APTD-1346
Final Report
LEAD/ACID BATTERY DEVELOPMENT FOR
HEAT ENGINE/ELECTRIC HYBRID VEHICLES
November 1971
Prepared for DIVISION OF ADVANCED AUTOMOTIVE
POWER SYSTEMS DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
Ann Arbor, Michigan
Contract No. EHSH 71-009
By
J. Giner
A.H. Taylor
F« Goebel
Tyco Laboratories, Inc.
16 Hickory Drive
Waltham, Massachusetts 02154
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Final Report
LEAD/ACID BATTERY DEVELOPMENT FOR
HEAT ENGINE/ELECTRIC HYBRID VEHICLES
November 1971
Prepared for DIVISION OF ADVANCED AUTOMOTIVE
POWER SYSTEMS DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
Ann Arbor, Michigan
Contract No. EHSH 71-009
By
J. Giner
A.H. Taylor
F. Goebel
Tyco Laboratories, Inc.
16 Hickory Drive
Waltham, Massachusetts 02154
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FOREWORD
This report contains a summary of work performed by Tyco Laboratories for the
Divisionof Advanced Automotive Power Systems Development, Environmental Protection Agency
under Contract No. EHSH 71-009.
iii
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ACKNOWLEDGEMENTS
Problems associated with the development and operation of a high power density lead acid
battery were discussed with Mr. John Nees of N.L. Industries (Heightstown, N.J.), Dr. Everett
Ritchie of I.L.Z.R.O. (Joplin, Missouri), Mr. Cooke also of I.L.Z.R.O. (New York) and Mr.
Rooney of W.R. Grace Co. (Cambridge, Mass.). Information and materials resulting from
these discussions were used in the course of the contract, and we would like to thank these
gentlemen and also Mr. Bob Bowen of Tyco's Mule Battery Division for their help. The helpful
discussions with our contract monitor, Mr. Charles Pax (Ann Arbor, Michigan), and, with Dr.
Mark Salamon (D.O.T. Cambridge) and Mr. Bill Robertson (NASA Lewis) are also appreciated.
We would also like to acknowledge the work of Mr. L. Gaines (Tyco Laboratories, Inc.) in the
development of preliminary concepts and calculations for the bipolar plate and modular battery
system.
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ABSTRACT
A program has been undertaken to develop a lead acid battery system for use in a hybrid
heat engine/electric vehicle. The basic requirements are that the battery be capable of supplying
high rate power pulses and of accepting high rate charge pulses, both of short duration. The
maximum power ratings specified are for 92.5 KW for a 10 sec period with an average maximum
power output of 70.5 KW over a 25 sec period. The maximum recharge rate is 39 KW and in the
most severe cycle 980 Whr of energy are transferred to or from the battery. A five year life-
time is envisaged and the battery must withstand a total of 200, 000 cycles but not all at the above
high rates. The minimum working voltage is 200 V with a minimum of 1.5 V/cell. The preferred
battery weight is 450 Ib maximum with a projected cost of no greater than $550.
The feasibility of developing a bipolar lead acid battery system which conforms to these
specifications has been investigated using a modular approach to system design. The candidate
test plates, herein defined as "quasi-bipolar" plates, are approximately one-sixth full scale and
have a thermoplastic substrate as active material support. In the preferred design, a vertical
array of lead strips placed on either side of each substrate are connected with adjacent .strips
on the opposite side only over the top of the substrate to provide electrical conduction through the
substrate. Inter-cell leakage is minimized by removing these conduction points from direct con-
tact with the acid. The full-size plate is made relatively long (Sin.) and shallow (4 in.) to minimize
resistance losses. The strips are held at fixed points to the plastic substrate by an overlying
plastic grid so as to permit unidirectional expansion of the Pb down the plate without buckling
it. Each complete quasi-bipolar plate is 60 mil total thickness with a maximum paste thickness
of 20 mil on both the positive and negative sides. No Sb is present in the design.
The plates were tested at 30°C by repetitive cycling at currents and for times equivalent
to those required to achieve the most severe ratings specified by EPA in the preliminary power
profile (page 1 of this report) using a full scale battery system based on these plates. Thus, the
2
plates were discir d at 150 mA/cm corresponding to the 55 KW rate and were charged at up
2
to the 40 KW rate (83 mA/cm ). Prior to cycling experimer' .-.••.}' . dditions of HgPO. were
made to the 1.28 sp gr. electrrlyte. Following each group igh rate cycles, the capacity
retaine "~v each test plate wa.i ,. ''nated at the C/5 rate. . ere compared with those on
fre? >lates (Pb/Sb rrids'i :;-• • mmercial SLI battery tested ui -slightly less severe condi-
tion .tis, atcurrenr .- . . ,g to the 47.5 KW and 25.9 KW ratings on discharge and charge
respectively using a fui. -dzu Lc-uery system based on the conventional plates. The actual
vii
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22 '
currents used were 175 mA/cm and 72 mA/cm . No H-PO. additions were made to the
electrolyte in the latter case. Note also that the bipolar system operates at lower current
densities than does the conventional system to achieve the same power rating.
The conventional monopolar positive plates lasted for a maximum of 350 complete high
rate cycles prior to failure. After 300 cycles the C/5 capacity retained by three positive test
plates was 57%, 23% and 3.5%. The conventional negative plates still performed well after 500
complete cycles, losing only ~30% of their original C/5 capacity. In contrast five "quasi-
bipolar" test plates retained 87%, 102%, 90%, 91% and 89% of their C/5 capacity after 300 cycles.
Furthermore, four of these five plates lasted for 1000 complete high rate cycles before showing
signs of failure and the capacity retention at this point was still 47%, 61%, 51% and 48%. The
fifth plate failed only after 730 complete cycles. Failure is denoted here as the point at which
the voltage fell below 1.5 V/cell before completion of a (25 sec) discharge cycle.
Calculations show that a full size modular battery system based on the quasi-bipolar plates can
2 '
operate at 143 mA/cm to achieve the maximum average power output of 70,5 KW (for 25 sec).
Each module weighs 54.5 Ib and 10 parallel modules are employed each with 133 plates in series.
The power density is 128 W/lb. Alternatively, to achieve the maximum specified power output of
92.5 KW (for 10 sec) within the desired weight requirement of 450 Ib maximum, only 8 parallel
2
modules may be employed and the operating current density is increased to 234 mA/cm (212 W/lb).
However, a preferred approach to achieve such a power output with minimum modifications to
thepresent system is to decrease the paste thickness by 25% (i.e., from 20 mil to 15 mil/electrode)
2
when the operating current density per plate may be reduced to < 190 mA/cm . No design diffi-
culties or manufacturing problems are anticipated and the active material per electrode is still
about five times that required for the most severe cycle specified in the final power profile
(980'Whr on one cycle).
Vlll
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Table of Contents
Section No. . Page No.
ABSTRACT vii
SUMMARY OF WORK xiv
I, INTRODUCTION
II. TASK I: INVESTIGATION OF THE STATE OF THE ART 7
A. Cycle Life Testing, Equipment and Procedure 7
B. Performance Evaluations of Commercial SLI Plates 9
III. TASK II: PRELIMINARY DESIGN STUDIES 21
A. Design Concepts 21
B. Design Equations and Concepts for a
Preliminary Bipolar Concept A 22
C. Design Analysis for Preliminary Concept A 28
IV. TASK III: STUDY OF ELECTROCHEMICAL PROBLEM AREAS
RELEVANT TO DESIGN OF A HIGH POWER DENSITY BATTERY ... 35
A. Utilization of Active Material 35
B. Effect of Sb and HgPO4 on Paste Performance 42
C. Factors Not Varied in the Study of Electrochemical Performance . . 54
D. Conclusions 55
V. TASK IV: CORROSION OF SUBSTRATE MATERIALS 57
A. Metal Substrates 57
B. Plastic Substrates 68
IX
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Table of Contents (Continued)
Section No. Page No.
VI. TASK V: DEVELOPMENT AND MECHANICAL TESTING
OF STRUCTURES 79
A. Factors Influencing Choice of Design
Materials and Techniques * 79
B. Conclusions 94
C. Preliminary Plate Development . . . 94
D. Second Design Plate 96
E. Final Plate Design 98
F. Construction of the Battery Using Quasi-Bipolar Plates 100
G. Method of Construction of the Quasi-Bipolar Plate 101
H. Modifications to the Final Design Structure 110
I. Design in Which the Plastic Substrate is Conductive 112
VII. LIFE TESTING OF NEW DESIGN PLATES 117
A. Test Cell and Test Procedure 117
B. Test Results 119
VIII. BATTERY DESIGN AND PRELIMINARY COST ANALYSIS 135
A. Design, Operation, and Characteristics of a Quasi-Bipolar
Battery System Based on the Preliminary Power Profile
Specified by EPA 135
B. Design, Operation and Characteristics of a Quasi-Bipolar
System Based on the Final Power Profile Specified by EPA .... 140
C. Energy Density of a Full-Size Battery System Based on
the Quasi-Bipolar Plates (Concept I) 144
D. Preliminary Cost Estimate for the Quasi-Bipolar
Battery (Concept I) . .' 145
IX. SUMMARY OF ACHIEVEMENTS, EVALUATION OF THE MAIN
AREAS REQUIRING FURTHER DEVELOPMENT, AND PRELIMINARY
WORK PLAN , 147
A. Summary of Achievements 147
B. Areas Requiring Further Development 149
C. Work Plan 149
X. REFERENCES 151
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Table of Contents (Continued)
Page No.
APPENDIX I: Calculation Details for a Full Size Battery Based
on the Preliminary Bipolar Concept A, with Plastic Substrate and
Pb Conductors, Using the Preliminary Power Profile 155
APPENDIX II: New Design Equations for the Preliminary Bipolar
Concept B with a Plate Dimension of 8 in. x 4 in. Using the
Preliminary Power Profile 159
APPENDIX III: Comparison of Battery Systems Based on the Preliminary
Power Profile and on the Two Different Bipolar Plates Outlined in
Preliminary Concepts A and B 161
APPENDIX IV: Energy Density Comparison of Thin Plate Conventional
SLI and Quasi-Bipolar Batteries (Final Design Plates) at High and Low
Discharge Rates 163
APPENDIX V: Curing and Formation Techniques 165
APPENDIX VI: Engineering Data for Battery Materials of
Possible Interest 167
XI
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List of Illustrations
Figure No. Page No.
1. Battery maximum power design curve for
6 passenger hybrid car ........ . ..................................... 3
2. Performance characteristics of a fresh thin conventional
SLI positive plate under severe cycling conditions - Plate 1 .............. H
3. Performance characteristics of a fresh thin conventional
SLI positive plate under severe cycling conditions - Plate 2 .............. 12
4. Performance characteristics of a fresh thin conventional
SLI positive plate under severe cycling conditions - Plate 3 .............. 13
5. Photograph of a typical thin commercial SLI positive
plate prior to cycling ................................................ 14
6. Photograph of a typical thin commercial SLI positive
plate after 500 cycles ................................................ 14
7. Photograph illustrating plate buckling in a conventional
thin positive SLI plate after 500 cycles ................................ 15
8. Performance characteristics of a fresh thin conventional
SLI negative plate under severe cycling conditions - Plate 1 .............. 17
9. Performance characteristics of a fresh thin conventional
SLI negative plate under severe cycling conditions - Plate 2 .............. 18
10. Photograph of a typical thin conventional SLI negative plate
prior to cycling [[[ 19
11. Photograph of a typical thin conventional SLI negative plate
after 500 cycles [[[ 19
12. Illustration of the production of a basic bipolar plastic plate
as in Preliminary Concept A .................... ...................... 24
13. Initial visualization of bipolar plates with plastic support .and
"lead fingers" folded over the top of the support ........................ 25
14. Graph of the coulombic efficiency of the active materials as
a function of current density .......................................... 29
15. Plots of the system weight versus the substrate thickness for various
lead plates using the Preliminary Concept A ............................ 30
16. Plots of the system weight versus the ratio (F) of the required
capacity /initial capacity using the Preliminary Concept A ................ 31
17. Photograph of anodized aluminum mold used in the preparation
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List of Illustrations (com)
Figure No. Page No.
18. Schematic of anodized aluminum mold used in
the preparation of iR-free plate laboratory test structures 38
19. Photograph of an as-cast, pure Pb, iR-free laboratory test
structure having a grid structure 44 mil in depth 39
20. Performance of Barton VLY positive paste in iR-free laboratory
test grids as a function of paste thickness „ 40
21. Performance of universal Grenox positivepaste in iR-free laboratory
test grids as a function of paste thickness 41
^
22. Cycling performance characteristics of Universal Grenox positive
material pasted in an idealized iR-free, one-sided laboratory test
Pb/Sb grid to a depth of 20 mil - Pb/Sb-1 45
23. Cycling performance characteristics of Universal Grenox positive
material pasted in an idealized iR-free, one-sided laboratory test
Pb/Sb grid to a depth of 20 mil - Pb/Sb-2 46
24. Cycling performance characteristics of Universal Grenox positive
material pasted in an idealized iR-free, one-sided laboratory test
Pb/Sb grid to a depth of 20 mil - Pb/Sb-3 47
25. Cycling performance characteristics of Universal Grenox positive
material pasted in an idealized iR-free, one-sided laboratory test
Pb grid to a depth of 20 mil and with HqPO. added to the electrolyte —
Pb H3PO4-7 48
26. Cycling performance characteristics of Universal Grenox positive
material pasted in an idealized iR-free, one-sided laboratory test Pb
grid to a depth of 20 mil and with H,PO4 added to the electrolyte -
Pb H,POA"8 49
u 1
27. Cycling performance characteristics of Universal Grenox positive
material pasted in an idealized iR-free, one-sided laboratory test
Pb grid to a depth of 20 mil and with H,>PO4 added to the electrolyte —
Pb H3PO4-9 50
28. Cycling performance characteristics of Universal Grenox positive
material pasted in an idealized iR-free, one-sided laboratory test
Pb grid to a depth of 20 mil and with no additions-Pb-5 51
29. Cycling performance characteristics of Universal Grenox positive
material pasted in an idealized iR-free, one-sided laboratory test
Pb grid to a depth of 20 mil and with no additions — Pb-6 52
30. Corrosion current of Pb, Pb/Ca and Pb/Sb grid samples held
at 1.25 V(Hg/Hg2S04) inl.28 spgr H2S04ax30°C 60
31. Corrosion currents of Pb, Pb/Ca and Pb/Sb grid samples held
at 1.25 V(Hg/Hg2S04) in 1.28 sp gr H2SO4 at 60°C 61
xiv
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List of Illustrations (cont)
Figure No. Page No.
32. Corrosion currents of Pb, Pb/Ca and Pb/Sb grid samples held
at 1.25 V (Hg/Hg2SO4) in 1.28 sp gr at 90 °C 62
33. Photograph of "bare" grids after corrosion in 1.28 sp gr H9SO.
at 1.25 V (Hg/Hg2SO4) at 90 °C after 60 days 63
34. Photograph of grids corroded in 1.28 sp gr H-SO. (with an
overcoating of PbCL) at 90 °C for 60 days ......T 66
Ct
35. First mold design for plastic plate manufacture 97
36. Typical photograph of an unpasted "quasi-bipolar" plate
newly thermoformed. .•, 99
37. Schematic of an individual module 102
38a. Dimensions of aluminum mold for quasi-bipolar plate
manufacture .... 103
38b. Photograph showing one face of the mold used to thermoform
the final quasi-bipolar plate 104
39. Preparation sequence for quasi-bipolar plate manufacture 105
40. Section through the various components of the bipolar plate
prior to thermoforming 109
41. Photograph of a quasi-bipolar plate prior to pasting with a surface
treatment of Dynel fibers to enhance paste adhesion Ill
42. Construction of a bipolar plastic plate with conduction at the top
and bottom of the plate and at those points where the Pb strips
and plastic grid intersect on the surface of the plate 113
43. Photographs of a pasted and cured quasi-bipolar plate and of a
formed quasi-bipolar plate 118
44. Performance of quasi-bipolar plate no. 6 "repasted" under severe
cycling conditions 120
45. Performance of quasi-bipolar plate no. 8 "repasted" under severe
cycling conditions 121
46. Performance of quasi-bipolar plate no. 10 under severe
cycling conditions 122
I
47. Performance of quasi-bipolar plate no. 11 under severe
cycling conditions 123
48. Performance of quasi-bipolar plate no. 12 under severe
cycling conditions 124
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List of Illustrations (cont)
Figure No. Page No.
49. Performance of quasi-bipolar plate no. 22 under severe
cycling conditions 125
50. Performance of quasi-bipolar plate no. 13 under severe
cycling conditions 126
51. Performance of quasi-bipolar plate no. 23 under severe
cycling conditions 127
52. Capacity retention (C./5) for the limiting electrode of quasi-bipolar
test plates as a function of the number of prior high rate cycles
undergone. The dotted curves show the equivalent data for three
conventional positive plates tested under slightly less severe
conditions 128
53. Photographs of the positive (a) and negative (b) electrodes
of plate no. 8 after extended (1000) high rate/shallow
discharge cycles 131
54. Photographs of the positive (a) and negative (b) electrodes
of pkte no. 12 after extended (1000) high rate/shallow
discharge cycles 132
xvi
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List of Tables
Table No. Page No.
I. Design Equations for the Preliminary Bipolar Concept A 26
2
II. Design Values for the 150 mA/cm Operating Point 27
III. Design Analysis for Preliminary Concept A 28
IV. Comparison of the Weight Losses (g) of Pb and Pb Alloys in
1.28 sp gr HgSO. at Various Temperatures After 60 Days Immersion. . 64
V. Comparison of Weight Changes (%) in Pb and Pb Alloy Grids With
and Without an Overpasting of Positive Active Mass When Immersed
in 1.28 sp gr HSO. at Constant Potential for 60 Days ......... 65
VI. A Comparison of the Relative Advantages (+) and Disadvantages (-)
of Three Grid Materials in Lead Acid Batteries ........... 67
VII. Weight Changes of Various Plastics in 1.28 sp gr HgSO. at
(30°C, 60°Cand90°C) ............ 7 . ........ 69
VIII. Chemical Resistance of Unfilled Epon 828 as a Function of Curing
Agent in 25% Sulfuric Acid Over a 189- Day Immersion Period ..... 73
IX. Chemical Resistance of EMI- 24 Versus CL Cured Epon
828 Castings ......................... . . . 74
X. Properties of Glass Fabrics .................... 75
XI. Properties of Glass Fabrics .................... 81
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List of Tables (Continued)
Table No. Page No.
