of  the  lithium high-
energy  non-aqueous battery  system and to gain  a  better perspective
of its function and the spectrum of possibilities for vehicular propul-
sion,  it  is of  interest  to examine briefly  all  other electro-chemical
power sources that  can at  least  potentially  be considered  for this
purpose and to  analyze their relative merits and disadvantages.  An
examination of possible power sources rapidly reduces the possibilities
to the following six:
EISENBERG                                                  209

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1.  Fuel cells operating on a storable fuel and using air as a cathodic
   depolarizer  (oxidizer).

2.  Electrically regenerative fuel cells, i.e.,  devices fundamentally
   analogous to a storage battery.

3.  Metal-air hybrid cells.

4.  Rechargeable  battery systems of the aqueous type  (room tem-
   perature).

5.  Rechargeable  battery systems of the fused salt type (high tem-
   perature) .

6.  High-energy battery  systems of  the non-aqueous  type (room
   temperature).

    Before  examining the  potential  applicability  of  any devices
within the above six classes to the problem of electric  vehicle pro-
pulsion, it might be useful to review briefly  the technical and eco-
nomic requirements that  these electrochemical sources  would  have
to meet.

    The most important question, aside of the problem of  the torque
characteristic of a direct-current motor, which will  not  be discussed
at present,  is  the  general disparity  between maximum  advertised
horsepower and the brake horsepower  of today's automobiles.  Only
60 percent of the advertised horsepower (Hoffman, 1962  and 1966) is
left  available  as  brake  horsepower  to overcome  the  aerodynamic
drag and the tire drag, and to provide for acceleration.  Considerations
of this type lead to the  conclusion that a compact-type passenger
vehicle can be conceived with a direct-current motor in the range
of 20 to 30 brake horsepower. If we  assume an average electrical load
of 20 kilowatts, an average vehicle speed of 40 mph,  and  a  reasonable
distance range goal of 200 miles between refueling or recharging, it is
obvious that an  energy  storage capability  of 100  kilowatt-hours is
necessary if the electric vehicle is to be something more than a curi-
osity item or a convenience cart.

     There are considerable savings in weight when one converts from
internal combustion engines to electric propulsion.  It has been esti-
mated in one case that as much as 49 percent of the electric auto-
mobile's weight  could be in batteries  (Hoffman, 1966).  Since this
figure may be somewhat optimistic, we shall assume  a  more con-
servative figure of 30 percent  for a  2,400-pound vehicle. This would
provide for a battery or fuel cell  system allowance of 720 pounds. For
a storage of 100 kilowatt-hours of energy, this means an  energy dens-
ity of at least 140 watt-hours per pound per cycle. The emphasis is on
the  words "per  cycle" since  it  is  obvious that for a  rechargeable
system this energy delivery must be obtained  to whatever  percentage
depth of  discharge is  necessary in order to provide  for  a  reasonably
good,  i.e., economical,  cycle life.  A range of  200 miles is  considered
a  reasonable minimum  to  meet the  performance  requirements  to
 210                                 Non-Aqueous Battery Systems

-------
which modern man has become accustomed.  The vehicle also must
have  enough power level, as discussed  previously, in order  to  reach
top speeds if the vehicle is to qualify for admission to parkways and
freeways.

    Thus,  in summary, in considering electrochemical power sources
as potential candidates for electric vehicle propulsion, we shall look
toward those capable of meeting an energy density of about 140  watt-
hours per  pound, or preferably more.  There are other criteria that
must  of course  be employed in the analysis  of the  suitability of the
many electrochemical devices that can be proposed. These include
the cost of fuel per mile or  per kilowatt-hour, the cost of equipment
amortization over  its useful life, the associated safety problems, the
startup and shutdown procedure requirements, maintenance consid-
erations, and availability of  recharge or refueling facilities. It is diffi-
cult within the scope of this paper to deal with  all of these aspects.
It is  for this reason a limitation will be made to  the considerations
of the following three criteria:  energy  density, cost per mile, safety,
and public acceptance.
                          FUEL CELLS

     There are many different types of fuel cells under development,
some using hydrogen or other gaseous reactants, others using stor-
able fuels. Although these systems  have different characteristics,  one
fundamental aspect common to all  fuel cells,  unfortunately  and sur-
prisingly enough, is not being recognized.  The fundamental problem
is that a fuel cell must be regarded as an electrochemical or galvanic
engine, that unfortunately has a high ratio of weight to power, com-
pared to the internal combustion engine.  The  superiority of a fuel
cell  comes through in a shining manner when small amounts  of power
are  required for a long period of time.  Then its inherent efficiency
resulting from the galvanic  energy conversion  (free of any Carnot
cycle limitations) results in the achievements of high-energy-density
ratios in terms of watt-hours per pound.

   It really matters little what the  anodic fuel in a fuel cell  is, as far
as the weight of  the fuel cell plant  itself is concerned. It may there-
fore be convenient to examine the data shown in Table 1, which con-
siders a 20-kilowatt  hydrogen-air  fuel  cell operating at an over-all
efficiency of 60 percent.  On the basis of near term technology, a rather
optimistic weight of 1,850 pounds was assumed for the fuel cell  itself,
including controls but excluding  tankage of fuel.  In  this system there
is no \veight penalty for the use  of oxidant since air would be used
and  only an air compressor has to be considered. This weight of 1,850
pounds is  based on  anticipated  technology resulting  from current
work on  the  Gemini  and Apollo fuel  cell programs and compares
rather favorably with the 3,380-pound  weight of a 32-kilowatt fuel
cell  employed in the  recently demonstrated General Motors Electro-
van.
EISENBERG                                                    211

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   Table 1.   20-KILOWATT  HYDROGEN-AIR FUEL  CELL POWER  PLANT
                    FOR VEHICULAR PROPULSION"
Fuel cell and controls             1,850 Ib                   1,410 Ib
    weight              (Near-term technology)        (Long-term technology)

Mission duration,
    hours                5   10   24  100  200     5   10   24  100   200

Vehicle range,
    miles              200   400   960 4,000 8,000    200  400  960 4,000 8,000

Total energy
    storage, kw-h        100   200   480 2,000 4,000    100  200  480 2,000 4,000

Total system
    weight, Ib          1,898  1,939 2,024 2,782 3,624   1,448 1,489 1,584 2,292  3,174

Overall mission
    energy density,
    w-hr/lb            52.6   103   237  719 1,100    69.1   134  303  872 1,262

aBasis: 0:115 Ib H0/kw-h (60% overall efficiency).  Average speed: 40 mph.

     If we define, as a mission duration, the total integral time of use
of  the vehicle between refuelings and assume a mixed road average
speed of 40  mph,  then a 200-mile-range vehicle  corresponds  to a
mission  duration of 5 hours  calling for a total energy storage of 100
kilowatt-hours,  and  the resulting total system weight  leads to an
overall energy density for this particular 5-hour mission of only 52.6
watt-hours per  pound.  When we consider  future  long-term tech-
nology and a possible cell weight of only 1,410 pounds, only an energy
density  of  69.1  pounds  results.  Extending  the mission  to 10 hours
over a  vehicle  mileage range of 400 miles gives  us corresponding
energy  density ratios of 103  and 134 watt-hours per pound,  respec-
tively.  The  fundamental problem can  be  even  better  seen by the
presentation  shown in Figure 1, which shows that  the realization of
high energy densities by a fuel cell system  does not occur until  mis-
sion durations well in excess of 10 hours occur, and that, even  with
future technology, inadequate energy densities are obtained in the
primary region  of interest. Thus, the fundamental  difficulty with all
fuel cell systems is that in the case of an electric vehicle in the  least
favorable range of mission  duration  it compares unfavorably  even
with conventional batteries.

     There are a number of other comments  one can make about fuel
cells.  For instance, a hydrogen fuel cell would raise, no doubt, serious
 objections  from a  safety point of view.  Furthermore, the cryogenic
 storage  problems  or high-pressure storage  problems associated  with
 212                                  Non-Aqueous  Battery Systems

-------
hydrogen would represent serious  technical and distribution difficul-
ties.  The hydrazine  fuel cell,  however  attractive because  of  the
storage nature of the anodic reactant, is not considered feasible for
economic reasons.  The hydrocarbon fuel  with its  inherent stability
difficulties and requirements of costly catalysts  also appears far from
a practical realization.  However, as pointed out previously, the  funda-
mental difficulties  discussed above — namely,  that in the region of
interest for an electric vehicle regardless of its  fuel type, low  energy
densities  result — represent a problem  common to  all fuel  cell
systems.
CO
>-
o
o:
 1,000

  500

  300



  100

   50
   30
                                    CELL WEIGHT ALONE: 1,410 Ib
            PRIMARY REGION
              OF
                                      CELL WEIGHT ALONE: 1,850 Ib
       400
     200f  960
      I-
        5 10  24   40
                           DISTANCE RANGE, miles
                                  4,000
                          	1	I	1	
—I	1-
 60    80   100   120   140

    MISSION DURATION, hr
+
                                   7,200
                                  	1—
                                                    160   180
    Figure  1.   Energy  density  yields for  20-kw  H2 —
      air fuel  cell as  a  function  of  electric  vehicle
                       mission duration.

    With reference to Table 1 and  Figure 1, it should be noted that
even the optimistic long-term fuel  cell weight of 1,410 pounds rep-
resents almost twice the weight allowance that  can  be made  for  a
compact  family car.  In other words, even if one would wish to  settle
for a low-energy-density  yield,  this would result in  the  removal of
the payload capability of such a vehicle.


      ELECTRICALLY  REGENERATIVE FUEL  CELLS

    The  fundamental point made above applies also  to fuel cells of
this type. Furthermore, an additional increase of weight would  result
from the necessity  of providing for a  separate  loop  for  handling
oxygen  in  a closed  system if this  were, for instance,  a hydrogen-
oxygen rechargeable fuel cell; whereas, in a primary  (non-recharge-
EISENBERG
                                                                213

-------
able) fuel cell, one would simply use  air without weight penalty in-
volved.  Also, from an electrochemists's point of view,  the  polariza-
tion  and consequent energy penalties involved in an electrolysis to a
gaseous form are too excessive to make such  a system attractive.


                      METAL-AIR CELLS

    These represent a hybrid concept between a fuel cell and a con-
ventional battery. Actually, the concept  is old and cells of this type
known as "air depolarized cells" have been in use for a  long time for
railroad signalling. As a  result,  thin,  lightweight, and efficient cath-
odes for the reduction of air have  been developed  and it  has been
possible to  design and develop efficient high-energy-density systems.
Of all the systems proposed, the alkaline zinc-oxygen,  or air system,
so far appears  to be  the  most promising. Primary batteries in such
a system have been built; they exceed the performance  of silver-zinc
batteries.  However,  rechargeable  batteries  suffer  from   the  same
fundamental difficulty that  the zinc  anode  suffers  in  a silver-zinc
battery, namely, short cycle life due to dendritic  electrocrystallization
of the zinc upon recharging.

    A variant  of the approach  to the metal-air system calls  for the
use of a primary cell with consumable, replaceable zinc anodes. Under
such a concept, solid zinc would be used as a fuel.  The engineering
complexities of such an approach remain, however, to be worked on;
regardless of the approach to the zinc-air system, it must  be recog-
nized that there is a considerable weight penalty involved because  of
the need of providing air cathodes.  As a result,  despite a high theo-
retical energy density, when one considers the weight of zinc only, the
system  is not  expected  in a rechargeable form  to provide  energy
densities in  excess of 80 watt-hours per pound (see discussion below).


                     AQUEOUS BATTERIES

     The well-known limitation of aqueous batteries, as  far  as energy
density  is concerned, allows us to reduce the discussion of this class
of devices to the  silver-zinc battery. With an open circuit voltage  of
1.86 volts, this system already represents borderline stability of any
galvanic couple in an electrolyte employing water as a solvent.  The
decomposition  potential  of water (in these batteries)  is somewhere
between 1.8 and 2.2 volts.  Indeed, a silver-zinc battery  cannot  be
sealed  for   this very  reason,  since a spontaneous, however  small,
generation of hydrogen gas occurs on open-circuit stand. This  battery
then represents the most energetic system in an aqueous medium with
a theoretical energy  density of 208 watt-hours  per  pound, when  we
consider the weight of  active  materials only.  The highest  energy
densities achieved for primary  cells  in  this system range between
90 and  105  watt-hours per  pound.  For  secondary cells, energies  as
high as 55  watt-hours per pound have  been achieved. Thus, a re-
chargeable  silver-zinc battery can hardly be  expected to provide the
214                                  Non-Aqueous  Battery Systems

-------
energy density required for a vehicle with a practical distance range,
and indeed, all  designs for vehicles with such batteries  point toward
a distance range of the order of 40 to 60 miles.

              FUSED SALT BATTERY  SYSTEMS

     The achievement  of  higher  energy  densities can, of course,  be
considered in electrolyte media that are water-free.  Such would then
permit the resorting  to  alkali metals  in which the combination  of
high electromotive force forms and low equivalent weight is advan-
tageous. Table 2 shows  an  interesting tabulation of the individual
weight contributions   (i.e., a form  of  a negative  merit figure) for
certain metals as anode  materials.  As can be seen,  lithium appears
the  most attractive,  and surprisingly,  some metals  like  calcium are
more advantageous than sodium.  Lithium is approximately 17 times
more advantageous than zinc.  On the  basis of such elementary con-
siderations, the attractiveness of a lithium battery needs hardly any
emphasis.

   Table 2.  INDIVIDUAL WEIGHT-TO-ENERGY AND VOLUME-TO-ENERGY
           MERIT FIGURES FOR SELECTED ANODE MATERIALS
Material
Lithium
Beryllium
Magnesium
Aluminum
Calcium
Sodium
Strontium
Zinc
Cadmium
g/cm'
0.53
1.82
1.7
2.7
1.5
1.0
2.6
7.14
8.65
Density/
amp-hr
5.70x 10-'
3.70x10-'
10.0 xlO-i
7.40 x 10-'
16.4 x 10-'
19.0 x 10-'
36.0 xlO-'
26.8 xlO-'
46.2 xlO-'
in/ ;amp-hr
0.0298
0.0056
0.0163
0.0076
0.0303
0.0526
0.0384
0.0104
0.0148
Half-
cell"
poten-
tial
(E'),v
3.02
1.70
2.34
1.67
2.87
2.71
2.89
0.76
0.402
Wa'"
Ib/w-hr
1.89x 10-i
2.175x10-*
4.27x10-'
4.43 x 10-'
5.71 x 10-i
7.01 x 10->
12.4xlO-i
35. 3 x 10-J
111.5x10-*
V
in;l/w-hr
9.86x 10-'
3.29 xlO-'
6.96x 10-'
4.55x ID-'
10.5 x 10-'
19.4 x 10-'
13.3 x 10-
13.7 x 10-'
36.8 x 10-'
   " For simplicity  of comparison, the standard  potential values in aqueous
     systems, in reference to the standard hydrogen electrode, are taken.
   '•As an individual electrode contribution,  Wu is defined  as:
                                    Ib
                          W
                               amp-hr x E°
   l' As an individual electrode contribution,  Sn is defined as-.
                               amp-hr x E°
EISENBERC,
                                                                 215

-------
    Fused salt  systems can be used for  alkali materials,  and such
systems  as lithium-chlorine and sodium-sulphur at temperatures  in
excess of 1,000°F are being worked on.  Although these efforts are
essentially in a preliminary laboratory stage,  some  judgment can
be made as  to  the  ultimate value.  Molten  sodium reacts violently
with  molten sulphur.  Since no ceramic  diaphragm that would be
used between the two can be expected to be completely failure-proof,
a very serious hazard of a violent explosive reaction would exist. This
would raise serious  objection toward incorporation of such a system
in a vehicle.  In addition, all molten  salt systems are handicapped by
very serious materials  of corrosion problems. Last, but not least, is
the problem  of  startup time that would be required for a vehicle of
this type.  A  startup time  in  excess of 5  minutes would hardly  be
acceptable to the general public. At the  same time, it is difficult to
foresee how  a fused salt system could ever be expected to offer a
startup time  to full power in less than 30 minutes.  Thus, the possible
high-energy-density advantages of these systems would be seriously
overshadowed by the problems discussed above.


       THE  NON-AQUEOUS ORGANIC ELECTROLYTE
                       BATTERY SYSTEM

    If it is recognized that lithium is a most  desirable  anode material
in a battery and if one  wants to build a  battery  at room temperature,
the use of a non-aqueous solvent with a broad liquidity range is indi-
cated.  Before proceeding to discuss energy densities of batteries, it is
important to realize that they  are a function of  rate of discharge and
of the cell size  expressed  in  terms of ampere-hour capacity.   These
relationships are pictured in Figure 2 for both the silver-zinc battery
and the non-aqueous  battery.  It  will  be noted  that  the slope is
steeper for the non-aqueous battery.  Because of the generally  lower
conductivity  of  non-aqueous electrolytes, compared with that of the
aqueous  ones, the very high rates of discharge tend to result in a rela-
tively larger impedance losses  for the non-aqueous battery. This ex-
plains the steeper slope for the plot against the rate of discharge. At
the same time,  it takes the packaging  efficiency  of larger cells  for
the weight advantages of  lithium  as an anode  material to come  to
the fore. This again  explains the steeper slope in Figure 2. It is there-
fore important in the discussion of any type of a battery to define the
conditions at which the watt-hour-per-pound figures are given. This
explains why rather  broad ranges  are given  for  the operational,
practical energy  densities in Table  3  for a series of aqueous and non-
aqueous  batteries.  It will  be noted, however, that the non-aqueous
batteries based on lithium offer very substantially  larger theoretical
energy densities.

    Of the non-aqueous systems, from  which so far reasonably suc-
cessful  results  have been  obtained  for  a  secondary battery, the
lithium-silver chloride, the  lithium-copper  chloride, and the lithium-
nickel  fluoride  systems should be  mentioned.  The  rechargeability
216                                 Non-Aqueous Battery  Systems

-------
          mm
                                           hours
                       DISCHARGE RATE
.c

5
\-_

C/5
LJ
Q
ce
LJ
z
LU
     FIXED DISCHARGE

          RATE
                   NON-AQUEOUS
                           10


                     CELL CAPACITY, amp-hr
                                                100
   Figure 2.   Relationship  between (top)  energy  density
     and discharge rate  and  between  (below) energy
                 density and  cell  capacity.
 EISENBERG
                                                        217

-------
characteristics of these systems have been investigated; indications of
favorable performance have already been obtained, even at consider-
able depths of discharge.  Figure 3 shows a non-aqueous  cell, type
LN-6, cycled at a charge rate of 15 hours (typical of an  overnight
charge)  and discharged at a mild rate  of 30 hours. As can be seen,
most charging occurs under 4.0 volts and typical discharge voltages
are of the order of 2.5 volts. The performance of another non-aqueous
cell, Type LN-7, at a rather high discharge rate of 1 hour is shown in
Figure 4. Here, the discharge  occurs at  an average plateau voltage of
the order of 2.1  volts.  At a typical average rate of discharge corre-
sponding to 5 hours, an average cell voltage of 2.4 volts with fluctua-
tions of the order of ±0.4  volt, can be  assumed on the basis of these
initial results. As far as a temperature-range capability is concerned,
the broad liquidity range of the non-aqueous electrolyte provides the
basis for both low-  and high-temperature  operation. Indeed,  one
series of cells has been found  to operate satisfactorily  over  the entire
range of —40° to -4-165°F (Kuppinger and Eisenberg, 1966).
          CYCLE 1   |  CYCLE 2   CYCLE 3
        INTERRUPTIONS         I
       D          C |  D     C I D
       CYCLE 4
  C I D
                  50             100            150
                     TOTAL OPERATING TIME, hours
                          200
  Figure  3.   Case  history of  discharge  (d) — charge (c)
                   cycling  a type LN-6  cell.
    It appears, thus, that non-aqueous battery systems can indeed be
constructed,  and  performance exceeding  that  of  the  silver-zinc
battery, the highest-energy-density aqueous  type, can be obtained.
This is illustrated in Table 4,  where a general comparison is  made
between aqueous batteries, metal-air cells, and non-aqueous systems.
A distinction is made in the table between primary and rechargeable
secondary systems, which generally yield lower energy density ratios
218
Non-Aqueous  Battery Systems

-------
SENBERG

Table 3. SECONDARY BATTERIES
Aqueous batteries
Types Lead-acid Nickel- Nickel- Silver- Silver-
iron cadmium zinc cadmium
Non-aqueous batteries
Li /copper
chloride
Li /copper
fluoride
Li /silver
chloride
Energy density:
  Theoretical on active
     material, w-hr/lb
  Operational, w-hr/lb
  Operational, w-hr/in.-
     115         138          107         208         120          503         746          230
   5 to 15      7 to 10      12 to 15     25 to 50     16 to 25    (25 to  175)   (25 to 200)   (25 to 90)
  0.4 to 1.0    0.7 to 1.0    0.7 to 1.0    1.7 to 3.5    1.4 to 2.9       --          —           —
Operating voltage per cell
  (mid-point)               1.7 to 1.95       1.2       1.1 to  1.23   1.3 to 1.5    1.0 to 1.10    2.3 to 2.8    2.3 to 2.8    2.3 to 2.8
Cycles
                           200 to 500    2,000+    300 to 3,000   10 to 200   300 to  1,500
                                                                                         50 to 200
                                                                                           (Exper.)
Operating temperature
  range, °F
                                                                 —40 to
-^»0to+140—10to+115—40to+140  0 to +140 —10to+140   +165±

-------
                CELL
          0     1351
          A     1352
         20
                                                             80  100
               min
                                                      mm
   Figure  4.   High-rate operation of  cell  type  LN-7  —
          discharge rate, 1  hr; charge rate,  12 hr.

Table 4.  ENERGY DENSITIES OF  ELECTROCHEMICAL BATTERY SYSTEMS"
                             (in w-hr/lb)
System
Pb-acid (sec)
Nickel-Cd (sec)
Silver-Cd (sec)
Silver-zinc (prim)
Silver-zinc (sec)
Metal-air cells
Zinc-air (prim)
Zinc-air (sec)
Non-aqueous high energy
CuCI2-Li (prim)
CuCI,-Li (sec)
CuF2-Li
Theoretical
115
107
120
208
208

671'
671

503
503
750
Practical rangeb
7 to 12
8 to 17
12 to 45
20 to 100
15 to 55

30 to (140)
30 to (80)

28 to (230)
20 to (160)
?
"Specific comparison: 10-amp-hr cells;  10-hr rate of discharge
  Silver-Zn:                      38 to43 w-hr/lb    2.4 to 2.7 w-hr/in.3
  Non-aqueous (ELCA Type LN-3):   75 to 82 w-hr/lb    4.3 to 4.8 w-hr/in."
                                          78
                       90
  % Increase of energy densities:
t> Practical energy yield is a function of rate, size, and construction type.
c Considering the weight of zinc only.
220
Non-Aqueous Battery Systems

-------
 because of electrochemical design and  mechanical design considera-
 tions.   Thus,  a  non-aqueous cupric  chloride-lithium  rechargeable
 battery, with  a  cell capacity  in  excess  of  500 ampere-hours, is
 estimated  to yield 160 watt-hours per  pound per cycle compared to
 55 for the  silver-zinc battery.
     The lower portion of Table 4 shows a specific comparison between
 primary cells, comparing a non-aqueous cell, Type LN-3, to a silver-
 zinc cell of the same capacity, discharged at the same  rate.  As  can
 be seen, an average improvement of 90 percent in energy density  per
 unit weight and 78 percent  in energy  density per unit volume,  has
 been achieved.

     The importance of the effect of cell size  (capacity)  upon both
 gravimetric and volumetric  energy densities can  be seen from  the
 experimental data given in Figure 5. Indeed, these results provide the
 first corroboration of the qualitative figures  shown in Figure 2. Going
 from a 1-ampere-hour to a 10-ampere-hour cell improves the watt-
 hour per pound ratio for silver-zinc batteries  about  25  percent. The
 improvement  is well  over 100  percent for  the  non-aqueous cupric
 chloride-lithium battery.

     Similarly,  as  shown in the data  of Figure 6, a change  in the rate
 of discharge has  a  much more pronounced  effect  on  the energy
 density of  a non-aqueous cell. In the operation of an electric vehicle
 the  5-  to  10-hour rate  of  discharge would  be more typical than a
 20-hour rate of discharge.
     Engineering computations for the non-aqueous cupric chloride-
 lithium rechargeable battery  indicate that a 700-pound battery could
 be built with a base power level of  20  kilowatts and overload capa-
 bilities (for  acceleration) of  100 kilowatts, i.e.  a rate  of 5.  When
 the overload is applied,  the 1-hour  discharge ratio would correspond
 to the average 5-hour discharge rate.  The  battery would then have
 an  average power density of 28 watts per  pound and an overload
 power density of 142 watts per pound. If required, still higher power
 densities are possible  as  a  result of recent  improvements  in  current
 density capabilities  of the system.  With a  storage capability of  100
 kilowatt-hours, the  corresponding energy  density yield would be  142
 watt-hours per pound  per  cycle.  This would correspond to  a 75
 percent depth  of  discharge.   On this basis, the lithium  battery at
 least offers the possibilities of achieving the design performance dis-
 cussed earlier in this paper.