XII. Technical Data for Carbon and Graphite Cloth 83
XIII. Pricing Schedules for Carbon and Graphite Fabrics 84
XIV. Properties of Prepreg 85
XV. Price Schedules for Thermoplastic Materials 86
XVI. Lexan Resin Bonding Data 89
XVII. Heat Deflection Temperatures of EPON Systems 92
XVIII. Construction Details on Bipolar Plates with Plastic Substrate
and Pb Conductors 114
XIX. Basic Assumptions and Design Parameters of a Full-Size Battery
Based on the Quasi-Bipolar Plate with Conduction Over the Top
(Concept I) 139
XX. Summary of Weight Requirements for Each Module Based on the
Quasi-Bipolar Plates (Concept I) and Operating Under the
Preliminary Power Profile . 139
^i
XXI. Percentage Weight Distribution Comparison in Conventional and
Quasi-Bipolar Batteries. 140
XXII. Summary of the Weight Requirements for Each Module Based on
the Quasi-Bipolar Plates (Concept I) and Operating Under the
Final Power Profile 142
XXIII. Preliminary Large Volume Material Costs and Individual
, Component Cost Estimates for a Module Conforming to the
Final Power Profile and Incorporating the Quasi-Bipolar
Plates Outlined in Concept 1 145
XVlll
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SUMMARY OF WORK
I
The following summary incorporates a review of the many aspects of battery development
examined in the program, and brief conclusions are drawn on each, irrespective of whether or
not the information obtained was used in the final design concept. This summary follows the
sectional outline of the report itself.
SUMMARY OF SECTION I. INTRODUCTION
The preliminary power profile specified by EPA for development of design concepts and
plate testing is given. The final power profile for ultimate design and performance evaluations
is included. It is noted that fresh thin plate SLI batteries already have the necessary discharge
power density but that the main problem is the effect of cycling and standby life on subsequent
performance. Little data are available on this, especially under the specific cycling regime
supplied.
The concept of a bipolar plate was first introduced and the following advantages and
disadvantages were noted.
A. Advantages
1. The active material can be distributed over a greater area without in-
curring too great a weight penalty.
2. The active material is discharged evenly over the entire plate.
3. External intercell connections are not necessary.
4. Intercell resistance losses are minimized.
B. Disadvantages
1. Since all the cells of a battery module operate in series, greater demands
are made on reliability and reproducible behavior from each electrode.
2. Intercell electrolyte leakage could cause discharge of the plate by an
electrochemical mechanism.
3. Corrosion of the substrate could produce leakage and plate buckling.
xix
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SUMMARY OF SECTION II. INVESTIGATION OF THE STATE OF THE ART
Typical plates from a thin plate conventional SLI battery were examined under a specific
cycling regime designed to simulate the most severe conditions specified by EPA in the pre-
liminary power profile. The effect of the cycling was investigated by C/5 capacity evaluations
after every ~ 100 high rate cycles. The following results were recorded.
1. Performance is limited by the positive plates which last only a maximum of
350 complete high rate cycles. The C/5 capacity retained after 300 complete cycles on each
of the three positive test plates was 57%, 23%, and 3.5%.
2. Positive plate expansion and consequent poor paste adhesion, particularly
close to the current takeoff terminal, apparently limit the performance of the positive plates.
3. Fresh commercial negative plates stand up very well to such cycling and a
decrease of only ~ 30% of total capacity (capacity after full charge) is noted after 500 cycles.
The following more general conclusions were also evident.
4. The positive plates in fresh conventional thin plate SLI batteries are mar-
ginal in obtaining the high discharge power densities required for hybrid vehicle purposes.
They are less than satisfactory in providing adequate power after extended cycling life.
5. Particularly on cycling, there is a serious problem with conventional
positive, thin SLI battery plates which is caused by longitudinal resistance losses along and
down the grid. This results in uneven utilization of active mass and, therefore, high local
depth of discharge even when the overall depth of discharge is shallow. y Paste shedding results
particularly close to the current takeoff terminal. Designs which overcome this problem are
desirable.
SUMMARY OF SECTION III. PRELIMINARY DESIGN STUDIES
This task was aimed at developing preliminary design concepts suitable for use in a
high power density/long life battery. Provision was made in the designs for the reduction of
electronic iR gradients along each plate and for decreasing active mass thickness. Further
important considerations were those of improving plate reliability and minimizing corrosion,
plate buckling, and intercell electrolyte leakage problems, all of which can adversely affect
performance. The basic design concepts considered were:
1. Bipolar plate with a nonconductive plastic substrate as support for the active
material and with metal strips as electronic contact. The strips, which are laid vertically down
the plate and in a parallel array along the plate, on both sides, are in contact with the adjacent
strips on the opposite side only over the top of the plate. The contact points are all encased
in a plastic border.
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2. Same as (1) but with contact at the top and bottom of each plate, the latter
points also being encased in a plastic border.
3. Same as (2) but with contact also at localized points down and across the
plate surface via holes through the plate. The latter points are also covered with plastic.
Two additional bipolar designs were considered:
4. A bipolar plate with plastic substrate as active material support. The sub-
strate, however, is also electronically conductive. Conductivity is achieved either by using a
conducting filler, e.g., graphite powder, or by sandwiching a layer of carbon or graphite cloth
between plastic sheets. In both cases, however, it is not necessary for the strips to make
physical contact over, under, or through the plate. The conduction path is via the Pb strips, to
the graphite and then through to the Pb strips on the opposite side of the plate. The plastic
isolates the graphite conductor (which also reinforces the structure) from the H,SO., and so
<2 4
prevents electrolyte leakage through the plate.
5. Bipolar plate with conductive, corrosion resistant, light weight/high
strength metal backing.
The approach of developing a high power density, long life lead acid battery system
based on a preliminary bipolar concept was illustrated using a modular approach to the problem.
The effects of various design variables on system weight were demonstrated and the most
crucial design values were found to be the operating current density and the electrochemical
yield of the paste (Ahr/gm of active paste).
SUMMARY OF SECTION IV. STUDY OF ELECTROCHEMICAL PROBLEM AREAS RELEVANT
TO THE DESIGN OF A HIGH POWER DENSITY BATTERY
There are several problem areas associated with the use of lead-acid batteries for
high power density batteries. The most important of these problem areas were examined
in the course of this program, and the following major conclusions were drawn.
1. To optimize a lead acid battery for use in hybrid electric vehicles, a large
number of thin plates should be used. The operating current density is thus reduced. Paste
utilization is substantially increased in thin plates compared to that in conventional plates
operating at the same current density.
2. Particularly on cycling, there is a serious problem with conventional plates
operating at high power densities which is caused by longitudinal resistance losses along and
down the grid. This result's in uneven utilization of active mass and, therefore, high local
depth of discharge even when the overall depth of discharge is shallow. Paste shedding results.
When these resistance losses are minimized there is a marked improvement in paste perfor-
mance at the same, high operating power densities.
xxi
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3. To maintain cycle life in a battery which contains no Sb in the grid, paste
or electrolyte (for example, when pure Pb is used as grid material), small additions of
HgPO. to the electrolyte are very effective.
SUMMARY OF SECTION V. CORROSION OF SUBSTRATE MATERIALS
The literature was reviewed and a wide range of plastics and metals were studied
in 1.28 sp gr. HgSC^ at up to 90 °C. The following conclusions were drawn.
A. Metals
1. Metals such as Ti, TiN, Al and Mg either with or without conductive
coatings, Pb overplating, etc. are not suitable for use in Pb acid batteries without additional
development work. The materials all corrode severely or form oxides which act as a dielectric.
2. Pb or Pb alloys cannot be used in sheet form as active mass support and
current conductor in a practical bipolar high power density battery for hybrid vehicles. To
resist corrosion and to be mechanically capable of supporting the active mass, the sheets have
to be of impractical thickness with particular regard to battery weight limitations.
3. The use of Pb or its alloys as current conductors in conjunction with a
plastic substrate material support is not precluded from a corrosion or expansion aspect. Pure
Pb is the material of choice by virtue of its corrosion resistance in acid compared to Pb/4.5%
Sb and Pb/0.08% Ca alloys. It also has less expansion problems than the Pb/0.8% Ca alloy.
It is estimated that a covering of active mass will reduce Pb corrosion in H-SO, by at least
20%.
B. Plastics
1. The majority of thermoplastics, for example, Lexan, polystyrene,
polysulfone, PVC, polypropylene and Noryl are stable in 1.28 sp gr. HgSO. at ambient tem-
perature for extended periods. From mis aspect they are suitable for use as substrate material.
2. Reinforced laminates with thermosetting resins are subject to attack by
H0SO. at the resin to glass reinforcement bond. The base resins, and particularly epoxy and
2 4
phenolic resins, if suitably selected and carefully cured, can be quite resistant to acid attack.
3. The major outlet for thermosets in Pb acid batteries is not as a structural
paste support material, but as an adhesive or sealant in selected areas of the plate or battery.
4. No data have yet been generated on the corrosion resistance of reinforced
thermoplastics in H0SOA. Literature information suggests that this is generally as good as that
« 4
of the unreinforced plastics.
xxn
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SUMMARY OF SECTION VI. DEVELOPMENT AND MECHANICAL TESTING
OF STRUCTURES
The additional aspects of plate development not already considered in previous sections
were examined here. Due to corrosion problems, structures involving metals other than Pb or
Pb alloys were not considered further. Emphasis was placed on those alternative designs out-
lined in Section 111 of this report. The selection of materials and techniques for further study
was closely controlled by the results of corrosion and other parameters influencing design
which are described in earlier sections. Literature surveys of material performance capa-
bilities were carried out and, where necessary, these were backed up by laboratory tests.
The following specific factors were considered.
1. Strength
2. Ease of fabrication
3. Cost and availability
4. Bonding of the plastic to Pb or Pb alloys
5. Adhesion of active mass to the plastic
6. Oxidation of the plastic by PbO,
7. Temperature and corrosion resistance
8. Ease of handling (e.g., brittleness) and sealing (plastic to plastic)
in a battery case.
Only plastic materials were investigated since it was clear by this stage that the maxi-
mum chance of success lay in the use of plastic substrate materials as active mass support in
the grid.
The following specific conclusions were drawn as a result of this study.
1. Both thermoplastics and thermosets have adequate mechanical strength to
support the active mass in practical design configurations. With thermosets a reinforcement
medium is required for this purpose, especially for substrates of ^ 20 mil thickness. Engineer-
ing thermoplastics may be suitable as support material in the unreinforced form, especially when
strengthened by the incorporation of a thicker plastic rim surrounding the main substrate area.
For substrates of < 20 mil thickness, the thermoplastics also require reinforcement.
2. A wide range of reinforcement techniques is available using glass, carbon
and graphite cloths, or chopped fibers as reinforcing media. Suitable surface treatments are
applied to these materials to enhance their compatibility with the plastic of choice.
3. Whereas thermosets are most usually reinforced with cloth material,
thermoplastics generally use chopped fibers. Hot press techniques are used to form structural
laminates with thermosets. Reinforced thermoplastics are formed to shape by injection molding
methods. The latter technique is not suited to the thin plate structures desired here because of
inadequate mold filling.
xxiii
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4. A thermoforming technique is suggested when fabricating plates from
thermoplastics. The latter may be reinforced if desired by hot pressing a suitable cloth between
thin sheets of the plastic in question.
5. Mainly because of H»SO. corrosion stability, thermoplastics are preferred
to thermosets as substrate material.
6. Thermosets form superior bonds with Pb than do thermoplastics. The former
may then be used to provide seals in plates at localized points if desired. Careful choice of the
resin and its curing technique and curing agent are, however, necessary.
7. Because carbon and graphite can be used as reinforcement, a means of
obtaining conductive plastic substrates is offered if concurrent problem areas can be solved.
8. Lexan thermoplastic is an ideal starting material for substrate fabrication.
It is relatively low cost, is thermoformable, stable in H2SO4, light weight/medium strength,
is easy to handle, and is resistant to oxidation by PbO,.
9. There are techniques available to enhance sealing of thermoplastics to Pb.
Also, paste adhesion to such substrates may be enhanced by suitable surface treatments.
10. No temperature stability problems are anticipated with the plastics.
A plate, defined here as a "quasi-bipolar" plate, was constructed based on the above and
additional information obtained in previous sections. The most important aspects of this plate
are summarized below.
1. It is approximately 1/6 full size and may be scaled up to full size directly.
Final plate dimensions (pasting area) are 8 in. x 4 in. The 4-in. dimension is in the vertical
direction. Relatively long and shallow plates result. The reason for this can be seen from the
current conduction paths which in this plate are over the top of the plate only. By making the
plate relatively shallow, resistance losses down the plate are minimized.
2. The materials of construction are Lexan as substrate and pure Pb as current
conductors. Lexan is a light weight/high strength plastic which permits relatively easy handling
of the plate with sufficient flexural strength capabilities. Pure Pb has minimal corrosion problems
and also is quite good from an expansion viewpoint.
3. The current conductors of Pb have been held at 20-mil thickness.
4. The conductors are separated by 0.15-in. intervals along the plate. This
separation permits easy charge and discharge of active mass without introducing excessive ,
resistive losses. The separation is equivalent to that of horizontal grid members in conven-
tional lead acid batteries, but since each lead strip carries only the current generated.around
it, the additional leads used in conventional plates to collect the current at the terminal are not
necessary here.
xxiv
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5. A plastic rim is provided to facilitate sealing of each plate within a case
(Lexan). Lexan is an extremely easy material to handle from this aspect.
6. Paste thickness is held at 20 mil per positive and negative electrode with a
plastic substrate thickness of 20 mil also. Pasting thickness is governed by the plastic border
round the circumference of the plate (as is the case with the outside rim in conventional plates).
The rim also adds rigidity to the structure.
7. Paste adhesion to the plastic substrate is enhanced using glass mats or dynel
fibers attached to the substrate surface in a prior step. Very good paste adhesion has been
observed so far.
8. Current is removed from each electrode over the top of each plate only, using
Pb conductors looped over the base plate prior to layup. The points where each conducting strip
make contact with its equivalent strip on the opposite face of the substrate are not directly im-
mersed in electrolyte. The problem of intercell leakage is thus minimized significantly.
9. The Pb conductors are held mechanically to the plastic substrate by a plastic
overlying grid only at those points where the plastic and the Pb intersect down and across the
plate. During cycling, this setup permits expansion of the Pb down the plate without introduction
of any stresses resulting in plate buckling and poor paste adhesion.
10. As discussed, production of the entire plate is relatively easy. It appears
that it can be carried out on a large scale.basis.
11. There is scope in the design for both thinner base plates and also thinner
pastes. No substantial changes are required. The plastic base plate can easily be reinforced
with glass cloth to provide sufficient flexural rigidity in < 20 mil thicknesses. Paste thicknesses
< 20 mil also give superior paste utilization and reduce weight requirements.
The construction of designs (1) - (5), Section III, are outlined in this section together
with the production of a basic module. Designs (1) - (3) could be made relatively easily whereas
there were problems associated with the manufacture or operation of designs (4) and (5) which
were insurmountable in the time period of this contract.
SUMMARY OF SECTION VII. LIFE TESTING OF NEW DESIGN PLATES
The construction of test cells and steps leading up to the high rate cycle testing of the
quasi-bipolar plates is described. HgPO, was added to all test cells (Sb-free) prior to cycling.
The cycling regime was again at currents corresponding to the 55 KW and up to the 40 KW rates
on discharge and charge respectively for a full scale battery system built with the plates. As
before, the capacity (C/5) retained by the test plates was periodically measured (~ every 100
cycles). The performance of five plates tested (design (1), Section III) was extremely good and
four of these withstood 1000 high rate cycles before signs of failure were observed. With the
xxv
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fifth plate, failure was observed after 730 complete cycles. Comparatively, with the conven-
tional positive plates tested in a similar cycling regime, only 350 complete cycles at best could
be obtained. After 300 complete cycles, the capacity retained (C/5) was 57%, 23%, and 3.5%
for the three positive conventional plates. Even after the 1000 cycles, the (C/5) capacity
retained by the four "quasi-bipolar" test plates was 47%, 61%, 51%, and 48%.
A plate made according to design (3) , Section III, stood up to 1158 complete high rate
cycles without showing any signs of failure, and its capacity retention (C/5) at the latter point
was 74%.
SUMMARY OF SECTION VIII. BATTERY DESIGN AND PRELIMINARY COST ANALYSIS and
SUMMARY OF SECTION IX. SUMMARY OF ACHIEVEMENTS, EVALUATION OF THE
MAIN AREAS REQUIRING FURTHER DEVELOPMENT AND
PRELIMINARY PROPOSED WORK PLAN
The design of a module and complete battery system conforming first to the preliminary
power profile and then to the final power profile specified by EPA is discussed. The choice of
design parameters is rationalized. The preliminary cost estimate for the quasi-bipolar battery
is given and an estimate of the energy density of a typical bipolar system at both high (55 KW)
and moderate (C/5 rate) rates is given and compared with that of a conventional thin plate SLI
battery operating at the same rates. Problem areas requ iring further development are outlined and a
proposed plan of work is included. The following conclusions were drawn.
1. A new quasi-bipolar plate has been developed in which the active material
support is plastic, and conduction through the plate is achieved by parallel Pb strips laid vertically
over the top of each plate and along it. The conduction paths through the support are so arranged
as to be not immersed in electrolyte during normal cell operation. The possibility of short
circuits via intercell electrolyte leakage is thus minimized.
2. The Pb conductors are held at fixed points to the plastic substrate via a
plastic grid with horizontal cross-members. Expansion is thus permitted in a vertical direction
without introduction of excessive strains resulting in plate buckling.
3. The plate uses dynel fiber or glass mass backing to enhance paste adhesion.
Pure Pb strips act as conductors and no Sb is used in the plate components. Cycling life is main-
tained using HgP04 additions to the electrolyte.
2
4. On operation at high rates of charge and discharge (150 mA/cm ), the bipolar
plates show very good performance characteristics. They last typically for 1000 high rate/
shallow discharge cycles and capacity retention at the C/5 rating is also extremely good.
Comparatively, fresh commercial battery positive plates degrade excessively after ^ 350 cycles
and capacity retention is relatively poor.
XXVI
-------
5. In the preliminary power profile the maximum discharge rate specified is
55 KW and the minimum desired power density is 100 W/lb. In a full size system using the
above quasi-bipolar plates,. 14 parallel modules may be used each with 100 bipolar plates in
scries and weighing 40.9 Jb/module. The required operating current density per plate is only
2
110 mA/cm . A modular system constructed from the above plates operating to the limits
2
of their tested cycling capabilities, i.e., at 150 mA/cm , incorporates 10 parallel modules
and exhibits a power density of 136 W/lb.
6. To conform to the specifications given by EPA in their final power profile
(Fig. 1), the only change required in the above modular system is to incorporate 133 quasi-
bipolar plates in series per module instead of 100 plates/module. Module weight is recalculated
at 54.5 Ib. At the 70.5 KW average maximum discharge rate and the minimum required power
2
density of 128 W/lb, the operating current density per plate is 143 mA/cm (10 parallel modules).
At the preferred operating point of 156.6 W/lb the operating current density is close to
2
180 mA/cm while to achieve the maximum discharge rate of 92.5 KW for 10 sec (205.5 W/lb)
2
the rate must be increased to 234 mA/cm . In the latter two cases only 8 parallel modules are
used. Also, though cycling behavior is not demonstrated in the latter cases, the plates with
20 mil thickness of paste per electrode do contain more than sufficient excess of active mass
for such deeper discharge cycles.
7. In the preferred mode, it is anticipated that the best module design for operation
under the final power profile would again be one incorporating 133 quasi-bipolar plates in series
but on each plate the paste thickness would be reduced by at least 25% to 15 mil per electrode.
More than sufficient capacity is still available in the plates to meet the most extensive capacity
demands (980 Whr on two consecutive cycles for 25 sec at an average 70.5 KW rate). In this
manner the ope
of 205.5 W/lb.
2
manner the operating current density can be reduced to < 190 mA/cm even at a power density
8. A battery built from 11 parallel modules, each with 100 quasi-bipolar plates in
2
series and with incorporation of sufficient acid, can operate at ~ 130 mA/cm and its energy
density is 9.7 Whr/lb at this rate (100 W/lb). Under the same circumstances, a battery con-
2
structed from conventional plates must operate at >200 mA/cm and its energy density here
is 5.9 Whr/lb. Such a battery does not perform adequately under extended high rate cycling.
9. At medium discharge rates (C/5-rate), the respective energy densities for the
bipolar and conventional systems are 20 Whr/lb and 17.3 Whr/lb respectively.
10. A modification of the quasi-bipolar plate in which multiple Pb conduction paths
are made across and down the plate has also been constructed and an initial plate exhibits superior
performance on extended cycling (compared to the initial quasi-bipolar plate above).
xxvii
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The most important areas requiring further study to develop the quasi-bipolar plate
and battery discussed above are as follows:
1. Extend cycling data on a large number of quasi-bipolar plates under a
range of conditions and at higher rates as specified in the more recent EPA requirements. Tins
will establish plate reliability on a more realistic basis.
2. Construct full scale plates to demonstrate structural stability and
feasibility of large scale fabrication techniques.
3. Extend evaluations of long term plate corrosion resistance, particularly of
the thin cross section Pb conductors but also of the plastic substrate. This will establish a
realistic value for the minimum cross-section per conductor which is compatible with cell
performance, weight, and reliability.
4. Establish the exact volume of electrolyte and electrode gap separation
necessary to permit successful operation of the plates under high rate/shallow discharge
cycling. Here the dimensions of separator and retainer are crucial regarding their effect on
interelectrode volume and also gas bubble retention between electrodes.
5. Construct prototype modules to develop technology in this area and isolate
any plate sealing problems.
6. Complete a more thorough cost analysis particularly with relation to
manufacturing and assembly costs.
7. Identify alternate applications for such a system.
8. Investigate the behavior of the bipolar plates under two consecutive high
rate power pulses for 25 sec within a 60 sec interval and followed by high rate recharge. *
*Such a test has been performed successfully for 6 successive cycles on one of
our plates (quasi-bipolar plate no. 6 in the report) which had already been tested for >700
high rate cycles.
xxvm
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I. INTRODUCTION
It has long been recognized that the internal combustion engine is a serious source of air
pollution. An attractive alternative to the pure combustion engine vehicle is the hybrid car in
which a heat engine produces more nearly a constant power output. A battery, charged by a
generator when the requirements of traction at the wheels are low, delivers the pulses for
acceleration. This concept, either in the series arrangement, in which all the mechanical
2
energy of the heat engine goes through the alternator, or in the parallel arrangement, in which
only a portion of the energy goes through the alternator, offers the advantage of having the heat
engine (for instance, an internal combustion engine) working under conditions of minimum pollu-
tion. By bypassing the crucial problem of the all-electric car, i.e., the lack of batteries with
sufficient energy density, a viable vehicle might be produced with current technology.
The battery required for this vehicle has to be capable of high power pulses of relative
short duration. In addition, economic considerations dictate that the battery tolerate a very
high number of cycles (although the depth of discharge of these cycles is low). The following
operating characteristics of such a battery which were drawn up as a result of preliminary
q
information regarding the operation of a hybrid automobile .
Preliminary Power Profile
I. 55-KW discharge rate sustained for 25 sec and performed for two such 25-sec
periods within a 60-sec interval.
2. 30-KW recharge rate sustained for 90 sec directly following the two above
discharges of item 1.
Voltage:
200 to 220 V open circuit; 150 minimum working voltage.
Life:
The battery should be capable of operating at the above power rates and durations
after operating for 5 years and 200,000 cycles which include the following number and types.
- 1 -
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Number of
Cycles
500
3000
3000
Balance of
200,000
Discharge Rate,
KW
55
55
55
Charge Rate,
KW
30
30
30
5
Energy Transferred
from the
Battery per cycle, Whr
380
130
80
30
10
Weight:
550 Ih maximum
Cost:
The battery should be capable of a mass production cost of less than $550.
Operation:
Suitable for safe use in a family automobile without undue care and mainten-
ance.
In the performance of the present contract, the preliminary battery was designed and
the plates tested in accordance with the above specifications. Calculations given in Section
VIII for final battery performance using the chosen design plate are also based on these initial
power levels. The effects on battery weight, performance and operating current density in-
curred by the more advanced specifications recently received from EPA, and shown below,
are discussed also in Section VIII of this report.
The more advanced performance schedule is as follows:
Final Power Profile
1. The power profile of Fig. 1 with peak power of 92.5 KW.and performed
for two such 25-sec periods within a 60 sec interval.
2. A minimum recharge rate of 39 KW sustained for 90 sec directly follow-
ing the two above discharges.
Voltage:
Minimum working voltage of 200 V. Minimum cell voltage of 1. 5 V.
Life:
The battery should be capable of operating at the above power rates and dura-
tions after operating for 5 years and 200,000 cycles which include the following number and
types:
Energy Transferred
from the
Charge Rate,
CW
70.5 39
55 30
55 30
Number of
Cycles
Discharge Rate,
KW
500
3000
3000
Balance of
200,000
Battery per cycle, Whr
490
130
80
10
30
- 2 -
-------
PEAK POWER =92.5 KW
80
70
DURING 25 SECONDS
60
50
30
20
10
I I
1 I
I 1 I
8 10 12 14 16 18
TIME,SECONDS
20 22 24 26
Fig. 1. Battery maximum power design curve for 6 passenger hybrid car
- 3 -
-------
550-lb maximum, (Goal 450-lb maximum.)
Cost:
The battery should be capable of mass production cost of less than $550.
Operation:
Suitable for use in a family automobile without undue care and maintenance.
Clearly, the new battery is very different: in requirements from batteries being developed
for the all-electric cars. In fact, the power demands of this battery are more similar to those
encountered by the SLi battery or by the high power, extra thin plate airplane batteries. In
particular, the cycling conditions are very specific and very extreme. Designs guided by a care-
ful tradeoff between power density and life are therefore necessary to meet the specific goals.
Preliminary experiments at our laboratories confirmed that new, off-the-shelf SLI
batteries already have the necessary discharge power density. Thus, a conventional SLI battery
with 0.080-in. positive plates (15 Ahr at the 20-hr rate) gave a discharge of 150 sec at the
10 C rate. Lead-acid batteries used for airplane starting have plates about 0.050 in. thick
and show still higher rates of discharge than SLI batteries.
The problem of obtaining the required rate of discharge with fresh batteries did not
seem to be a serious one. Aside from the problems related to charge acceptance at the pre-
established power densities (which were examined during the performance of the contract),
we considered that the main problem was the effect of cycling and standby life on the subse-
quent performance. Since the cycling regime is a very specific one and there was very little
information at the present time on the magnitude of the problem, a thorough study was in-
dicated. Remedial action to achieve a high power density battery with specified long useful
life was directed to developing stable battery components and/or obtaining batteries with a
reserve of power and energy density which would guarantee the required performance even
after part of the power and energy density had degraded as a consequence of the specified
cycling and standby waiting periods.
The development, of multicycle, long life, high rate lead-acid batteries is a new area
of battery technology. The two basic approaches available were to modify existing SLI lead-
acid cells to improve and stabilize their power density or to develop a novel lead-acid battery
system, for example, a bipolar lead-acid battery. Our major emphasis in this work has been
directed at the latter approach since we felt that the advantages of using such a design (over
conventional monopolar structures) were such that a more practical and improved power
density system would result.
The bipolar battery derives its name from its electrode configuration. The positive
electrode of one cell and the negative electrode of the next cell are on two sides of an elec -
trically conductive but electrolyte impermeable substrate. All the current produced by the
battery passes across this substrate. Since external intercell connections are not neces-
sary, a bipolar battery can exhibit both high specific power and energy. The use of the bi -
polar configuration in high rate rechargeable batteries is not a new concept, and the specific
advantages of its use are as follows:
- 4 -
-------
1. The active material can be distributed over a greater area without incurring
too great a weight penalty.
2. The active material is discharged evenly over the entire plate.
3. External intercell connections are not necessary.
4. Intercell resistance losses are minimized.
The effects of these accrued advantages on battery weight, performance and life were ex-
amined in detail in the contract period.
On the other hand, there are the following disadvantages with bipolar designs:
1. Since all the cells of a battery mofiule operate in series, greater demands are
made on reliability and reproducible behavior from each electrode.
2. Intercell electrolyte leakage could cause discharge of the plate by an elec-
trochemical mechanism.
3. Corrosion of the substrate could produce leakage and plate buckling.
These problem areas were also the subject of close study in this contract. Experi-
ments were all aimed at generating information on the extent of the problems. Materials
and design concepts were investigated with the utlimate aim of overcoming or minimizing
the problems.
As a result of this study, a plate was developed which has many of the advantages
of the bipolar battery plate without some of its disadvantages. This plate which we call a
"quasi-bipolar plate" is described later.
The report is presented in accordance with a schedule of work followed in this
program. Comparative data were also recorded on conventional
plates from commercial batteries tested under the extreme cycling conditions specified in the pre-
liminary schedule. Several preliminary design concepts were chosen based on a bipolar
type plate and a detailed analysis of the effects of variations of the design parameters then
carried out. This not only established optimum design figures but also indicated those areas
in which subsequent research would provide the most significant improvement in perform-
ance. In all of this work, the need for a long life battery was also borne in mind. Pro-
vision for the extension of small scale plate and battery fabrication techniques to full scale
commercial production was also of prime concern. In later sections of the report
fabrication techniques of the final design of choice (and specific reasons for this choice) are
given together with extended cycling data on the new plates under the same conditions of test
as for the commercial plates. Comparisons between the two are shown and the advantages
of the new plates are noted.
- 5 -
-------
IL TASK 1: INVESTIGATION OF THE STATE OF THE ART
There were no data available to date on the performance of conventional high power
density batteries operated under the conditions specified in this contract, that is, high rate
charge discharge cycles with a shallow depth of discharge. Results shown below record the
behavior of plates from such batteries under these conditions. Comparative performance
evaluations on novel design plates are given later in this report.
A. Cycle Life Testing, Equipment and Procedure
I
In order to perform cycle life testing within the time frame of this contract, it was
necessary to develop an accelerated test. This test, although inadequate to give an absolute
value regarding the battery life, has to serve to compare cycling life of novel designs of plates,
cells and batteries with those which are in the state-of-the-art under conditions which are rele-
vant to the final use. For this purpose, we chose to use continuous cycling under the most
severe charge and discharge conditions specified for the battery; (i.e., currents corresponding
to a discharge.rate of 55 KW and a charge rate of 30 KW, and times to allow an energy transfer
of 380 Whr).3
We constructed a cycle tester with ten separated test stations. The system operates by
galvanostatically charging and discharging the test batteries which are placed in series. The
power current is regulated by a Sorensen power supply with a nominal output of 40 V and 60 A
(the actual maximum current is 66 A). Timers are provided to adjust the duration of charge
and discharge from 0 to 120 sec. The unit will also permit the application of two consecutive
discharges (e.g., two 25-sec discharges within a 60-sec interval, as required for final battery
test) followed by a charge. In addition, the timers can be bypassed to allow manual operation.
Voltage cutoffs limits during charge and discharge can be set automatically at each test
station within the limits of 0 to 10 V. When an individual cell reaches its preset cutoff limit, it
is automatically removed from the circuit, to be reconnected again on completion of the
individual cycle in which voltage cutoff occurred.
Initially it was observed that every time a cell was removed from the circuit during
charge, a large current pulse of up to ~200 A for ~20 msec passed through the remainder of
the cells. This was due to the discharge of the capacitors on the power supply (used to reduce
AC ripple). We have overcome this problem by using backup cells. On operation, when the
- 7 -
-------
test, cell reaches its cutoff point, the backup cell is first connected in parallel and the "failed
ceJl" then removed from circuit. The entire switching operation is completed in ^0.5 sec.
On discharge, the voltage of the output must rise when a test cell fails. Therefore, no
transient current surge is observed when a test cell is removed after reaching the cutoff limit
on discharge.
A typical test procedure used to test individual battery plates is as follows:
1. Plate is completely discharged at C/5 rate to determine capacity.
2. Plate is completely charged at C/5 rate.
3. Plate is discharged 20% of capacity at C/5 rate.
4. Hate is cycled for 100 cycles, starting with the discharge portion of cycle,
under the following conditions.
a. Charge and discharge currents are those necessary to obtain the 55 KW
and 30 KW rates respectively from a battery system built with the test plate.
b. Durations of discharge and charge are 25 and 61-67 sec, respectively,
as long as the cutoff potentials are not exceeded. (These times are calculated using the
values of discharge and charge rate, of energy transferred during discharge and of cell
potential given in the specifications.)
c. The cutoff potentials are 2.75-3.0 V for charge and 1.5 V for discharge.
On reaching this cutoff voltage, the particular cell is bypassed, but connected again in the
next cycle.
5. At the end of the 100th cycle, plate is charged completely at C/5 rate..
6. Plate is completely discharged at C/5 rate to determine capacity. (It is
realized that this step adds to the severity of the test.)
7. Repeat from step 2.
The procedure was repeated for 500 cycles or until cell failure. We considered that
a cell had failed when it could not be discharged for 25 sec at a voltage higher than 1.5 versus
an overdesigned counterelectrode. In addition, the capacity determination after groups of
100 cycles gives a good indication of the effect of cycling on the plate.
For the testing of plates, overdesigned counterelectrodes (Pb or PbOg, depending on
whether we are testing a positive or a negative plate) were used, and both the cell voltage
and the potential of the test plate (versus HgyHgSO4 reference electrode) were recorded.
- 8 -
-------
We chose a test temperature of 30°C for all our cycle testing. This permitted a
comparison of individual cell performance under well defined conditions though not necessarily
at the final operating temperatures. Our cells contained a relatively large volume of electro-
lyte (~1400 mil) and during testing we observed no more than a 2eC rise in temperature.
Cooling was achieved using glass U-tubes in each individual cell through which thermostattixi
water was circulated. In practice, temperatures in excess of 40°C can be attained during
our test schedule if no cooling is employed. As discussed, however, our cycling procedure
is rather severe and we do not anticipate such temperature fluctuations in actual battery
operation. In preliminary experiments, we observed that the faster deterioration of the
plates expected at high temperatures was more than compensated for by the higher perfor-
mance of the aged plates at this higher temperature. Therefore, under the selected test
cycle, the cycling life was better at 40°C than at 30°C.* Acid specific gravity has been fixed
A
at 1.28, which is typical for high power density batteries.
B. Performance Evaluations of Commercial SLI Plates
Plates were tested from a commercial thin plate, SLI battery having the following
specifications:
Number of plates
Plates per cell
Dimension per plate, in.
Thickness of positive plate, in.
Thickness of negative plate, in.
Weight of paste in positive, g
Weight of grid in positive, g
Weight of paste in negative, g
Weight of grid in negative, g
Capacity of battery at C/20,
Ahr
Shipping weight, Ib (with 1.28
sp gr acid)
Grid alloy
90
7 positives and 8 negatives
5.2 by 6.1 (including surrounding
grid structure)
0.060
0.050
126
70
100
70
96
55
Pb/Sb
*In separate experiments, we examined active and passive component corrosion
problems under practical conditions at elevated temperatures (up to 90 °C).
- 9 -
-------
In order to conform to the specified weight restrictions (550-lb maximum), we could
use ten such batteries (i.e., 420 positives and 480 negative plates). To meet voltage require-
ments, we would have to rearrange the plates to form 100 cells in series, each cell containing
four positives and five negatives in parallel. Effective pasted area of each commercial plate is
2
377 cm (both sides). Assuming a discharge voltage of 180 V, the maximum current called
2
for at 55 KW is 305 A. The current required per plate is thus 76.25 A or 202 mA/cm . On
2
charge at 30 KW and 240 V, the relevant^ current is 31.25 A (83 mA/cm ). Note that the cal-
culation is an approximate one, taking no account of precise weight requirements for electrolyte,
cases, intercell connections etc., in such a rearranged configuration. It does permit us to evaluate
commercial plate performance under realistic conditions.
2
In practice, the plates were discharged at 66 A (175 mA/cm ) and charged at 27 A
2
(72 mA/cm ), respectively, corresponding to the 47.5 KW and 25.9 KW ratings. The use of
these slightly lower rates (compared to 55 KW and 30 KW) was necessitated by the limits of
the discharge unit which was designed for testing of plates requiring much less current to
achieve the battery specification. If anything, longer plate life on cycling would be anticipated
than at the 55 KW and 30 KW rates because the cycle is less severe. Discharge time was 25 sec
and cutoff voltage 1.5 V/cell. Charge time was 61 sec and cutoff voltage 2.75 V/ce\l.
Three commercial positive test plates were evaluated and we show the results of
cycling in Figs. 2-4. Fig. 2 shows the initial and final cell voltage on the best of these plates
during charge and discharge, and the percentage of time for which the plate accepted charge
and discharge (i.e., a percentage of 61 sec and 25 sec, respectively). The capacity retained
by the plate after each group of cycles is also shown. In this mode of cycling, the plates
performed well until a maximum of < 350 complete cycles when each positive plate either had
already failed or had begun to fail (Fig. 3). Failure was preceded by an increase in the
charging voltage (with early cutoff) and a rapid decrease in voltage on discharge below 1.5 V
(with early cutoff also). The capacity retained at the C/5 rate is shown in the figure and was
57% after 300 complete cycles and 34% after 400 cycles, within which period failure on dis-
charge was observed. With the remaining two positive plates, failure occurred after 300
cycles (23% capacity retained) and after 200 cycles (66% capacity retained), respectively.