     The new lithium high-energy  battery is  beginning  to  emerge
 from the pure  research area into  the initial hardware  development
 phase. Methods are already being developed for construction of cells
 and  battery hardware that once sealed can  be handled in ordinary
 atmospheric environments and that can have the general appearance
of conventional batteries.
    Relative to the economic outlook, estimates indicate an eventual
lithium metal price  of the order of  $2-$3 per  pound  (Private com-
munication with American Potash Co.).  The costs of other com-
EISENBERG                                                   221

-------
  100


   90



£  8°

170


o  60
UJ

—  50
H
in
5  40
Q

I  30
LU

5  20


   10
   0  ELCA LN-3 NON-AQUEOUS

   A  Ag-Zn CELLS

                                                                    c

                                                                    SI
                                                                 3
                                                                   >-
                                                                   K
                                                                   C/)
                                                                   "Z.
                                                                   LLJ

                                                                 2  °
                                                                   CD
                                                                   (X
                                                                   UJ
                     468
                      CELL CAPACITY, amp-hr
                                                         10
 Figure  5.    Effect of  cell  capacity  on  energy densities
 — non-aqueous  lithium  battery  and silver-zinc  battery.


ponents are essentially in line with present-day conventional batter-
ies.  With proper production tooling, the lithium battery  is not ex-
pected to be  unusually costly.

    In summary, on the basis of fundamental considerations of energy
density, if we eliminate the fused salt, high-temperature system, only
the lithium-anode-base organic electrolyte batteries appear to offer an
approach toward an  energy  density of  at least  140 watt-hours per
pound per cycle, which is considered essential for a practical vehicle
with a practical distance range.
222
                                         Non-Aqueous Battery Systems

-------
  110


  100





I 80

P
5 70
UJ
§
r eo
   50
I 40
  30


  20


  10
        0   ELCA LN-3 NON-AQUEOUS

        A
                  -tY— '
                                        _ — —	A~~ '
                                  10

                          DISCHARGE RATE, hr
                                                 20
         Figure 6.   Effect  of  rate of  discharge  on  energy
      densities —non-aqueous  lithium  battery  and  silver-zinc
                 battery (cell  capacity,  10  amp-hr).
                             REFERENCES

     Hoffman, G. A.,  1966 the electric automobile. Sci. American. 215:34-
         40  (Oct.).

     Hoffman, G. A.,  1962. Memo.  RM 2922 FF.  The Rand Corp. (Nov.).

     Kuppinger,  R.  E.,  and M.  Eisenberg, 1966.  Non-aqueous organic
         electrolyte  batteries for  a wide temperature range  operation.
         ECS Meeting. (Oct.).
                                                                    O
     EISENBERG
                                                                223

-------
  AN ELECTRICALLY  RECHARGEABLE  ZINC-AIR
            BATTERY  FOR MOTIVE POWER
                         D.  V. Ragone,

          General Atomic Division / General Dynamics

    The major obstacle in the  path of the development of a significant
electrically driven vehicle is the excessive weight of presently avail-
able electrical energy  storage systems. General  Atomic, since  1960,
has been engaged in a program to develop a secondary battery system
with a high energy density for use in vehicles.  During the process of
selection of  an  appropriate  electrochemical  couple, emphasis  was
placed on the use of low-cost materials, relatively low-temperature
operation, and freedom  from potential operational hazards  for the
user.  These considerations led  to the selection  of  the  zinc-oxygen
(air)  couple, operating with an aqueous electrolyte at  temperatures
below the boiling point of water.

    Some of the important features  of the General Atomic zinc-air
battery are as follows:

1.  A  solid zinc "front  surface" electrode is used with the zinc plated
   on an inert substrate so that substantially all of it  can be used
   during discharge.

2.  The electrolyte, an aqueous solution of potassium hydroxide, cir-
   culates.  This allows  the reaction product to be swept from the
   cell and stored externally.

3.  Atmospheric oxygen  is introduced as a reactant through a porous
   nickel "bubbling" electrode.


                  OPERATION OF  BATTERY

    During discharge,  air  from a  pressurized  air  plenum  seeps
through  the porous nickel cathode and bubbles  into the electrolyte.
A large fraction  of the  oxygen in the air (assuming that the air supply
is  compatible with the cell current  demand)  combines  electro-
chemically with the zinc to form zinc oxide.  After some discharge
operation, zinc oxide is formed  in the electrolyte as  a finely  divided
solid.   The waste air with its  unused nitrogen is continuously swept
from  the cell by the circulating electrolyte, as is the excess zinc oxide.
The excess zinc oxide is separated  from the electrolyte and stored
outside the cell.

    During charge,  essentially  a reverse reaction  takes  place.  A
potential is applied across the  cell  while  the electrolyte circulates.
Zinc from the zinc oxide is replated  on the backing sheet, and pure
oxygen is evolved at the surface of the porous nickel electrode.  The
RAGONE                                                     225

-------
   electrolyte continuously  dissolves zinc oxide  from the storage point
   outside the cell.
       The  cells and cell stacks, containing no stored reactants other
   than the  metallic zinc, can be quite compact  and relatively light for
   any given  active cell area.  The system requires several pieces of
   equipment in addition to the cell stack,  as shown by  the schematic
   diagram  in  Figure 1.  The  electrolyte  circuit  contains  a pump to
                                  WATER CONDENSER
                                                          SPENT AIR
                                                          OUT
   AIR IN

                                                             ELECTROLYTE
                                                             RESERVOIR
AIR
COMPRESSOR
                     INSULATION
       Figure  1.    Schematic  of zinc-air  battery  system.

   circulate the electrolyte reservoir and an air  separator  to  remove
   spent air entrained in the cell outlet electrolyte. These items are all
   arranged close to the cell stack, and the whole  assembly  is insulated
   for temperature  control. Two other equipment  items, which may be
   located  some distance  from  the cell stack,  are the air  compressor
   and the zinc oxide separator and storage  container. The zinc  oxide
   separator  removes most  of  the  precipitated  zinc oxide  from the
   electrolyte  and stores it as a relatively dry sludge.  Some zinc  oxide
   remains in  electrolyte  suspension  during  discharge.  Figure  1 also
   shows a condenser,  which cools the  air that has  been through the
   cells in order to  remove most of the water it has picked up from the
   electrolyte.  The  waste  heat from this condenser  can be  used to warm
   the passenger compartment of the vehicle.

      During  discharge,  voltage  varies with the  power  demand in  a
   manner  similar to most battery systems. The voltage variation during
  226
Rechargeable Zinc-Air Battery

-------
   discharge time is relatively flat, until nearly full discharge is reached
   (Figure  2), because of the front-surface operation of the zinc elec-
   trode.  The zinc that participates in the reaction is  taken off  the elec-
   trode and leaves the cell in the circulating electrolyte.  The reaction
   products, thus,  do  not  impede the reaction.  The  zinc remaining on
   the electrode provides the electrical connection to the terminals. The
   discharge may  continue until  essentially all of  the  zinc is  removed
   from the backing sheet.
  2.0
  1.5
o
  1.0
o
  0.5
                   CHARGE
                       MAXIMUM
                       CONTINUOUS
                       POWER
                      -PEAK
                       POWER
                             % POWER
                             DISCHARGE
                                                                      10
              Figure 2.
     TIME, hours

Cell  voltage characteristics.
        Charging is accomplished at a voltage of about 2 volts per cell.
   The speed of charging is fast as compared to average discharge times.
   A cell that would give 8 hours of use in an  average  lift-truck cycle
   could be charged in about 2 hours.

                    HISTORY OF THE PROGRAM
        Early experiments (1960-1963)  on the air electrodes were per-
   formed on small (2 cm2)  electrodes.  These experiments were  mainly
   BAGONE
                                                                  227

-------
 concerned with the performance (polarization) of the electrode as a
 function of electrode parameters such as porosity, pore size distribu-
 tion, and thickness.  When satisfactory performance of the air elec-
 trode had been achieved and  the experiments on the plating  of zinc
 from a circulating alkaline solution had demonstrated the feasibility
 of producing relatively flat zinc electrodes, then a  1-kilowatt-hour
 "breadboard" battery was assembled  (1964).  This was  followed  by
 the construction of 7-  and 14-kilowatt-hour prototypes  in  1965 and
 1966.

     Figure 3 shows present estimates of the achievable energy density
 plotted  against battery size.  Because the size and weight  of  the
 auxiliaries  do not scale linearly with battery capacity, the larger
 batteries show higher energy densities. The system allows flexibility
 of design on the question of power versus energy.  For  example,  to
 obtain higher power levels a given quantity of zinc may be distributed
 over a greater cell  area. This increased cell weight lowers the energy
 density but raises  the  power  density.  Delivery vans, which require
 higher power densities than transit buses, are shown in Figure 3  at
 the lower portion of the energy-density band.
    100
              100   200
 300    400    500
NUMBER OF CELLS
                                                 600    700
       Figure  3.    Energy  density  of zinc-air  battery
                     as a  function  of size.

    The amount of space occupied by batteries is  also important  in
vehicular applications.  Figure 4 illustrates  one possible  configura-
tion of the  zinc-air battery in a delivery van.  The  battery system
pictured has a capacity of about 100 kilowatt-hours and a  maximum
228
         Rechargeable Zinc-Air Battery

-------
  rated output of 60 kilowatts.  Gross weight  of  the  van is about
  5,000 pounds.

      The  General  Atomic program during the  next  2  years  will be
  directed at the design, building, and testing of a battery for a delivery
  van. Capacity will be between 50 and 100 kilowatt-hours. The proto-
  type is scheduled  to be ready for bench testing in early 1968  and for
  preliminary  vehicle tests toward the end of 1968.
CONTROLS
                                                  ZINC OXIDE STORAGE
                                                    .WATER CONDENSER
         ELECTROLYTE RESERVOIR (2)
    CELL STACK MODULE (6)
'AIR COMPRESSOR
    Figure 4.   Zinc-air battery  system  in  a  delivery  van.
  RAGONE
                                                              229

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            ZINC-AIR  BATTERIES FOR  THE
                    ELECTRIC  VEHICLE


                         Nigel I. Palmer

                   Leesona Moos Laboratories
                        Great Neck, N. Y.

                        INTRODUCTION

    The current renewal of interest  in the electric automobile can
be attributed  largely  to two significant developments.  The first is
the increasing public concern with air pollution and possible means
of reducing it.  The second development is the recent progress that
has been made  in energy-storage technology. The prospect of new
power sources with higher ratios of energy to weight  has permitted
the electric car designer to project performance levels approximating
those expected by the  average driver. The two primary performance
requirements  for  power  sources  of  the electric car  are  (1) high
discharge rate capabilities to satisfy  acceleration specifications and
(2)  high  energy capacities  to meet  operating range  requirements.
Although  energy conversion devices such as fuel cells, in "which  the
source of energy is  stored  externally, are generally attractive  as
regards capacity, they are at present excessively bulky and costly.
Most  available storage batteries,  although able to sustain reasonably
high  drains, have insufficient capacity  to give acceptable  operating
ranges. The purpose of this  paper  is to review a new  type of power
source —  the zinc-air battery,  which  promises to meet both  the
rate and capacity requirements of  the electric vehicle.

    The zinc-air battery can be regarded as a hybrid fuel cell and
storage battery in that half of the over-all electrochemical couple, the
zinc,  is stored within the battery, while the  other  half, oxygen, is
taken from the surrounding air and  electrocatalytically reduced at
a non-consumable electrode.

    The essential  electrode reactions  occurring  in  potassium hy-
droxide electrolyte are
Zinc
Oxy;
Anode:
ien Cathode:
Zn
l/2
+
o..
2(OH)--
+ H3 0 +
ZnO -
. 2e^
f H2 O +
2(OH) ~
2e
(1)
(2)
Over-all Reaction:    Zn -f 1/2 O2 — ZnO E =1.62 volts           (3)

    Zinc-air and zinc-oxygen primary batteries have been described
(Chodosh,  Katsoulis, and  Rosansky, 1966" and 1966'1).  Briefly,  the
basic  cell consists of a porous zinc anode,  impregnated with aqueous
potassium  hydroxide electrolyte,  surrounded by a porous  separator,
and contained  within a structure comprising  two hydrophobic  air
cathodes electrically  connected in parallel  (Figure  1).  A zinc-air
PALMER                                                      231

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cell  operating  at  theoretical voltage  (1.62 volts),  would  have  an
energy density of 600 watt-hours per pound, based on the weight of
zinc only.  In  practice, this figure is reduced by the weight of non-
zinc components, electrochemical irreversibility, etc., to about  150
watt-hours per pound for a primary battery.
              CATHODE-
              TERMINAL
                              V V


                              V
                                       ./- ELECTRODE
                                     //   SEPARATOR
                                    r
                                            ANODE TERMINAL
                                              -ANODE COVER SEAL
                                          CATHODES
                                          ZINC ANODE
                                          ANODE  CONDUCTOR
     Figure 1.   LML zinc-air single cell  cross section.
             SECONDARY ZINC-AIR BATTERIES

    It is axiomatic that a battery intended for use in electric vehicles
must have long life and full recharge capability. The approach being
followed at  Leesona Moos  Laboratories in the development of such
batteries is to adhere as closely as possible to  the basic configuration
of the  primary  zinc-air   batteries,  incorporating  modifications  as
necessary to  achieve the additional capabilities. The purpose of the
following brief analysis is to review the major problem areas of the
over-all system, their present status, and  prospects of solution.
232
Zinc-Air Batteries

-------
Cycle Life
     The  principal single requirement  that must  be added to  the
capabilities of the primary battery is cycle life.  Some of the factors
that affect cycle life can be accommodated in a design tradeoff; others
require absolute solution.  Depth of discharge is probably the most
important factor  in determining  cycle life. Battery  research  has
established that  the lower the depth of discharge, the greater  the
number of cycles  obtained. This could  be  expected, since the ability
to store charge depends on the conversion of the  zinc oxide produced
during discharge  back completely to zinc  and, more importantly, in
a morphological  form  suitable  for  the  next discharge.  Clearly,  the
greater the proportion  of zinc converted to oxide during  the previous
discharge, the less remains to exert an influence on the morphology
of the recharged zinc.  At present, 50 percent depth of discharge  ap-
pears  to be about the maximum  for  good cycle  life. Note that this
factor of  electrode morphology refers only to  the  consumable  elec-
trode. The structure of the air electrode remains unchanged during
the cycling.

Discharge Rate
     There is  evidence that sustained,  high discharge rates reduce
the capabilities of the zinc-air cell  for repeated cycling. As analysis
of the urban  driving cycle show, however, the sizing of the  battery
for peak loads on acceleration results in average discharge currents
of 25  to 35 milliamperes per square centimeter.  This  rate  is con-
sidered relatively low  and favors  a high cycle life.

Charging Process
     Work to  date has  shown that the charging rate has a profound
effect on the cell cycle  life. A critical process to be controlled during
the charge stage is  the production  of zinc dendrites. The  formation
of these crystalline zinc deposits  can lead to  shorting  between  the
cell  plates  and result  in sudden  failure  of the battery.  One im-
portant factor in  reducing this hazard is  selection of  the optimum
separator  material.  New, improved separators,  both ceramic and
polymeric,  offer  considerable promise. Charging  rate, method  of
charge, anode thickness,  and the quantity  of electrolyte  are  other
factors affecting both the growth of zinc dendrites and the life of  the
zinc anodes.  In general,  the lower the charging rate, the more  com-
plete the  recharging  process.  The critical step in the recharging
process is  reduction of zincate dissolved in the electrolyte to zinc.
                     Zn(OH)4-~+ 2e-< Zn +  4(OH)-         (4)
Work  at  LML has shown that the  crystalline  nature  of the zinc
deposited on  charge will vary depending on whether the process is
activation  or  diffusion  controlled  (Oxley,  Fleischmann, and Oswin,
1966).  Under activation control   (low charge  rates),  the  zinc is
deposited in a dense, adherent  'mossy'  form, whereas diffusion con-
trol  (high charge rates)  leads to  more-crystalline,  less-dense zinc
deposits  giving dendrites. This  process  in turn  depends  on  the
PALMER                                                      233

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concentration of zincate, and hence on the quantity of electrolyte.  In
this  connection  a  significant  difference between  silver-zinc  and
zinc-air  cells may be  noted.  The latter, having  a low-volume air
cathode as the positive  electrode, contain proportionately less electro-
lyte.  This results  in a more activation-controlled process  favoring
the preferred 'mossy' type of zinc crystalline growth.

    In addition  to  the  technical aspects of the charging process, it is
important to consider vehicle utilization, which ultimately determines
the preferred charging rate;. Obviously  the- ideal  battery would  be
rechargeable  in  a few  minutes, i.e.,  in  the time  it takes to refill  the
gasoline  tank of a car. For many  military and space applications,
such rapid charges are highly  desirable; this  has dictated the need
for charging  rates  of  10  minutes  to  1  hour1 for  some'  of  the studies
funded by the government. Although such rates are partially  feasible,
they do  incur a  penalty  of reduced  cycle life.  For the electric  car
application  it is clearly  reasonable  to consider  overnight charging
(i.e., an  8-hour  rate)  as  the normal situation.   This  assumption is
particularly  justified, if the; capacity of  the; battery is sufficient Coi-
n-lost daily  driving requirements.  As  the subsequent  analysis will
show, this  appears to be the case  of the zinc-air  battery.

System Factors
    In addition to the  battery, a  number of system factors  must  be
considered: air flow, heat removal, water control,  and contamination
by  COL,.   Clearly,  each of these  is  affected  by the  others, so that
optimization  of  the over-all  power  source  requires considerable
systems  engineering.   The  thermoneutral voltage  corresponding  to
the enthalpy change  for  the over-all zinc-air  process is approxi-
mately 1.80  volts.  Operation at  voltages lower  than this results  in
evolution of  heat.  At low rates this heat is advantageous, producing
the natural  convective flow of  air  necessary  to provide.1  oxygen  to
the cell.  At  high rates, however,  heat evolution becomes  significant
and  at  the  same  time oxygen demands cannot  be satisfied  on a
continuous  basis  by  natural  connection.  Under  these   conditions,
forced convection by a blower becomes desirable.  A system of this
type is shown in Figure 2, a proposed design for  a secondary zinc-air
battery.  The  blower imposes small weight and  parasitic power penal-
ties on the battery.

    During operation,  water vapor is transferred into the air stream.
Since,  unlike operation with fuel cells,  no net  water  is  formed by
the process, water  losses must be made up or prevented. liumidifica-
tion of the air stream is  one option that has been studied.  At  the'
highest rates, however, it may be necessary  to  supplement  convec-
tive cooling   with  additional  cooling by evaporation.  Designs  are
therefore being considered in which  additional  water make-up would
be provided  directly through the anode top. Finally, the  problem  of
carbon dioxide take-up from the air by the alkaline1 electrolyte-  must
be considered. In practice, primary zinc-air colls have been operated
for 400  hours  with no  deterioration  attributable  to  COL,  uptake
234                                              Zinc-Air Batteries

-------
                                 •AIR FAN
                                           GAS  VENT
                                                    WATER  MAKE-UP
                                                    HEADER
                                                          INTERCELL
                                                         SEPARATOR
                                                     CELL  BRACKET
                                                END PLATE

                                            CELL FRAME
Figure  2.   A 120-volt zinc-air battery—10-kw-h capacity.

Nevertheless, for truly long-term operation in an  electric car,  some
form  of  CO;, removal  may be required. Soda-lime scrubbers of the
type used in fuel cells are being studied for this function.  Periodic
electrolyte  replacement  is  an  alternative  solution that  will  be
considered.

    DESIGN OF BATTERIES FOR THE ELECTRIC CAR

    In sizing a battery for an electric car, one method  could  be to
analyse  the maximum power  and energy  requirements of  existing
passenger vehicles and translate these directly to battery dimensions.
Such  an approach  is  considered  unrealistic, however,  not  only in
terms  of available battery performance but  also  in terms of the
use patterns for which the electric  car is specifically designed.  Since
the pressures generated  within  the  urban  areas  have  created the
requirement for the  electric  car,  it  is  clearly appropriate  to  base
design of the car  and the power  plant on  urban  driving patterns.
As regards the car  itself, recent studies have shown how reductions
in over-all  vehicle weight, improved vehicle design, and optimum
PALMER
                                                              235

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 tire selection can significantly  reduce the energy requirements  for
 road and drag  losses (SAE, 1967).  The present  design  study en-
 visions a small commuter-type vehicle with a gross weight including
 passengers of 2,000  pounds.

     In determining power and energy requirements, the  California
 City-Driving Cycle  was  used as  the basis  for  design.  This typical
 urban cycle, widely applied  in air pollution studies, defines  the per-
 centage  of  driving  spent in  the various regimes of  acceleration,
 cruising, deceleration,  and  idling.   A car  operating on  this  cycle
 would cover approximately 22 miles  in 1  hour of driving.

     The energy required by an electric vehicle will be that  required
 to overcome road and aerodynamic drag losses  during cruising, plus
 energy expended during  acceleration.  These represent the energy
 expended on the wheels.  The total energy required from the battery
 would be higher to  account for inefficiencies  in the motor,  controls,
 and transmission. An overall efficiency  of 78 percent was  assumed
 for these factors. Estimated energy requirements  are 2.9 kilowatt-
 hours  per  hour  of urban driving,  increasing to 8.4  kilowatt-hours
 per hour at 50 mph steady cruising.  Maximum power requirements
 for the urban car will occur during acceleration from 0 to  30  mph.
 Based on a  moderate acceleration  performance of 0 to 30 mph in
 10  seconds  (4.4 ft/sec2), peak  power requirement for the 2,000-
 pound vehicle is estimated at 20 kilowatts.  This requirement would
 increase to 33 kilowatts if acceleration from  0  to 30 mph in 6 seconds
 were demanded.


                 BATTERY SPECIFICATIONS

     For the  purpose of this analysis a nominal voltage of  100  volts
 has  been assumed.  For a point of  reference, the  requirements are
 first analysed in terms of existing primary zinc-air batteries. These,
 in effect, represent the ultimate limit of performance  of the equiva-
 lent secondary batteries.  For convenience, a  standard Leesona bat-
 tery, the 12-volt, 100-ampere-hour model was selected as  the  basic
 design unit.  This battery consists of  10  bicells, each with  an area
 of 278 square centimeters. In specifying the battery, the rate limita-
tion will reflect  the  current-voltage curve  of  the cell,  whereas
 capacity will be controlled, for a given size cell, by the anode thick-
 ness and the utilization  of zinc.  A  voltage-current discharge char-
 acteristic of the cell is shown in Figure 3. Although the voltages at
 the lower current densities are stable  under natural convective flow
 conditions, forced air circulation is required  for stable  sustained
operation at current densities over  approximately 70 milliamperes
per  square  centimeter.  This is shown  in  Figure 4,  which shows
transient load response for current  densities up to 250 milliamperes
 per square centimeter and periods up to 30 seconds.  Note  that for
 periods of 1  to 5 seconds  voltages may actually be  better  with
natural convection.
236                                             Zinc-Air Batteries

-------
   1.6
   1.4
   1.2
   1.0
 9 0.8
 UJ
 o
   0.6
   0.4
   0.2
                         i	,	i
                        100                 200
                       CURRENT DENSITY, ma/cm2
                                              300
   Figure 3.
Discharge characteristic of zinc-air battery
          with  blower.
    Selecting a  current density  of  200  milliamperes per  square
centimeter to correspond to the peak load indicates  a requirement
of 50  batteries,  connected 5  in  parallel  and  10  in series.  These
would yield a  total capacity  of  58  kilowatt-hours, equivalent to
about  11  hours of  operation  on  the urban cycle,  with an  energy
density of  150  watt-hours per pound.
    In estimating the probable specifications of rechargeable secon-
dary  zinc-air batteries,  one  must consider the  factors mentioned
earlier. Thus,  to  obtain satisfactory  cycle life, depth  of discharge
must  be reduced  and  zinc anode porosity increased, both tending
to reduce  the  energy-to-weight  ratio.  In  addition,  the  systems
associated  with control of  water  level,  heat  removal,  and  possible
CO.,  removal will  also  contribute to weight  and  volume.  Table 1
shows estimated specifications  of  batteries for the present electric
vehicle application. The first  column is  based on  the  performance
PALMER
                                                                237

-------
 currently available with Leesona standard primary zinc-air batteries.
 The second column presents estimates for secondary  zinc-air batter-
 ies based  on current laboratory results.  Specifically, the  estimates
 are based  on 200-mil anodes, with 80 percent porosity and operation
 at  50  percent depth of discharge  (corresponding  to  40  percent zinc
 utilization).   The  third  column  presents  some  projections based
 on assumed  future technical progress,  such as higher zinc-utilization
 factors,  use  of  thicker anodes,  and lighter weight construction for
 the non-zinc components.
    1.4 r
    1.2
    1.0
 UJ
 e>
 o
UJ
o
   0.8
   0.6
   0.4
                                                        •OCV
                                                        50 ma/crrf
                                                        100 ma/cm2
     160 ma/cm2


     200 ma/cm2



     250 ma/cm2
                                             KEY
                                                  • WITH BLOWER
                                                   WITHOUT  BLQWER
                    10
                                   20
                               TIME, sec
30
   Figure 4.   Zinc-air  cell transient  load  performance.
238
                                                Zinc-Air Batteries

-------
Table  1.  BATTERY SPECIFICATIONS FOR  2,000-POUND ELECTRIC VEHICLE

Weight, Ib
Volume, ft3
Capacity, kw-h
Energy density,
w-hr/lb
kw-h /ft3
Operation in urban cycle, hr
Range (at 50 mph), miles
Present
primary
batteries
370
3.6
54
148
15
19
320
Estimated for
rechargeable
batteries
under
development
360
4.5
20
55
4.4
7
120
Longer-term
projections for
rechargeable
batteries
350
4.0
25 to 35
75 to 100
6.0 to 8.0
9 to 13
150 to 220
             ALTERNATIVE  OPERATING MODES

     One of the novel  features of the  zinc-air  battery investigated
at LML is the  ability  to  remove and  replace the zinc anode after
discharge.  This is made possible by the non-changing form  of  the
fuel-cell-type air cathode, which in the bicell  configuration forms
a  case  within  which  the anode is  contained.  This  capability  in
effect  gives  an extra  degree  of freedom  to  the battery  designer
and  offers the possibility of a number of alternative operating modes,
shown  m Figure  5.  These operating modes may also be  considered
in the  context of the electric car.  Scheme  1 in a standard throw-
away primary  cell  and is not applicable  here.