For the latter plate, only 3.5% capacity was retained after 300 complete cycles.
The general trends in the data for all these plates were toward an increase in charging
voltage (with consequent greater gas evolution) and, on discharge, a decrease in cell voltage
with increase in number of cycles. The cells which failed first of all exhibited the highest
voltages on charge and lowest on discharge and showed the greatest reduction in capacity
after a given number of cycles. We have examined each of these positive plates visually
after the above cycling regime for changes in appearance. Typical photographs are shown
in Figs. 5-7 for the plates before and after testing. Fig. 5 shows a typical positive plate
prior to testing. After testing, we found excessive buckling of the grids in each plate and in
one case the grid itself was actually broken along approximately two-thirds of its length
- 10 -
-------
CHARGE PORTION OF CYCLE
to
UJ
o
_
O
2.4
2.2
100
r
PERCENT^ CHARGED TIME BEFORE OJTOFF
0
100
91
PERCENT CAPACITY RETAINED
84 57
34
21
S
o
UJ
e>
O
1.5
100
DISCHARGE PORTION OF CYCLE
>—••••
88
PERCENT DISCHARGE TIME BEFORE CUTOFF
• •• •••••••••
100
200 300
CYCLE NUMBER
40O
500
Fig. 2. Performance characteristics of a fresh thin conventional SLI positive
plate under severe cycling conditions - Plate 1
-------
to
V> n c
b2'6
UJ
2.4
2.2
100
100
b
o
o
1.9
1.7
o
> 1.5
100
87
CHARGE PORTION OF CYCLE
I
PERCtNT CHARGE TIME BEFORE CUTOFF
I
PERCENT CAPACITY RETAINED
86 23
I I
DISCHARGE PORTION OF CYCLE
PERCENT DIjSCHARGE TIME BEFORE CUTOFF
I
100
200 300
CYCLE NUMBER
400
500
Fig. 3. Performance characteristics of a fresh thin conventional SLI positive
plate under severe cycling conditions - Plate 2
-------
CHARGE PORTION OF CYCLE
CO
111
2 2.4
H
2.2
100
5S
PERCENT, CHARGE TIME BEFORE CUTOFF
• • •
100
75
PERCENT CAPACITY RETAINED
66 3.5
1.7
O
DISCHARGE PORTION OF CYCLE
100
55
PERCENT DISCHARGE TIME BEFORE CUTOFF
100
200 300
CYCLE NUMBER
400
500
Fig. 4. Performance characteristics of a fresh thin conventional SLI positive
plate under severe cycling conditions - Plate 3
-------
Fig. 5. Photograph of a typical thin cumm<.rci;il SLI positive plate prior to cycling
'
Fig. 6. Photograph of a typical thin commercial SLI positive plate after 500 cycles
- 14 -
-------
Fig. 7. Photograph illustrating plate buckling in a conventional thin positive
SLI plate after 500 cycles
- 15 -
-------
across the plate in the midsection. [It must be noted here that even at the start of the cycling
regime, each positive plate was slightly buckled (see Fig. 7), but not so severely as on com-
pletion of the cycling]. Paste material was actually widely separated from the grid in many
2
sections (forming "bubbles" over several cm area) of each plate. Retention of material
was virtually nonexistent in some plate areas, particularly close to the current takeoff ter-
minal (Fig. 6). The poorer paste retention close to the current takeoff terminal can be
interpreted as due to higher local depth of discharge as caused by iR drop along the grid.
The predominant failure mechanism appears to be a combination of extensive expansion
of each plate during cycling, with consequent buckling of the plate (see Fig. 7) and therefore
poor paste adhesion and shedding (see Fig. 6).
We have plotted the data on the two negative test plates in a similar way and these
are shown in Figs. 8 and 9. Data on these two plates paralleled each other very closely and
even after 500 cycles, 70% and 76% of the original (C/5) capacity still remained in each
plate. Cell voltages on charge rarely exceeded 2.5 V maximum (and 2.2 V minimum). On
most cycles, there was a distinct trend towards lower maximum voltage on charge in a given
group of 100 cycles (suggesting an overall loss in capacity during the sequential discharges).
On the last series of cycles, the initial maximum charging voltage was 2.75 V (and 85% charge
was accepted); whereas, on the previous groups of cycles, 100% charge was accepted and the
maximum voltage was generally ~2.6 V. This is due to having commenced our last series
of cycles from the 100% capacity point (and not 80% as before);
On the discharge cycles, there was again a trend towards lower voltages during each
group of 100 cycles. As the capacity of each cell fell, the discharge voltages also decreased.
In effect, we are apparently shifting from the 80% capacity starting point towards smaller
values within each group of 100 cycles. In addition, we observe a steady decrease in total
capacity (i.e., capacity after full charge) as cycling proceeds. The decrease is relatively
small when compared with positive plate performance. The negative plates, when removed
from the test rack, exhibit a much roughened surface structure (Fig. 11) compared to their
initial appearance (Fig. 10). No excessive shedding of active mass was observed though the
roughening is probably a prelude to such shedding.
Based on these experiments, the following conclusions were drawn on the performance
capabilities of these fresh thin commercial SL1 battery plates operated at high power density.
1. Performance is limited by the positive plates which last only a maximum of
350 complete high rate cycles. The C/5 capacity retained after 300 complete cycles on each
of the three positive test plates was 57%, 23%, and 3.5%.
2. Positive plate expansion and consequent poor paste adhesion, particularly
close to the current takeoff terminal, apparently limit the performance of the positive plates.
3. Fresh commercial negative plates stand up very well to such cycling and a
decrease of only ~30% of total capacity (capacity after full charge) is noted after 500 cycles.
- 16 -
-------
CHARGE PORTION OF CYCLE
Jj2.6
O
—
UJ
<5 24
O
2.2
!00
3*
0
10
O
VOLTAGE (V
*-g
1.5
100
3*
0
—
—
—
•
p
1
•
PERCENT .CHARGE
—
0
93
0
M
TIME BEFOF
E CJJTO
-F
I
PERCENT CAPACITY RETAINED
91 80
•
—
'
—
—
9
—
67
~ DISCHARGE PORTION OF CYCLE ~~
—
l|
(
I
•
PERCEIV
—
1,
«
i
IT DISCHARGE TIME BEFORE CUTOFF
1
I
• •
[1
Ml. I-
—
• ** • • •
—
too
200 300
CYCLE NUMBER
400
500
Fig. 8. Performance characteristics of a fresh thin conventional SLI negative
plate under severe cycling conditions - Plate 1
-------
CHARGE PORTION OF CYCLE
00
I
O
IU
«*24
O
2.2
100
0
** 1C
O
VOLTAGE
'->!
1-5
0
—
_
-
•
<
.
<
•
1
ll
1 I
PERCENT CHARGE
0
—
1
—
.
,
92
<
1
1
1
t ~"
-_,_
• • • ^* 4*t * ' '
TIME BEFORE CUTOFF
—
PERCENT CAPACITY RETAINED
94 82 71 7
c
>ISC
HARC
PERCENT D
_
iE P
ORT
'
ON
OF CYCL
A
,
E • ~
1 1 i ! It 1 1 1
1 I'1'] 1 1-
—
ISCH.ARG^ Tl
ME BEFORE CUTOFF
100
200 300
CYCLE NUMBER
400
500
Fig. 9. Performance characteristics of a fresh thin conventional SLI negative
plate under severe cycling conditions - Plate 2
-------
Fig. 10. Photograph of a typical thin conventional SLI negative plate prior to
cycling
Fig. 11. Photograph of a typical thin conventional SLI negative plate after 500 cycles
- 19 -
.
-------
Within each group of cycles, the negative plates lose charge steadily, but much of this
loss can be recouped by a periodic recharge at regular intervals (every 100 cycles in this
case). Charge acceptance on the negative plates appears to be more efficient as the overall
state of charge decreases. Such an effect in the positive plates is masked by the overall
degradation of the plates.
The following more general conclusions are also evident:
1. The positive plates in fresh conventional thin plate SLI batteries are mar-
ginal in obtaining the high discharge power densities required for hybrid vehicle purposes.
They are less than satisfactory in providing adequate power after extended cycling life.
2. Particularly on cycling, there is a serious problem with conventional positive,
thin SLI battery plate which is caused by longitudinal resistance losses along and down the
grid. This results in uneven utilization of active mass and, therefore, high local depth of
discharge even when the overall depth of discharge is shallow. Paste shedding results
particularly close to the current takeoff terminal. Designs which overcome this problem
are desirable.
- 20 -
-------
IIL TASK II: PRELIMINARY DESIGN STUDIES
This task was aimed at developing preliminary design concepts suitable for use in a high
power density/long life battery. Provision was made in the designs for the reduction of electronic
iR gradients along each plate and for decreasing active mass thickness. Further important con-
siderations were those of improving plate reliability and minimizing corrosion, plate buckling,
and intercell electrolyte leakage problems, all of which can adversely affect performance. All
of these aspects are discussed in full later.
A. Design Concepts
The basic bipolar design concepts which we considered in the contract period are outlined
below in concepts 1 through 5. Concepts 1-3 are the bipolar, designs which were considered to
be of more practical interest after initial experimentation, literature surveys and design cal-
culations. Concepts 4 and 5 are alternative bipolar designs having both advantages and disadvantages
over 1-3. It was considered that their disadvantages outweighed their advantages but neverthe-
less they were examined briefly here. In addition to these designs which were experimentally
tested, we also discussed two preliminary conceptual designs: Concept A - on which the feasibility
of constructing a full scale high power density battery system was first analyzed and Concept B
which is exactly the same as A except that the bipolar plate size is larger. (See Section III.B and
Appendices I-III.)
The basic design concepts considered were: -
1. Bipolar plate with a nonconductive plastic substrate as support for the active
material and with metal strips as electronic contact. The strips, which are laid vertically down
the plate and in a parallel array along the plate, on both sides, are in contact with the adjacent
strips on the opposite side only over the top of the plate. The contact points are all encased in
a plastic border.
2. Same as (1) but with contact at the top and bottom of each plate, the latter
points also being encased in a plastic border.
3. Same as (2) but with contact also at localized points down and across the plate
surface via holes through the plate. The latter points are also covered with plastic.
- 21 -
-------
The above designs range from what we have termed a "quasi-bipolar" plate [as in (1) ] to modi-
fications which more closely approximate a true bipolar design [particularly as in (3) ]. In a
true bipolar plate, conduction is achieved over the entire plate area. A major problem in bipolar
plates can be encountered as a result of leakage through the plates (e.g., by corrosion attack)
causing short circuits. We anticipated that reducing the number of possible leakage paths and
locating their geometry so that they were as far removed from corrosive attack as possible
would alleviate the problem. In the event that corrosion problems are successfully overcome,
the modifications in (2) and (3) permit the more complete realization of the overall advantages
of bipolar plates.
Two additional bipolar designs were considered: '
4. A bipolar plate with plastic substrate as active material support. The sub-
strate, however, is also electronically conductive. Conductivity is achieved either by using a
filler, e.g., graphite powder, or by sandwiching a layer of carbon or graphite cloth between
plastic sheets. In both cases, however, it is not necessary for the strips to make physical
contact over, under, or through the plate. The conduction path is via the Pb strips, to the
graphite and then through to the Pb strips on the opposite side of the plate. The plastic isolates
the graphite conductor (which also reinforces the structure) from the HgSO. and so prevents
electrolyte leakage through the plate.
5. Bipolar plate with conductive, corrosion resistant, light weight/high strength
metal backing.
In both of the above designs, conduction is achieved over the entire substrate area. The advan-
tages of the true bipolar plate are thus fully realized. Unfortunately, so are all the problems -
particularly corrosion, and with design (4), the possibility of gas evolution on exposed graphite
also exists. All these aspects have been considered in subsequent sections and a balance has
been made between the desirability of having reliable and long life plates and that of maximizing
plate performance on final design plates.
B. Design Equations and Concepts for a Preliminary Bipolar Concept A
Below, discussion.calculation and design details relevant to the construction of a high
power density battery system based on a preliminary concept of a bipolar plate (Concept A) are •
given. This demonstrated the feasibility of the approach. It also provided useful design values
for critical comparison with those on modified and improved designs. Subsequent calculations
for a full size battery using the improved designs were basically the same as those given in '
detail for this Concept A. The effects on battery characteristics of changes in design variables
and in particular, changes in the operating current density are also clearly outlined using the)
Concept A as a particular case. The present section summarizes the results of these calcula-
tions which are given in more detail in Appendix L (Compare Appendices 2 and 3 also).
- 22 -
-------
For u high power density battery system it was initially considered that a large number
of thin plates should be employed, imposing quite a severe strain on the mechanical stability of
the plate suppport material (the grid). To support the active material, it was felt initially that
a plastic substrate might be suitable. Since plastic grids also greatly reduce the constructional
problems associated with a bipolar configuration, particularly sealing, it seemed highly advan-
tageous to use both these concepts in the same battery. As described below, the use of thermo-
plastic structural materials obviates many of the difficulties inherent in the bipolar configuration.
In view of the electrical, weight, and economic constraints given in the work statement,
it was felt that a modular approach to the battery system would be most sensible. By building the
system from uniform sized components (modules), maintenance, system reliability, as well as
the economics of component failure could be made more attractive. In principle, we chose a
fixed cross-sectional area for the module and took into account in the influence of the variable
parameters by changes in the overall length (in effect, plate thickness and electrode separation).
The basic system module as initially conceived consists of a nominal 180-V battery containing
100 bipolar cells with an active area of 15 sq in. per electrode. The external dimensions of the
module case are 6 in. wide by 4 in. high. Module length is dependent on the design parameters
selected.
Fig. 12 illustrates the preliminary view of the production of the basic plastic plate. The
first step involves the casting of individual pure lead ribs. These are subsequently incorporated
in the casting of the plastic support, and end up as horizontal protruding ribs from a flat plate.
In this configuration, they provide the required interelectrode conductivity. Note that the ex-
posed portions of the ribs are wider away from the electrode face. In this manner, contact of
the active material with one grid is optimized.
The entire plastic sheet is then given a thin coating of lead. This lead coat has a dual
purpose. Primarily, it provides good electrical conductivity over the entire plate surface. A
further objective is to prevent electrolyte from penetrating the plastic-lead interface. .The
thickness of this layer is dependent on the corrosion rate of lead under the required electrical
constraints. Application of the protective lead is currently conceived as a two step process.
After an initial layer of lead is vacuum deposited, the bulk of the lead layer is electroplated
via standard techniques. As a final step, the plates are pasted and cured in a conventional
manner.
Though in principle attractive, several possible problem areas were anticipated with
the above design relating primarily to constructional problems, intercell corrosion at the
Pb/plastic interfaces extending through the plastic support, and expansion of the positive
electrode leading to the plate buckling. Thus the alternative designs summarized in (1) -(3)
above were proposed. Numbers (1) and (2) were visualized initially as in Fig. 13. [See Fig. 36
for the final design for (1) and Fig. 42 for the final design for (3) ]. The number of corrosion
paths is greatly reduced and the path lengthened by folding lead strips over the plastic support.
In the first modification, contact between positive and negative plates in each cell is not through
the plate but over it, at the top of the plate. In the second modification, electrical contact is
- 23 -
-------
LEAD RIB
CAST
PVC
PLATE
LEAD PLATE
PVC
SEALING
AREA-
ACTIVE
MATERIAL
Pb02 (+)
OR
Pb (-)
C
J-
ELECTROLYTE
EQUALIZATION
SLOT LEAD RIBS
Fig. 12. Illustration of the production of a basic bipolar plastic plate as in
Preliminary Concept A
- 24 -
-------
PLASTIC COVER
ACTIVE
IMASS
.RIBS
PLASTIC
BACK
L£AD
^STRIP
ob
cd
ef
ACTIVE MASS
B
\e
,LEAD STRIP PLASTIC RIBS
I—'
LASTIC SUPPORT
MODIFICATION OF "A" WITH CONTACTS ON TOP AND BOTTOM
o
V
A
Co
PLASTIC
Fig. 13. Initial visualization of bipolar plates with plastic support and "lead fingers" folded
over the top of the support [basically, designs (1) and (2) on page 21]. The final
construction of this plate is shown in Fig. 36
- 25 -
-------
maintained by the lead strips at both top and bottom of the plate. The latter of course now increases the
number of corrosion paths but the path length is still relatively long compared to the original design
configuration (Fig. 12). Expansion holes are also provided in the strips on the positive side only. Note
also the plastic ribs provided in the plate to give good paste adhesion.
The following design va riables were considered to be of major importance and were assigned
symbols as indicated below. Though specific to the preliminary Concept A outlined in Fig. 12 above: rho
calculations are easily modified to include design variations such as those shown in Fig. 13. This has
been done in the final design calculations, discussed later. Table i shows the design equations or the
preliminary bipolar Concept A.
o
X = operating current density, mA/cm
Y = electrochemical yield Ahr/g of active paste (assumed equal for both positive
and negative material)
F = decay allowance, dimensionless (required capacity/initial capacity)
T = thickness of the plastic plates, in. :
T, = thickness of the lead ribs, in.
P = thickness of the lead plate, in. each side
S = spacing of the lead ribs, in.
A = acid utilization, dimensionless: this factor incorporates an allowance for the
actual ampere hour equivalent (i.e., Ahr/gm HgSO. of a given sp gr.) of the acid
compared to the theoretical ampere hour equivalent of the same acid. The factor
4
was estimated from the data of Vinal.
Table L Design Equations for the Preliminary Bipolar Concept A
Component Weight/Module, g
Active paste: 0.269 X/FY
Plates; 5.5 x 105 P+5.5 x 104 T + 1.94 x 105 TL T /S
+ 1.09XTL/SFY
Acid: 1.42 X/A
PVC case: 0.53 X/A +11500Tp +2.98 x 10'2 X/FY +276 +23000P
Terminal plates: 695
Interelectrode wiring: 60
Number of Modules: 3150/X
Battery weight, Ib: 7090/X + 2.07/FY +4.61 x 105 Tp/X +13.4 x 105 TLTp/SX
+ 7.56 Ty /SPY + 39.5 x 105 P/X + 13.5/A pounds
The following parameters were not varied:
Module height and width 4 x 6 in.
Plastic case thickness 0.25 in.
Electrode size 3 x 5 in.
3*
Paste density 4.2 g/cm
Acid density 1-26 g/cm3
Interelectrode wiring 50 g/foot of wire
Module terminals 0.25-in. lead plated aluminum
- 26 -
-------
Consideration of the design requirements showed that the deepest depth of discharge,
764 Whr, occurred at the highest power .level, 55 KW. The battery was designed soley with
regard to this' most severe situation, and hence may be considered to be conservatively rated
for the other cycle types. The weight breakdown shown in Table II was summarized from the
calculations presented in Appendix L
Table II. Design Values for the 150 mA/cm Operating Point
Active Paste, Ib
Plates (Pb 4-plastic), Ib
Acid, Ib
Plastic Case, Ib
Terminal Plates, Ib
Intermodule Wiring, Ib
Total Module Weight, Ib
Separators, Ib
Retainers, Ib
3.3
10.0
0.9
2.3
1.5
0.1
Distance between plates, in.
Active paste thickness, in.
Substrate thickness, in.
Case thickness, in.
Module Length (100 cells) , ft
18.1
(not considered) **
(not considered) **
0.014
0.007***
0.0038
0.2 50
0.59
*Although the paste density is not an important design variable, its basic influence on the
performance of the battery electrodes must be considered.
**Separator weight was not included in the preliminary calculations but was later shown to
contribute only 1.5% to.total battery weight. Similarly glass retainers, also not considered,
constribute only 1% to total battery weight.
***The calculated thickness of paste necessary to supply the required capacity is only 7 mil per
electrode for two consecutive 25 sec, 55 KW pulses. We chose to use 20 mil initially to
facilitate plate fabrication and handling. As is illustrated in Section VIII, a battery prepared
from such a plate still conforms to weight requirements and has a sevenfold excess of active
mass based on the two consecutive 55 KW pulses for 25 sec each. There is thus wide scope
for optimizing the final design even further by reducing the paste thickness. The knowledge
gained during the development of the 20 mil pasted plates is directly applicable to thinner
structures, e.g., with 15 mil paste thickness, and no problem areas are anticipated.
- 27 -
-------
C. Design Analysis for Preliminary Concept A
The most crucial design values were found to be the operating current density (X) and
the electrochemical yield ( Y). These two parameters are not independent and hence cannot be
selected arbitrarily. Data derived from Rerndtwas used to prepare Fig. 14 which illustrates
how the utilization of active material may be expected to vary as a function of current density.
We have examined this aspect also in the contract period. Coulombic capacities range from
0.125 Ahr/g (50% of theoretical) at 2.5 mA/cm2 to 0.0375 Ahr/g (15% of theoretical) at
2
250 mA/cm . Since these experiments employed relatively thick plates, the results are conser-
vative for present purposes.
2
As an illustration, three representative cases are shown in Table III; 50 mA/cm ,
150 mA/cm , and 250 mA/cm . The other design parameters were held constant at the nominal
values shown. In view of the detrimental effect of cell temperature increases, these designs
were also evaluated from a heat transfer standpoint. Consideration of convective heat transport
from the electrodes to the electrolyte and conductive transport through the case walls showed
that these interfaces did not result in significant temperature gradients. At the 55 KW level,
the battery temperature rise (assuming adiabatic operation, a worst case) is less than 3°F/min.
Table III. System Designs for Three Different Current Densities
Current Density, mA/cm2 50- . 150 250
Coulombic Yield, Ahr/g 0.081 0.054 0.037
Decay Allowance 0.5 0.5 0.5
Plastic Plate, in. 0.03 0.03 0.03
Lead Ribs, in. 0.03 0.03 0.03
Lead Plate, in. 0.004 0.004 0.004
Rib Spacing, in. 0.5 0.5 0.5
Acid Use (parameter "A", dimensionless) 0.5 0.5 0.5
Module Length, ft 0.42 0.47 0.55
Number of Modules 63 21 13
System Weight, lb 868 380 319
System Volume, ft3 4.2 1.8 1.2
2
Based on the above results, the 150 mA/cm operating level was selected for detailed
analysis since it easily fulfilled theweight requirement and yet permitted operation at approx-
imately three-fifths of the current density of standard SLI batteries discharged at the same
2
power density. The detailed design analysis of the 150 mA/cm operating point is shown in
Table II. All data were based on the nominal values given in Table I.
The effect of variations of the other design values were also considered. In particular,
the effect on system weight of changes in the lead plate thickness, the plastic plate thickness,
the decay factor, and the acid utilization were of interest. These results are summarized in
Figs. 15 and 16. All data are at the 150 mA/cm2 design point.
- 28 -
-------
100
90
80
70
>-"50
o
2 40
o
u_
u.
30
o
QD
20
O
O
10
1
50
100
150 200
mA/cm2
250
300
Fig. 14. Graph of the coulombic efficiency of the active materials as a function of
current density [data to conventional monopolar thick plate (~ 75 mil)
performance as abstracted from the data of Berndt Ref. 6]
- 29 -
-------
600
550
500
JO
- 450
I
o
UJ
400
UJ
K
Crt
350
300
250
I
I
LEAD PLATE, in.
P 0.008
P O.006
oQ.004
0.002
0.02 0.04 0.06
PLASTIC SUBSTRATE THICKNESS, in
Fig. 15. Plots of the system weight versus the substrate thickness for various
lead plates using the Preliminary Concept A (based on the term 39.5 x 105 P/X,
where X = operating current density mA/cm2 and P = lead plate thickness, inches)
see Table I on page 28
- 30 -
-------
600
550
500
£ 450
I
UJ
$
5
UJ
to
>
4OO
350
300
250
25%
ACID USE
5O% or 75%
I
I
I
O.2 0.4 0.6 0.8 I
REQUIRED CAPACITY/INITIAL CAPACITY
Fig. 16. Plots of the system weight versus the ratio (F) of the required
capacity/initial capacity using the Preliminary Concept A (that
is, as a function of those terms in Table I on page 28 which contain
the factor F. The effect of varying the term "A", the acid use,
is also shown)
- 31 -
-------
Fig. 15 depicts the effect of substrate geometry on the system weight. The thickness of
the lead plate used to enhance paste adhesion and minimize corrosion through the plastic substrate is
determined by the corrosion rate on the positive side of the electrode. As can be seen, a total
lead thickness of 0.015 in. is a probable maximum. However, this thickness could be divided
unequally with 4 mil on the negative side and 12 mil on the positive side. The necessity of incor-
porating the Pb plate in the final design was a factor studied in the course of the contract. Note
that plastic substrates up to 0.050 in. thick can meet the weight specification of 550 Ib. The actual
thickness is, of course, a function of the strength and molding behavior of the plastic.
Fig. 16 shows the relatively minor effect of acid usage on overall system weight. Hence.
it was concluded that investigation of acid concentration for weight minimization purposes was not
a particularly useful approach. Note that the reserve capacity, i.e., the initial ampere-hours
available in the electrode divided by the ampere-hours required by the discharge [all determined
O
by Berndt's data, (Fig. 14) ] necessitated by the duration and stresses of the cycle regime is of
significant impact. The system as designed can tolerate the inclusion of a five-fold excess of
active material (a fact which should be borne in mind in view of our later plate designs).
We recalculated these preliminary design equations on a bipolar-battery and based the
data on an 8-in. x 4-in. plate dimension. This is defined here as Preliminary Concept B. (See
also Appendices 2 and 3). The aim was to have a plate which was relatively long and shallow
(for reasons discussed later) and in addition, a weight savings in case materials and intermodule
connectors was also anticipated. The calculations in the Appendix (2 and 3) show that at an
2
operating current density of 150 mA/cm the total battery weight is 364 Ib. This compares with
a value of 380 Ib for an equivalent battery with a plate dimension of 5-in. x 3-in. A comparison
2
of design values for each module for the 150 mA/cm operating point indicates where the weight
savings is incurred. This was indeed in the case materials and to a minor extent in the inter-
module wiring. Because of the greater capacity of the larger area plates (8-in. x 4-in., cf. to
5-in. x 3-in.) , fewer modules are required in this latter design - 10 modules compared to 21
modules. It is important to note also that the operating current densities are the same in both
designs so no disadvantages in the larger modules were expected here.
The above calculations demonstrate the expected weight of a high power density battery
based on a bipolar plate as initially conceived with plastic substrate and Pb conductors. In the
course of the contract period, we have not adhered strictly to the design concepts outlined above
(see designs 1 - 3 at the start of this Section and also later in the report). For example, the
rib spacing has been changed and no lead plate is incorporated in the final design. Paste and sub-
strate thickness have also been varied and the reasons for all these changes are given later. We
2
have, however, used the 150 mA/cm operating point as our reference in all test data and include
in Section VIII the final calculations of battery weight based on this current density. This is dis-
cussed subsequently. In the following sections, we have considered those factors, e.g., corrosion
and strength of the substrate, which we deemed to be important in the choice of a final design
structure. The most important aspects of plate design as they affected paste performance,
- 32 -
-------
e.g., the paste thickness, were also studied. Electrochemical factors governing plate design,
e.g., the presence or absence of Sb in the grid, were also of direct concern. These factors are
all discussed in the following sections. In all of these, the need for a long life battery was also
borne in mine.
- 33 -
-------
IV. TASK III: STUDY OF ELECTROCHEMICAL PROBLEM AREAS
RELEVANT TO DESIGN OF A HIGH POWER DENSITY BATTERY
There are several problem areas associated with the use of lead-acid batteries for
high power density batteries. The most important of these problem areas were examined
in the course of this contract.
A. Utilization of Active Material
High rate charge and discharge capabilities are required for traction purposes. Even
at low rates of discharge (low current densities), the coulombic efficiency* of the active ma-
A fZ
terial is no greater than 50%. ' As the discharge current density is increased, the paste
utilization, as such, also decreases rapidly and can be <20% at high discharge rates, '
The above is true for plates of all thicknesses but there is another important consider-
ation. This is that the utilization,* in depth, of active mass at a given discharge rats decreases
as plate thickness increases. This is due in a large part to the inability of the electrolyte to
diffuse across the electrode thickness. In addition, there are iR losses along the grid of a
conventional plate which can affect paste utilization. Whereas the effect of paste thickness on
performance has been demonstrated beforehand with relatively thick (s 1/16 in.) commez'cial
plates, no information is available on performance of thin plates ( s 40 mil) in the absence of
these iReffects (which also can cause poor paste utilization). Studies were carried out with
two commercial oxides in iR-free plates described below.
1. Choice of active material
Two materials only have been studied, namely Barton VLY oxide (<2%Pb, 60%
orthorhombic PbO, and 40% tetragonal PbO) and Universal Grenox oxide** (25% Pb and a balance
of orthorhombic PbO) both from N.L. Industries. Though the curing schedule of the former
is ideal in that it permits good control over the amount of tetrabasic lead sulfate formed in
the paste (with long needlelike crystals and consequently a good porous interlocking mass),
we did not observe good paste adhesion with this material. In contrast, plates pasted with
Grenox oxide have, almost without exception, performed well. We consequently confined our
*we have referred in diis report both to coulombic efficiency and more often, to utilization of the
active mass. The first term refers to the observed capacity expressed as a percentage of the
theoretical capacity calculated from the known amount of electrochemically. active material in
the plate. The utilization term used here refers to the capacity measured at a given current
density and expressed as a percentage of the capacity measured at the C/20 rate. In this
sense the 50% and 20% coulombic efficiencies quoted above become 100% and 40% when expressed
as paste utilization.
**The curing schedules are given in Appendix V.
-35 -
-------
studies to plates pasted with the Grenox oxide. This report includes data on those plates pasted
with Barton VLY oxide which showed good adhesion and performance capabilities.
2. Design of ill-free plate laboratory test structures
We designed and constructed three anodized aluminum grid molds for casting iR-
free grid structures. A photograph of one of the molds is shown in Fig. 17. A schematic is
shown in Fig. ISanda typical as-cast plate is illustrated in Fig. 19. Grid depths in each of these
molds are 20, 28, and 44 mil. Pb or Pb/Sb casts were prepared using a loading of ~4 Ib. The
use of this amount of material permited good grid definition. Before use, a commercial release
agent was applied to a heated mold and the casting process then carried out using freshly acid-
washed (HC1 O^ or CHgCOOH) Pb or Pb/Sb to provide clean castings. The actual casting was
made at ~450°C in a hydrogen atmosphere. We found that grid thickness in the plate agreed very
well with the mold depth. For example, when using the mold with 44-mil grid depth, the height
of ribs in the cast alloy was also 44 mil. Each of these grids has an area of 77.8% available for
active material. The large bulk of the backing on each plate ensures insignificant problems from
iR losses along the plate.
3. Effect of paste thickness
Performance of Barton VLY oxide and Universal Grenox oxide was examined by
2
evaluating capacities as a function of current density up to 310 mA/cm . The grids were all
n
cast from Pb/4.5% Sb and pasting area was held at ~90 cm .
The results are shown in Figs. 20and 21 for plates pasted with the above thick-
nesses of both oxides. We have examined .three separate samples of each paste at each thickness.
Capacities were all evaluated initially at the C/20 rating. For the Grenox paste, we have plotted
the capacity per cubic inch (volume capacity) at each rate of discharge as a function of current
density. For the Barton VLY oxide (which did show an identical capacity to thickness ratio at the C/20 rate
for each of the three thicknesses of oxide), we have plotted the ratio of the capacity at a given rate to the
C/20 capacity versus current density. It is apparent from the figures that, for both pastes, utilization of
active mass is greatest for the 20-mil plates over the entire range of current densities. This
is especially evident in Fig. 21 obtained with Grenox oxide. There one can see that at, e.g., the
2
150 mA/cm operating point, the utilization of active mass is almost doubled in the 20-mil plate
2
compared to the 44-mil plate. At the 155 mA/cm operating point for the Barton VLY oxide, the
utilization of paste in the 20-mil plates is 53% compared to 39.5% and 31% for the 28 and 44-mil
plates, respectively - in good agreement with the trends for the Grenox oxide.
The inference to be drawn from these data is that especially when operating at
high rates of discharge, a large number of thin plates should be chosen. For example, to achieve
the power density specified in the contract (100 W/lb), a conventional battery (> 60-mil plate
2
thickness) must operate at ~250 mA/cm . At this point, the efficiency of paste utilization is
only about 27%. As will be discussed, a battery incorporating new design plates can achieve the
2
same 100 W/lb power density when operating at ~105 mA/cm . From Fig. 21 , the efficiency of
active mass utilization is ~48% at this point, that is, almost a twofold improvement with the new
design.
- 36 -
-------
Fig. 17. Photograph of anodized aluminum mold used in the
preparation of iR-free plate laboratory test structures
37 -
-------
8.
7.00"
6.875
3.0
"o
fO
i
I .
i
l
i
.TO:
8 "8
ro
O
10
oq
to
to
CD
Fig. 18. Schematic of anodized aluminum mold used in the preparation
of iR-free plate laboratory test structures
- 38 -
-------
Fig. 19. Photograph of an as-cast, pure Pb, iR-free plate laboratory test
structure having a grid structure 44 mil in depth
- 39 -
-------
1.0
0.9
0.8
0.7
UJ
O
CJ
"Q5
5
O
<
0.
"
O
O.I
0.0
o.o
155 310
CURRENT DENSITY (amps/cm2) x ioj
Fig. 20. Performance of Barton VLY positive paste in iR-free laboratory test
grids as a function of paste thickness (O, 20 mil; °, 28 mil; A, 44 mil)
at various current densities
- 40 -
-------
IO
8
10
c
6
o
<
Q.
3 5
ui
I
1
I
50 100 150 200
CURRENT DENSITY (mA/cm2)
250
Fig. 21. Performance of universal Grenox positive paste in iR-free laboratory
test grids as a function of paste thickness (0, 20 mil; O, 28 mil; •,
44 mil) at various current densities
- 41 -
-------
4. I xmgitudinal resistive losses affecting paste utilization
In conventional thin battery plates which have a single current takeoff terminal, a
posHihle problem in paste utilization and cycling lifetime is encountered because of iR losses
along and down the plate, away from the terminal. Because of the increase in resistance in the
latter directions, it is easier to discharge the paste in those areas closest to .the takeoff I
terminal. Poor distribution of active mass utilization and high local depth of discharge can thus
occur even if the overall depth of discharge is low. Again, subsequent paste shedding problems
^ 12
w'ould ensue since shedding is worse at high local depth of discharge.
We have also examined this aspect of battery performance. Data on the plates
described above (Fig. 21) were compared with similar data on fresh conventional positive plates of
60-mil and 80-mil plate thickness. This is approximately equivalent to our 28-mil and 44-mil
2
one-sided plates, respectively. At the 150 mA/cm operating point, the "volume capacities" for
3
the 28-mil and 44-mil resistance-free structures were 3.3 and 2.2 Ahr/in. respectively; while
3
they were 3.1 and 2.8 Ahr/in. for the 60-mil and 80-mil conventional plates respectively. That
2
is, there was no marked difference in paste utilization. At 250 mA/cm , however, the volume
3 3
capacity for the 28-mil one-sided plate was 2.7 Ahr/in. compared to 1.9 Ahr/in. for the con-
ventional plate of 60-mil thickness. A similar trend applied to the resistance-free plate of
44-mil thickness compared to the conventional plate of 80-mil thickness.
For a conventional battery to operate at a power density of 100 W/lb, the plates
2
must support current densities > 200 mA/cm . Under such conditions, there is an effect of
longitudinal iR losses in conventional plates which is manifested by poorer paste utilization
compared to that in resistance-free plates. Higher local depth of discharge can thus be antici-
pated even when the overall depth of discharge is relatively shallow. As noted in previous sec-
tions, we have tested conventional positive and negative plates under high rate cycling conditions
(equivalent to47.5 KW on discharge with a 2 5.9 KW charge) and found that excessive positive paste
shedding occurs in the area of the current take off terminal. This is shown in the photographs
in Figs. 5 and 6 which are of a positive plate before and after cycling (> 300 complete high rate
cycles). Clearly then, designs aimed at eliminating these resistance effects are desirable and
should permit a more even utilization of active mass with consequent greater plate life on
cycling.
2
At the 150 mA/cm operating point, we observe no severe discrepancies between
conventional plates and resistance-free plates. Thus, at this point, the problem of longitudinal
resistance losses is not a serious one with battery plates. We reemphasize that whereas a
2
battery constructed from the new design plate can operate at 150 mA/cm (the power density
here is actually 135 W/lb), a battery with conventional plates can not (the power density of a con-
2
ventional SLI thin plate lead acid battery operating at 150 mA/cm is only 74 W/lb).
B. Effect of Sb and HgPO. on Paste Performance
It has been established 13-17 that, for conventional batteries cycled at relatively deep
depths of discharge, Sb presence lead to increased cycle life. Similar results apparently
- 42 -
-------
18 -21
followed H,PO. additions to the electrolyte using pure Pb or Pb/Ca grids. Unfortunately,
«5 4
the above data did not consider the very shallow discharge cycles at high rates required in the
present case; for this reason, we decided to investigate the effect of Sb and HgPO. on paste per-
formance under these conditions. Our prime concern here was to determine if Sb could be re-
moved from the battery grid without affecting cycling lifetime. Since the present battery has to
last for 5 yr, we also anticipated serious restrictions to lifetime from self-discharge, poor
charge acceptance and grid corrosion if Sb additions were necessary.