     In  Scheme  2, the  discharged anode is  replaced by a new one
at the end of the discharge,  the  old  one being  discarded.  Batteries
of this type  are  already  in  limited  production for a number  of
applications.   Although such  a  system  would  not be economical
for the  present  application, this mode of operation does  offer distinct
advantages  for the  immediate  testing  of  prototype   electric  cars
under realistic  conditions  of  battery weight and power.

     Scheme  3 is  a  logical extension of the second.  By  recharging
the  discharged  anodes  externally under controlled conditions in an
electrolytic  bath,  one may circumvent many of the difficulties  en-
countered in an internally  recharged true secondary battery. Because
of the  higher depth of discharge capability, competitive economics
might be obtained with this  approach.  A further operating advan-
tage  includes  automatic  replenishment  of water  and elimination
of COL, contamination  through equilibration in the charging bath.
As with the previous schemes, this system does not seem appropriate
for  the private  automobile,  although  it might be  feasible for an
industrial application.
PALMER
                                                                239

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 1. PURE  PRIMARY
   (THROWAWAY)
2. PRIMARY WITH ANODE
   REPLACEMENT
3.  EXTERNAL RECHARGE
4. SECONDARY  WITH
  PERODIC ANODE
  REPLACEMENT OR
  EXTERNAL RECHARGE
                                                               [HS( AR[( OR

                                                               HI I HARC.E
             [JlSCMARut
5.  PURE SECONDARY
I
     Figure  5.   Alternative operating schemes  for  zinc-air
                              batteries.

       Scheme 4 does appear practical and possibly even optimum for
  the electric car application.  In this scheme,  the replacement and/or
  external recharging technique would be  used in conjunction with
  a true secondary zinc-air capability.  The  anodes  would  be  replaced
  or recharged  periodically  as well  as  during long trips.   The addi-
  tional capability  would  offer  both  operational  and performance
  advantages. Operationally, the replacement  could effectively repre-
  sent a rapid (almost instant)  recharge technique.  This feature would
  be important  during long-distance traveling; the discharged anodes
  could  be simply replaced at  service stations  and later recharged for
  other customers.  As regards  performance, by accepting a  lower cycle
  life  (or life between periodic external charges)  one could probably
  design for higher depths of  discharge.  Again, as in Scheme 3, the
  CCX problem  might be bypassed, although in  this case an  effective
  water control  system  would still  be  required.  Incidentally,  the
  periodic  anode  replacement could  be  regarded  as  equivalent  to
   240
              Zinc-Air Batteries

-------
 the  regular  car maintenance  cycles  now  standard  for  existing
 automobiles.

     Scheme 5 represents a true long-life, high-capacity, secondary
 zinc-air battery. Such a battery would  only be recharged 'internally'
 and would have ultra-high cycle life.  It  may be  that  if sufficient
 performance  and reliability are  obtained,  this  would represent  the
 ultimate goal for development of a  secondary zinc-air battery.

                           REFERENCES

 Chodosh, S. M., E.  G. Katsoulis,  and M.  G.  Rosansky, 1966a.  Pri-
     mary  zinc-air  battery systems.  Proceedings  of 20th  Annual
     Power Sources Conference.

 Chodosh, S. M., E.  G. Katsoulis, and M. G. Rosansky,  1966b.  A
     high energy density zinc 'oxygen  battery system.  Proceedings
     of  Intersociety   Energy  Conversion   Engineering  Conference,
     Los Angeles, Calif., September  26-28.

 Oxley,  J. E.,  C.  W.  Fleischmann, and H.  G. Oswin, 1966. Improved
     zinc  electrodes  for secondary  batteries.  Proceedings  of 20th
     Annual  Power  Sources Conference.

 Society of Automotive Engineers, 1967  (Jan. 13).  D. M. Tenniswood
     and H. A. Graetzel.  Minimum road load for electric cars, Paper
     presented at Automotive Engineering Congress (S.A.E.), Detroit,
     Mich.

 Question by Dr. Samuel Ruben:  Would enough zinc be available to
 meet the needs  of an  electric automobile if  the zinc-air battery were
 to be chosen as the  power source?

 Answer by Albert R.  Cook, Internationl Lead Zinc Research Organi-
 zation,  Inc.:  If a 20-kilowatt motor were needed for a small car,  the
 battery would require approximately 250  pounds of zinc.  The zinc
 used would  eventually be reclaimed so  that  the demand for zinc
 would be expected to build up gradually with electric vehicle produc-
 tion and then level  off.

     Approximately nine million new automobiles are registered each
 year in the United States. In the event that  electric automobiles were
 produced at  the  rate of one million  per year, it would be necessary
 to produce annually an additional 125,000  tons of zinc.  I would not
 expect this to disturb the present market on account of the number
 of new mines coming into full economical  production.  World  mine
 output  of zinc is expected to increase by over 400,000 tons in  1967,
 compared with an increase of 206,000 tons in 1965. The consumption
 of zinc in the United States during 1966 was 1,400,000 tons at a stable
price of 14^/2  cents per  pound.  It would be necessary to watch the
capacity available for the production of 99.99  per cent pure  zinc,
since this  may  be  required.  Fortunately,  such high-purity  zinc is
traditionally available commercially, and no difficulty is anticipated.
PALMER                                                      241

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     Comments have been made concerning the energy density of the
 lead-acid battery. It should be appreciated that the starting, lighting,
 and ignition battery used in automobiles  is most efficiently  designed
 for  its  purpose.   It can  achieve approximately  17  watt-hours  per
 pound.  It is designed for operation under float  conditions  with oc-
 casional heavy current drain and is not, therefore, suitable  for  deep
 cycling. The industrial battery can typically provide up to  12 watt-
 hours per pound  and  successfully withstands deep cycling  for  long
 periods. Given an incentive such as is now provided by the prospect
 of a battery- or hybrid-powered automobile, it should be possible to
 plan on the near-term achievement of 20 watt-hours per pound for
 a lead-acid battery of optimum life.  The International Lead  Zinc Re-
 search  Organization, Inc., has just commenced a 6-month  study to
 define  the contribution the lead-acid  battery  can make  to the  de-
 velopment of the electric vehicle and to  identify the characteristics
 that should be designed into the optimum power source.  The results
 of this study will  be available to anyone interested.
     PROBLEMS RELATED TO HIGH-ENERGY BATTERIES

                          Samuel Ruben

                       Reuben Laboratories

    When current flows  in  any electrochemical system,  electrode
reactants  are consumed and end products are formed. If the products
are soluble, they change  the  characteristics or  the  conductivity  of
the electrolyte, particularly the temperature coefficients, until satura-
tion is reached,  and then accumulation on the electrode surface such
as the anode  decreases ionic  mobility  and ion  diffusion.  Ions im-
mediately adjacent to the cathode  must be discharged in  order  for
current to flow through the circuit,  otherwise an ionic gradient is
established, which is equivalent  to  electrode polarization drop. This
process is very  temperature sensitive, depending upon  the depth  of
the ionic gradient, the transport number of the ions  in  solution, and
the concentration of  the diffusing ions  in mols per liter.  To  obtain
the minimum  electrode polarization drop of potential and the  neces-
sary ion diffusion requires large effective anode  areas and  relatively
close  spacing.   This  would necessitate  the use of a porous  zinc
amalgam  electrode and  a  residual anode structure  that could main-
tain its porosity  during  recharge cycles.

    One important factor  that must be considered with  zinc alkaline
cells is that as soon as  a current  is discharged  ionization of the zinc
occurs (Zn  — 2e —' Zn-+), with the formation of  zinc hydroxide,
which dissolves  into the alkaline electrolyte, forming  zincates.  When
the electrolyte is saturated with zincate, the anode reaction product
is  then  deposited on  the anode as a white pasty mass  that consists
essentially of  zinc  oxide  (Zn(OH)., ^ ZnO -j- H.,O).  This layer  of
242

-------
zinc oxide, if thick enough, is gravity sensitive and can, under vibra-
tion, fall off and deposit  at the lower end of  the electrode.  The  im-
portant variation  is not  so  much the  mechanical  effects, but  the
change in the temperature coefficients of the  system, as it affects the
IR and electrode polarization drop. With a new cell it is possible to
operate at low temperatures without excessive voltage  drop or polar-
ization, but as soon as the alkaline electrolyte becomes zincated. the
cell requires higher temperatures and the output drops off very rapidly
with  the  lowering  of  ambient  temperature.   This temperature  co-
efficient imposes a problem with an electric  car, where atmospheric
changes  m  temperature  can be wide enough to  reduce the  cell or
battery output to an inadequate value.

    One specific problem in  zinc alkaline cells is  the  spacer, which
must allow  ionic conduction with a low voltage gradient, particularly
at lower operating  temperature, yet prevent  any migration of elec-
trode  composition  or  reaction products.  Our experience with  re-
chargeable  cells  is that the ma.ior function of the spacer is to main-
tain as uniform a current distribution over the electrode area as pos-
sible.  With localized currents of high density, dendritic zinc deposits
produced force their way through the  spacer, producing  bridging
paths with  internal discharge of the cell.  In  our work with alkaline
cells  over  the past 25 years,  we  have  found that sintered ceramic
spacers, particulary magnesium oxide, are the only ones with which
we could obtain repetitive results.  Once dendritic  growth has been
formed on  one section of the anode,  its mass increases  even  at  low
current densities. Placement of the spacer close to the  anode surface
confines  solid anodic products  and prevents  mechanical change.  At
the same time, however, it also becomes important to avoid com-
pression of  the zinc oxide formed, since  a high-density layer rapidly
increases  the  ionic gradient,  causing  greater electrode polarization
drop  of potential.  If the  cathode is soluble or if colloids are formed,
the s'oacer must  also have a filter action to prevent  its metallization
with  bridging circuits.  Alkaline battery  systems  utilizing  consum-
able  anodes such as zinc are inherently not  well adapted to  series
connection  over  long cyclic  operation.  Unless a  sustained balance
between the coulombic capacities of anode and cathode  is maintained.
progressive changes  in unbalanced cells  can  take  place, with detri-
mental effects.  The  problem of series connection could be a  factor:
if a cell is prematurely exhausted, it would set up a reverse potential
This  could  happen  if the cell had  excessive  local  action or initially
insufficient  zinc for the proposed current and time of discharge. With
air-zinc cells,  the carbonation of the electrolyte by the carbon dioxide
content in the air could materially affect performance

    Another problem that mu>t be considered for rechargeable  air-
zinc cells,   other than  the electric power  facilities  in  the average
garage, is the hazard introduced by the  generation of  oxygen at the
cathode during  recharging  Oxygen is  released at the rate of 0.658
pound per  1.000  ampere-hours.  For a 50-kilowatt-hour  battery,  this
would amount to 35 pounds or more of oxygen per  charge
RUBEN

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      Although other high-energy anode materials look attractive, the
 major problem is to cope with their high reduction potentials, which
 make  necessary  the use  of  non-aqueuous electrolytes.  In some in-
 stances,  inhibitors can make the  electrode passive,  but as  soon as
 current is discharged  through an  aqueous electrolyte, the electrode
 area becomes active to the aqueous component of the electrolyte  and
 hydrogen is displaced, with  a loss  of anode material.
244                                                           Note

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            THE  ATOMICS  INTERNATIONAL
                    SODIUM-AIR  CELL*


          L. A. Heredy, H. L. Recht, and D. E. McKenzie

                      Atomics International
           a Division of North American Aviation, Inc.
                        Canoga Park, Calif.

                        INTRODUCTION

    The aim of Atomics International's sodium-air cell project is the
development  of  a  compact sodium-air cell  operating  isotherm-
ally at a temperature  slightly  above the melting  point  of  sodium.
Preliminary engineering studies have shown that this system can be
developed into a  battery system with high energy and power density
for application as a power source in automobiles.

    The first part of this paper summarizes  the general criteria used
in the engineering studies that led to the selection of the  sodium-air
system for experimental development.  This  is followed by a descrip-
tion of the sodium-air cell, a review of the experimental results,  and
a discussion of the potential performance of the system.


          BATTERY CRITERIA  FOR AUTOMOTIVE
                    POWER APPLICATIONS

    The technical and  economic feasibility  of using secondary bat-
teries  as  power  sources in automobiles  requires  that the  battery
system satisfy a large variety of criteria.  The criteria summarized in
Table 1 were used in our study of possible power sources for passenger
automobiles. Although  we  recognize that  possibly no system will
meet  all these criteria,  the one best filling these requirements would
be  most attractive  for  automotive use.  An estimate of  energy  and
power density requirements in various vehicle applications is shown
in Table 2.

    The requirement of high energy density can be best satisfied by
using hydrogen or a light alkali or alkaline earth metal as the anodic
reagent  together with  a  strong   oxidizing low-molecular-weight
cathodic reagent.  A consideration of other important criteria  (e.g.
high power-to-weight  ratio, which requires high  current density;
long cycle life, which requires  uniform  deposition  of  the metal on
charging) shows  that  the  use of molten alkali metals has  several
advantages. The rate  of electrode  reactions at a liquid  metal and
*Work performed under company sponsored  research program. Patents
 pending.
HEREDY, RECHT, McKENZIE                                245

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 electrolyte interface is generally very high and therefore high current
 densities can be achieved.  Furthermore, the molten state of the metal
 assures uniform deposition on  charging and thus long cycle life  of
 the metal electrode. The use of molten metals also  permits the con-
 struction of very compact  cells  since most of  the metal can be stored
 outside of the cell and supplied continuously to  the anode compart-
 ment at the required rate.  In this sense the system can be regarded  as
 an electrically rechargeable fuel  cell as well  as a secondary  battery.

 Table  1.  CRITERIA  FOR  POWER SOURCES IN ELECTRICAL AUTOMOBILES

          Performance criteria11
              Energy-to-weight ratio15 of cell  battery: > 150 w-hr/lb
              Power to weight ratiob of cell battery, nominal: > 35 w/lb
              Overload capability: greater than 200%
              Energy efficiency (% energy out/energy in): — 50%

          Other criteria
              Long shelf life and cycle life
              No severe materials or corrosion problems
              Low production cost
              Durability and reliablity
              Easy startup

             "For 4  hours of  operation at nominal  power level.
              This power level permits continuous  operation at
              a speed of 60 mph on a level road.
             b Based  on  total  weight of battery and reactants.
        Table 2.   ENERGY AND POWER  DENSITY  REQUIREMENTS
Application
Industrial carts,
small delivery trucks,
other small vehicles
Standard delivery
trucks
Army vehicles
Automobiles
Energy density,2
w-hr/lb
10
40
100
150
Nominal power
density,"''1
w/lb
2.5
10
25
35
       "For 4 hours of operation at nominal power level.
       bThe  battery system  should  be capable  of  delivering at least
       twice the nominal power output for short periods.

     Sodium was chosen  from the  light alkali  metals as  the most
promising anode feed material.  It has  the advantages of a lower
molecular weight than potassium  and  a lower  melting  point than
246                                                  Sodium-Air  Cell

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lithium.  The  low melting point is  a  very important factor because
it permits a low operating temperature, and many important require-
ments  (materials  compatibility,  corrosion  resistance, safety, ease of
startup)  can be best satisfied at low temperatures.

    Air was selected as the cathode  feed material because it is readily
available from the atmosphere and thus need not be stored and carried
in the  vehicle. This advantage outweighs the drawback of  relatively
high polarization losses at this electrode.

    On the basis  of a detailed analysis, the  system selected as the
most promising for experimental  investigation was a sodium-air cell
operating somewhat above the melting point  of sodium.  In principle,
the electrochemical reaction of sodium with  oxygen from  air can be
carried out in one step. However,  one-step oxidation requires a highly
conductive electrolyte  that is chemically compatible with both molten
sodium and oxygen.   Since  the  development of such an  electrolyte
presents a  formidable problem, a two-step  method was chosen for
development.

    THE ATOMICS INTERNATIONAL  SODIUM-AIR CELL

    The two-step or dual sodium-air cell system can be characterized
as follows:
  (—) Na
Molten sodium
     salt
NaHgx
Aqueous
 NaOH
02 (air)  ( + )
              Step A                           Step B

 The two cell reactions involved are:
     2 Na + 2x Hg = 2 NaHgx                   (in Step A)      (1)
 and
     2 NaHgx + V2O2 -f H,O = 2 NaOH -f 2x Hg (in Step B).     (2)

 The amalgam electrode acts as the cathode of cell A and the anode of
 of  cell  B.  Sodium  is transported across the  amalgam  electrode by
 diffusion and convection.

     The net cell reaction and the calculated value of the correspond-
 ing reversible cell potential at an operating temperature of  130°C are
     Na  (liq) +  V4 O, (air) -f Vz H,O (50 wt % NaOH)
         =NaOH (50"wt %  NaOH) '                             (3)
     E = 2.72 ± 0.03 volt

     If the  amalgam electrode contains  2 atom  percent sodium, the
 calculated reversible cell potentials of the two subcells are as follows:
     Na/Na-amalgam (2 a/o Na) ;               E = 0.83 volt
     Na-amalgam (2 a/o Na)/0., (air);          E = 1.89 volts

     A schematic diagram of the cell is  shown in Figure 1. The cell
 consists  of  a sodium compartment, a molten salt electrolyte matrix,
 an amalgam electrode, an aqueous  NaOH  electrolyte compartment,
 HEREDY, RECHT, McKENZIE                                 247

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an air electrode, and an  air compartment.  On discharge sodium is
supplied continuously from an outside container to  the sodium com-
partment.  Cell  reaction  (1) takes place in the Na/NaHgx  subcell,
and sodium is deposited on the sodium side of the amalgam electrode.
Sodium migrates across the thin, stationary amalgam electrode under
the effect of  a concentration gradient and is made available  for cell
reaction  (2), which takes  place in the NaHgx/O2 (air) subcell, where
aqueous  NaOH,  the product of the overall reaction, is formed.  The
aqueous NaOH solution is kept in circulation through the  cell  and the
electrolyte storage tank.  Its concentration is kept constant by the
addition of water at a rate proportional to the rate of NaOH formation.
               Na
 MOLTEN
  SALT
ELECTRO
  LYTE
                              Na-
NaOH (aq)
(50-70 wt%)
                                                (AIR)
                                                          AIR
                                                          OUT
    Figure  1.    Schematic  diagram  of sodium-air  cell

    On recharge, the aqueous NaOH solution is electrolyzed (reverse
of reaction (2) in cell B); sodium is deposited on the amalgam elec-
trode;  and oxygen evolves on the  air electrode.  The  oxygen is re-
leased to the atmosphere.  The concentration of the aqueous electrolyte
is  kept  constant by evaporating water at  a rate proportional to the
rate of NaOH electrolysis. Sodium migrates across the amalgam elec-
trode, and in cell A the reverse of  reaction (1) takes place.  Sodium
is  deposited on  the sodium  electrode and the excess sodium flows
back into the sodium storage tank.
    Note that these operating features distinguish the Atomics Inter-
national cell concept from previously proposed designs for a primary
sodium-oxygen cell (Eidensohn, 1962)  or  a secondary potassium air
cell (Koch and Karas, 1963), in which the two subcells were operated
at widely different  temperatures and a circulating amalgam electrode
connected the two subcells.
248
                              Sodium-Air Cell

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                  EXPERIMENTAL  RESULTS

                    Component Development

    Preliminary engineering studies indicated that a key requirement
for  developing  a  high-power-density sodium-air battery  is  the
achievement of  current  densities in the range of  100  to 200  milli-
amperes per square centimeter.  This current  density range — with
other major criteria — denned  the basic requirements  of  the  cell
components and set the goals of the component development  program.
The component requirements and the results of the first phase  of the
experimental program are summarized in this section.

Electrolyte for the Sodium/ Sodium Amalgam Cell
    The principal requirements of the  electrolyte are
1.  It should have a specific conductance greater  than 0.1  mho per
   centimeter.

2.  It should be chemically compatible with sodium and  dilute sodium
   amalgam.

3.  It should contain Na+ as the only cation, and oxidation and reduc-
   tion at the electrodes should involve only this  ionic species.

    A molten sodium salt electrolyte of proprietary composition that
satisfies these requirements was developed. The freezing point  of the
electrolyte is  127°C. Its specific conductivity was measured in the
temperature range of 130° to 165°C with a conductivity cell  made of
alumina.  Conductivity values  in this temperature  range  fit the  fol-
lowing equation:

         K _ 1,370 exP-L°
where K is the specific conductance in mho per centimeter.  The value
of K, calculated  from this equation, is 0.28 mho per centimeter at
130°C.
    Chemical compatibility  of  the  molten salt  electrolyte with the
liquid metal electrodes and various cell structural materials has been
investigated.  No significant  degradation of the  electrolyte could be
detected at temperatures  up to 150°C  over test periods  of  several
hundred hours.

Amalgam Electrode
    The amalgam  electrode must form  a  thin,  continuous layer
anchored firmly  in a stable supporting  structure.  Design  studies
have  shown  that the  thickness of  the  amalgam electrode must be
less than 0.3 millimeter (preferably as small as 0.1 mm)  to give high
energy and power density  and low materials cost.

    Electrodes with amalgam layer thicknesses  in  the range of  0.35
to 1.0 millimeter  have been tested successfully.  At operating temper-
atures of 130° to 135°C, current densities  up to 70 milliampere per
HEREDY,  RECHT,  McKENZIE                                 249

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square centimeter  (on discharge)  and  50 milliampere  per square
centimeter (on charge) were obtained with an amalgam  layer  about
0.4 millimeter thick.

Air Electrode
    Good cell performance and economical operation require durable,
low-cost electrodes with polarization  (with respect to the theoretical
oxygen reduction potential)  less than  0.4  volt at current  densities
greater than 100 millamperes per square centimeter.

    Most work performed to date has been concerned with the interim
goal of testing commercially  available electrodes and adapting them
to the  operating conditions of the sodium-air cell.  We found that the
required performance could be obtained with electrodes made with
a platinum loading of 10 milligrams  per square centimeter,  but the
lifetime of these electrodes at 130°C in 50 to 70 weight percent NaOH
was much less than under normal conditions (25° to 70°C in 6N KOH
electrolyte).  Flooding of the electrode and solidification of NaOH on
the electrode surface  were  found  to contribute significantly to the
deterioration of performance. Precise  control of the humidity  and
temperature  of the air feed is required to alleviate these difficulties
and  ensure  stable  operation.   Typical cathodic  polarization  data
obtained with a commercially available electrode  (American Cyana-
mid AB-6) are shown in Table 3.

            Table 3.  AIR ELECTRODE  POLARIZATION DATA

Air feed                   Humidified, C02 removed; air pressure: 2.5 psig
Catalyst loading             10 mg Pt/cm2
Electrode surface area        16 cm2
Electrolyte                 50 wt % aqueous NaOH
Operating temperature        135°C
Reference electrode         Hg/HgO/50 wt % NaOH at 25°C

                                       Measured electrode
            Current density,                  potential,
                ma/cm2                       mv

                  0                     +100 to+110
                                           (drifting)
                 20                          +35
                 40                           —5
                 60                          —53
                 80                         —125

                        Cell Experiments

    Several  complete sodium-air cells were fabricated and tested at
various stages of component development.  Figure 2 shows one type
of test cell prior to operation. The sodium  feed tank  (located  to the
250                                                Sodium-Air Cell

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left) is not yet connected to the sodium compartment  (at the bottom
of the cell).  Connections on top are to aqueous NaOH  and air feed
and exit lines.
               Figure  2.   Sodium-air  test  cell.

    Cells of 0.3- to  2.0-watt output have been operated successfully
at 128  to 136 :C for 50 to  150 hours. Typical  data obtained with a
cell of 1.0-watt nominal output (at 50 ma/cm- current density)  are
shown in Table 4.
            EXPECTED PERFORMANCE OF THE
                SODIUM-AIR CELL BATTERY

    The expected energy  and power  density values of a developed
sodium-air cell battery were calculated on the basis of an engineering
design study (Table 5).  Design I is based on the assumption that a
current density of 120 milliamperes  per square centimeter can be
achieved at an operating voltage of 2.1 volts.  Experimental data indi-
cate that  this  current density could be achieved with  moderate im-
provements  in the performance of various cell components.  Design II
is  based on  a  current density of 200 milliamperes per square centi-
meter  at  the  same operating voltage. Significant improvements  in
cell performance are needed to achieve this goal.
HEREDY,  RECHT, McKENZIE
                                                               251

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              Table  4.   SODIUM-AIR CELL OPERATING DATA
                             Cell Description
             Component
                                             Structural materials
     Sodium compartment
     Molten salt electrolyte Matrix

     NaOH and air compartment
     Air electrode
Polypropylene
Porous ceramic impregnated
with molten salt
Teflon
Gold-coated nickel screen with
porous Teflon backing; platinum
loading 10 mg/cm2
                  Active surface area of electrodes: 8 cm2
Operating mode
Open circuit
Discharge


Charge

Cell
voltage,
V
2.60
2.40
2.30
2.20
3.10
3.20
Current
density,
ma/cm2

20
50
70
20
50
Power
density,
mw/cm2

48
115
154


Table 5.   EXPECTED  PERFORMANCE  OF THE SODIUM-AIR CELL BATTERY
Energy density,
w-hr/lb

Theoretical energy density
of reactants b>c
Power density of cell
battery1
Energy and power densities,
complete battery assembly1"'
Operating period: 4 hr
8 hr
Design la
930
160
240
Design 1
930
215
300
Nominal power
density,
w/lb
1" Design \a Design IIs
60 100
40 55
30 37.5
"Design I based on a current density of 120 ma/cm- at 2.1-v operating voltage.
 Design II based on  a current density of 200 ma/cm- at 2.1-v operating voltage.
''Based on reversible cell potential.
l'One half of the weight of the stoichiometric  oxygen  requirement was used in
 calculating  energy  densities, because, on the average, only this amount  will
 be present  as  chemically bound  constituent  in  the  aqueous  electrolyte  and
 thus contribute its  weight to the  system.
dExcluding weight of reactants stored outside  of cells.
"•Cell  battery and  reactants;  weight of  reactants includes weight  of  water
 required to dissolve the produced NaOH to form a 70 wt % aqueous solution,
252
              Sodium-Air  Cell

-------
    Since the cell reactants are stored in tanks outside of the battery,
the energy density of the complete battery assembly is a function of
the operating time or the total amount of reactants carried. Two sets
of data were calculated, for a 4-hour and an 8-hour operating period.