The desirability of having a maintenance free battery also necessitates the removal of
Sb from the system. Apart from lowering the Sb content from 4.5% to ~ 0.5% and using
AC
a microporous rubber separator to prevent Sb reaching the negative plate, there is little
alternative to overcoming the desirability of Sb presence in regard to enhancing cycling life
without the undesirable side-effects quoted above, other than finding an additive which has the
same effect on cycling behavior, but not the same adverse effects. The above alternative in
fact is also not very feasible since only very small amounts of Sb are required to introduce the
undesirable effects of selfdischarge and gassing, etc., on the negative plate.
For this study, we used our iR-free, one-sided plates pasted to a depth of 20 mil. Nine
plates were prepared, three from a Pb/4.5% Sb alloy and the remainder from pure Pb. Universal
Grenox oxide was cured and formed in the conventional manner and plate capacities determined
at the C/5 rating. To the electrolyte in three of the cells with pure Pb grids, HgPO. additions
(1.8 vol % of 85% H0POJ were then made. The amount of H,PO,, used corresponds to the opti-
6 4 21 J 4
mum addition used by Tudor, et al. The additions were made after forming the plates since
the latter authors report lower capacity values on prior addition of H,PO,. To minimize the
O 4
temporary early cycle capacity losses in cells containing H,PO4> we also cycled each of the
above three plates five times (to 1.8 V) prior to our high rate charge/discharge investigations
of paste performance. We also cycled all the other plates in the same way so that each plate
for testing had exactly the same prior history.
After this conditioning, the C/5 capacities of the three plates containing Pb/4.5% Sb
were 2.28, 2.18 and 2.35 Ahr (plates numbered 1-3, respectively). The plates pasted in pure
Pb grids and with no I-LPO. additions had capacities of 0.83, 1.44 and 1.50 Ahr (plates numbered
4-6, respectively). Interestingly, the capacities of these plates were 1.97, 2.34, and 2.36 Ahr
on first measuring the C/5 capacity. (Plate number 4 showed very poor paste adhesion even
prior to any cycling.) Degradation in performance is obvious for pure Pb plates even within
these relatively few (bu^ deep) discharge cycles. Some degradation was also observed with the
Sb containing plates but to a much lesser extent. The initial C/5 capacities of the Pb plates
numbered 7, 8, and 9 prior to H-PO. additions to the electrolyte were 2.28, 2.01, and 2.42 Ahr,
respectively, and fell to 1.69, 1.39, and 1.61 Ahr immediately after HoPO. additions. After
four further cycles to 1.8 V, values of 1.65, 1.60, and 1.70 Ahr, respectively, were recorded.
The cycling tests were performed basically as described for the commercial plates.
When testing Sb-free positive plates, pure Pb or Pb/0.08% Ca grids were used in the negative
2 2
plates. The current densities for cycling were 150 mA/cm for discharge and 82 mA/cm for
- 43 -
-------
charge (equivalent to 55 KW and 40 KW, respectively, in our design). Discharge time was
25 sec and charge time 61 sec. Only positive plate performance was evaluated in detail and
large capacity negatives were used. Test temperature was again 30°C + 1°C.
The results of these experiments are plotted in Figs. 22-29. These show initial and
final voltages during groups of cycles and also the capacity (C/5) retained by each plate after
approximately each group of 100 cycles. The cutoff voltage was kept constant at 1.5 V on dis-
charge but was permitted to vary from 2.55 V to ~3.5 V on the charge cycle. The reasons for
this were that the negative plate potentials at end of charge in the absence of Sb were shifted to
more negative values because of the greater H-overvoltage on pure Pb. Also, the positive plate
potential is apparently polarized when no Sb is present. Therefore, when the cutoff voltage was
set at 2.75 V on charge for example, we found that the cells containing no Sb cut out excessively
early and, as a result, not enough charge was put back into the cell during the charging part of
the cycle. When the cutoff point was set at, e.g., 3.0 V, many of the cells responded very well
to the cycling conditions without any severe capacity losses. In some cases also, we raised or
lowered the cutoff point on charge merely to examine subsequent cell response on discharge.
In the figures we have also noted these changes.
Generally, when the cutoff point was raised (and cells stayed in for greater times on
charge), the subsequent discharge cycles were at higher voltages throughout and the final dis-
charge voltage gradually increased during cycling. Exactly opposite effects were noted when the
cutoff point was lowered. Excessive raising of the cutoff point may induce early cell failure due
to excessive gassing of the plates.
1. Overall cell performance of plates with lead-antimony grids
a. The Pb/Sb positive plates all behave well on cycling and show good performance
on charge and discharge at least up to 320 complete cycles. The capacity retained after this
number of cycles is 45%, 20% and 65% for the three plates. This is better on average than
commercial positive plate performance under similar cycling conditions. One of the plates lasted
for 430 cycles before beginning to fail. The better cycling behavior of these plates when compar-
ed with the commercial plates is probably related to the drastically different grid geometry. It
would support the view that the failure mechanism with the latter plates under the test conditions
was due to paste shedding caused by grid corrosion and buckling, rather than to paste deterioration.
b. During discharge, the cell voltage falls on average only by 0.13 V when the
cells are performing well. This also is much superior to commercial thin SLI positive plate per-
formance (where the average voltage decay on discharge was 0.22 V).
c. At the onset of failure, no significant enhancement in performance is achieved
when the voltage cutoff is raised above 2.75 V. On the contrary, excessive gassing and paste
shedding result.
d. The final discharge voltage is ~1.75 V when each cell is performing well.
Even on fresh conventional plates, the final discharge voltage never exceeded 1.65 V.
- 44 -
-------
CUT-OFF POINT (VOLTS)
2
3.2
3.0
UJ
O o o
«t Z-°
h-
O
>2.6
24
2.2
100
O
1C
1.9
UJ 1.7
e>
i-
§ ,.5
too
o
.75 2.65 2/^.5 2-55 2.75
2.75 3.1 3.2 2.75 3.0
11 1 11
CHARGE PORTION OF C
—
—
—
—
j
I
YCLE
—
—
—
—
—
— PERCENT CHARGE TIME BEFORE CUT-OFF ~
: '
50
J
— '
—
II
• •
1
• • .
• 4
PERCENT
87.6 96.3
«
DISCHARGE
i n 1
• * *
• • * •
CAPACITY RETAINED ' . —
1
II
45.4 6.9 2.
POF
me
IN (
PERCENT DISCHARGE TIME
BEFORE CUT-OFF
•
li i
DF (
I
;YC
LE
<
—•
• * __
• *
1
1 —
100
200 300
CYCLE NUMBER
400
500
Fig. 22. Cycling performance characteristics of Universal Grenox positive
material pasted in an idealized iR-free, one-sided laboratory test
Pb/Sb grid to a depth of 20 mil - Pb/Sb-1
- 45 -
-------
CUT-OFF POINT (VOLTS)
2.75 2.65 2.6 2j5|5 255 275
i i i^5 i -
f-
3.O
2.75 3.0
LU
3.0
2.8
2.6
2.2
CHARGE PORTION OF CYCLE
PERCENT CHARGE TIME BEFORE CUT-OFF
100
• • ••
PERCENT CAPACITY RETAINED'
IOO
86.1
97.6
2O.6
22.0
100
2OO 300
CYCLE NUMBER
400
4.8
1.9
UJ 1.7
O
5
0 |5
100
0
~1| I |j 1
(1
1
DISCHARGE PORTION OF
1 1 III I I |
CYC
~~ PERCENT DISCHARGE TIME BEFORI
» . _ -i - « • * • • 4^
i
1 i
:
LE
CUT-OFF ' *
—
—
• • *
; • • • r • j ~
500
Fig. 23. Cycling performance characteristics of Universal Grenox positive
material pasted in an idealized iR-free,one-sided laboratory test
Pb/Sb grid to a depth of 20 mil - Pb/Sb-2
- 46 -
-------
CUT-OFF POINT (VOLTS)
2:
2.8
UJ 26
*-,
O
> 24
2.2
100
O
10
,,|
u
r
0
> 1.5
IOO
0
r5 2.65 2-55 2
Ll
,_._
—
•- .1 I.. • •
0
—
1
—
55
t
•
114
2.75
1
CHARGE PORTION OF CYCLE
PERCENT CHARGE TIME BEFORE CUT-OFF
• • •
*•• **•• ••
PERCENT CAPACITY RETAINED
.3 102.2 64.9
DISCHARGE PORTION OF CYCLE
T t
I'l ||
PERCENT DISCHARGE TIME BEFORE CUT-OFF
11 i
*Zi
» •
4
•
14.7
i
5
•
f
~— "
_
e
—
•
.0
100
2OO 300
CYCLE NUMBER
400
500
Fig. 24. Cycling performance characteristics of Universal Grenox positive
material pasted in an idealized iR-free, one-sided laboratory test
Pb/Sb grid to a depth of 20 mil - Pb/Sb-3.
- 47 -
-------
100
1.9
CUT-OFF POINT (VOLTS)
3.4
3.2
3.0
2.8
UJ
e>
Q2-6
2.4
2.2
100
0
Q 2.75 a65 3.0 2.75 3.0 2.75
'
r
—
—
.
CHARGE
3.0
1
PORTION OF CYCLE
PERCENT CHARGE TIME BEFORE
• * •
•• ...
•
*«
PERCENT CAPACITY
»
3.0 3.2 3.4 3
11 1
I
•
5
—
—
—
—
—
* -L.-I-'-
CUT-OFF ~
- — •
• • •
RETAINED ~
98.8
97.6
104.8
80.0
42.1
LU
< 1.7
O
1.5
100
DISCHARGE PORTION OF CYCLE
PERCENT
DISCHARGE TIME BEFORE CUT-OFF
0 —
1
100
200 300
CYCLE NUMBER
40O
500
Fig. 25. Cycling performance characteristics of Universal Grenox positive material
pasted in an idealized iR-free, one-sided laboratory test Pb grid
to a depth of 20 mil and with PLPO. added to the electrolyte —
Pb HgPO4-7 6 *
- 48 -
-------
CUT-OFF POINT (VOLTS)
3
3.5
34
3.2
UJ3.0
(0
^2.8
2.6
24
2.2
100
0
10
1.9
UJ
O
O
1.5
100
0
c
3 35 2.75
i
•——
—
—
—
—
32 3.2 3-3 3£>
111 1
3.4 3.5 3.0
1 1
CHARGE PORTION OF CYCLE
•
1
3-2 3 5 IN EXCESS
1 1 OF 3.5
— — •
—
~~ PERCENT CHARGE TIME BEFORE CUT-OFF
c •
*
•
* ' " PERCENT CAPACITY
0 IO5.6 93.8
t
•
i
RETAINED "" ~
9O.O 63.8 4O.6
DISCHARGE PORTION
— • •
P
ER<
* • ' • • • •
• • •
... ... • * »
J
:EN
T D
ISC
HA
R
*
•
L
i
) 100 200
GE
TIN
OF CYCLE _
IE BEF
•
n
• •
RE
01
IT-
OFF
•
•
a
i •• • • i — *
•
i""
300 400 5OO
CYCLE NUMBER
Fig. 26. Cycling performance characteristics of Universal Grenox positive material
pasted in an idealized iR-free, one-sided laboratory test Pb grid
to a depth of 20 mil and with hLPO. added to the electrolyte -
Pb H3P04-8 3 4
- 49 -
-------
CUT-OFF POINT (VOLTS)
2
3.2
3.1
u,3-0
O
tj
0 2.Q
2.B
2 A
2.2
100
0
1C
1.9
LU
_)
O
> 1.5
100
0
.1 ' i
2-7,pfi=2i7oB 3.0 2.753.0 3.33.02.75
1* IP 1 11 111
1 CHARGE
—
—
r—
_
-
i-
—
»"• »
PERCENT
•
•
3.0 3.1 3.2 3.4
1 111
PORTION OF CYCLE
.
•
—
—
—
—
—
CHARGE TIME BEFORE CUT-OFF —
PERCENT
O
95.9
98.2
t
>
»
CAPACITY
— DISCHARGE PORTION
H
I]
f
—
PERCENT
1
I
I
1
DISCHARGE
t
TIME
i
• • • • • — •
•
RETAINED '
OF
103.5
CYCLE
1
• (
84.1 535
—
BEFORE CUT-OFF
1
1
i
—I
• • . . — t
1 ' ~~
IOO
200 3OO
CYCLE NUMBER
400
500
Fig. 27. Cycling performance characteristics of Universal Grenox positive material
pasted in an idealized iR-free, one-sided laboratory test Pb grid
to a depth of 20 mil and with H«PO. added to the electrolyte -
Pb FLPO.,-9 J
- 50 -
-------
CUT-OFF POINT (VOLTS)
2
3.4
3.2
O
0 2.8
2.6
2.4
2.2
100
0
10
1
0 2.75 2.8302.9 3'?33 3,5 3.035
—
—
I
•
. . 1.
CHARGE
•
1
PORTION OF CYCLE
—
—
—
—
—
— PERCENT CHARGE TIME BEFORE CUT-OFF —
• • * § • •
___ PERCENT _
CAPACITY RETAINED
0 1 3.2 I7.4 I6.0
r
![
e> i .7
b
o
1 00
0
—
DISCHARGE PORTION OF CYCLE
\
. .
—
—
. .... PERCENT DISCHARGE TIME BEFORE CUT-OFF _
'*••••*• • ••
L ' ' ' 1 I 1 i -
100
200 300
CYCLE NUMBER
400
500
Fig. 28. Cycling performance characteristics of Universal Grenox positive material
pasted in an idealized iR-free, one-sided laboratory test Pb grid
to a depth of 20 mil and with no additions — Pb-5
- 51 -
-------
CUT-OFF POINT (VOLTS)
3.2
3.0
LU go
<•> «•**
2.6
2.4
2.2
100
0
1C
1.9
tu
|..r
O
100
0
c
4.
—
5
3.
— — .• • • 1
)0
—
)
0 2.75 3.0 2.75 3.0
1 1 11
CHAR
PERCENT Ch
GE
m
» •
• " . • •
PERCENT
1 1
-. PORTION OF CYCLE
RGE TIME BEFORE CUT-OFF —
• • 1 1 . i ....
CAPACITY RETAINED
60.7 42.7 24.0 26.0 C
DISCHAR
'III!
PERCENT DISCHAR
GE PORTION OF CYCLE _
GE TIME BEFORE CUT-OFF
fi
• *•• ¥ 999 9 9 4 •*• • • — • 9
i 1 I 11
IOO 200 300 400 50
CYCLE NUMBER
Fig. 29. Cycling performance characteristics of Universal Grenox positive material
pasted in an idealized iR-fr.ee, one-sided laboratory test Pb grid
to a depth.of 20 mil and with no additions - Pb-6
- 52 -
-------
e. The oversized negative plates all behaved very well on discharge, generally
exhibiting a voltage of ~1.0V versus Hg/HggSO^ On charge, negative plate potentials varied
somewhat. When the plates were undercharged, the voltage was < 1.15 V. When gassing, volt-
ages as high as 1.45 V were recorded.
f. When performing well, positive plate potentials on charge were ~1.45 V at
the end of the charge cycje while on completion of the discharge cycle the potential was generally
-0.84 V versus Hg/Hg2SO4.
g. Failing cells exhibited positive plate potentials in excess of 1.6 V versus
Hg/Hg-SO. on charge and down to 0.6 V on discharge."
h. Failed positive plates exhibited very poor paste adhesion in the onesided
iR free grid.
2. Overall cell performance of plates with pure lead grids and HgPO.
additions to the electrolyte
a. The Pb/H,PO. positive plates all behave extremely well on cycling over most
of 4'00 complete cycles. After 320 cycles, the capacity retention is 105%, 104% and 90% - far
superior to the Pb/Sb plates. After 500 complete cycles, the values are 42%, 54% and 41%.
b. The decay in voltage during discharge is more marked for these plates and
occurs also at lower values. When performing well, the voltage decay during a discharge cycle
was on average 0.19 V.
c. During charge, cell voltages in excess of 3.0 V were common on completion
of the charge cycle.
d. Final discharge voltages are in excess of 1.6 V when each cell is performing
well.
e. On charge, the positive plate potentials are of the order of ~1.6 V versus
Hg/Hg,SO. when the cell is behaving well. Values in excess of this were recorded towards
£t 4
completion of the cycling experiments. On discharge, the voltage approaches 0.74 V versus
Hg/Hg2S04.
f. Negative plate potentials (oversized plates) are constant near 1.0 V versus
Hg/Hg-SO. during discharge but depending on the state of charge of the plate, may vary during
charge from 1.06 V to > 1.6 V versus Hg/Hg2SO4. This is caused by an increase in the hydrogen
overvoltage on the plate when no Sb is present and is one reason why such large cell voltages are
observed at end of the charging cycle. In addition, there is increased polarization of the positive
plate.
g. Even after 500 complete cycles, there was still very good paste retention in
the one-sided plates.
3. Overall cell performance of plates with pure Pb grids without H^PO.
additions to die electrolyte
Very poor performance was observed with all these plates and most did not last
more than 200 complete cycles. After 200 cycles, 19%, 42%, and < 10% capacity was retained
- 53 -
-------
by the three test plates. As with the Pb/FUPO.. plates, excessively high cell voltages are ob-
o 4
tained during charge. The cells have no apparent durability as regards cycling life. Failed
cells showed very poor paste adhesion reminiscent of that in the Sb containing cells after more
extended cycling tests.
Our basic conclusions with respect to the above are that Sb can be removed from the
cells provided H.PO. additions are used instead. Though there is a fall in overall capacity
(C/5) following HgPO. additions (~25%), the capacity retention during cycling of the latter
plates appears to be better than on the plates containing Sb, when both are cycled in the same
manner. The final voltage of laboratory test cells containing Sb is > 0.1 V higher than that of
the Pb/H,PO. test cells during discharge. If the negative plates are near full charge, gassing
o 4
occurs on the Sb-free plates at potentials substantially more negative than on those plates con-
taining Sb. No excessive negative-plate degradation is observed, however. Because the negative
plate potential shifts markedly according to its state of charge, it can seriously affect investiga-
tions by cutting out cells when the positive plate is still capable of performing well. This is a
factor which requires careful consideration in examining the results presented here. The posi-
tive plate, when fresh, is polarized by 0.1-0.2 V when Sb is absent from the cells. When the
cells have been tested for > 300 cycles, the Pb/Sb plates also have high positive plate potentials
on charge. With the H~PQ. containing cells, no paste degradation is noted as a result of positive
plate polarization.
We have examined the plates visually after cycling and find poor paste retention and
softening in those plates with Pb/Sb grids and with pure Pb grids. The plates of pure Pb with
M«PO. added to the electrolyte exhibit a much better surface appearance and have not nearly so
much shedding. They are still, however, softened somewhat on the surface of the paste. A
"slippery" whitish film is also present on these plates - probably a phosphate containing com-
pound. No X-ray or electron microscopic investigations or paste microstructure were carried
out here due to time limitations.
C. Factors Not Varied in the Study of Electrochemical Performance
Mainly because of time limitations the following were not varied in our experiments:
1. Surface area of active material (as defined by additions of Pb^O. to litharge).
2. Separator material: For tests with commercial plates, the.separators supplied
with the batteries were employed. The same type of separators were used when examining the
effect of Sb and H-PO. on paste performance. For tests with novel designs, industrial Daramic
27
separators were employed. This is an extruded polyethylene material.
3. Electrode retainer: For tests with commercial plates and in examining the
Sb and HoPO. questions, no retainers were used. For tests with bipolar plates 3-mil glass mat
o 4
retainers were used.
4. Sulfuric acid concentrations: Constant at 1.28 sp gr.
5. Cycling temperature: Constant at 30°C± 1°Q
- 54 -
-------
6. Nature and amount of expander in the negative plate: This was kept constant
at 2% of an industrial "KX" expander supplied by ML Industries.
7. Specific gravity of HJSO. used in the formation process: This was kept con-
stant at 1.08.
8. Use of tetrabasic lead sulfate based paste instead of lead oxides as starting
material: This was not examined.
9. Morphology of the active material (as defined by the curing process and the
nature of the original oxide mix): We did attempt to use Barton VLY oxide with and without a
high temperature curing schedule. Particularly in the latter case, poor adhesion of paste was ob-
served so we did not extend these evaluations. With Universal Grenox oxide, a conventional room
temperature cure was employed at all times.
10. Paste stabilizers: < 1% of dynel fibers were added to the positive paste to
enchance mechanical paste stability during cycling. This is a common industry procedure. With
later novel plate designs the same amount of fibers was added to the negative paste for the same
purpose.
11. Porosity of active material (as defined by the amount of HJ30. added during
the mixing): This was kept constant at 42.5 cc of 1.4 sp gr H0SO. per Ib of positive oxide and 38 cc
& 4
of 1.4 sp gr H-SO. per Ib of negative oxide. For early experiments with Barton VLY oxide, this
amount was varied but with varying success as indicated by subsequent performance results.
D. Conclusions
The following major conclusions were drawn from the foregoing data:
1. To optimize a lead acid battery for use in hybrid electric vehicles, a large
number of thin plates should be used. The operating current density is thus reduced. Paste
utilization is substantially increased in thin plates compared to that in conventional plates oper-
ating at the same current density.
2. Particularly on cycling, there is a serious problem with conventional plates
operating at high power densities which is caused by longitudinal, resistance losses along and down
the grid. This results in uneven utilization of active mass and, therefore, high local depth of
discharge even when the overall depth of discharge is shallow. Paste shedding results. When
these resistance losses are minimized there is a marked improvement in paste performance at
the same, high operating power densities.
3. To maintain cycle life in a battery which contains no Sb in the grid, paste or
electrolyte, (for example when pure Pb is used as grid material) small additions of HgPO^ to
the electrolyte are very effective.
- 55 -
-------
V. TASK IV. CORROSION OF SUBSTRATE MATERIALS
22 28-30
The problem of corrosion in a lead acid battery is a severe one ' and greatly
reduces the number of candidate materials. Particularly in a bipolar design, with thin plate
structures, corrosion may be expected to seriously affect plate life if adequate materials
are not chosen. This is particularly true in the 1.28 sp gr H^SO^ electrolyte chosen to
meet the desired high power density applications. Corrosion of the grid, which, in a bi-
polar design, can be either a conductive, high strength/light weight metal sheet of suit-
able design, or a system based on a plastic substrate with metal strips as conductors laid on
the surfaces of the substrate, was of prime concern. Because there are a number of commer-
4 27
cially available separators and retainers of suitable type and dimension, ' these were not
considered further from the corrosion aspect. Choice of appropriate plastic for the battery
case was, however, also examined.
The choice of a grid material or materials involves a compromise between the
increase in active mass utilization concurrent with a reduction in active mass thickness and the
increased likelihood of plate failure by corrosion of thin cross-section grid members. The aim
of this study was to provide information on the most suitable material for grid and case construc-
tion. In particular, plastic materials, both conductive and nonconductive metal substrates, e.g.,
Ti, TiN, Al, Mg, C and conventional Pb based grid alloys were investigated.
A. Metal Substrates
1. Metals other than Pb and Pb based alloys
There are several materials of choice, namely Ti, TiN, Al and Mg, all of which
are theoretically very desirable. They are light weight/high strength materials and because of
their good conductivity can be used both to support the active mass and also to conduct the cur-
rent over the entire plate area during discharge. Even in thin cross-sections, no reinforcement
is necessary (in contrast to Pb or Pb based materials of similar dimensions). Most of these
metals have been examined at one time or the other in the past but there are few recorded results
of their behavior in Pb acid batteries. Unfortunately, Al and Mg both corrode rapidly when ex-
posed to HoSO* and attempts to protect Al from corrosive attack in hUSO, by an overplating
with Pb have also proven unsuccessful due to imperfections in the plate. Ti metal at the po-
O 1
tential of the negative lead acid plate also corrodes readily. At the positive plate potential,
01
TiO9 is formed and inhibits further corrosion but acts as a dielectric. TiN does not corrode
31 32
in H2SO4 at either the positive or negative plate potentials. However, on the positive
plate at the interface between the nitride and the pasted lead oxides, a dielectric TiO9 film is
32
again formed. This gives poor paste adhesion and results in insignificant charge and dis-
- 57 -
-------
32 33 33
charge capabilities of the paste. ' The use of a flash of Au on the TiN has been proposed
to alleviate the latter problem. In the context of the present contract, this solution was thought
to be unacceptable because of the economics involved. Instead, we studied briefly the use of
conductive plastic coatings to protect the metals from the corrosive environment while still
maintaining electronic contact with the paste.
Tests were initiated on metal plaques using Al, Mg and Ti coated with a conductive
epoxy material. The conductive coating was made from epoxy resin no. 828 and curing agcric-
Z, *using60% TiNpowder of 325 mesh as conducting medium. Typically, after the coating
process, it was necessary to grind the coating to achieve adequate conductivity. This was
because the TiN particles tended to settle during curing of the epoxy. Conductivities varied
2
with coating thickness. For example, at 1-mil thickness, the resistances were 3 £2/in. for
2 2
the coated Al plaque, 4.4 n/in. for the Mg, 3 ft/in, for the Ti. For a 2-mil thickness, the
2
Mg plaque exhibited a very high resistance, whereas for Ti the resistance was 4. 4 J7/in. .
Difficulty was encountered in preparing a conductive coating of suitable consistency, in that if
the coating was too thin the epoxy tended to flow off the surface and the TiN particles settled
rapidly, leaving a rough granular surface of low epoxy content. If the coating was too thick,
then it was very difficult to apply. This was an even greater problem with graphite 325 mesh
material as conductive medium. Here it was necessary to use a 50 wt % graphite/epoxy mix-
ture to achieve any type of coating. Even after grinding to'1-mil final thickness, such coat-
2
ings still exhibited 1 Kn/in. resistance on each panel. We did not use conductive materials
/> A
in less than 50 wt % quantities because poor conductivities are observed at values lower
than this.
The TiN conductive epoxies coated on Al, Mg and Ti panels were potentiostatted at
1.25 V versus Hg/Hg2S04 in 1.28 sp gr HjSO^ at 60°C. After 6 days, the Mg panel showed
severe blistering and the current was 60 mA. After 8 days, the Al panel also showed severe
blistering and the current was 29 mA. Both Al and Mg panels showed severe dissolution of
the underlying metal. After 10 days, the Ti panel.showed small blisters in the center of the
plate which gradually spread until after 27 days total, the coating showed no adhesion to the
panel. The corrosive current was 0.1 mA.
The results emphasized the difficulty in working with metals which corrode in I-^SO.
media. As has been noted before, e.g., with Pb cladded Al, if any imperfections in the
coatings develop, then catastrophic failureOccurs. These imperfections were obviously
present in our coatings. The Ti did not exhibit such a high corrosion rate because of its
protective oxide. Because of these problems, we did not extend our experiments on these
metallic substrates any further but concentrated instead on what we felt were the more
attractive alternatives of plastic based substrates with Pb based materials as electronic
conductors laid on each side of the substrate.
2. Pb and Pb alloys
Pure Pb or Pb alloys can theoretically be used as grid (active mass support and
current conductor) in a bipolar design but in practice, the sheets have to be of impractical
thickness for this purpose. Thus, there is a problem of corrosion through the sheets which
would have to be excessively thin to conform to battery weight requirements. Also, such
thin sheets (^40 mil) would in any event be unable, solely, to support the active mass.
*Supplied by the Shell Chemical Company.
- 58 -
-------
28
Due to predominant formation of PbO? on the positive side, buckling can also be expected.
These factors, however, do not preclude the use of Pb or its alloys as current conductors in
a bipolar plate with a plastic substrate to support the active mass. Because of this, we have
also examined the corrosion and expansion of these materials in F^SO^.
A substantial quantity of data have been published on the corrosion and expansion of
99 OC-"lfl Qc: |
Pb and Pb alloys in H2SO4> . ' ° JU»o;5 These have been reviewed and, in the following, a
brief discussion is given of the factors we considered in the selection between the three con-
ventional current conductors, namely: Pb/Sb alloys and Pb/Ca based alloys and pure lead.
Results of corrosion tests in this laboratory are also recorded.
a. Strength: As noted, by itself pure Pb does not have sufficient
mechanical strength to support the active mass even In conventional automotive plates. Pb/Sb
and Pb/Ca grids are intrinsically much stronger but for the thinner plate structures (<50 mil)
which are desirable for high power density batteries, are themselves marginal. Such thin
grids are also more difficult to cast.
b. Corrosion and expansion of positive grid: We have demonstrated
earlier that to achieve a high power density lead acid battery, a larger number of thinner
plates with minimized resistance losses would be desirable. Setting aside the mechanical
strength aspect - which must also be considered in plate thicknesses <50 mil (even for
Pb/Sb or Pb/Ca alloys) - the limiting factor then becomes that of the plate failure by grid
corrosion. As the grid thickness is reduced, so the likelihood of this mode of failure is in-
creased. Of the three materials Pb, Pb/Sb and Pb/Ca, the former was believed to be least
susceptible to this mode of failure. We carried out corrosion tests on annealed Pb, Pb/4.5%
Sb and Pb/0.08% Ca grids at 30, 60 and 90°C over a 60-day period to confirm this. Tests
were also carried out on the annealed materials coated with active mass (PbC^) and on un -
coated specimens. The latter were potentiostatted at the potentials attained by the coated
specimens in the same solution (close to 1.25 V versus Hg/HgoSOJ. The aims were to
compare the corrosion rates of the three materials and to investigate differences in cor-
rosion rates as a function of coverage with active mass.
Testing of the uncoated specimens shown in Figs. 30-32 gave the relative corrosion
' ^ A
rates of the three materials plotted as corrosion current versus time. As noted by Lander,
current measurements should not be taken as an absolute measure of the corrosion rate of
Pb alloys since some gas evolution may also occur on the samples. No detailed analysis of
the curves was carried out but it is evident that the most severe attack is experienced by the
Pb/Sb alloy while the Pb and Pb/Ca samples exhibit similar rates of attack. Fluctuations in
measured current are particularly evident with the Pb/Sb alloy possibly due to formation of
passivating PbSO4 layers and their periodic shedding from the specimens. Also, with the
Pb/Sb alloy, the initial high rate of attack is presumably caused by depletion of Sb in the
surface layers of the alloy.
After testing, the samples were removed and cleaned in ammonium acetate solution
ox
following the method of Lander. Weight loss measurements are given in Table IV.
Clearly, the data confirm the current measurements and point to an increasing sus-
ceptibility to corrosion attack in the order Pb/Sb > Pb> Pb/Ca. This also is somewhat mis-
leading as may be seen from Fig. 33 which is a photograph of the 90°C test samples. The
- 59 -
-------
01
o
15
20
25 30 35
TIME (day)
40
45
50
55
60
65
Fig. 30. Corrosion current of Pb, Pb/Ca and Pb/Sb grid samples held at
1.25 V (Hg/Hg2SO4) in 1.28 sp gr H2S04 at 30°C (O, Pb/Ca; •,
Pbj O, Pb/Sb)
-------
0.8
0.7
0.6
E
u
0.5
Z 0.4
UJ
cr
-------
3.0
2.5
2.0
CM
E
o
4) in 1.28 sp gr H2SO4 at 90 °C (O, Pb/Ca; • ,
Pb; O, Pb/Sb)
-------
.
,--.
, • .
Fig. 33. Photograph of "bare" grids after corrosion in 1.28 sp gr
at 1.25 V (Hg/Hg2SO4) at 90 *C after 60 days
- 63 -
-------
Table IV. Comparison of the Weight Losses (g) of Pb and Pb Alloys in
gSO at Various Temperatures After 60 Days Immersion
Temperature
Alloy
Pure Pb
Pb/0.08% Ca
Pb/4.5% Sb
Original
Weight
14.2865
13.8223
18.0567
30°
Weight
Change
0.0565
0.0423
0.5967
Original
Weight
13.7870
13.7155
17.9865
60°
Weight
Change
0.2270
0.1455
2.9965
Original
Weight
14.0395
13.3297
17.9925
90°
Weight
Change
2.4695
2.0497
11.2825
Pb/Ca and Pb/Sb grids are almost completely disintegrated, whereas the Pb grid has corroded
but still maintained its shape. The latter may be attributed to severe inter granular attack in
28 37
the Ca and Sb containing alloys. As pointed out by Wesson, corrosion attack in soft lead
grids commences along grain boundaries even during the formation process. In lead calcium
alloys, grain boundaries are attacked only in service but to such an extent that not only the
individual grains, but whole areas, are cut off and consumed giving rise to cavity formation
and grid fracture, as we have observed. In Pb/Sb alloys, the eutectic corrodes, but since
this is of a finer structure than in the Pb/Ca alloy, the overall corrosion is more uniform
and therefore less destructive. The results confirm that pure Pb is the material of choice
to maximize corrosion resistance.
The effect of an overpasting of active material (PbC^) on the corrosion rates of the
above three materials was measured also. This was considered to be worth studying since
it is the practical situation in a battery and a review of previously recorded corrosion rates
on "bare" Pb based alloys had suggested that the life of conventional grids would be much
shorter than is actually observed. The inference was that an overpasting of active mass
led to decreased corrosion rates but no data were presented to substantiate this fact. Pb,
Pb/4.5% Sb and Pb/0.08% Ca grids of the same configuration as those in the above tests
were overpasted with active material which was then oxidized to PbOo on the grids in 1.08
sp gr HoS04 at 30°C. The samples were then immersed as before in 1.28 sp gr f^SO, at
30°C, 60°C and 90°C for 60 days. After this period, they were cleaned of active, mass, the
q £
oxide removed in ammonium acetate solution and weight loss then evaluated. This is ex-
pressed in Table V on a percentage basis and a correction has been applied for the weight
loss incurred during the formation of the positive active mass on the grids before corrosion
testing. (The correction factor was obtained simply by forming PbO? on exactly similar
grids under the same conditions and for the same time as before. The grids were then
cleaned of active mass and the oxide removed in acetate solution. Finally, the weight losses
incurred during paste formation were measured.) Comparative percentage weight losses
are included in Table V for the samples not covered with an overpasting of active mass dur-
ing corrosion testing.
*In all of these tests an attempt was made to keep the geometric area of the test grids
of the three different materials as closely similar as possible. This also applied to
the tests with overpasted grid samples.
- 64 -
-------
Table V. Comparison of Weight Changes (%) in Pb and Pb Alloy
Grids With and Without an Overpasting of Positive Active
Mass When Immersed in 1.28 sp gr HoSO4 at Constant
Potential for 60 Days
30°C 60°C 90°C
Alloy Pb Pb/Ca Pb/Sb Pb Pb/Ca Pb/Sb Pb Pb/Ca Pb£b
Unpasted Samples 0.4 0.3 3.3 1.6 1.2 17.5 17.5 15.3 62.5
Pasted Samples 3.7 0 3.5 3.7 1.8 11.1 13.7 7.2 15.8
The above method of correcting for corrosion weight losses during formation of the pasted
grids was not thought to be very accurate. In the case where comparable weight changes
were observed on subsequent corrosion of the samples by immersion at low temperatures in
1.28 sp gr H^SCL, an accurate evaluation of the effect of an overpasting of active mass on
underlying grid corrosion was not obtained. However, whereas the weight change arising
from corrosion of the grid during PbOo formation was both constant and low (since formation
temperature was low and constant), the magnitude of weight losses arising from subsequent
corrosion of the samples immersed in 1.28 sp gr acid^ increased with increase in tempera-
ture. Especially at 90°C, the correction factor was relatively small when compared with
the overall final weight change. At 90°C, it is evident that the samples overpasted with
active mass prior to corrosion all exhibit lower corrosion rates than for corresponding un-
pasted samples. Photographs of the former alloys corroded at 90°C are shown in Fig. 34
after removal of the active mass and ammonium acetate cleaning.
We conclude from the above that reduced corrosion rates may be expected in Pb
alloys overpasted with active mass. The extent of the reduction is estimated to be in
excess of 20% - which is a substantial improvement in terms of grid lifetime.
Associated with corrosion, there is an expansion of the grid due to the lower density
28
of the formed PbOn as compared with lead. This expansion sometimes leads to plate failure
due to loosening of the contact between the active mass and the grid. Expansion is somewhat
28
less in Pb than in Pb/Ca due to its slower corrosion rate. With Pb/Sb alloys of high Sb
content, expansion is still less of a problem because the Sb dissolution compensates for the
volume increase in PbOo. The choice between Pb and Pb alloys, however, does not rest
solely on the above characteristics. For example, Sb also has other effects on Pb acid
battery performance which are discussed below.
c. Effect of positive grid material on the negative plate: During
corrosion, Sb is released in the electrolyte from the positive grid and migrates to the nega-
1Q
tive plate where it deposits. Once there, it lowers the overvoltage for hydrogen evolu-
tion on the negative plate (see Task HI in this report) and this causes the following adverse
effects: (1) it facilitates gassing of the negative during charge resulting in higher consump-
90—2^ 28
tion of electrolyte and increased maintenance requirements; ' (2) it prevents adequate
charging of the battery particularly as more Sb plates out on the negative (the current in-
stead goes increasingly into gas evolution); (3) it gives rise to grid corrosion and overcharge
(also with gas evolution) on the positive plate; since more current is required on float, and
(4) it causes self-discharge of the negative plate by local cell action.