    The energy efficiency of the cell  on charge-discharge cycle at a
current density of 120 milliampere per square  centimeter is estimated
to be about 60 percent.


                           SUMMARY

    A novel compact sodium-sodium amalgam-air  dual cell has been
designed and operated.  Cell components and complete cells of 0.3-
to 2.0-watt  output have  been tested  successfully at  about  130°C
operating temperature.  Experimental  data  and  preliminary  engi-
neering studies  indicate that very  high energy and  power densities
could be achieved with a fully  developed sodium-air battery system.
High  expected performance and the advantages  of  relatively low  op-
erating  temperature make  this system very attractive  for develop-
ment as a power source for  electric automobiles.

                           REFERENCES

Eidensohn, S., 1962, Fuel cell systems.  U. S. Patent 3,057,946.
Koch, R. L., and H. R.  Karas, 1963. Development of a liquid metal-
    air secondary battery system. Test data cell concept and program
    status,  EDR No. 3660, Allison  Division, General Motors Corp.
HEREDY,  RECHT,  McKENZIE                                  253

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                    ALUMINUM  FUEL  CELL
                  FOR  ELECTRIC  VEHICLES


                        Solomon Zaromb

                  Zaromb Research Corporation
                          Passaic, N. J.


                           SUMMARY

    Although aluminum  has  long been recognized as a potentially
superior battery anode material, its practical use has been precluded
by excessive passivity in  most electrolytes or by excessive corrosion
in non-passivating electrolytes. Now  we have succeeded in inhibiting
the corrosion of aluminum in alkaline solutions reproducibly and over
long  periods of time while operating  an  experimental  60- to 80-watt
aluminum-air battery at  a  current density of 40  to 50 amperes per
square foot and  1.1 to 1.3 volts per cell.  This  battery has been per-
forming satisfactorily in intermittent tests since April 1966.

    Our  experiments  have generally confirmed  the  expected high
energy capacity  of  alkaline  aluminum-air  batteries.  In  a  highly
conservative  design  based on present performance data, an over-all
energy density of more than 200 watt-hours per pound was estimated
for a 30-kilowatt, 240-kilowatt-hour power  source including all  ac-
cessories.  Considerably higher densities should be achievable with
moderate  development effort.

    The chemical rechargeability  (by anode and electrolyte replace-
ment) of  our aluminum-air battery  should  constitute an important
advantage for vehicle  propulsion in that  no  overnight recharging
would be  required, nor would any megawatt power outlets be needed
for rapid  electrical recharging. Other  advantages, such as  a  1,000-
mile driving range between electrode refuelings,  exceptional  safety,
functional superiority, and over-all economy should allow aluminum-
driven automobiles not only to compete  fully with but to far surpass
present cars.

                        INTRODUCTION

    The fuel cell described here is unique in that  it uses solid  alumi-
num rather than a hydrogen-containing fluid as  its  chief anode re-
actant.  It also  differs  from  other metal-air  batteries in  that it is
chemically rather than electrically  rechargeable, and also  provides
for control of the voltage and power output through adjustment of
the electrolyte level or of  the depth of electrode immersion. Of course,
zinc-air batteries  with replaceable  zinc  anodes have  been  used for
special applications and  are  even considered  for motor vehicle pro-
pulsion. We  propose to show however,  that for the requirements of
 ZAROMB                                                     255

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broad-purpose passenger automobiles such as those currently in use,
the aluminum fuel cell  appears to provide a practical, economical,
and otherwise adequate primary electrochemical power source, po-
tentially capable of competing with internal combustion power within
the next few years.

    Table 1.   ELECTROCHEMICAL  COMBUSTION ENERGY DENSITIES
Fuel
Liq. H2
Liq. NHs
Gasoline
C
Li
Be
B
Na
Mg
Al
Ca
Zn
Faraday-volts/cm3
Theor. Pract.
0.087
0.18
0.16
0.24-0.3
0.6-1.2
0.32
1.13
1.31
0.166
0.51
0.87
0.31
0.43
0.06
7
0.1
0.09-0.12
?
7
7
0.09
?
0.36
7
0.28
Kw-h/lb fuel
Theor. Pract.
14.9
2.0
2.0
5.0
4.1
7.4
7.8
6.6
2.1
3.5
3.9
2.4
0.74
2.4
0.7
2.0
i
1
i
i
1.1
7
1.6
?
0.5
Remarks

Require prohibitive
catalyst area

Too expensive
Poor conductor
Too bulky
Poor current efficiency

Poorer than Al
Poorer than Al
    In Table 1 we speak of "electrochemical fuel" rather than "anode
reactants" to  emphasize that neither  the weight of oxygen nor  that
of water need be considered in preliminary energy-density compari-
sons as long as the latter substances are abundant and readily avail-
able from the surroundings. If we can seriously consider electrically
rechargeable vehicles with a  driving range of  merely 50 miles for
urban  applications, then we should not object to replenishment with
water  at  200-mile or even at 100-mile intervals, especially  if  the
main fuel charge could last for 500 or 1,000 miles. The  combustion
energy densities based on the weight of fuel alone may therefore  pro-
vide fairly meaningful figures  of merit for  the best available electro-
chemical fuels.

    Table 1 shows that aluminum is  one of the most energetic fuels
in terms  of both volume and weight.  On a  volume basis aluminum is
fourth  highest, and its combustion energy content is close  to two-
thirds  of the highest possible value. On a  weight basis aluminum is
seventh highest after hydrogen, beryllium, lithium, boron, gasoline,
and carbon.  Beryllium and lithium can be immediately excluded as
economically prohibitive  for large-scale  primary  fuel requirements.
Boron  is  a poor  conductor and has otherwise unsatisfactory  anode
characteristics, at least in the present state of the art.  This  brings
aluminum again  up to fourth  place, after  liquid hydrogen, gasoline,
and carbon, with its practical  energy content per unit weight again
amounting to two-thirds of the highest possible value.

    Our  analysis  thus far  fully covers all the  readily  oxidizable
elements in the first two rows  of the periodic table.  As the elements
get heavier, the energy  densities become obviously poorer.  Never-
theless, to ascertain that  the attractive energy density of  aluminum
256
Aluminum Fuel  Cell

-------
is not somehow outweighed by some of the other potential fuels, let
us review the remaining metals in  the third and fourth rows of the
periodic  table that might be considered for metal-air batteries.  Al-
though sodium may provide a respectable  energy density on a weight
basis, it is bulky. In addition, its use in amalgamated form and possi-
bly also at high temperatures renders it far less practical than alumi-
num. Magnesium might come closest to aluminum in terms of theo-
retical energy  per unit weight and  per  unit volume.  Yet,  in the
strongly  alkaline or acidic electrolytes   required  for air  cathodes,
magnesium  poses much more severe passivation and corrosion prob-
lems than are encountered  with aluminum.  The same objection may
apply to  calcium.  Thus, zinc  is left  as  the only  material  having
sufficiently  attractive anode  characteristics  to be  worth  further
consideration.

COMPARISON OF ALUMINUM-AIR  AND  ZINC-AIR  CELLS

    Our system resembles  the  well-known zinc-air  batteries  in
several  respects. We use aluminum  anode sheets between two  air
cathodes just as in the  Leesona-Moos type of primary battery de-
scribed  by Palmer  or as in the General Dynamics type of secondary
battery  described by Ragone, both in  this volume.  The reactions are
of the same type:

         metal -)- oxygen -)- water —* metal hydroxide.

An electrolyte circulating system has also  been used with aluminum-
air  cells since  1960  (Zaromb and  Foust, 1962).  There  are  several
differences,  however.  No anode grids are required,  since the alumi-
num is to be consumed entirely. No separators are used; it is a  free
electrolyte system.  The energy  per reactant weight  is at least two-
fold higher  for aluminum, as shown in Table 2. Theoretically, alumi-
num would yield a 3 times higher energy density.  In practice, how-
ever, the usual operating  cell  output  may  be about 1.3  volts with
zinc and around 1.2 volts with aluminum, which still yields  the 2:1
ratio  in  favor  of aluminum  shown in the  last  column  of Table  2.
Applying Mr. Shair's (in this volume) rule of thumb (approximately
20  percent  of the  theoretical energy density for the density to  be
expected in practice) to Table 2, one reaches an estimate of 160 to 400
watt-hours  per  pound for a practical aluminum-air battery.  On the
basis of  the 2: 1 ratio in favor of aluminum, one might double the
energy  densities available  from present  or  projected zinc-air bat-
teries, 60 to 100 watt-hours  per second for secondary cells and 150
watt-hours  per pound for  primary cells, and thus  again  arrive  at
an  estimate of  160  to  300  watt-hours  per pound for practical
aluminum-air batteries.  These estimates  are generally confirmed by
the experimental data and  design analysis presented  in the following
sections and summarized in Table 3.

    The  well-known and  quite satisfactory  anode  performance  of
zinc, its  relatively  slow  corrosion rate in alkaline  solutions,  and its
electrical rechargeability have  contributed  to  the  widespread ac-
ZAROMB                                                       257

-------
 ceptance of zinc anodes for miscellaneous low-power electrochemical
 devices. But, for long-range portable power sources in the range of
 10 to 30 kilowatts, we believe that electrical recharging is inferior to
 chemical recharging.  Moreover, both the anode performance and the
 corrosion behavior of aluminum can  be controlled.

         Table 2.   COMPARISONS  OF ALUMINUM AND ZINC CELLS


Al
Zn
Total
g/F
26.0
49.7
Without 0.,
g/F
18.0
41.7
cm3/F
12.3
13.5
Kw-h/(lb
Theoretical
1.94
0.58
M H90)
Practical
0.8
0.4
                                            iM(OH)z
                     = Zn or Al; z = 2 or 3
  Table 3.   WEIGHT ANALYSIS  OF A 30-KILOWATT,  240-KILOWATT-HOUR,
                       ALUMINUM-AIR BATTERY
                                      Scheme I   Scheme  II  Scheme
Weight, Ib                          	
     Anode charge                          150       150
     Electrolyte charge                      650       350
     Uncharged battery assembly             200       200
     All accessories                         200       200
         Total weight, Ib                  1,200       900
Component life, kw-h
     Electrolyte replaced and ppt removed
              after                        240        120
     Anodes replaced after                  240        240
Energy density, w-hr/lb, based on
     anode replacement intervals             200        267
     electrolyte replacement intervals         200        133
Power, kilowatts
     Average power                          30        30
     Peak power without cathode boosting
         provision                          45        45
     Peak power with cathode boosting
         provision                        >90       >90
Power density, w/lb
     Average power density                   25        33
     Peak power density without cathode
         boosting                          38        50
     Peak power density with cathode
         boosting                        >76     >100
Design based on:
     (1)  1.2 Faraday-volts/9 g Al or 1600 w-hr/lb Al.
     (2) 4.3 Ib  initial electrolyte/Ib Al consumed.
                                                               300
                                                               500
                                                               200
                                                               200
                                                              1,200
                                                              120
                                                              480

                                                              400
                                                              100

                                                               30

                                                               45

                                                              >90

                                                               25

                                                               38

                                                              >76
258
                                                Aluminum Fuel  Cell

-------
            PERFORMANCE OF EXPERIMENTAL
            70-WATT ALUMINUM-AIR BATTERY

    The  experimental battery apparatus is shown in Figure 1. Am-
bient air is pumped first through a  concentrated KOH solution, which
removes  COL, and humidifies the air, and then to a manifold leading
to 14 parallel porous cathode compartments. The air pressure within
the cathode compartments is usually about 2 to 3 inches of water,
comparable to  the maximum  height of electrolyte within  the  cell
compartments during  battery  operation. The anodes are held by  a
plastic cover that fits exactly over  the cathode assembly.
  Figure  1.   Experimental  70-watt  aluminum-air  battery.
    The electrolyte level within the cell compartments is  controlled
by  a  small lab-jack,  which raises  or lowers a base  plate pressing
against a  collapsible  electrolyte  reservoir.  The latter also collects
the Al(OH) ;  battery  reaction product. This reservoir is  easily  un-
clamped from  or clamped onto the base of the battery during pre-
cipitate removal and  electrolyte replacement.

    When no  power  is drawn,  the electrolyte is  allowed to drain
into the reservoir to prevent exposure and corrosion of the  aluminum
anodes.  For battery operation the reservoir is collapsed  partly, as
ZAROMB
                                                               259

-------
shown in Figure  1,  so  that  electrolyte is  forced into  the battery
compartments. The electrolyte is  also pumped through a  heat ex-
changer to remove the heat dissipated in the battery reaction.

    Any hydrogen evolved as a result  of  anode  corrosion is  chan-
neled through a single gas-outlet tube connected to the battery cover.
This outlet  tube  constitutes  a simple and  rapid corrosion  detector;
the nascent hydrogen formed in  any corrosion reaction  is readily
detectible through  its pungent odor, especially when it  is  all chan-
neled through a single  outlet.  The  occurrence or  absence  of  any
significant  corrosion  could thus  be  diagnosed,  and  the  corrosion
could be  prevented  or  kept  to  reasonable  levels through proper
battery  operation.  We have acquired enough  understanding of the
corrosion  reaction  to  prevent  or induce corrosion within  the  same
battery, reversibly and at will.

    Our battery  discharge curves  tend  to confirm the  absence of a
significant corrosion rate under our experimental  conditions.  Figure
2 is representative  of the kind of output voltage, current, and power
drawn from an immersed  electrode area of  1,400 square centimeters
with  anodes  0.05  centimeter  thick  consumed simultaneously  from
both sides.  At 100 percent  current efficiency  and an average cur-
rent density of 50 milliamperes per  square centimeter, the  anodes
would be expected to last for 4 hours, or  about 700 coulombs per
square centimeter.  Actual integration of the current curve  of Figure
2 yields  around  500  coulombs  per square  centimeter.   Since  about
one-third of the original anode thickness was left at the end of the
run, the figures given here  are  roughly consistent  with nearly 100
percent efficiency.

    The data in  Figure 2 were obtained in June 1966.  Data  from
an  experiment performed in  March  1967  are  shown  in  Figure  3.
The same battery  and experimental apparatus were used  as in the
earlier runs; however, the anodes were  0.3  centimeter thick and cut
narrower. The immersed  electrode  area was therefore only  1,250
square centimeters. Nevertheless, the average power output was still
between 60 and 70  watts,  at  around  40  milliamperes per  square
centimeter and 1.2 volts per cell.  Similar  results were obtained  in
even  more  recent  experiments  (June  1967).  Thus, no observable
deterioration  in  battery  performance occurred during  a   12-month
period.

    The run  of Figure  3  was designed to  determine the minimum
weight ratio of electrolyte  to aluminum required for satisfactory con-
tinuous  battery operation.  To obtain this  information it  was  most
expedient to allow 2  kilograms of  aluminum to corrode away in an
initial 8-liter  volume of 3 M  KOH solution.  Additional water  was
added to make up  for evaporation  losses. After complete dissolution
of the aluminum, the  total volume was again brought to 8 liters.  The
final mix therefore contained around 5.8  kilograms A1(OH)S plus
6.7  kilograms  4 M  KOH solution.  This  mix was then re-introduced
into the electrolyte reservoir, and the run was completed.
260                                           Aluminum Fuel Cell

-------
<

I—
<
cc
o
o:

UJ
Q.

2

<
   60
        ALUMINUM ETCHED FROM BOTH SIDES

        TOTAL APPARENT ELECTRODE AREA -= 1,400 cm-

        ALUMINUM THICKNESS ~ 0.02 in. =- 0.05 cm.
                                               70 amp

                                                \

                                            50 ma/cm2
                                                            1.1
                                                            1.0
                                                               O

                                                            0.9 >
                                                      0.8
     0    20   40   60    80   100  120  140  160  180  200

                           TIME,  min.


        Figure  2.   Typical  performance  of a  70-watt

      aluminum-air battery  with thin anodes.   Kinks in

    curves  correspond  to load  adjustments  (June,  1966).
    70
    60
    50
    40
    30
                             CONSUMED 2 kg Al    -

                            PER 7 kg of ELECTRODE |
                           CURRENT (I)
-T

 I
J  TOTAL ELECTRODE AREA = 1,250 crrv
    ALUMINUM THICKNESS = 0.125 in.;
                         50 amp <-» 40 ma/cm-
                                                    _L
                                                            1.3
                                                            1.2 LU
                                                            1.0
     0     60     120     180    240    300


                             TIME, min.
                                             3,000  3,060
      Figure 3.   Performance  of  the same  battery  with
        thick  anodes  of smaller  area  (March,  1967).
  ZAKOMB
                                                           261

-------
    Figure 3  shows that the battery performance near  the end  of
the run  was  not  much worse  than  at  the  beginning.  Hence, the
residual electrolyte weight need not exceed 3.3 pounds per pound  of
aluminum consumed, and the corresponding initial electrolyte weight
need not exceed 4.3  pounds per pound of aluminum.

    In these experiments we obtained  about  1.2 faraday-volts per
gram equivalent (9 grams)  of  aluminum, or  1,600  watt-hours per
pound of aluminum at current  densities of at  least 40 milliamperes
per square centimeter.  Further, such  performance could  be  obtained
even without  replenishment of electrolyte or of water if the initial
charge included 4.3 pounds  of  electrolyte per pound of aluminum
consumed.

    In addition, our single-cell experiments have  yielded consider-
ably higher current densities  and output voltages  with somewhat
more active aluminum alloys.  Unfortunately, our present  stock  of
alloys  is not easily  adaptable for testing  in the multicell battery  of
Figure 1.  On the basis of our experience to date, however, we expect
no  serious difficulty in obtaining  at  least 1.2  volts  per  cell at 100
milliamperes per square  centimeter  and nearly 100  percent current
efficiency with at least one type  of a readily available aluminum  alloy.

       SIGNIFICANCE OF EXPERIMENTAL RESULTS

    A design  analysis has been performed for a 30-kilowatt alumi-
num-air power  source. The block diagram of Figure 4 shows all the
required accessories. The air supply system, including a  compressor,
air scrubber, and connecting tubes or manifolds, is essentially similar
to those used  in other fuel cells. The electrolyte circulating system,
including a heat exchanger and auxiliary reservoir, is also similar to
those generally  used.  A multichannel pump, possibly  of the peristal-
tic type, is proposed for the  purpose  of eliminating leakage currents
between series-connected  cells.  Furthermore, the electrolyte volume
in the reservoirs can be readily altered  by application of  air pressure
within spaces enclosed by collapsible inner linings  and  rigid  outer
shells.  The electrolyte level in the  battery  assembly is  thus  pneu-
matically controlled by  a simple air-pressure regulator.  This also
provides a  simple,  light,  and  inexpensive means of  controlling the
current,  voltage,  and power output  without  recourse to any elec-
tronic circuitry.

     The  aluminum hydroxide precipitate  formed  in  the battery
reaction is  to be  collected in  one of the electrolyte reservoirs and
preferably returned for credit  at  a  refueling  station.  Alternatively,
the precipitate  may be disposed of  whenever fresh water  is  added
to  the  system.  At  least  two  simple arrangements  are  being con-
sidered for ejecting the precipitate safely and conveniently.

     The cathode boosting means  shown in Figure 4  may consist of
a  solution of  oxidant, such as hydrogen peroxide, which may be in-
jected into  the  electrolyte entering the battery assembly.  The chief
 262                                           Aluminum Fuel Cell

-------
power limitation of the oxygen or air electrode is known to  be  as-
sociated with the low solubility of oxygen in aqueous alkaline electro-
lyte. Hence, during periods of peak power demand  it may be desir-
able to  inject an alternative oxidant  into the electrolyte. Although
such oxidant would have an adverse  effect on hydrogen  anodes,  we
have found  no  deleterious effect and even  an enhancement  of  the
activity of aluminum anodes upon introduction of around 1 percent
H.,O., into the electrolyte.  This simple  method of boosting the cathode
performance should double the peak power output and thus meet all
peak power  requirements; no  auxiliary batteries or other auxiliary
power sources would be needed.
                                SCP
                                                       AEC
                                                       »ROS
EP
J
-


\
x 	


1

f 	
1
K 	 ' — I —
                                                        AE
  AB —AIR BLOWER
  AC —AIR COMPRESSOR
  AE—AIR ENTRY
  AO —AIR OUTLET
  AS —AIR SCRUBBER
  BA —BATTERY ASSEMBLY
  CB —CATHODE BOOSTING MEANS
  EP —ELECTROLYTE AND PRECIPITATE
       CONTAINER
  GC —GASKETING  CLAMPS
GM —GASKETING MOLDING
HE-HEAT EXCHANGER
SA —SIDE ARM
AEC —AUXILIARY ELECTROLYTE
      CONTAINER
CIL —COLLAPSIBLE INNER LINING
LLR —LIQUID-LEVEL REGULATOR
ROS —RIGID  OUTER SHELL
MCP— MULTI- CHANNEL PUMP
          Figure 4.   Block diagram  of a  proposed
                 aluminum-air  power source.
 ZAROMB
                                                            263

-------
    Since the required accessories do not otherwise differ appreciably
from those in similar systems, we can formulate a weight analysis of
our proposed power  source  by referring to the  weights quoted by
Dantowitz and Gaddy for an operational hydrazine fuel cell.  The re-
quired accessories for 20-kilowatt and 40-kilowatt hydrazine  systems
weigh  185  pounds and  235 pounds, respectively. Hence, the acces-
sory weight  for  a  30-kilowatt  system may amount  to  around  200
pounds.  The remaining weight evaluation in Table 3 is derived di-
rectly from the experimental data presented  in the preceding section.

    The three schemes in Table 3 may again demonstrate the  pro-
priety of disregarding the weight of water in the preliminary  energy-
density comparisons of Table 1.  The initial electrolyte charge will
last for a complete 8-hour operation at average load. Hence, a vehicle
traveling at  60 mph  at average power would  have a range of  480
miles between refueling stations. By another scheme, however, the
range between stations would be the same, but the driver would have
to stop  off midway for a fresh electrolyte charge. The total fuel  cell
weight  is thus reduced by around 25  percent, and the  peak power
density is correspondingly increased to around  50  watts per pound
without recourse  to cathode boosting, and possibly to more than 100
watts per pound with our cathode boosting provision.

    Where the power density achievable by  the first  scheme  may
be entirely adequate, one can easily  increase the range between re-
fueling  stations to around  1,000 miles by  doubling  the aluminum
charge  and  still  keep  the initial electrolyte charge  down to  500
pounds, of which 150 pounds  would be in form of  three  separate
50-pound dry KOH cartridges providing fresh electrolyte upon addi-
tion of water at successive 200- to 300-mile intervals.

    Although the energy and power densities given by  Table 3 are
already attractive, they do not reflect  the important  weight savings
provided by  the simple pneumatic power control already mentioned.
The  power  controller used  with the  20- to  40-kilowatt hydrazine
fuel  cell weighs  300  pounds, and even if this weight is eventually
reduced by a factor of 2 it would still represent around 15 percent of
the total weight of the power source.  Since an air pressure regulator
need not weigh more than  2  pounds, our power control weight is
clearly  negligible. Hence, the 15 to 30 percent saving on the weight
of electronic controls becomes  equivalent to a corresponding further
increase in effective energy and power densities.

    One might argue that electronic inverter circuitry might be re-
quired in any event for use  with alternating-current motors, which
weigh only about 1 pound per horsepower, whereas  present commer-
cial direct-current motors weigh more than 5 pounds per horsepower.
At least one  lightweight direct-current  motor  has  been developed
with an estimated weight  of around Vz pound per horsepower (Zeisler,
1964).   This  motor also requires lower voltages, 2 to 5 volts, which
may further  simplify the fuel  cell design, e.g., by reducing  the re-
quired number of separate electrolyte pumping channels.  The heavy
264                                          Aluminum  Fuel Cell

-------
bus bars required with large currents could be kept down to a reason-
able level by placing the battery  close to the  motor.  For example, a
rod of copper 1 square centimeter  in cross section and 100  centimeters
long weighs less than 2 pounds.  The type of homopolar direct-current
motor reported by  Zeisler  apparently would provide not  only an
adequate but a highly  desirable  combination with any type of  cell.

         NEAR-TERM AND LONG-TERM  PROSPECTS
               OF THE ALUMINUM FUEL CELL

    In addition to its important functional advantages, the aluminum
fuel cell appears to be economically attractive both immediately and
long term.  At current prices, the cost of aluminum fuel (25 cents/lb)
less the cost of the recoverable A1(OH):1 product  (around 5 cents'lb
Al(OH)., or 10 to 15 cents lb Al) may be already comparable to or
lower than the  average cost of gasoline consumed in present internal-
combustion engines for the same motive energy yield.  In  competitive
mass consumption the costs of aluminum should come down, since the
over-all aluminum consumption and recovery cycle would utilize the
cheapest available resources—carbon, and the cheapest available elec-
tricity (usually processed  directly near a hydroelectric power  plant)
—at a fairly reasonable overall energy efficiency.  Modern aluminum
reduction plants can operate  at  current efficiencies of  at  least 90
percent and less than 4.1  volts per cell  (Oehler,  1963).  Hence, the
fraction of  electric  energy input that may be  regained  in form of
motive  power  should amount to  at least 90  percent times 1.2 volts
divided by 4.1 volts, or  26  percent. In addition, the salvageable heat-
ing value of the heat generated in the battery may considerably in-
crease the effective efficiency in cold weather.

    The production of aluminum near sources of cheap  electricity,
i.e., in predominantly rural  areas, would also prevent further intro-
duction of  smoke-stack  pollutants from  power plants in  urban  sur-
roundings.  Although aluminum reduction plants do inject pollutants
into the atmosphere, their emissions should  be  much more  readily
amenable to control  than motor  vehicle  exhausts or  flues in  urban
areas. In addition, the total amount of carbon dioxide that would be
introduced into the  earth's atmosphere by each complete aluminum
reduction-consumption  cycle can  easily be shown to be around  half
of what might  be produced  in a few decades for  comparable energy
production by hydrocarbon fuel cells.

    This discussion  thus far has  failed to point out some of the ob-
stacles to an early realization of practical and  competitive aluminum-
driven vehicles. The present high cost of air  cathodes  may constitute
the chief and perhaps only genuine technical-economic barrier.  This
high cost cannot be due only to  catalyst requirements, since the silver
required for satisfactory cathodes need not cost even $1 per  square
foot.  We believe that at considerably greater  cathode costs ($107ft2)
the aluminum  fuel cell  may start competing with gasoline engines.
The present costs  of $50 to $100 per square foot of cathode area are
ZAROMB                                                       265

-------
 thus  only 10 times higher  than what we  regard as the maximum
 costs allowable for motor vehicle applications, and these costs may
 be attributed chiefly to the  small production scale and to initial de-
 velopment outlays. Discussions with  cathode suppliers  lead to the
 conclusion that a  cost of $5 per  square  foot  on a mass production
 scale may be a realistic forecast.

     One must also take cognizance of past failures to develop practi-
 cal aluminum batteries  (Brown, 1893; Sully, 1897;  Polcich,  1926;
 Vince, 1933;  Ruben, 1933, 1951, 1952; Stokes, 1955; Lozier et  al., 1959,
 1961; Sargent, 1951; Zaromb, 1962). These past attempts were, how-
 ever, directed toward small cells for low-power applications where
 the use of auxiliary mechanical accessories could not be considered.
 It is  chiefly  for  high-power  and high-energy-storage  applications
 that the aluminum fuel cell  is  attractive.

    Other problems have been met since the inception  of this work
 some 8 years ago (Zaromb and Faust, 1962; Zaromb, 1962;  Bockstie,
 Trevethan, and Zaromb,  1963).  Throughout, we have had to steer a
 narrow course between passivation of the anodes and excessive cor-
 rosion.  We believe we now have enough knowledge of these difficul-
 ties and of how to circumvent them to be confident that a practical,
 aluminum-driven  vehicle will  sooner  or  later  make  a successful
 appearance.

                     ACKNOWLEDGEMENTS

    Acknowledgements  are  due  especially to  L. Bockstie,  J. O. M,
 Bockris, and M. Lasser for help in the early stage of this work  (in
 1959-1961), and  to W. Bojman, R. Edwards, and J. Teale for contri-
 butions made in  the last  2 years.

                          REFERENCES

 Bockstie,  L. D., Trevethan, and S. Zaromb, 1963.  Control of Al cor-
    rosion in caustic solutions. J. Electrochem. Soc.  110:267-71.
 Brown, C. H., 1893. U. S. Patent 503,567.
 Lozier,  G. S.,  R. Glicksman,  and C. K. Morehouse, 1959.  U. S. Patent
    2,874,079.
Lozier,  G. S.,  R. Glicksman,  and C. K. Morehouse, 1961.  U.S. Patent
    2,976,342.
Oehler, R. E., 1963.  In: Extractive  metallurgy of  aluminum, G.
    Gerard,  ed.  Interscience,  New York,  N. Y. Vol.  2,  pp. 231-37,
    especially p.  232.
Polcich, G., 1926. U. S. Patent 1,771,190.
Ruben,  S., 1933.  U. S. Patent 1,920,151.
Ruben,  S., 1951.  U. S. Patent 2,638,489.
Ruben S., 1952. U. S. Patent 2,783,292.
266                                           Aluminum Fuel Cell

-------
Sargent, D. E., 1951  U. S. Patent 2,554,447.
Stokes, J. J., Jr.,  1955.  U. S. Patent 2,796,456.
Sully,  J.,  1897. U. S. Patent 585,855.
Vince, C. H.,  1933.  British Patent 397,475.
Zaromb,  S.,  1962.   The  use  and  behavior  of  aluminum  anodes  in
    alkaline primary batteries.  J. Electrochem. Soc. 109:1125-30.
Zaromb, S., and  R.  A.  Foust, Jr.,  1962.  Feasibility of electrolyte  re-
    generation in  aluminum  batteries.  J.  Electrochem.  Soc. 109:
    1191-92.
Zeisler, F. L., 1964.  IEEE National Conference Record on Automotive
    Electrical and  Electronics Engineering.
ZAROMB                                                       267

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     PERFORMANCE AND ECONOMICS  OF THE
 SILVER-ZINC BATTERY  IN  ELECTRIC  VEHICLES


                        George A. Dalin

                  Yardney Electric  Corporation
                        New York,  NY.

    Two principal arguments have been  advanced  for the electric
car:  freedom from pollution of the air, and economy. The pollution
argument is clear  enough; each gasoline-powered car emits an esti-
mated  ton  of pollutants  each year.  The concentration of pollutants
in  New York approached the crisis level  last  Thanksgiving (1966).
With the increase  in the  number  of cars, the crisis level  may be sur-
passed at any time.  Although engine manufacturers are working on
reduction of emissions, there  is no guarantee that the achievements
in  this direction will not be swamped  by the increase in the concen-
tration of cars in urban areas. Since the internal combustion engine
produces more than  half  the total pollution  in  urban areas,  it  is
evident that replacement by electric cars could result in a substantial
decrease  in pollution.
    Evaluation of  the  economics  of the electric car is more complex.
Additional factors such as range, speed, acceleration, life,  and  even
method of financing must be taken into account. To  start with, con-
sider the energy-storage capacity of the batteries that are  now used
for various purposes and that might be used to power an electric car.
The  energy densities for  the various batteries in terms of watt-hours
per pound are (FPC, 1967) lead-acid, 8 to  12; nickel-iron, 11; nickel-
cadmium, 12 to 14; silver-cadmium, 30; and silver-zinc, 40  to 60.
    Lead-acid,  with the lowest energy density  of the lot, has had the
field to itself since  1870, when  Sir David Solomons built the first
electric vehicle.  The business burgeoned, and between 1900 and 1915
over 100 manufacturers were in operation.  By  1912, the business
amounted to  6,000 passenger and 4,000 commercial  vehicles yearly.
Range  was 20 miles and top speed was 20 mph. It  is worth empha-
sizing that traveling at top speed cuts the range, so that  top speed
and maximum range cannot be achieved in combination. This is true
of  the other batteries and also of internal  combustion.
    The  cost ranged from $2,600 for a Baker Electric to $5,500 for a
Borlund  Electric.  It would be interesting to  calculate  the cost per
mile in today's dollars for the Borlund Electric.
    After 1914  the manufacture  and sale of  electrics  fell off,  and
internal  combustion took over the market. By  1933, electrics  had
gone off the market (Ference, 1967). Nevertheless, during this period
a number of concepts were proposed that may prove important today.
To eliminate the energy loss at the differential, the rear  wheels  were
driven by individual motors.  Charging at metered  outlets and ex-
change of exhausted batteries for  fresh batteries at service stations
were both proposed.
DALIN                                                       269

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    In this .country lead-acid batteries are now used for the propul-
sion of  fork-lifts,  of  which about  100,000  are in use.  The battery-
powered fork-lifts are used  in enclosed  spaces in which  internal
combustion  fumes cannot be tolerated.

    In  England  there  are about 40,000  battery-powered urban
delivery vans,  and 60,000 fork-lifts.  We see, then, that where the
daily range is sufficiently limited, even lead-acid batteries can  meet
the needs.

    With reference again to batteries  mentioned earlier,  it is evident
that nickel-cadmium  and nickel-iron do not give a sufficient increase
in energy density over lead-acid to warrant their  use in passenger
cars.  Nickel-iron  batteries  are extremely  long-lived,  however,  and
thus are suitable for powering trucks. Some of the batteries originally
put into use around 1910  are believed to  be still in  operation.

    Silver-cadmium,  from  the  standpoint  of energy  density, is far
superior to the other three batteries; however, it is by far more expen-
sive.  It is  also substantially more expensive than silver-zinc.   The
silver-zinc  battery not only tops the list in  energy density but is  also
a high-rate battery.  The General Motors Electrovair II reached  a
speed of 80 mph, powered by Yardney silver-zinc batteries.

    The first cost of  silver-zinc appears  high relative to  lead-acid,
but a more significant parameter is the cost per mile.  To calculate
this, we use the  data obtained by installing four  Yardney  Electric
batteries in a modified Renault Dauphine automobile.  The car  was
originally modified for use with lead-acid batteries, and was fitted
with a  7.1-horsepower direct-current  motor. The Yardney batteries
were designed  for aircraft use  and therefore were  not optimum for
the car. Each consists of fourteen  85-ampere-hour  cells, which give
about 120 ampere-hours when new. Figure 1 shows typical discharge
curves  for  a 100-ampere-hour cell,  which is very similar  in  con-
struction and of only  slightly larger capacity. Figure 2  shows voltage
as a function of current density.  This  curve makes  it  possible to
predict  wattage as a function of current.

    The car was run on  a  flat  road; both  voltage and current  were
observed. Wattage is  plotted as a function of speed  in Figure 3.  Note
that the wattage at each speed varied over a substantial  range.  Evi-
dently wind is a factor, with low wattages indicating a following  wind
and high wattages a  head  wind. To  estimate the  energy expended
in traveling 1 mile, a  value for  40 mph can be taken from the graph,
a value from the  middle of the zone. A speed of 40  mph requires
6,500 watts.  With the proper mathematical manipulation  we  find
that 1 mile requires 160 watt-hours.

    At  a battery voltage of 75, the number of ampere-hours required
per mile is  160/75 or 2.1. For city driving, an  average speed of 25
mph is  more likely. At this speed the wattage is about 1,700 and the
voltage  about 80. This works out to 68 watt-hours  and 1.05 ampere-
hours per mile. On this basis the range would be 85/1.05 or 81 miles.
270                                            Silver-Zinc Battery

-------
   1.8-

   1.6-
 UJ
 |l.4
 d
   1.2-

   1.0-
          12   24    36   48    60   72    84   96   108   120
                           OUTPUT, amp-hr
            Figure  1.   Typical  discharge curves  for
                     100-ampere-hour  cell.
 2.0-
LlJ
CD
_
o
 1.0-
    0
                                                          0.20
            0.05          0.10          0.15
                    CURRENT DENSITY, amp/in.2
Figure  2.   Voltage as a  function of current  density.
  DALIN
                                                            271

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  14 -
                              SPEED, mph

   Figure  3.   Wattage as  a  function  of  vehicle  speed.

In practice the range  is about  77 miles.  This range gradually de-
creases as the battery  ages and is shorter at higher speeds.

    The four batteries, including metal cases, weigh 240 pounds. The
weight can  be cut by 30 pounds through the use of plastic  cases.
The car,  without batteries or occupants,  weighs  1,335 pounds and is
not streamlined. Maximum speed is 55 mph. The motor is 7.1 horse-
power and  is series-wound.  With  the car on  blocks, turning  the
wheels at 40 mph requires 2 horsepower.

    The  speed control in this model  is  the one that was  installed
when it was originally fitted  for lead-acid batteries and  consequently
is  primitive.  The control was not changed for the tests with silver-
zinc  because the objective was to obtain performance data  on  the
battery. For the same  reason, the low-power motor also was  retained.
The control can achieve six  speeds by placing the  four batteries in
parallel,  series-parallel,  or  series, and through  the use  of  a  series
resistor (at bottom speed)  and a field  shunt.

    As stated earlier,  the batteries  described  were not designed for
use in the car —  they occupied only  about  half the available space
in the front and rear trunks. Yet the  data can serve as the  basis for
a more suitable design and for cost estimates. The  number of cells
will be taken as 60 because this number can be charged  directly from
110-volt  alternating  current, with a suitable rectifier, of course. The
space available  in the car is adequate for 60 cells  of  any capacity
up to about 250  ampere-hours;  the  technology is  available for  a
battery of almost  any  size.
272                                            Silver-Zinc Battery

-------
    Let us start with the assumption that a second family car will
be driven about 50 miles per day.  Also, assume that a safety factor
of 2 in the range must  be provided. This will require that battery
capacity  be increased to 124 ampere-hours.

    To  compare  the costs of  operating  internal combustion and
electric vehicles, we must  make some basic assumptions:

Internal combustion vehicle
   Retail cost, $3,000.
   Life,  6 years at 12,500 miles per year.  This figure is based on 50
   miles  per  day, 5 days  per week,  50 weeks per year.  Gasoline
   mileage, 13 miles per gallon at $0.35 per gallon, or 2.7 cents per
   mile.

Battery-powered vehicle
   Retail cost, $2,500 without battery. Cost  is lower than that of the
   internal combustion  car because cost of engine,  transmission, and
    auxiliaries is subtracted.  Cost of motor, controls, and charger  is
   included.

   Life,  10 years at 12,500 miles per year.  Car life  is assumed longer
    than  for internal combustion because the system is  much simpler.
    Electricity mileage,  cost of  electricity is $.01  per  kilowatt-hour
    and charge wattage efficiency is  50  percent.  At 160  watt-hours
    per mile,  cost is 0.33 cents per mile.

     Retail cost of the battery, exclusive of  silver, is estimated to be
$700 to  $900.  Our  accounting department  has  suggested that the
lower figure be used for calculations.  Life is  taken as  2 years when
the vehicle is operated  for 12,500 miles per year and  as  4  years for
7,500 miles per year.

     The silver can be leased or rented. This is now the practice with
batteries for  fork-lifts.  The silver  can  be re-used indefinitely with
virtually no  loss,  and  can therefore be  regarded as  indestructible
collateral for a loan.  This  places its cost in a different category from
that for  the remainder of the battery and the vehicle.*
     Battery  life, on  the  basis  of laboratory  data, can be taken  as
500 cycles at  50 percent  depth of discharge. The cycle-life is extended
as the depth of discharge is decreased.   Moreover, recent develop-
ments in battery construction have demonstrated substantial increases
in cycle  life  over that quoted here.

     With  these  assumptions,  the  cost  of  operating  the battery-
powered vehicle  is somewhat  lower than that of  operating the in-
ternal combustion vehicle.

     The costs are compared in Table 1 for mileage of 12,500 per year.
The picture  changes  if the daily mileage is lower.  The life  of the
battery  will  be substantially longer at  the shallower  depth  of dis-
charge.  We   now examine a new  set of  assumptions.  Traveling  30
 *Cost estimates based on silver at pegged price of $1.29 per'ounce.



 DALIN                                                         273

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   Table  1.  COST COMPARISON BASED  ON 12,500 MILES PER YEAR


Fixed costs
Depreciation
Battery
Insurance
License and taxes

Internal
Combustion

$500
0
200
20
720
Battery
Power

$250
350
250
20
720 870







870

Operating costs
Gasoline
Silver rental, 9%
Oil, grease, tires, etc.
Charging

Cost per year
Cost per mile

337
0
140
0
477


Table 2. COST COMPARISON BASED


Fixed costs
Depreciation
Battery
Insurance
License and taxes

Operating costs
Gasoline
Silver rental, 9%
Oil, grease, tires, etc.
Charging

Cost per year
Cost per mile
Internal
Combustion

$500
0
200
20
720

203
0
84
0
287



0
96
75
41
477 212
1,197
9.6C
ON 7,500 MILES
Battery
Powered

$250
175
250
20
720 695

0
96
45
25
287 166
1,007
13.40





212
1,082
8.70
PER YEAR







695





166
861
11. 50
274
                                             Silver-Zinc  Battery

-------
miles per day,  5 days per week, 50 weeks per year yields 7,500 miles
per year.  Battery life  increases to 4  years.  Table  2  presents  the
cost comparison for 7,500 miles per year.  At this mileage, the battery-
powered vehicle provides an even greater cost advantage.

    Since the assumptions  on which these accountings are based in-
volve some uncertainties,  it would be overstating the case to claim
that battery power is  substantially cheaper  than gasoline.  Never-
theless, it appears that silver-zinc battery power is no more expensive
than gasoline power, and if anything is cheaper.  Consequently, cost
is no obstacle to the use of silver-zinc  for low-mileage applications.
Since batteries emit no pollutants, silver-zinc offers the  possibility of
a fast  start toward eliminating the pollution blight.

    In  concluding, I should mention that  work  is proceeding in a
number of laboratories on systems of  still higher  energy  density.
Specific examples of couples under investigation are zinc-air, lithium-
nickel halide, sodium-sulfur, and lithium-chlorine. Speaking for our
own laboratory, I  can say that progress on zinc-air is very satisfactory
and we expect to  present results before long.

                            REFERENCES

Federal Power Commission, Bureau of  Power, 1967.  Development of
     electrically powered vehicles. 50pp.  (Feb.).
Ference, M., 1967. Electric vehicles. Statement before Committee on
     Commerce and Subcommittee on Air and Water Pollution of the
     Committee on Public Works, U. S.  Senate.  (Mar. 16).
 DALIN                                                         275

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     A SODIUM-SULFUR SECONDARY BATTERY
                          T. W. DeWitt
                      Ford  Motor  Company
                        Dearborn,  Mich.
                        INTRODUCTION

    One of the major barriers  to the general use of electric power
in mobile applications is the inadequacy of the power  source.  This
has been true for over half a century, yet the advantages that could
be gained through the use of electric power are such that  technological
advances, as they occur, are continually reviewed for their potential
in overcoming  this barrier. A  case  in  point is  the widespread
resurgence of interest over  the last  decade in fuel  cells and high-
energy-density rechargeable  battery systems.

    Research and development in this  area has taken many paths
and has had many origins. The result of one approach is the subject
of this paper.

    The work that  will be  described  did not originate directly  as
a conscious search for a high-energy-density electrical power system,
but is a product of the  interaction of fundamental research in solid-
state  science  and a  continuing awareness of the major  problems
of the energy  storage and conversion field.

                    SOLID  ELECTROLYTES

    Common to all secondary cells is an ionically conducting mem-
brane  separating  reactive  materials.   The  reactive materials  are
constrained to  combine by ion transport through the membrane and
electron transport through an external  circuit where the free  energy
change corresponding to the  cell reaction is extracted as useful work.
The fundamental idea in this concept of a  sodium-sulfur cell  is that
of using a  solid ionically (but not electronically)  conducting mem-
brane between reactants. When such a solid membrane, which takes
the place of the usual  liquid electrolyte,  is also  impermeable and
inert to reactant materials in other than  ionic form, the possibility
exists of using energetic reactants in the liquid state.  Molten elec-
trodes  suffer  from  no  irreversible changes  on charge-discharge
cycling and often present fewer problems from polarization  at phase
interfaces.

    Figure  1 compares the  sodium-sulfur cell schematically  with
the common lead-acid  cell.  In the latter,  electrons  pass  through
the external circuit (where  they do work)  and  ions  through  the
sulfuric acid electrolyte to complete the  reaction, which  is essentially
the oxidation of lead and the reduction of lead dioxide.  The reactants
DEWITT                                                       277

-------
and products are solid, and the  electrolyte, liquid.  In the sodium-
sulfur  system,  liquid  sodium, which serves as  its own  electrode,
yields electrons to the external circuit, passes through the separator
as a  sodium  ion,  and  reacts with liquid sulfur,  which receives
electrons from  the external circuit,  to  form sodium sulfide, which
is  also kept liquid by  operation  at  elevated temperature  (300°C).
 LEAD-ACID STORAGE BATTERY
LEAD
~ SULFURIC-
~ ACID

--^-1
— —
LEAD
DIOXIDE
      SOLID  REACTANTS,
      LIQUID  ELECTROLYTE
 On  discharge, energy is  extracted
 in external circuit while both
 electrodes and electrolyte
 undergo chemical change.
    FORD SODIUM BATTERY
                                                r  .LIQUID  SODIUM
                                               ;/   CERAMIC
                                                     ELECTROLYTE

                                                     CONDUCTING
                                                     SULFUR
                                                     ELECTRODE
       LIQUID REACTANTS,
      SOLID  ELECTROLYTE
Current is  carried by sodium atoms
that give up  electrons to external
circuit, traverse solid ceramic
electrolyte, and react with sulfur.
Figure  1.   Schematic representation  of sodium-sulfur cell
            and  comparison  with  lead-acid  cell.

               THE SODIUM-SULFUR SYSTEM

    Sodium and sulfur are attractive  reactants for several  reasons.
Under proper conditions the reaction is electrochemically reversible.
Both  are molten at 115°C, and if sodium is  added to a fixed amount
of sulfur, a high specific  energy can be obtained before the melting
point of the reaction product exceeds 300°C.  Both sodium and sulfur
are plentiful and inexpensive and can be contained at 300°C in vessels
made  of common materials such  as  stainless steel and aluminum.
The highest pressure encountered is the  vapor  pressure  of pure
sulfur, about  60 millimeters  of mercury at 300°C.

    Figure  2 shows the open-circuit potential of  the  sodium-sulfur
system as a function of composition.   The voltage remains constant
at 2.08 until  a composition corresponding  to sodium  penta-sulfide
is reached.  It  then drops almost  linearly to 1.76 at  a  composition
corresponding  to  sodium  trisulfide.  The temperature  of operation
is dictated by the melting point of the product, and the constraints
thus imposed are illustrated in Figure  3, which is  the phase diagram
for the system Na,S-S (Pearson and Robinson, 1930).  At the opera-
278
                                 Sodium-Sulfur Secondary Battery

-------
   ting temperature of 300°C, solid will begin to separate out at  about
   the  composition Na.,S3. This  composition is the maximum contem-
   plated degree of reaction, or the discharged state. On the right-hand
   side  of  the  diagram,  the sulfur  side,  the system  is  two  phase at
   300°C,  liquid sulfur and liquid sodium pentasulfide.
   2.0
UJ
13
O
o
    1.0
Q.
o
                        DEPTH OF  DISCHARGE, percent
                   25            50            75
                   _j	I	I
100
 I
                       I                \                I
                     0.2              0.4              0.6              0.8
                          MOLE  RATIO (SODIUM/SULFUR)

   Figure 2.    Open-circuit  voltage  of sodium-sulfur  cell  vs.
                         state  of  discharge.

               CONDUCTING  CERAMIC MEMBRANE

       The heart of this battery concept  is the  ionically  conducting
   solid electrolyte  around which most  of  the research centered.  The
   original materials examined  for use as solid  sodium ion conductors
   were  glasses,  principally  those  in the  soda-alumina-silica system.
   The requirements for a  solid electrolyte material separating sodium
   and  sulfur  are  stringent.  Good conductivity,  chemical  corrosion
   resistance to the reactants, usable strength, and impermeability are
   essential properties.
       No one glass composition was found perfectly  satislactory,  but
   in the  course  of investigation a crystalline material known as beta-
   alumina was encountered  and recognized as having  the sought-after
   properties.  Beta-alumina  is  not  a form  of A1..O.,,  but is a sodium
   DEWITT
                                                                  279

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1,000
                                              .  SULFUR  ,
  100
    40
60        70         80
   SULFUR, percent
                                                                  100
  Figure  3.    Phase  diagram  of  the  system   Na2S-S  (after
                     Pearson and  Robinson).
  aluminate with the generally  accepted  formula Na,O-HAl,O3.  This
  is not a new material, but its high ionic  conductivity has not been
  previously recognized.  The structure  of beta-alumina (Beavers and
  Ross, 1937) is known and is shown in Figure 4.  It is a layer structure
  in which sodium  ions are found  in relatively  open planes  together
  with bridging oxygen ions that have the effect of providing a spacing
  that  results in nearly  optimum mobility  in  this  structure for  a
  monovalent  ion the size of sodium.  The oxygen ion  ''prop"  is what
  distinguishes beta-alumina from other materials with a layer struc-
  ture  such as  mica.   Application of  theories and  techniques from
  solid-state and crystal chemistry resulted in producing proprietary
  280
         Sodium-Sulfur Secondary Battery

-------
derivatives of beta-alumina that can be made into highly conductive,
stable,  impervious  shapes by conventional  ceramic-forming pro-
cedures.   The  electrical  resistivity  of the  formed  polycrystalline
ceramic is shown in Figure  5. At 300°C the resistivity  is about 5
ohm-centimeters, which is comparable to the values for molten salts
and aqueous  sulfuric acid and potassium hydroxide.
                             *    $    9    *
                           •  (i, If    #    9    9
                                                 *     •
Figure  4.   The structure  of  beta-alumina  (after  Beavers
            and  Ross).  White  balls  are  sodium.
DEWITT                                                     281

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             300
                     TEMPERATURE,
                      200
                   100
  100 —
E
o
E
-§

t  30
Ul
o:
   10
     1.5
2.0
                                    2.5
                                                    3.0
                                               3.5
                             T(°K)
   Figure  5.    Electrical   resistivity  vs.  temperature  of   ion-
                       conducting  ceramic.
                   LABORATORY SCALE  CELL

       Ceramic  membranes  in  the form of  thin-walled  tubes have
   been used to construct sealed cells like that shown in  Figure 6.
   Sodium is contained  in a reservoir  sealed to the top of  the ceramic
   tube, the other end  of which  is closed.  Surrounding  the ceramic
   tube is sulfur contained in a porous graphite electrode that  makes
   contact with  the ceramic and  a backing electrode.   Typical charge-
   discharge curves for a cell  of  this type with a 3  millimeter thick
   layer of sulfur and 0.8-millimeter ceramic wall thickness are  shown
   in Figure 7.   Of note are the high current densities, computed from
   surface area  of ceramic,  that  can  be achieved at terminal voltages
   282
              Sodium-Sulfur Secondary Battery

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consistent  with  only pure  ohmic  resistance  of  ceramic, sodium
sulfides, and porous electrode.  The  data contain little indication of
polarization  from charge transfer  or diffusion-controlled  electrode
reactions.

    Operating experience has confirmed  the  expected  advantages
of this battery concept over other systems. Being liquid, the reactants
are regenerated to the same physical form during  repeated charge-
discharge  cycling,  obviating a source  of  limited  cycle life  as in
cells with solid  reactants.  The  cell reaction  is simple;  it has  no
gaseous reactants  or products  and no  known side reactions  or
mechanisms  for self  discharge.  No  auxiliary equipment  is required
except  thermal insulation.
                         ,-y;
                                       SEAL
                                       LIQUID SODIUM
                                         RESERVOIR
                                        BACKING
                                       ELECTRODE
                                        SODIUM-ION-
                                        CONDUCTING
                                      CERAMIC TUBE
                                         SULFUR-FILLED
                                      POROUS ELECTRODE
Figure 6.   The construction of a small  sodium-sulfur cell.
                   PROJECTED SCALE-UP

    This  battery  is still in the  advanced  laboratory stage,  and
current emphasis is on obtaining data necessary  for proper design
of larger  units.  No basic  barrier to its  larger scale  development
is known at present, and although problems associated with materials
of construction,  configuration, reliability and the  like remain to be
faced,  it is anticipated that these can be solved.
DEWITT
                                                            283

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        CONSTANT CURRENT CHARGE AND  DISCHARGE, amp-hr/lb
o
3.0


2.5

2.0




2.5


2.0


1.5


1.0

0.5
    0
                                          1 — 170 ma/cm2 -120 min
                                          2 — 340 ma/cmz- 60 min
                                          3 — 680 ma/cm2 - 30 min
               DISCHARGE-
                                               OPEN  CIRCUIT
            -CHARGE
               0.5
                      0.4
                                   0.3
                                          0.2
                                                       0.1
     0
               0.1        0.2
            DISCHARGE ->
                                0.3        0.4       0.5
                             MOLE RATIO (SODIUM/SULFUR)
                                                                  0.6
   Figure 7.   Terminal voltage vs. state of discharge for steady
   discharge and charge currents of 170, 340, and  680  milli-
      amperes per square centimeter of ceramic membrane.
       When the laboratory data are projected to the design of larger
   size units, one  result is the proposed cell  shown  in Figure 8.  The
   specifications for such  a unit are  given  in  Table  1.  The  rated
   energy  density, 148  watt-hours per  pound,  represents about  45
   percent of the theoretical 346 watt-hours per pound. These numbers
   are compared in Table 2 with those for several conventional batteries.

       At  the  present  time it is expected  that a  battery  of  the size
   shown in Figure 8 will  be in operation in a year and one in the
   20- to 40-kilowatt  range in 2 years.  It will  certainly be several
   years before any  appreciable  number of these  batteries  will  be
   available for the purpose of exploring other applications. Although
   the primary interest, and  immediate  focus, is  in the  use of this
   battery system for motor vehicle propulsion,  it is anticipated that
   it  will ultimately  have many other applications,  both civilian  and
   military.  Since it  operates at elevated temperatures,  its usefulness
   284
                                   Sodium-Sulfur Secondary Battery

-------
in areas such  as miniature  batteries  and  small portable power
sources  is  limited,  except for very  special applications.   In  sizes
of a kilowatt or more,  the  temperature problem diminishes  con-
siderably in magnitude, and in some instances the higher operational
temperature  may even be an advantage.  A few of the areas in
which it may have applicability include: electric lawnmowers, garden
tractors, farm tractors, submarines, electric  railway cars, and mate-
rials handling equipment.
 Figure  8.   Mock-up of a proposed 2-kilowatt cell, showing
         planar array of sodium-filled ceramic tubes.
 DEWITT
                                                              285

-------
           Table 1.   SPECIFICATIONS OF PROPOSED CELL
            Average power, kw                      2
            Maximum power, kw                     4
            Open  circuit voltage                     2.08
            Average discharge  voltage                1.75
            Ampere-hours                          1,850
            Weight, Ib                              22
            Volume, in.3                            400
            Table 2.  COMPARISON OF BATTERY  SYSTEMS

Lead-acid
Nickel-cadmium
Silver-cadmium
Silver-zinc
Ford sodium-sulfur
Energy Density, w-hr/lb
(slow discharge, 5 hr)
10
14
24
50
150
Weight/ power ratio,
(rapid discharge, x/4
31
25
15.5
6.5
10
Ib/kw
hr)





                 APPLICATION  IN VEHICLES

    It is  premature to do anything  but speculate  on what this
battery could mean for  an electric car since there are many problems
to be  solved, not only with the battery, but with motors and controls,
before it can become a practical reality.  It is  nevertheless possible,
and  useful, to  make  a tentative calculation of  what  might  be
achieved.  For  example, 350  pounds of sodium-sulfur battery in a
1350-pound commuter  car  should  allow it to cruise at  40 miles  an
hour  for 200-300  miles, at 60 miles an hour for 125 to 200  miles,
and have  a top speed of about 70  miles an hour. Such  a car's per-
formance  should  be adequate in  an urban-suburban environment.

    The chief disadvantage of this battery,  even for  motive power
use, is the high temperature of operation.  The battery is  in-operative
at room temperature, so a  cold start is impossible,  unless auxiliary
heating is  used.  A  large battery  has  a considerable  heat capacity,
and the time required to bring it up to operating temperature with
any practical auxiliary system would probably be unacceptable except
for very infrequent occasions.  However, the solution to this problem
is to  keep  the battery hot all  the  time. This should  present  no
problem for an urban-suburban vehicle that  will be garaged almost
286                              Sodium-Sulfur Secondary Battery

-------
every night for overnight charging anyway.  Indeed this has some
advantages  since  the car  would  require  no  warmup  period  and
would be  ready  for  instant  starting  at  all  times.  There  is  no
problem  during operation,  since  internal  power  dissipation  in  the
battery is more than sufficient to  keep it  hot.  Indeed,  cooling  will
undoubtedly be necessary-  There will  be, of course, occasions when
the  car  will  not have access to  charging facilities,   perhaps  for
several days or even a  week  or  more, and here  it should be very
simple to arrange it so the battery uses its  own energy to keep itself
hot  for such  periods of time and still have enough left  over for
operation of the car.  The  minimum  charging time for the battery
might be as short as a half hour,  depending on the cooling  facilities.

     Clearly, the question of safety  must  be  faced.  There is little
danger arising  from an internal  breakage in  the battery with  a
consequent  mixing of the reactants. As has been mentioned, there
are no gaseous  products involved  at all, and  under certain circum-
stances, direct reaction between sodium and sulfur is self-attenuating
because  the product, sodium sulfide,  provides  a barrier  between
the  liquid  reactants.  The one  thing   that must  be  prevented, of
course, is the escape of hot  sodium and sulfur from the  container
in the event  of an accident,  and proper  packaging is the answer
to this.

                          REFERENCES

Pearson, T. G., and P  L.  Robinson,  1930. The polysulfldes  of the
     alkali  metals.  I. Sodium.  J.  Chem.  Soc. (London).  1473-97.

Beavers, C. A., and M. A.  S. Ross, 1937.   The crystal  structure of
     (beta alumina) Na,OllAl,O,.  (In English). Z. Krist.  97:59-66.
 DEWITT                                                       287

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        LITHIUM  NICKEL-HALIDE BATTERIES
                    R. C.  Shair, A. E. Lyall,
                        and H. N.  Seiger

                      Gulton Industries, Inc.
                         Metuchen, N. J.

                       INTRODUCTION

    The battery industry is partial to a term called the theoretical
energy density.  This is calculated  by taking stoichiometric amounts
of the anode and cathode materials in their charged state.  Then we
look up  the  Gibbs free energy for  the  reactions and  calculate the
theoretical voltage of the system. Next, we use both the free energies
and the equivalent weights to obtain the theoretical watt-hours per
pound.  Unless the electrolyte is required in balancing the chemical
reaction, it will not be used in the  weight calculations.  To  have a
practical working  battery, a case is needed, and so are grids  to hold
the active materials,  tabs  to  connect  plates  to terminals,  and  a
separator that prevents  electronic  short circuits  while holding the
electrolyte that supplies the electrochemical conductivity. The weight
of these items cannot be readily calculated, but  practical batteries
have watt-hour per pound  ratios  that  are  about 20 percent of the
theoretical values.  So let  us  consider  the  theoretical value  as  a
Figure  of  Merit  for comparison  purposes,  and  bear  in mind that
20 percent of these numbers are realistic.

    The present battery systems have been pushed rather far, and it
is  difficult  to visualize how the watt-hour per pound ratios  can  be
increased much more.  Significant increases in energy-to-weight ratios
must come from systems that have  not previously been reduced to
practice  as batteries.  The first  step is a tabulation of  materials that
may serve  as anodes and  materials that  may  serve as  cathodes.
Lithium is the first metal encountered in the table of electromotive
force, and it  is the lightest metal.  Between its half-cell potential and
equivalent weight,  coupling it with  almost any cathode makes an at-
tractive system. Lithium supplies the energy, and the cathode supplies
the weight.

    Because lithium is so energetic, it is, as a consequence,  extremely
reactive  with water, oxygen, hydrogen, and even  organic liquids that
contain  active hydrogen.  As an example of the latter,  lithium reacts
with ethyl alcohol to form lithium alcoholate, a reaction that proceeds
with the release of hydrogen gas.

    This paper is  essentially a progress  report on our efforts to de-
velop a  battery using lithium as the anode  and the nickel  halide as
the cathode.  The fluoride system  has a  theoretical energy-to-weight
ratio of  620 watt-hours per  pound, which I now feel obliged to divide
SHAIR, LYALL, SEIGER                                      289

-------
by 5 to obtain 120, and the chloride system has a theoretical value
of 437  watt-hours per pound, a fifth of which is 87.

                        ELECTROLYTE

    Since lithium is  so reactive, the first thing one must do is find
a liquid  medium with  which it is  not spontaneously reactive.  But
the list of required criteria is quite long.  The electrolyte  consists of
a solvent and at  least one solute. If only one solute is used, then it
must supply the  ions that  migrate under the electric field, and  these
ions must also participate in the charge transfer steps at the  elec-
trode and electrolyte interface.  If two solutes are used, the  one that
does not participate  in the charge  transfer process at the interface
is called the supporting electrolyte.  The supporting electrolyte merely
carries the current in the  electric field. The fraction  of the current
carried by  each kind of ion is its transport number.
    In Table 1 are listed some non-aqueous solvents of interest.  Five
of these contain a double-bonded oxygen,  and the sixth, acetonitrile,
is  also an unsaturated  compound containing a triple  bond-nitrogen.
The dielectric constants  for  the   double-bond-oxygen  compounds
range from 38 to 64 and that for acetonitrile is  38.

Solvent


Dimethyl sulfoxide
Nitromethane
o-Butyrolactone
N-methyl-2-pyrrolidone
Acetonitrile
Propylene carbonate
GO
&%
1. 1
.2 •=
:> QJ
0
1.98
0.62
1.75
1.65
0.345
2.53
^V
c
? !E
s <=>
"^ 0.
18.45
—29
-44
—24
—41
^49
c_p
00 o
c
"I =
CD 0
0.
189
101
206
202
82
241
O
-t C
o J2
.32 to
QJ =
.2 S
0
46.7
38
39.1
45.4
38.3
64.4
Specific conductivity,
millimhos/cm
LiCI

9.91
31.8
0.008
0.16
—
0.34
Aid,

0.37
33.3
4.4
—
—
4.5
KPFe

10.2
5.91
—
—
12.0
7.2
NaPF,

10
12.3
13.2
8.2
43.0
7.5
    The boiling points and melting points of these solvents are im-
portant because they  define the temperature range  over which  the
battery may operate.  This temperature range is  widened, however,
by the freezing point depression and the boiling point elevation that
come about upon dissolution of salts.
    The solute must dissolve  in the solvent, naturally, and it must
ionize. The goal here  is to have a high conductivity. There must be
an anion  that  is  the same as  the  anion in the electroactive species
in the cell.  As mentioned before, these requirements may be met  by
using two solutes instead of  one.
    Candidate electrolytes were  originally  tested for compatibility
with  the  electrode materials.  These tests were  run by  placing  the
electrode  and the electrolyte in sealed Kel-F containers for periods
up to 6 months. Two electrolytes have done  well  in these posts, thus
far — propylene carbonate  and dimethyl sulfoxide.  The solute was
290                                Lithium Nickel-Halide Batteries

-------
potassium hexafluorophosphate for both. The concentrations of solute
taken at the maximum conductivity are:

    Propylene carbonate         90g/l  KPF(;   7.2 x 10~3  mho/cm
    DMSO                     190g/l  KPF0  11.6xlO-3  mho/cm

Dimethyl sulfoxide is also a solvent for nickel chloride and thus can-
not be  used  because there will be a  self-discharge process at the
lithium electrode. When  the propylene carbonate KPFB is used with
this chloride system, LiCl is added to  the electrolyte, a specific ex-
ample of the use of two solutes.

                LITHIUM ANODE ELECTRODE

    When  an electrode is fabricated,  it must possess electrical con-
ductivity in both the oxidized  and reduced states. This statement is
equally true for both anodes  and  cathodes.  Many of the  oxidized
materials  commonly used are  found to  be semiconductors.  Other
electrodes  may  have only thin films, or  there may  be  an  intimate
mixture; the graphite and flake nickel in  Edison storage  batteries is
an example of such mixture.

    A pasted lithium electrode was developed with the  paste con-
sisting  of a mixture of  powdered lithium and  conductive  granular
carbon, a binder and a vehicle.

    The paste was spread onto the substrate in a dry box.  It was
then pressed, after which the  solvent was removed by heating in  a
vacuum oven and the vehicle leached out.

    The electrical capability of an electrode is shown by  a polariza-
tion diagram as depicted  in Figure 1.

    The electrode was discharged against  a counter electrode. A ref-
erence electrode, mercury/mercuric chloride, was used to monitor the
voltage of the  lithium electrode,  while  a  motorized potentiometer
varied the  current through the electrode.  The electrodes used had an
area of 10  square centimeters.  The charge region is to the  right of
zero current, and the discharge behavior  is shown on the left  of the
origin.  The  maximum  current density  shown  corresponds  to  65
milliamperes per square  inch.  The attendant polarization  was 0.1
volt.  In a conventional nickel-cadmium battery, 65 milliamperes per
square inch is equal to about the 1-hour discharge rate.

    The lithium anode is far  from the limiting factor in this cell,
with regard to performance, and we are not attempting any further
improvements in performance  at  this  time.  Our concentration of
effort is on the  cathode materials.

         NICKEL HALIDE  CATHODE ELECTRODE

    A survey of cathode  materials  to be  used with a lithium anode
reveals several attractive anion materials. A  few  selected materials,
SHAIR, LYALL, SEIGER                                      291

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their voltage as a lithium cell, and their total energy content in watt-
hours per pound, are listed in Table 2.


  Table  2.  THEORETICAL CELL POTENTIAL  AND ENERGY CONTENT OF
                 SELECTED LI — CATHODE COUPLES
Li Cell
athode potential,
actant Product volts
"2 F- 6.05
:i2 ci- 4.02
)uF2 Cu + 2F- 3.55
;uCI2 Cu + 2 CI- 3.06
•JiF2 Ni + 2F- 2.83

-------
 At the beginning of the program we were ready to drop NiF2 because
 anything more than an electrometer brought the voltage of a cell to
 zero rather quickly.

     The nickel  chloride electrode was more favorable, and a pasted
 electrode similiar to the lithium electrode was developed. The initial
 current densities achieveable were low, however. Investigations were
 directed at doping  the nickel halide, improving the conductive di-
 luents, and improving the fabricating techniques to get higher current
 densities.  The techniques developed when applied to  the NiF2 elec-
 trode made an  attractive  electrode.  A current density  of  18  milli-
 amperes per square inch, equivalent to the  5-hour rate of discharge,
 has been achieved.

                              CELLS

     Cells have been constructed using the pasted lithium and nickel-
 fluoride  formulations. The  active area for  20 ampere-hour cells is
 45 square centimeters per electrode side,  and eight lithium electrodes
 and nine nickel-fluoride electrodes were incorporated  into each cell.
 The separator was  a  60 percent porous  sheet  of  non-woven poly-
 propylene.  The electrolyte was  propylene  carbonate   with  KPF6
 added.  These cells  have the energy  content of  two nickel-cadmium
 cells that weigh 4 pounds compared to the 0.5 pound per lithium cell.

     The contribution of electrolyte to the  cell's internal resistance was
 calculated to  be 0.027 ohm. Pulse data  such as shown in  Figure 2
 show an internal resistance of 0.35 ohm. The cell pulsed at 2 amperes
 shows a terminal voltage  of 2.5 volts. At 4 amperes, the C/5 rate
 cell voltage is 2.0 volts.

     Several small  laboratory  cells were built and cycled  unsealed
 in  an  argon atmosphere glove box.  They  were  discharged  at the
 C/10 rate and recharged at 3.6 volts.  Figure 3 shows cycle data after
 2 and 20 cycles.

                          DISCUSSION

    The feasibility  of the  lithium-nickel halide battery has  been
 demonstrated. As a  low-rate cell or as a primary cell, its performance
 is  very attractive. Recent development has been directed at achieving
 higher rates of  discharge suitable for electric vehicles.  At the C/5
 rate of discharge, which has been realized,  the battery  can provide
 power for cruising of  a vehicle and its energy density of 100  watt-
 hours per  pound provides  an  attractive  mileage range.   Its present
 limitation is its  power density of 50 pounds per kilowatt, which re-
 quires too large a battery to provide acceleration peaks.

    Bipolar nickel-cadmium batteries have  been developed in our
laboratories.   Because of their unique  geometry and  construction,
 these batteries have a weight to power ratio  of 3 pounds per kilowatt
for short periods of  time — of the order  of minutes.
SHAIB, LYALL, SEIGER                                      293

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Q.
E
uJ  3
cc
cc
Z3
o
Q  2
o
                                      -OCV
                                TIME
   Figure  2.   Current  voltage  trace  for  20-ampere-hour
     lithium cell at  18  milliamperes per square  inch.
   4
LJ
<  3
—'  o
0  2

   1
                                                   ---CYCLE 2
                                                   — CYCLE 20
                                          |
                                                         I
         Figure  3.
                              TIME, hours
                      Discharge  data for  lithium  cell
     A  small bipolar nickel-cadmium booster battery  coupled  in
 parallel with the lithium battery can provide the  necessary  peak
 power. It can be small compared to  the lithium battery, since the
 duration  of  acceleration  peak loads is  short, and  during cruising,
 the bipolar  battery  can  be recharged  in  minutes  from the  main
 battery. Bipolar nickel-cadmium battery technology is well-advanced.

     Let us look at the application of  the lithium battery to electric
 vehicle propulsion.  A vehicle weighing about 3,000 pounds requires
 about 5 horsepower  to cruise on  level road at 30 mph.  For grades
 and acceleration peaks, it would require up to 15  horsepower.  If we
 294
                                   Lithium Nickel-Halide Batteries

-------
assume approximately a 75 percent conversion of electrical power to
mechanical power, then the same number  of kilowatts can be used
as indicated  above  for horsepower.  For  cruising at  5  kilowatts  a
lithium battery  with a weight-to-power capability of 50 pounds  per
kilowatt would have to weight at least 250 pounds. At 100 watt-hours
per pound, it would be capable of 5 hours  of  operation, which at
30 mph is 150 miles. To provide the 15-kilowatt  peaks would require
about 45 pounds of bipolar nickel-cadmium battery  at 3 pounds  per
kilowatt.  Since  5 kilowatts would still  be coming from the lithium
battery, 45 pounds allows some margin of safety and the peak would
be available for  several minutes if necessary.

    The non-aqueous lithium-nickel halide battery coupled with  a
bipolar nickel-cadmium booster has attractive features for vehicular
propulsion. Further work is in progress to optimize the lithium system
and to evaluate  its capabilities.
 SHAIR, LYALL, SEIGER                                      295

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                   A  STATE-OF-THE-ART
                AUTOMOTIVE  FUEL  CELL
                        Philip Dantowitz

                 Monsanto Research Corporation
                          Everett, Mass.

                          Lonnie Gaddy

  U. S. Army Engineer Research and Development Laboratories
                         Ft. Belvoir, Va.


                       INTRODUCTION

    Interest in the  electric automobile has recently been widely re-
vived.  In most of the articles published on the subject, the  lead-acid
battery is examined as a source of electrical energy for the vehicle.
But all agree that the lead-acid battery is marginal at best, its basic
shortcoming  being  the limited range it affords the vehicle  at any
reasonable battery weight.  Attention has naturally turned to supply-
ing electrical energy by other means, and among these the fuel cell
is almost invariably proposed.

    Little factual data exist on large, air-breathing fuel cells suit-
able for automotive use.  This paper describes one existing fuel-cell
automotive power plant to allow a comparison with other sources of
energy, such as the lead-acid battery.


          THE 5-KILOWATT FUEL-CELL MODULE

    Monsanto Research Corporation in  cooperation with  the  U. S.
Army  Engineer Research  and  Development  Laboratories has de-
veloped a hydrazine-air fuel cell module that when used in  multiples
provides  power to drive an M-37 Army truck.  The fuel cell  module
is designed so that  fuel dissolved in the electrolyte can be  circulated
through the  anode compartments.  The circulation rate is high  enough
that the  electrochemical fuel consumption  hardly changes the fuel
concentration, even at high  load.  This  circulating liquid  also pro-
vides the means for cooling the fuel cell.  The module consists of 140
cells spatially arranged so that anode faces  anode  (as opposed to a
bi-polar  scheme).  The anodes are connected electrically in parallel
by a metallic grid;  the current is collected and  brought to the edge
of the  electrode.  Similarly,  adjacent cathodes face each other, but
in operation they are at different potentials, typically being 0.78 volt
apart.  An insulating plastic grid is incorporated in the cathode com-
partment. As with the anodes,  the cathode  current is collected and
brought to the  edge of the electrode. External  electrical connections
DANTOWITZ, GADDY                                         297

-------
 are made so that each pair of cells (one cell being one cathode and
 one anode) is in series with the next, and appropriate cathodes  are
 in parallel.  Figure 1 shows a schematic diagram of the arrangement
 and the external electrical connections. The module consists of two
 side-by-side decks of 70 cells each, connected in parallel electrically
 and clamped between  common  end plates.  At rated load each cell
 is designed to deliver 0.78 volt.  Since each pair of cells is wired in
 parallel, the rated voltage of the module is:

         70
        — x (0.78)  = 27.3 volts
 EXTERNAL PARALLEL
 CONNECTIONS  FOR
 CATHODE
                           NONCONDUCTING GRID
                           IN AIR PASSAGE
                                        ANODE
                                                       SEPARATOR
                                                         CATHODE
      Figure  1.
                   CONDUCTING  GRID IN
                   ELECTROLYTE/ANODE
                   COMPARTMENT

Hydrazine-air fuel  cell  module  with
  external connections.
298
                                           Automotive Fuel Cell

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Each electrode has an  active area of 62 square inches and is rated
at 44.5 amperes at a rated current density of 103 amperes per  square
foot.  Two cells in parallel deliver 89 amperes, which  is the current
carried  by each deck.  Twin decks in parallel carry 178 amperes at
28 volts and yield a 5-kilowatt rating. The module is shaped like a
box  with  overall dimensions of 9 by 9 by 22 V2 inches and a weight
of 95 pounds with electrolyte  (Figure 2).  At the 5-kilowatt  rating,
the power density is 4.38 kilowatts per  cubic foot, and the specific
weight  is  19 pounds per kilowatt.  Under  design  conditions about
700  watt-hours are  generated per pound of hydrazine  monhydrate
(about 90^, of ideal).  Figure 3 shows the average single-cell  polar-
ization curve, based  on  module tests.
. *
 Figure 2.   Five-kilowatt hydrazine-air  fuel cell  module.

    At rated power the average single-cell voltage is 0.78 volt, which
is about 48 percent of the thermodynamically reversible voltage for
the hydrazine/oxygen couple.  Thermal  efficiency  at this condition
is about 50 percent, based on the higher  heating value of hydrazine.

     THE  POWER PLANT IN THE M-37  ARMY TRUCK

    The power plant consists of three major elements:  the fuel cell,
with its controls and accessories; the electric motor;  and the motor
DANTOWITZ, GADDY
299

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0.90—< - —>
                                                 103 amp/ft2
                     CURRENT DENSITY, amp/ft-'

      Figure  3.   Average single-cell  polarization curve.
    40-kw
  HYDRAZINE
   HYDRATE
  FUEL CELL
  P.C.M.
CONVERTER
STANDARD D-C
   SERIES
   MOTOR
                               VARIABLE
                                 D-C
                               VOLTAGE
                               0 to 375
                                       o
                                                            X
                                                            bj
                          VARIABLE
                           TORQUE
                                       §5
                                       < ""
                                       co Q
                                 PROTECTION AND
                                 CONTROL LOGIC
                                         VEHICLE WEIGHT  6,000 Ib
                                         CARGO CAPACITY  1,800 Ib
                                         TOTAL           7,800 Ib
            FUEL TANK
   Figure  4.   The power plant  for  the M-37  army  truck.
  300
                                           Automotive Fuel Cell

-------
and vehicle control system.  Figure  4  shows a schematic block  dia-
gram of the power plant.

     At present, the fuel  cell is made up of four of the 5-kilowatt
modules described above with a full  load rating of 20 kilowatts.  The
modules are  mounted  on  a bedpost  frame,  which in turn is shock-
mounted on the truck  chassis under the hood (Figure 5).  Although
four modules have been used thus far, space for eight has been pro-
vided  and  much  of the system  is designed  for eight-module power
of 40 kilowatts. The modules are connected in series, giving a full-
load voltage of over 100 volts for the  four-module system and over
200 volts for the eight.
  Figure  5.   Four 5-kw  hydrazine-air fuel  cell modules
         installed  as power  plant  for M-37  truck.

    The installed fuel-cell-plus-accessory weight is 525 pounds for
four modules and 915 pounds for eight.  Four modules weigh about
340 pounds  dry.  The weight of electrolyte required to charge the
system is  100 pounds. The radiator, which is an air-to-electrolyte
heat exchanger, weighs about 45 pounds. The  latter is  a finned, tube
radiator,  very similar  to those found on many American cars. To
enhance ram-air  cooling,  an electric-motor-driven  fan is  provided.
Fuel is supplied intermittently by  a pump to the  electrolyte tank.
The "on" versus "off" time of the fuel flow determines the average
DANTOWITZ,  GADDY
                                                             301

-------
quantity of fuel delivered. This in turn is regulated by the voltage
on the terminals of one of the modules.  Furthermore, the control
voltage is a function of current and is highest at no load.  This ensures
good transient  performance  following  the sudden  application of a
large load despite the inevitable dip in voltage. Parasitic power drain
for the 40-kilowatt  system is about 600 watts.

    A  direct-current  traction  motor  is mounted  under the truck
body forward of the differential  that it drives.  The motor is rated
at a stall torque of  625 foot-pounds; starting current is 525 amperes.
The latter is a short-time rating only. The motor weighs 700 pounds,
and is  being  used at present only because of its availability.  To do
the same  job, a motor weighing  only  300  pounds  has  been ordered
and will very shortly be installed in the truck.

    The controller  for the motor  is mounted under the driver's seat.
The basic purpose  of  the controller  is to  convert  the  voltage  and
current output of the  fuel cell to that  required by the motor.  The
controller ensures that neither the operator  demand nor motor load
shall exceed  the power capability of the fuel cell.  Figure 6a shows
how motor  current,   voltage,  and  power  very  as a  function of
vehicle  velocity  following a full-throttle  start from  a standstill.
Figure  6b shows the  fuel  cell voltage and current on the same
scale.  In  the span marked A the controller  limits the  current to
the motor to 525 amperes.  Since  the short-circuit current of the
fuel  cell  is  about  2,500 amperes,  protection  is  clearly required.
As  the vehicle and  the motor  pick  up   speed,  motor  voltage  is
increased  to  maintain the current  limit.   At the  end  of  span A,
the motor power is equal to 40  kilowatts, which is  equal to the
peak fuel cell  power  (for  the  eight-module  installation).  During
the span  marked  B  the vehicle continues  to  accelerate  and the
motor  back  electromotive  force  continues  to  increase,  requiring
a higher voltage and  a  lower  current  to  maintain constant power.
Note that during span B the motor voltage is first below and then
above the fuel cell voltage,  requiring  a controller with  both step-
down and step-up capabilities.  At  the  beginning  of  span  C the
vehicle  has  reached its  maximum  speed  and  no further change in
voltage, current, or power occurs.  The  present  controller weighs
300 pounds,  but  a  redesigned version that  weighs 150 pounds  will
soon be installed.

      The peak acceleration  of  the  vehicle  equipped  with four
fuel  cell modules  and a supplementary  lead-acid battery pack  is
compared with that  of a truck  equipped  with the  standard 94-
horsepower  gasoline  engine  in Figure 7.  With only  20 kilowatts
of fuel cell capacity the  truck readily climbed grades of 20 percent.
The  maximum  speed on  a good  level  road  was  47  mph.  Fuel
consumption  was between 10 and 15 miles  per  gallon  of hydrazine
menohydrate; that  of a standard M-37 vehicle is 7 miles per gallon
of gasoline.  The reliability  of the  fuel cell has been  good  in the
120 hours it has been used.
302                                          Automotive  Fuel Cell

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                                                375 volts
  (b)
                         224 volts
                          180 amp
                      VEHICLE VELOCITY
  Figure 6.   (a)  Motor  current,  voltage,  and  power as
 functions of  vehicle  velocity,  and  (b)  fuel  cell  voltage
         and  current  as a  function of velocity.
DANTOWITZ, GADDY
                                                        303

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     UJ
     Q.
94-hp  GASOLINE ENGINE
      WITH GEAR  SHIFT
                              TIME

    Figure  7.   Comparison  of acceleration  of electric-
             and gasoline-powered M-37 truck.


              SIGNIFICANCE OF THE PROJECT

    As  installed in  the truck  the hydrazine-air  fuel  cell  system
(excluding  the  motor  and controller)  gives a very  high  energy
density, nearly  350 watt-hours per pound for an  18-hour mission.
For an  eight-hour mission the energy density drops to  210 watt-
hours per pound, still  much  higher  than  is offered by  any other
readily  available  system.   The successful operation of  the M-37
truck with  a system having  such a  high power  density must  be
considered an important step  forward in  the practical  application
of fuel  cells.

    Using the hydrazine-air system,  the  Army has gained valuable
experience in the operation and control characteristics of an electric
vehicle. The relative simplicity and  ease  of  operation of this large
hydrazine-air fuel cell power plant has  been demonstrated by over
100 operating hours in the  truck.

                  FUTURE DEVELOPMENTS

    We have seen that a start has  been  made  in applying fuel
cells to automotive  use.  To  make further progress, research and
development efforts  must  be  continued  and  intensified.  These pro-
grams have been split  into short-range  and long-range  efforts for
which successful completion is visualized  in  2 and 5 years, respec-
tively.
304
                                            Automotive Fuel Cell

-------
     The  highest  priority short-range program is the minimization
 of  the use  of platinum in the  electrodes.   With  two  5-kilowatt
 modules  as  they presently exist,  and reasonable  reclamation  and
 capital costs for the  platinum,  annual  expenditure  of  well over
 $500 is incurred by the use of precious metal.  This figure probably
 must be  reduced to around $100  per year for wide acceptance by
 the  public.  Monsanto has already  demonstrated  the feasibility of
 achieving such a light platinum  loading.  Much  work  remains to
 be  done,  however, to optimize the platinum  loading and to reduce
 the resulting electrode to a practical, reliable, and durable component.

     Improvement of  reliability and durability  of the fuel cell  is
 second  on the priority list.  In concept the fuel  cell promises to be
 highly reliable and very durable, matching and ultimately exceeding
 the  lead-acid battery in these respects.  Although the fuel cell of
 today has not lived  up to this promise,  in  a relatively short time
 great improvements have been made.  Most first-order failure mecha-
 nisms have been identified  and eliminated  so that 1,000  hours of
 life  is common  on a single cell. Since a practical fuel cell battery
 contains 30 or  more cells in a series,  the problem of battery  life
 is more severe than that of a single cell.  Consequently, much work
 needs to  be  done to identify second-order life-limiting phenomena
 and to  find  ways to  extend life  and reliability.  A goal of 1,000
 hours of  stack life is  reasonable for the short term,  since it would
 give  the  average  motorist 2 to 3  years  of operation.

     Third priority for the short term is reduction of specific weight.
 Engineering studies  have shown that a  10-kilowatt fuel cell module
 weighing  only  75 pounds can  be  developed  in the  short  term.
 Although  optimistic, this  goal  can  be reached  by  the  application
 of sound  engineering principles in  a  disciplined design effort.

     If all three of these goals are met, an  attractive  first-generation
 fuel-cell  power  plant will  result.  An  annual  market  of 25,000
 units of 10 kilowatts  each  could very well be captured by such a
 machine.  A  2,000-pound  vehicle  so equipped would use  about  a
 pound of  hydrazine for every 5  miles.   If  each vehicle  traveled
 an  average of  15,000 miles per year, the total annual consumption
 of hydrazine would be  75  million  pounds  per year  at the end of
 the first year and 150 million  pounds  per year at  the end of  the
 second.  Without a  doubt, production rates  this  high would bring
 the price  of hydrazine down.  How far down is  a matter of specu-
 lation, but it appears  possible  that  with a high enough demand the
 price could be reduced to a level roughly competitive with  gasoline
prices.  The  retail hydrazine sales volume would  be several mil-
lion dollars a  year,  sizeable enough to warrant appreciable plant
investment.

    Because  the early realization  of all the goals just  described is
unlikely,  only  an extreme optimist would cite such a probability.
The main point is, nevertheless, that the fuel-cell-powered vehicle,
even  for  the short range, remains  a possibility.
DANTOWITZ, GADDY                                        305

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    If the  hydrazine  industry does  not  meet  the challenge  of
achieving a  competitive  price, a  cheaper  fuel  will have to  be
found. Much of the work done on the  hydrazine system  will  be
applicable  because the  air cathode  will  still  be  used.   A  possible
alternative to  hydrazine  is hydrogen obtained  by  on-board  con-
version of  one of the following: saturated hydrocarbon, methanol,
or ammonia.
    In each  case the annual  cost of fuel  for  15,000  miles of travel
would be less  than  $300  (a 2,000-pound vehicle dissipating  160
watt-hours per mile at the wheels).  Production of hydrogen by any
of the three  methods offers no scientific obstacle.  That is, processes
and  materials  such as  catalysts are well  defined and  have been
reduced  to practice.  It  remains to engineer the  best of them into
a practical, lightweight hydrogen generator for  use in an automobile.
Logistic  considerations allow  only liquid  saturated hydrocarbons to
be considered for widespread military use.

    In moderate quantities, production of fuel  cells with minimized
platinum loading  could  be easily  sustained by present  production
of the precious metal.  If the  fuel  cell is to  replace the  internal
combustion  engine to a  significant degree, however, then  a  long-
term  goal must be elimination of the use of platinum-group metals
in the fuel cell.

    Finally,  the ultimate objective of every fuel  cell  researcher
is the direct  oxidation of a low-cost liquid fuel. It has been demon-
strated that under the proper circumstances saturated hydrocarbons
can be  electrochemically  oxidized at appreciable rates.   Thus  far,
however, this has been  accomplished by using far  more platinum
(and  other  platinum-group metals)  than  can  be  tolerated for the
application under discussion.  Furthermore, the  power  density of
the cells produced has been very  low,  and therefore power plants
utilizing  them would be expensive,  heavy, and  bulky. Research
continues on direct  oxidation  of liquid  saturated hydrocarbons to
reduce the  platinum  loading  and  to  increase the power  density,
and thus decrease the cost, weight, and size of the resulting power
plant.  Many are convinced that for  nonmilitary use a more timely
consummation  of a practical  fuel  cell can  be  achieved  by  using a
fuel  that is more active  electrochemically than the  saturates.  The
two most important candidates are methanol and ammonia. These
fuels  are reasonably  priced for  automotive use; both are  plentiful
and  can  be  readily  stored and distributed.

    It has been demonstrated  that fuel  cells  for automotive  use
are a possibility.  The  chances for success depend upon the level
of support the  research  and  development  effort  gets.  A  vigorous
and determined program could very well make  the fuel cell automo-
bile a reality in  the  1970's.
306
                                             Automotive Fuel Cell

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   DIRECT  HYDROCARBON AND METHANOL-AIR
                         FUEL  CELLS
                   C. E. Heath, E. H.  Okrent,
                   M.  Beltzer, and  G. Ciprios

            Esso Research and Engineering Company
                          Linden, N. J.

    The  fuel cell has been proposed as a  potential solution to the
problem of automotive exhaust emissions. Such a power plant would
not be subject  to the limited range of  battery vehicles and would
serve a broader spectrum  of transportation needs.  The specific re-
quirements for  an automotive  fuel cell  power  plant have not  been
defined; however, as a first approximation a fuel-cell-powered vehicle
should at least  approach the performance  capability of the conven-
tional vehicle.  For  simple control,  reliability,  ease  of  start-up, and
adaptability to  a variety of driving  conditions, system complexity
should be avoided.  Thus, direct fuel cells are preferred to indirect
systems.  Although  high efficiency will reduce  operating costs, this
economic advantage would be quickly  offset by a fuel cell  that con-
tains costly components  and materials.  A practical fuel cell power
plant should use a readily handled, inexpensive fuel and air as the
reactants. Finally, if the fuel cell is to provide a solution to exhaust
emissions, the fuel  cell reactions should yield  inoffensive  products;
unconverted fuels and intermediates should be contained.

    Fuel cell research at Esso Research, although primarily aimed at
the development of military field generators, has identified some of
the problems that must be solved before  fuel  cells can meet  these
requirements.  This program includes  work on direct liquid hydro-
carbon and methanol-air fuel cells.  Both  fuels satisfy  the require-
ment of a readily handled inexpensive  fuel, but the higher cost per
Btu  of methanol  places  a  greater premium on high efficiency than
necessary for hydrocarbons.

    Substantial progress has been made on the development of hydro-
carbon fuel cells (Figure 1). Since 1959 when direct electrochemical
oxidation of ethane was first demonstrated in our laboratories (Heath
and Worsham,  1963), hydrocarbon  fuel cell power density has been
dramatically increased. A modified Bacon cell operating on ethane and
oxygen sustained  1.5  watts  per  square  foot at  400°F and 20
atmospheres. The voltage was 0.2 volt. In  1966, an octane-air fuel
cell,  operating at  525°F and atmospheric pressure generated 90  watts
per square foot at  0.5  volt.  The early  porous electrode required a
complex differential pressure control mechanism to maintain the fuel-
electrolyte-electrode interface.  Current electrodes, based on a  cata-
lyst-Teflon matrix, are not flooded  and can be designed  for either
HEATH, OKRENT, BELTZER, CIPRIOS                       307

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vapor or liquid reactants. Finally, the early work used a 30 percent
KOH electrolyte, which obviously would not remain invariant.  The
present cells all use CO2-rejecting acid electrolytes.
  l.Or
  0.8
  0.2
               1967
               OCTANE-AIR
               PYROPHOSPHORIC ACID
               268°C, 1 atm

1959
ETHANE-02
KOH
208°C, 20 atm
                                        I
               100         200         300
                    CURRENT DENSITY, ma/cm2
                                     400
500
      Figure 1.   Progress  in  hydrocarbon  fuel cells.

    These performance levels have  been achieved under conditions
that ensure rapid electrochemical oxidation and high current densities
— heavy catalyst loadings and temperatures of 500°F.  The fuel elec-
trode catalyst was platinum at 50 milligrams  per  square centimeter.
The catalyst  loading can be reduced by a carbon support, but at the
expense of some performance. For  example,  a butane-air  fuel  cell
with total catalyst loadings of 3.2 milligrams per square centimeter
for both electrodes yielded 53 watts per square foot. The temperature
was 525°F.  Thus, catalyst utilization was increased  from 0.7 to 17
milliwatts per milligram.  Other  supports have  been investigated,
but show no major advantage over carbon.

    High power densities can be obtained only at temperatures above
300°F. Although phosphoric acid is suitable up to 300°F, new electro-
lytes are needed for higher temperatures. Two new electrolytes now
under development make it possible  to reach increased power levels.
One, pyro-phosphoric acid, is similar to the aqueous systems investi-
gated in the  past and does not require  special electrodes.  However,
it is highly corrosive and new materials are needed. The other, mixed
alkali phosphates,  is not corrosive, but because of its viscosity will
require development of specific electrodes.  The current performances
of these and the conventional electrolytes are summarized in Table 1.
308
                                   Hydrocarbon  and Methanol-Air

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          Table  1.  HYDROCARBON FUEL CELL PERFORMANCE
                    IN  DIFFERENT ELECTROLYTES"

                                           Electrode polarization from
                                           theory,b v at 100 ma/cm2

      Electrolyte              Temperature, °F   Butane       Oxygen
H,S04
H3P04
Pyrophasphoric acid
Mixed alkali phosphates
205
300
480
480
30 ma/cm2 max.
0.35
0.18
0.27
0.35
0.30
0.08
0.18
aThese data are based on runs of several hours. During prolonged operation
 electrode structure can deteriorate through thermal stressing.
bPlatinum catalyst loading:  50 mg/cm2 at each electrode, except 0., in
                        H,S04 (20 mg/cm2).

    Obviously, a fuel cell power plant will consist of more than the
basic module.  The hydrogen-oxygen automotive fuel cell power plant
recently demonstrated by  General Motors contained  1,485 pounds of
auxiliaries, almost twice the weight of the conventional engine (SAE,
1967).  A decane-air battery system was developed and  constructed
in our laboratories to determine systems problems that must be faced
in a direct hydrocarbon fuel cell battery  (Okrent and Heath, 1967).
This system included auxiliaries for water balance, fuel and air circu-
lation, electrolyte concentration control,  and other necessary  func-
tions.  Although this system was not engineered as a prototype, this
study confirmed that auxiliaries would represent a substantial portion
of a practical power plant.

    The study also  indicated the  problems that  would be  faced in
using  practical hydrocarbon fuels.  The electrodes were designed for
use with decane.  Although equally effective  for vapor  and liquid
phase fuel,  the  electrodes  are sensitive  to  molecular weight.  Low-
molecular-weight hydrocarbons will diffuse through the structure into
the electrolyte chamber. When a wide-boiling-range  fuel is supplied,
some  light ends will cross to the cathode, give rise to a mixed poten-
tial, and reduce cell voltage.  This effect was  illustrated  by experi-
ments in a  three-cell  hydrocarbon battery  in which decane, the re-
search fuel, was replaced  with  a commercial jet fuel, OTF-90 (Sup-
plied  by  Humble Oil and Refining Co.).  This fuel  is a  low-sulfur
isoparaffmic fuel with a boiling range of 195° to 290°C.  As shown in
Figure  2, performance declined to  30 percent of that of decane. In-
spection of  the cells indicated that the fuel had diffused through the
anode.

    Based  on these  studies,  preliminary  projections  of  complete
hydrocarbon-air fuel  cell  power  plants  can  be made.  Projected
HEATH,  OKRENT, BELTZER, CIPRIOS                        309

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weights can be compared with the weight of the total fuel cell power
plant used  in the General Motors Electro van (Table 2).  This power
plant was rated at 21 pounds per kilowatt.  The hydrocarbon-air fuel
cell,  if built with today's technology, would clearly exceed the weight
and  volume of the hydrogen-oxygen battery, which itself was  ex-
cessively heavy.  The noble metal  catalysts alone preclude economical
application of the direct hydrocarbon fuel cell as an automotive power
plant.  The  search for active non-noble metal substitutes has been
under way  for 5 years. Many leads have been followed to extinction;
new  leads are being uncovered.  The nature of catalyst research makes
it impossible to predict when a suitable material will be found.

    Methanol  is  considerably more active than hydrocarbons and
might be considered for this application.  Much progress has been
made in improving this activity (Figure 3).  Methanol fuel cells have
yielded power densities as high as 50 watts per square foot at 160°
to 190°F in short  laboratory tests. However, it should be emphasized
that  deterioration occurs  and further  research  will  be  required to
maintain this performance. The low temperature activity would make
the methanol cell easier to start than the hydrocarbon cell, but it is
inadequate for an automotive power plant. Attempts to improve  the
power density significantly further by increasing  cell temperature
have been unsuccessful thus far, although the approach deserves more
consideration.
                                DECANE
                                MAXIMUM POWER 3.0 watts
                                      MAXIMUM POWER
                                      1.1 watts
COMMERCIAL JET FUEL
      (OTF-90)
                            1.0          1.5
                           CURRENT, amperes
        Figure  2.   Wide-boiling-range fuels  reduce
                    fuel  cell  performance.
310
                                   Hydrocarbon  and Methanol-Air

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   Table 2.  COMPARISON OF WEIGHTS OF COMPLETE  HYDROCARBON
        FUEL  CELL SYSTEMS, ELECTROVAIR POWER PLANT, AND
                      CONVENTIONAL  ENGINES.
                           System power density,"
                                  Ib/kw
Catalyst quantity,
     g/kw
 High-performance hydro-
     carbon fuel cell systemb         50 to 70
 Low catalyst loading
     hydrocarbon fuel cell
     systemb                      65 to 90
 GM Electrovan power plant                21
 Conventional engine                 8 to 12
     1,600
       60
"Fuel  cell  power  plant densities do not include electric  drive.  GM  system
 drive weighed 3.4 Ib/kw.

bBased on  fuel cell size.  Higher power densities are based  on  5-kw  design,
 lower on 30-kw systems.
                                                    T
                                     H2S04 60 to 95°C
                                 NOBLE METAL CATALYSTS
                              1967 SHORT-TERM
                                LABORATORY
                             40          60
                     CURRENT  DENSITY, ma/cm2
              100
       Figure  3.   Methanol — air fuel  cell  improved
             but noble  metal  catalysts  needed.

    The question of  whether the fuel cell can  reduce  air pollution
cannot be conclusively answered yet.  Direct hydrocarbon cells, oper-
ating at temperatures below 500°F, appear to offer no serious source
of contamination. Studies have shown  that  hydrocarbons are com-
pletely  consumed to carbon dioxide and water in sulfuric acid elec-
trolytes at 90°C.  Fuel cell fuels will probably be  sulfur and lead-free.
HEATH, OKRENT, BELTZER, CIPRIOS
             311

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Furthermore, the low temperatures  should  minimize nitrogen oxide
formation.  Hydrocarbon losses from manifolds and tanks may cause
a problem,  but using low vapor pressure fuels and proper engineering
should minimize  this contribution.  No  major  obstacles to a low-
emission vehicle are known, but clearly  much more experience will
be required to define pollution levels in operative systems.

    From this discussion it is evident that the present state of hydro-
carbon fuel cell technology cannot meet the requirements of a high-
output, low-cost system suitable for extensive  vehicular application.
Much progress has been made during the past 5 years.  If this progress
continues and suitable catalysts are developed, a fuel-cell-powered
vehicle could become practical. However, much more research and
development will be needed before this stage is reached.

                     ACKNOWLEDGEMENT

    Much of the work  described in this paper was made possible
through the support of the U. S. Army Electronics Command and the
Advanced  Research  Projects  Agency  under  Contracts  DA 36-039
AMC-03743(E) and DA-28-043 AMC-02387(E).

                          REFERENCES

Heath, C. E., and C. H. Worsham, 1963.   Fuel  cells (Vol.  2).  G. J.
    Young, Ed. Reinhold, New York, N.Y.
Okrent,  E.  H., and  C. E. Heath,  1967, A liquid hydrogen  fuel cell
    battery. Presented at Fuel Cell Symposium, American Chemical
    Society National Meeting.  Chicago, 111. September 10-15.
Society of  Automotive Engineers, 1967  (Jan.  13).  C. Marks,  E. A.
    Riskavy, and F. A. Wyezalek. Electrovan — a fuel cell powered
    vehicle. SAE Paper No. 670176.
                                  Hydrocarbon and  Methanol-Air

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               HYDROGEN-AIR  FUEL  CELLS
                FOR VEHICLE PROPULSION
                            G. E. Evans

                    Union Carbide Corporation
                           Parma, Ohio

     A  very large  variety of power sources have  been proposed  for
 the future electric vehicle.  In  broad terms  they can  be divided
 into two classes—rechargeable batteries and fuel cells.  Rechargeable
 batteries   include  conventional  types  such  as  lead-acid, nickel-
 cadmium,  and silver-zinc,  and  newcomers  such  as  rechargeable
 metal-air,  sodium-sulfur, and lithium-halogen  types.  Fuel cells  in-
 clude the  well-known  hydrogen-air types, direct  or indirect hydro-
 carbon-air types, and a large variety of miscellaneous types burning
 hydrazine  or other even less common fuels.

     In  general,  rechargeable batteries  are  characterized by  high
 power  density (watts  per pound)  and  low  energy density  (watt--
 hours  per  pound).  The converse is true of most fuel  cells:  they
 offer high  energy density, but usually at  a sacrifice in power density.
 Since  Union  Carbide Corporation  manufactures  both  rechargeable
 batteries and fuel  cells, we can  be impartial in  judgment, and in
 fact, what we will propose  is a  hybrid  system: a  fuel cell with a
 very high  energy density to provide long driving range  and  rapid
 refueling,  and a rechargeable  battery to supply  peak loads.

    When  discussing a proposed power  source, it is  important to
 define  and weigh  the  requirements,  so  as to  avoid the  danger of
 sacrificing  life for  low  initial cost,  or  safety for power  density.
 The following objectives or performance  goals for  a vehicular power
 supply  have  been  used in  arriving  at  the proposed  system;  not
 necessarily in order of importance:

    1.   High  power density, e.g., at least 40  watts per pound;

    2.   High  energy density, e.g., at least 40 watt-hours  per pound.

    3.   Freedom from  harmful emissions.

    4.   Low initial capital cost, rather arbitrarily set at a  maximum
        of  twice the price of an internal combustion engine vehicle.

    5.   Low fuel cost,  comparable  to  the price of  gasoline.

    6.   Low maintenance costs.

    7.   Long  life—as a  yardstick,  the  power  plant should last  at
        least  as long as the body.

    8.   Safety; last but not  least, the electric vehicle should provide
        greater safety on the road than the present gasoline vehicle.
EVANS                                                        313

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    A  package consisting of a  hydrogen-air fuel  cell,  using cryo-
genic hydrogen as fuel, and a rechargeable battery for  peak power
appears to be a leading contender for meeting  these requirements
in the near future.  The operational characteristics  of the hydrogen-
air  system  make  it  more suitable  for industrial  or  commercial
vehicles—delivery trucks  and vans, city  buses, taxicabs, etc.—than
for the private  automobile.  Thus,  we visualize  the hydrogen-air
fuel  cell as a practical power source for industrial and commercial
fleets of vehicles within  the  near-term  future, whereas improved
rechargeable  batteries may more readily meet the needs of lightweight
electric vehicles for use  as private automobiles  under  short-range,
urban  driving conditions.

    In the following discussion,  the present status and future poten-
tial of  hydrogen-air fuel  cells will be  discussed in the  light of the
above eight objectives. It is important to remember that these eight
objectives must  be met  simultaneously:  there is  little merit  in  a
system that  offers high power density  at the risk  of safety or long
life at  the expense of exorbitant cost.
                    CONCEPTUAL DESIGN

    Many  of the  advantages of the hybrid hydrogen-air fuel  cell
can be made more explicit by considering an actual vehicular system.
For this purpose we have started with the General Motors Electro-
van as a baseline.  The performance of  this vehicle, as well as the
detailed weight  and volume breakdown  of its components, has been
fully  documented  in a series of papers presented to the SAE  Auto-
motive Engineering Congress this  past  January.  As a short-term,
state-of-art approach, we have simply looked  at the problem of
replacing  the  hydrogen-oxygen fuel cell of the  Electrovan  with a
hydrogen-air fuel cell plus a rechargeable battery.

    Based  on  Electrovan performance data, a hybrid fuel cell sys-
tem  has been  sized to  provide 32 kilowatts  of continuous  power
and 160 kilowatts  of peak power. A weight breakdown of  the hybrid
system is  given in Table 1.

    In SAE Paper No. 670176,  Marks et al. (1967) mention that a
"production model" Electrovan could weigh  at least  1000  to 1500
pounds  less than the prototype model, by elimination of experi-
mental instrumentation and through normal engineering optimization.
Any  such  weight  savings are  in  addition to  the gains  shown in
Table 1, which result from  use of a different  type  power  source.
For example, Table 1 shows a weight of  164 pounds for the hydrogen
supply,  of  which  128 pounds is the weight of  the actual fuel tank
aboard the Electrovan. As a  conservative estimate, a fully optimized
hydrogen  fuel  tank for this  vehicle  will weigh no  more than 80
pounds.
314                                      Hydrogen-Air  Fuel Cells

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Table 1.  COMPARATIVE WEIGHTS OF ELECTROVAN AND FUEL CELL POWER
                       PLANT COMPONENTS
                           (in pounds)

Fuel cell stacks
Peak power battery
Fluid system
Fuel and fuel tankage
Oxygen and oxygen tankage
Electric system
Electric motor drive and controls
Power train total
Electrovan
1,345
—
1,097
164
208
569
550
3,933
Hybrid system—
this study
690
427
704
164
—
380
550
2,915
    The  weight of the fuel cell  stacks  is reduced  since  the  fuel
cell is no longer required  to handle  heavy overloads;  a hydrogen-
air system designed to a 32-kilowatt rating without overload require-
ments is  only about one half the weight and volume of a 32-kilowatt
hydrogen-oxygen system designed  to handle 160-kilowatt peak loads.
Reduced  fuel cell  volume produces corresponding reductions  in  the
weight and volume of  interconnecting plumbing, tankage, etc.  As
a result,  the 427 pounds added in  a  battery to handle peak loads is
more  than compensated for by reductions in fuel cell weight. Another
significant  weight  reduction results  from dispensing  with a 208-
pound liquid oxygen tank; only about one half of this weight need
be added on in air processing equipment aboard the  hydrogen-air
system.

    Table  2 lists the performance factors chosen for the Electrovan
system.  Simple replacement of the hydrogen-oxygen system of  the
Electrovan with the hybrid hydrogen-air system would give above-
target performance, because  of the lower power train  weight. This
permits design to a lower power  level,  or  alternatively  permits an
increase  in useful cargo weight.


                     Table 2.   PERFORMANCE

             Variable                               Electrovan

             Acceleration (0 to 60 mph), sec           30

             Top speed,  mph                         70

             Range, miles                           100 to  150
 EVANS                                                      315

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    Rather  than attempting  to  redesign  the Electrovan  to  a new
set of weight  figures,  a simpler way  is to  interpret the  data of
Table 1. The Electrovan weighs 7,100 pounds.  Table  1 shows that
with a  3,933-pound power train, 55 percent  of the  total  weight  is
required to  give  it the  design  performance of  Table 2.  With  a
hybrid hydrogen-air system, the same performance can be provided
in a 7,100-pound  gross  weight vehicle  with  a  power  train  weight
of 2,915 pounds,  or  41  percent of  the  total weight.  In  a recent
article  Hoffman  (1966)  indicated  that  up  to  50  percent  of  the
weight of an electrical vehicle could be assigned to batteries without
endangering utility;  by this criterion  the  Electrovan just  misses,
wherein the hybrid system is well  within the safe range.

    The data in Tables 1 and 2 are not  intended to project long-
range future goals, but rather to indicate  what can be  accomplished
in the  near future.   Our  longer-range  projections  are  far more
optimistic.

    Many criteria  other  than weight and power are  important in
evaluating a power system.  In the  following discussion,  the char-
acteristics of the  hybrid fuel cell  system are weighed against  the
eight  criteria previously listed.

High  Power Density
    Weights estimated for the  fuel  cell  of the hybrid system  are
based on a peak electrode power density  of about 75 watts per square
foot at  the  32-kilowatt  design point. This represents  performance
that  has been  achieved already in  smaller  multicell  hydrogen-air
systems. This electrode power density represents a reasonable design
goal for a number of nonnoble metal catalysts being investigated by
us and  in other laboratories. The trade-off  between  performance
and cost leads directly to the hybrid  system.  The many kilowatts of
peak power required for vehicle acceleration are most  economically
provided by a  rechargeable battery,  whereas  the  fuel  cell provides
instant  refueling  capability  and high  energy  density needed  for
an acceptable range in miles.

    The feasibility of the  hybrid fuel cell and rechargeable battery
combination was demonstrated  a few  months ago by  Kordesch in
a small motorcycle, using  a hybrid power plant employing an 800-
watt hydrazine-air fuel cell plus a set of nickel-cadmium 15-ampere-
hour  batteries.  No electronic  charge  controls were  necessary;  a
simple matching of the fuel cell and battery discharge characteristics
provided proper load-sharing.

    The rechargeable  battery employed in the hydrogen-air design
of this  study  has been  characterized  thus  far only  as  weighing
427 pounds,  and as being capable of delivering short bursts of power
up to  128 kilowatts. Several  of the rechargeable batteries presently
being proposed as the sole power source for electric automobiles
can meet or surpass this requirement; feasibility of the hybrid sys-
tem does not depend upon inventing a  new  battery  system.
316                                       Hydrogen-Air Fuel Cells

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High Energy Density

    The hybrid system contains 120 kilowatt-hours of energy  in the
fuel tank.  If  we  assume  that  storage  batteries  with an  energy
density of 50 watt-hours per pound become available for vehicle
propulsion use,  the  rechargeable  battery of the hybrid system can
store  an additional  21  kilowatt-hours  for a  weight of  427 pounds.
Since the power train weight is 2,195 pounds (including motors and
controls), this  gives  about  50 watt-hours per pound as the energy
density of the  total power  supply, including fuel  tank  and motors.

    The energy density  of  the  fuel  cell portion  of the system  is
about 77 watt-hours  per  pound.  If the fuel  tank size were doubled,
increasing the  range from  between  100  and 150  miles to  between
200 and 300 miles,  the fuel  cell  energy density would increase  to
about  140 watt-hours  per  pound, with  an  additional   140  pounds
added  to  the system weight.

    The use of the  rechargeable  battery for supplying  peak  power
provides  a  useful  fringe benefit; should  the  vehicle   run out  of
hydrogen,  the  battery will give about  20  miles  additional  range
to reach the next filling  station.

Freedom from Harmful Emissions
    The  absence  of noxious  exhaust fumes is perhaps  the most
obvious  and most  easily sold advantage  of  hydrogen-oxygen  or
hydrogen-air fuel cells.  The only  possible  reaction product, even
in  theory, is pure water.  By-product water  from Union Carbide
fuel cells has been checked  by the testing laboratory that  monitors
Cleveland's water  supply  and found to meet  U.S. Public  Health
Service standards for potable water.

     It might be argued, since we are proposing hydrogen-air systems
and commercial hydrogen  is produced largely  by steam  reforming
of  natural gas, that  we  are  simply  moving  the source of  pollution
from the vehicle back to the hydrogen manufacturing plant.  This
is not a valid  argument. A major hydrogen production plant can,
and does, cut down emission of atmospheric pollutants to a negligible
level,  using techniques that are  practical in a plant  covering city
blocks  in area, but  that would  be  totally  impractical to  apply to
each of millions of  individual vehicles.   For example,  even in the
long-range future when  fossil hydrocarbon fuels become unavailable
or  more expensive, the vehicle described  in  this study  could  be
operated on hydrogen produced  by  electrolysis of  water  by use of
nuclear electricity.

Low Capital  Cost
     The  question of initial  capital  cost for a  fuel cell installation
 has probably  limited  or at least confused  the growth of the  fuel
 cell industry more  than any  other item. Fuel  cell prices today  are
 quoted  anywhere  from about  $15,000  per kilowatt,  to  well over
 $40,000 per kilowatt, depending upon type.   A very large percentage
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of this cost is for labor.  There is scarcely a  component or part of
the Union Carbide fuel cell system  that  can  be purchased from  a
mass-production  supplier;  even such simple parts as pipe couplings
may have to be hand-crafted one at a time from bar stock.  Under
these conditions, the only  realistic gauge available for estimating
potential future prices is the cost of the materials that must be used.
Unfortunately, no studies  have been conducted in sufficient detail
to provide  quantitative information.  The following comments  are
intended  merely to set some qualitative guidelines.

    A fuel cell  system may be  visualized as  a  group of electro-
chemical cells plus a  group of auxiliary components such as pumps,
fans,  and  radiators.  These  auxiliaries can be made  of low  cost
materials  such as a variety of modern  plastics or nickel-plated steel
and in general are no more complex in design than the corresponding
pumps, fans, radiators, etc.,  of the internal combustion engine.  For
simplicity, then,  let us write off fuel cell auxiliaries as being com-
parable in  cost  to the corresponding  type of  equipment  required
to operate an  internal combustion  engine, and focus  attention on
the electrochemical cells, which represent the  largest unknown  in
the cost picture.

    The Union Carbide hydrogen-air fuel cell contains nickel, carbon,
and a variety of plastics such as polysulfone, epoxies, polyolefins, and
Teflon. Adding up all of the materials,  less catalyst, required for  the
32-kilowatt hydrogen-air  fuel  cell gives  a raw  materials  cost  of
about  $1,500,  or $50 per kilowatt.   This  estimate  is  based on our
present purchase prices for raw  materials, purchased in lots of  a
few hundred pounds  (or sometimes a few pounds)  per order.  There
is reason  to believe that a reduction in cost to one half this value
could  be  achieved under  mass-production conditions.  This  corre-
sponds  to a  figure  of  about  $1  per  pound  for  a  miscellaneous
assortment  of nickel, carbon, and plastics, which  seems intuitively
reasonable.

    In my earlier discussion of power  density, a conservative figure
of 75 watts per square foot was selected as the peak power density
for electrodes. This represents our judgment at Union Carbide  as
to the best power density achievable at the present state of the  art
without using precious metal catalysts, and for an acceptable life-
time.   Fabrication of  electrode stock  is  already   on  a  continuous
strip, semiautomatic  basis; full conversion to  a  high-speed auto-
mated production line is simply a matter of the  requisite production
engineering and  capital investment.

    We have  not discussed  two other problem areas: the controls
that  regulate motor speed and the motors  themselves.  The approach
used by General Motors in the Electrovan supplied a sophisticated,
but rather expensive, solution to the problem.  Not being manufac-
turers of  traction motors or motor controls, Union  Carbide will be
pleased to hear  of  any practical and economic  answers  to  these
problems  from specialists  in  the  field.  It is also  obvious that any
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electric vehicle powered  by a  direct-current source will have to
face and  solve the same problems.

     From this rather cloudy cost picture,  it appears likely  that a
hybrid  hydrogen-air fuel cell system will remain  more  expensive
than a  corresponding internal  combustion engine within  the  next
decade, perhaps  by  a  factor  of 1.5  to  2. A portion of  this  cost
differential can be written off against operating cost, a portion against
the advantages of silence, a portion against the necessity of air pollu-
tion control,  and  a  portion against the greater safety of a hydrogen-
fueled vehicle as  compared with  a  corresponding  gasoline-fueled
vehicle.

Low Fuel Cost

     One  of  the  advantages of  the  liquid  hydrogen  fuel  proposed
for the  hybrid system is  its low cost.  To establish a basis for  com-
parison, 1 pound  of  hydrogen  burned in a  hydrogen-air fuel cell
gives about  the same performance as 1  gallon  of  gasoline burned
in an internal combustion  engine.  In recent contracts,  government
agencies have purchased  liquid hydrogen for prices in the range of
20 cents per  pound. Projections indicate that full utilization of  plant
capacity with insured sales  to fuel  distributors could  lower the cost
to 10 cents per pound in large quantities.  This  corresponds to 10
cents per  gallon of gasoline, or in other terms, about  1 cent per
mile of travel for a 7,100-pound gross weight vehicle under urban,
start-stop  driving  conditions.  The  above figures  do  not include
road tax.   I am sure the  Government will find a way to tax  hydro-
gen when it is used  as a vehicular fuel,  but the  fuel cost will still
be  attractive.

Low Maintenance Cost

     Predicting maintenance costs  for a  system that has not  yet
been built invokes more  prophecy than  science,  but a few  clearly
defined maintenance  requirements can be foreseen.  Operation  of an
alkaline electrolyte fuel cell on air produces potassium  carbonate
from the  carbon  dioxide in the air. If  raw, untreated  air  is  fed
directly into an  alkaline fuel cell operating at high power density,
the buildup  of carbonate deposits on and in the cathodes can produce
a detectable  loss  of  voltage within a few days.  In order to  avoid
this problem, we extract a  majority  of the carbon dioxide from the
incoming  air in  a "CO2 scrubber," with the bulk  electrolyte  itself
used as the absorbent.  Laboratory experiments with small, 100-watt
hydrogen-air systems have shown  that we can get about 500  hours
of  operation before it  becomes  necessary to  discard the electrolyte,
flush out  the  system with  water,  and refill  with clean electrolyte.
Since 500  hours  of  operation  represents 15,000 miles  of  vehicle
operation at an  average  of  30 mph, this does not represent an
intolerable  maintenance  burden.  A  refill of KOH  electrolyte for
the present  32-kilowatt hybrid design would cost about  $38  (less
than !/4  cent per  mile).
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Long  Life
    The life of a fuel cell  is highly sensitive  to  the conditions  of
use and the criteria for failure; i.e., how much degradation in per-
formance can be tolerated before the system is  declared inoperable?
Under laboratory conditions, we  have operated small  fuel cell sys-
tems for over 50,000 hours of intermittent duty,  or  over 14,000 hours
of continuous duty, in the latter case at a time-average power density
comparable to that proposed here for the 32-kilowatt system.  Objec-
tively,  it must  be recognized that  these  are  "best results"—those
isolated results  that indicate merely that  a goal is attainable,  and
not that it has been routinely reached.  Consideration of the series-
reliability problem,  the fact that one bad cell  in  a stack can limit
its life, suggests several thousand hours of on-load time as a more
reasonable indication  of the state  of  the art.  We realize  that a
few thousand hours of life is not enough to provide the foundation
for large-scale use of hydrogen-air cells,  and  are  working  hard  to
bring  the  average  of  the  distribution up  to  the level  of  those
best results.

    The hybrid power source system contains  two electrochemical
devices; a fuel cell and  a rechargeable battery. Developing a suitable
battery for the hybrid system is a much  simpler task than developing
a rechargeable battery for use as the sole power source in an electric
vehicle.  In the  hybrid system,  the battery is subjected to very
shallow  discharges,  is  slowly recharged,  and  unless  the  operator
runs out of  hydrogen fuel, is never called  on for more than a small
fraction of its ampere-hour capacity. Any conventional rechargeable
battery available today shows long  life under  these use conditions,
and we foresee no major problem in meeting the  rechargeable battery
requirements of the hybrid  system.

Safety
    One of the  major  advantages  of  a  conversion  from gasoline
fuel  to cryogenic hydrogen  fuel  will be a reduced fire hazard  in
the event of  traffic accidents.  Weights assigned  to  the  cryogenic
tankage in the  hybrid  system are  based on the criterion  that  the
fuel tankage must not rupture unless impact is  so  severe that there
is no reasonable chance for survival of  the human occupants of the
vehicle.  Under  these  circumstances, the major hazard of concern
is  the  probability  that any resulting  fire  will   endanger nearby
humans, vehicles, or structures.  Upon  rupture and ignition of  a
liquid  hydrogen tank, the contents  vaporize immediately,  rising  in
a vertical  column of  nonluminous flame which   vanishes  within
seconds. In  contrast, rupture and ignition  of a  gasoline tank  results
in  the  flow  of heavy gasoline vapor and  liquid gasoline across  the
ground, acting as a spreading and persisting source of fire.  Further-
more,  the gasoline flame radiates far more infrared or heat energy
(because of incandescent carbon  particles  in the flame), leading  to
ignition  of nearby  structures or  personnel not  directly within  the
flame.   On the  basis of numerous experiments conducted  for  the
320
                                          Hydrogen-Air Fuel Cells

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government, the  deliberate  ignition of large  quantities of liquid
hydrogen unquestionably produces far less fire damage than ignition
of a comparable fuel value of gasoline.

    Union Carbide has been  engaged in fuel cell research for about
15  years now,  proving  in and  testing  hundreds  of kilowatts  of
hydrogen-fueled fuel cells.  In logging  over  5  million test  hours  on
fuel cells,  we have had  three small fires, each easily extinguished
and without injury or hazard to personnel.  More important, in each
of these incidents the causative factor could be traced to the use of
pure  oxygen.  In  a  pure  oxygen  atmosphere almost  anything  is
flammable  (and hydrogen in  particular).  We do  not  propose the
use of cryogenic oxygen in the future hybrid fuel  cell system for
this reason  (but also  because the use of oxygen would approximately
double the  operating cost per  mile).

    It is also noteworthy that our  15-year record  of handling  large
quantities  of liquid  and  gaseous  hydrogen  without  a hazardous
accident has been accomplished without our having to invoke extreme
safety measures  that might  be impractical to  apply in commercial
practice.  For example,  we  do not smoke while transferring liquid
hydrogen.   Neither  should  a filling  station  attendant  when  he  is
transferring gasoline.

    Another problem  related to  safety concerns  the  handling  of
boil-off  from  the cryogenic  hydrogen tank  while  the vehicle  is
garaged.  This problem is  easily  solved in the hybrid hydrogen-air
fuel  cell  vehicle,  especially  for   commercial  fleet  users  such  as
delivery trucks, buses and taxicabs. Such vehicles see heavy service
5  to  7  days every week. Over night or weekends  the  boil-off  gas
is simply supplied to the  fuel cell, providing the fuel energy required
to  restore the  rechargeable battery to full  charge  and maintain it
there on trickle charge.   This answer  is not  as directly applicable
to  the personal automobile, whose owner may leave it  garaged  for
a  month's vacation.

    As a further safety precaution, any garage in which  fuel cell
vehicles are stored  should be ventilated, to  avoid hazard in  the
event of  fortuitous  hydrogen leakage  from a  defective  system.
Adequate ventilation can readily be provided, indeed is often already
available,  in large  commercial garages of the sort used to  store
fleets of buses, delivery  service vans, taxis, etc., but is not usually
available in garages  for the personal automobile. This again suggests
that  the first application of  fuel  cell vehicles can  be to commercial
types.

                 SUMMARY  OF ADVANTAGES

     In  comparison  with the  internal-combustion-powered vehicle,
 the hybrid hydrogen-air vehicle will produce no  air pollution, will
 operate silently,  will operate at  a comparable fuel cost,  and will
 provide similar'acceleration,  speed, and  range.
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    In comparison  with the rechargeable-battery-powered vehicle,
the hybrid hydrogen-air  vehicle will provide  greater range (as a
result of higher energy density)  and will  permit instant "recharge"
by filling the fuel  tank.  This  ability  to  refuel  quickly  is  a very
important advantage.  The vehicle discussed  in this paper requires
140 kilowatt-hours  of stored energy to achieve the desired range. If,
as it has been suggested, the battery electric vehicle is to be recharged
in 15 to 30 minutes while parked,  this would call  for  a 280- to
560-kilowatt,  direct-current  charging station;  definitely  not a job
for an extension cord.  Consideration  of  charging problems again
suggests  that  the hybrid  vehicle may offer  competitive  advantages
in heavy-duty vehicles with high energy storage requirements, such
as buses and  trucks, whereas the  battery-powered vehicle may be
more  competitive in lightweight personal  cars.

    In comparison  with  the  vehicle powered  by  the  "pure"  fuel
cell the hybrid  system offers lower  weight,  lower cost, an energy
reserve in case the  vehicle runs out of fuel, and a means of utilizing
hydrogen boil-off in a safe  and effective manner.
              SUMMARY OF PROBLEM AREAS

    The following areas require investigation and development before
a vehicle powered by the hybrid hydrogen-air fuel cell can  become
a reality:

1.   Improvement in quality  and uniformity of  electrodes and fuel
    cell stacks to permit the  consistent achievement of long life at a
    power  density  of  at least  75  watts per  square  foot,  without
    increasing cost.

2.   Development of a low-cost rechargeable battery offering  at least
    50 watt-hours per pound  and  capable of  at least short bursts
    of power at a 128-kilowatt rate.

3.   Development of inexpensive, lightweight motors and motor con-
    trols.  This problem  is a common one for any type  of  electric
    vehicle. Both fuel cells  and batteries can provide high  voltage
    only by coupling a large number of cells in series.   Any  elec-
    trochemical  power source  can  be made lighter, more compact,
    and more reliable by  reducing the number  of  series elements
    to a minimum.  Furthermore,  the voltage  across the  cells of a
    battery or fuel cell remains "on," even  after the  power supply
    switch  is  turned  off.  At  high voltages,  this  can  present a
    serious hazard to personnel. Either  of the  above reasons pro-
    vides a strong incentive to design motors  and  controls to  the
    very lowest  voltage consistent with a tolerable weight and cost.

4.   The specific  32-kilowatt  hybrid system discussed  here has been
    presented as a conceptual design, with only a first-order approxi-
    mation of weights  and  other  characteristics. An actual engi-
    neering design study needs to  be conducted in  sufficient detail
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    to  permit an  accurate  appraisal  of  system characteristics.  In
    turn, this information will permit more meaningful  intercom-
    parisons  between vehicles  powered with a fuel  cell,  a  battery,
    and an optimized hybrid combination.

5.   Upon arriving at a design projecting desirable and competitive
    characteristics, one  must build and test a prototype. No amount
    of  paper  studies can provide the engineering advances achieved
    during  the building and testing of hardware.

                          REFERENCES

Hoffman,  G.  A.,  1966.  The  electric automobile.  Sci.  American.
    215:34-40  (Oct.).

Society of  Automotive  Engineers,  1967  (Jan.  13).

    E. R.  Rishavy,  W.  D.  Bond,  and T. A.  Zechin.  Electrovair—
        a  battery electric  car.  SAE  Paper No. 670175;

    C. Marks, E. A. Rishavy, and F. A.  Wyczalek.  Electrovan—
        a  fuel cell  powered vehicle.  SAE  Paper No. 670176;

    P.  D.  Agarwal  and  T.   M.  Levy.  A high performance  AC
        electric  drive  system.  SAE  Paper No. 670178;

    F. A. Wyczalek, D. L.  Frank, and G. E.  Smith. A vehicle fuel
        cell  system. SAE  Paper  No. 670181;

    C. E.  Winters and  W. L. Morgan.   The hydrogen-oxygen thin
        fuel cell  module.  SAE Paper No.  670182.
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