- 65 -
-------
Fig. 34. Photograph of grids corroded in 1.28 sp gr H£SO4 (with an
overcoating of PbOg) at 90°C for 60 days
.
- 66 -
-------
d. Effect of grid material on positive paste: A positive aspect re -
garding the use of Pb/Sb alloys in battery grids is that Sb becomes incorporated in the posi-
13-17 ^8
tive paste improving its performance. ' Hence, a larger number of cycles is per-
mitted before failure occurs. We have confirmed this finding (Section III) using high rate/
shallow discharge cycles, but have also shown that when no Sb is present in either grid or
electrolyte, (i.e., using pure Pb grids) HqPOA additions to the electrolyte have the same
18-21
positive effect on cycle lifetime. This latter observation obviates the need for Sb in
the grid in regard to cycle lifetime and thus facilitates the development of a maintenance-
free battery.
The preceeding discussion is summarized in Table VI which shows the advantages
and disadvantages of pure lead, Pb-Sb alloys and Pb-Ca alloys, as grid materials.
Table VI. A Comparison of the Relative Advantages (+) and
Disadvantages (-) of Three Grid Materials in Lead
Acid Batteries
Pb Pb/Sb
1) Strength - +
2) Expansion of Grid (+-) +
3) Corrosion of Grid + -
4) Self-discharge of -ve ' + - +
5) Non-charge of -ve -I- +
6) Effect on PbO2 of+ve - +
7) Gassing of -ve + - +
8) Maintenance of free operation + +
3. Conclusions
a. Metals such as Ti, TiN, Al and Mg either with or without con-
ductive coatings, Pb overplating, etc. are not suitable for use in Pb acid batteries without
additional development work. The materials all corrode severely or form oxides which
act as a dielectric.
b. Pb or Pb alloys cannot be used in sheet form as active mass
support and current conductor in a practical bipolar high power density battery for hybrid
vehicles. To resist corrosion and to be mechanically capable of supporting the active mass,
the sheets have to be of impractical thickness with particular regard to battery weigh limita-
tions.
c. The use of Pb or its alloys as current conductors in conjunction
with a plastic substrate material support is not precluded from a corrosion or expansion
aspect. Pure Pb is the material of choice by virtue of its corrosion resistance in acid com-
pared to Pb/4.5% Sb and Pb/0.08% Ca alloys. It also has less expansion problems than the
Pb/0.08% Ca alloy. It is estimated that a covering of active mass will reduce Pb corrosion in
.H2SO4 by at least 20% .
d. For maintenance-free operation, Sb should not be used in the
grid material.
- 67 -
-------
B. Plastic Substrates
These are attractive materials for use as plate substrates and as case materials
because they are light weight and can have high strength, particularly when reinforced. A
difficulty with bipolar plates in sealing each plate within the case is also minimized by the
choice of plastic plates. As with metals, these materials also must withstand l^SC^ de-
gradation.
The compatibility of plastics with Pb acid batteries has been examined by Butherus,
et al. A wide range of materials was also studied here. Basically, the latter can be
divided into two classes, namely: thermosetting plastics and thermoplastics. The former
materials are generally thought to be less resistant to J^SO^ than the latter. On the other
hand, thermosets exhibit superior bonding to metals such as Cu, Al, stainless steel, brass,
Pb and Pb alloys than do thermoplastics. In view of the desirability of preventing.short cir-
cuits by electrolyte leakage at those points where the Pb conducting strips extend through
the substrate, a more detailed study of the compatibility of the former materials with H»SO.
was justified.
Literature surveys of the compatibility of both classes of plastics with sulfuric acid
were carried out. ' Additional in house tests were also performed as elaborated below.
The engineering thermoplastics, being readily thermofor med, machinable, etc., and having
substantial inherent mechanical strength, were judged to be suitable for supporting active
material in thin structures ( ~ 20 mil) without further reinforcement by, e.g. , glass cloth,
or glass fibers. They were therefore tested in such a form. In contrast, thermosets for
structural purposes are most readily employed in reinforced form and are used in laminates
for a wide variety of purposes, e.g., printed circuit boards. We have, therefore, considered
the F^SO, compatibility of thermosetting resins reinforced with glass cloth and also the com-
patibility of the base resins themselves. Structural aspects of these materials are discussed
subsequently. Below, we give our own data on the compatibility of all these materials in
F^SOx , followed by literature data on the same subject where they were available. Since
the mode of preparation of the laminates is important and affects subsequent corrosion re-
sistance, information on this is also supplied.
The H^SO, compatibility of the plastic was tested by immersion in 1.28 sp gr H^SO,
at 30°, 60°, and 90°C for extended periods of time. Data are recorded in Table VII where
we show percentage weight losses or gains. In some cases, samples were almost com-
pletely destroyed. We have noted this also in the Table. Before weight measurements,
samples were washed free of acid and dried at 50°C overnight.
The Table shows the increased severity of attack as the temperature is increased.
Of the laminated thermosets, the phenolic and Dapon materials show most stability, while
the epoxy and polyester laminates exhibited decreased stability in that order. We have
shown the weight change for a phenolic SC 1008 base resin cured in two separate ways. In
general, both showed less attack than the corresponding laminates at equivalent tempera-
tures.
" Of the thermoplastics, plexiglass exhibited a 0.4% weight gain at 30°C, whereas the
other plastics exhibited < 0.1% weight changes. This trend continued at higher tempera-
tures except that hi-impact polystyrene was quite severely attacked at 60° and 90°C. At the
latter temperature also, PVC had a 3.5% weight loss. In general appearance, all samples
- 68 -
-------
Table VIL Weight Changes of Various Plastics in 1.28 sp gr
H2SO4 at 30°C
Resin ;
System
Epoxy
Micaply
No. 102-13
Laminate
Dapon
(From NELCO)
Laminate
Phenolic
SO 1008
Laminate
Polyester
XP-7289-L
Laminate
Noryl
Hi -Density
Polyethylene
Hi -Impact
Polystyrene
Lexan
Plexiglass
Polystyrene
PVC
Polypropylene
Sample
Number
1
2
3
1
2
1
2
1
2
1
1
1
1
1
1
1
1
Corrosion
Time,
Weeks
13
13
13
10
10
10
10
9.5
9.5
6
6
6
14
14
14
6
6
Weight
Change
%
+ 15.0
+ 5.3
+ 1.6
- 1.4
+ 4.1
+ 0.9
+ 0.4
+ 9.6
+ 6.6
0.0
- 0.1
< 0.1
+ 0.1
+ 0.4
< 0.1
< 0.1
< 0.1
- 69 -
-------
Table V1L Weight Changes of Various Plastics in 1.28 sp gr
H0SO^ at60°C
Resin
System
Epoxy
M ?.caply
No. 102-13
Laminate
Dapon
(From NELCO)
Laminate
Phenolic
SC-1008
Laminate
Polyester
XP-7289-L
Laminate
Noryl
Hi -Density
Polyethylene
HI -Impact
Polystyrene
Lexan
Plexiglass
Polystyrene
PVC
Polypropylene
Phenolic
Resin-SC1008
Phenolic
Resin-SC-1008
Sample
Number
1
2
3
1
2
1
2
1
2
1
1
1
1
1
1
1
1
1
1
Corrosion
Time,
Weeks
13
13
13
10
10
10
10
9.5
9.5
6
6
6
14
14
14
6
6
14
14
Weight
Change
%
+ 11.0
+ 10.1
+ 6.5
+ 0.2
+ 1.7
+ 7.5
+ 3.3
Destroyed
Destroyed
0.0
< 0.1
- 1.0
+ 0.1
+ 0.6
< 0.1
- 0.1
- 0.1
+ 0.1
+ 7.5
- 70 -
-------
Table VIL Weight Changes of Various Plastics in 1.28 sp gr
HS0 at 90°C
Resin
System
Epoxy
Micaply
No. 102-13
Laminate
Dapon
(From NELCO)
Laminate
Phenolic
SC-1000
Laminate
Polyester
XP-7289-L
Laminate
Noryl
Hi -Density
Polyethylene
Hi -Impact
Polystyrene
Lexan
Plexiglass
Polystyrene
PVC
Polypropylene
Phenolic
Resin-SC1008
Phenolic
Resin-SC1008
Sample
Number
1
2
3
1
2
1
2
1
2
1
1
1
1
1
1
1
1
1
1
Corrosion
Time,
Weeks
13
13
13
10
10
10
10
9.5
9.5
6
6
6
14
14
14
6
6
14
14
Weight
Change
%
T3
-------
showed some surface roughening at the higher temperature (90°C) and the polystyrene
curled up at this temperature. Below 90°C, only slight surface changes were evident for
all samples. The following curing schedules were used in the fabrication of the reinforced
thermosets noted in the table:
The epoxy was a Micaply no. 102-13 laminate with three plies of prepreg
and was cured at 350°F for 10 min at contact pressure and then 250 psi for 30 min followed
by cooling to •>• 70°F at pressure before removal from the press. The Dapon resin (modi-
fied polyester) was from New England Laminating Company. This was made from four plies
of prepreg (glass cloth style no. 7728) and was cured at 500 psi and 360°F for 30 min followed
by reduction in temperature to 70°F under pressure before removal from the press. No
precuring cycle was utilized to control resin flow. The polyester laminate no. XP-7289-L
from Fabricon Products was prepared using four plies of prepreg. Curing was affected at
250 psi and 300°F for 40 min followed by cooling to 70°F under pressure. Again, no pre-
curing cycle was applied. Phenolic laminates were made from no. 396 prepregs from Spauld-
ing Fiber Company, Inc. Three plies were used and cured at 350°F for 2 min at contact .
pressure followed by 40 min at 350°F and 300 psi and finally cooled under pressure to ~ 70°F.
The above curing schedules,and indeed, the above resins were not necessarily such
as to impart maximum chemical resistance. The materials and techniques were those most
readily available commercially. In addition, it was often impossible to obtain exact informa-
tion on the precise chemical make up of each thermosetting resin system, e.g. , resin, cur-
ing agent, promoter used. All these, and also the curing temperature, can have a marked
effect on the subsequent chemical resistance of the laminate. For example, the relatively
rapid rate of attack on our epoxy laminates was particularly surprising from several aspects.
Thus, in printed circuit board technology, laminated epoxies with Cu overlays are routinely
etched with much stronger acids than 1.28 sp gr H^SCs to selectively remove Cu. No ad-
verse effects are noted under such conditions. Also, Bell Telephone Company routinely en-
40
capsulates the terminal posts of their new standby lead acid battery in an epoxy resin.
Data shown in Tables VIII-X illustrate the chemical resistance of unfilled Epon 828 resin as
a function of curing agent in 25% H2S04 over a 180-day period at up to 225°F. Clearly, there
is a change in the rate of attack as the curing agent is varied and attack is also more pro-
nounced as the temperature is increased. The drastic changes we have noted in our test
specimens are not however evident here. Further examination of the test specimens in-
dicated that the attack was confined in the major part to the surface of the laminates and
particularly to the epoxy/glass reinforcement bond. In some test samples, exposed glass
edges were presented to the acid and subsequent greater rates of attack were observed with
these samples. Also, in some preparations (for an entirely different reason),, resin was
deliberately extruded in the form of 20 mil thick ribs on the surfaces of the laminates and,
whereas general attack was observed over the surface of the laminate, the ribs appeared
untouched (at up to 60CC). We have made similar observations with most of our other
laminates and generally find that though there is undoubtedly some attack by the acid at 90°C
(an excessively high temperature) the main cause of failure is at the thermoset/glass rein-
forcement bond. This is not surprising and many surface treatments (following section) are
applied to improve the strength of this bond prior to resin impregnation.
- 72 -
-------
Table V1IL Chemical Resistance of Unfilled Epon 828 as a Function of Curing
Agent in 25% Sulfuric Acid Over a 189-Day Immersion Period
75°F Immersion
Change in
Flexural Strength, Psi
Curing Agent
Triethylenetetramine
3 PHR BF3 • MEA
20 PHR Diaminodiphenyl-
sulfone (DOS)
20 PHR Curing Agent Z
14 PHR Curing Agent CL
75 PHR Phthalic Anhydride
110 PHR Chlorendic (HEX)
Anhydride
Triethylenetetramine
3 PHR BF3 • MEA
110 PHR Chlorendic (HET)
Anhydride
20 PHR Diaminodiphyenyl-
sulfone (DOS)
20 PHR Curing Agent Z
14 PHR Curing Agent CL
75 PHR Phthalic Anhydride
Appearance Changes
Solution Specimens
Original
After
180 Days
Immersion
No Change
No Change
No Change
No Change
No Change
No Change
No Change
Darkened
No Change
No Change
No Change
No Change
No Change
No Change
No Change
No Change
No Change
Greenish & Some
Slight Darkening
No Change
No Change
No Change
180°F Immersion
Some Slight Dark- 17, 700
ening, Swelling &
Sugar Like Odor
Some Slight 16,500
Darkening
Dull & Some Slight 14, 500
Darkening
Some Slight Dark- 17, 900
ening Particularly
Edged
Greenish & Some 20, 200
Slight Darkening
Slight Surface 19, 800
Dulling
Darkening 24, 000
••••— — ~—
9,200
14,500
13,400
16,300
11,300
15,000
23,600
(Taken from Shell Epon Resins for Casting 1967)
- 73 -
-------
Table IX. Chemical Resistance of EMI-24 Versus CL Cured Epon 828 Castings
EMI-24(2phr) CL (14 phr)
Formulation: Epon 828 Epon 828
Chemical Compound
50% Sulfuric Acid
50% Sulfuric Acid
50% Sulfuric Acid
Cure conditions for
Test
Tsmperature,
°F
150
200
225
above samples: Epon
Epon
Time of
Exposure,
Days
30
30
30
828/EM1-24
828/CL:
Weight Gain,
0.485
0.635
0.65
4 hr at 70°C, 1
3 hr at 204°C
%
1.415
1.63
3.32
hr at 120
gel at 55°C, 2 hr at 125°
^^.
°C
c
70% Sulfuric Acid
200
14
2 hr at 175 °C
0.45
Sample
Destroyed
Cure conditions for above sample: both - gel at 70°C, 4 hr at 150°C
(Taken from Shell Epon Resins for Casting (1967))
- 74 -
-------
STRENGTH
MODULUS
Wl
I
o
»- 100
z
Ul
£ 75
£
PERCENT
IM m
m O
'
1
^
X,
V
V
V
V
X
V
x
^
—
^•B
^^
•••
—
100
75
50
<*> "
7i
A
IN
s.
^
x
X
X
X
X
X
X
X
_
—
«••
SULFURIC ACID 25%
(AT I80°O
SULFURIC ACID 25%
CAT
CODE TO SYSTEMS
17773 TETA CURED
CL CURED
2 CURED
Ez3 BF, MEA CURED
o
Illlll PHTHALIC ANHYDRIDE CURED
•• V40CURED
(A) NOTE, THIS SYSTEM
EXPOSED FOR 60 DAYS
AT, I30°F ONLY
Table X. Flexural Strength and Flexural McxJulus Retention (%) of Epon Resin
Castings After Six Months Exposure to Various Chemical Media
-------
The above considerations apply to our phenolic laminates also. (Note that W. R.
Grace routinely supply a phenolic separator for use in Pb/acid batteries, trade name
Darak 2000). Here, during lamination, the resin was extruded along the outside edges of
the sample and at these points, little attack by acid was noted even at the higher tempera-
tures. Also, the phenolic laminate is based on Monsanto SC-1008 phenolic resin, and when
we tested bulk specimens of this resin at up to 90°C, (Table VII), surface darkening and
embrittlement was observed only at the latter temperature with little or no appearance
changes below this temperature. We conclude again that the phenolic/glass reinforcement
bond is the main point of acid attack.
A final point regarding corrosion susceptibility of laminated resins is that in our
early designs we were looking for structures which could be cast in one step and have plastic
ribs on the surface to enhance paste adhesion. For this reason, we used high temperature/
high pressure curing cycles to maximize resin flow. We have since changed our mode of
plate preparation as will be discussed shortly. However, since the corrosion test samples
were all prepared at high pressures and consequently had only a minimum of resin content
on the actual surface of the laminate protecting the resin/glass bonds, it is obvious that very
little local attack is required before acid penetration to the relatively weak resin/glass bonds.
When this occurs, accelerated attack throughout the reinforced system can then take place.
This, we believe, was a major contributing factor in the observed excessive disintegration
of these corrosion samples.
In summary, it is evident that thermosetting resins are attacked by FUSO., but .
to varying degrees. Of the materials we have examined, polyester and modified polyesters
(Dapon) show least stability. Phenolics and epoxies are susceptible to attack but not to the
extent indicated by test results. Rather, the resin/glass (or graphite) bond is the weak
point in laminated structures. This attack was enhanced in our corrosion test specimens by the rela -
tively high pressure laminating techniques employed. Although different techniques may be
used in forming laminates from thermosetting resins (e.g., by using lower pressures and
resins having lower flow characteristics), it is felt that the major outlet for use of epoxies
or phenolics in lead acid batteries would be as sealants or adhesives rather than as a possible
high strength active mass support material. Test data and literature information on epoxies
and phenolics reveal that they can have substantial resistance to H^SO, attack, particularly
if the resin (e.g. , Epon 828 epoxy), curing agent (e.g. , acid anhydride), and curing tem-
perature (high temperatures), are carefully chosen.
The thermoplastic materials generally all behaved very well in acid solution, even
at 90°C. Lexan (a polycarbonate) and polystyrene exhibited the lowest weight changes at the
highest temperature, but in practice all of these materials were deemed to be suitable for
use in a practical battery from a corrosion standpoint. Further plastics such as SAN (styrene/
acrylonitrile) and polysulfone are also corrosion resistant. In the Appendix further cor-
rosion data on polysulfone and polypropylene are given. The thermoplastic material of
choice as active mass support was governed by the factors discussed next.
The following specific conclusions were drawn:
1. The majority of thermoplastics, for example, Lexan, polystyrene, poly-
sulfone, PVC, polypropylene and Noryl are stable in 1.28 sp gr FUSO^ at ambient tempera-
ture for extended periods. From this aspect they are suitable for use as substrate material.
-76 -
-------
2. Reinforced laminates with thermosetting resins are subject to attack by
HoSO- at the resin to glass reinforcement bond. The base resins, and particularly epoxy
and phenolic resins, if suitably selected, and carefully cured, can be quite resistant to
acid attack.
3. The major outlet for thermosets in Pb acid batteries is not as a struc -
tura! paste support material, but as an adhesive or sealant in selected areas of the plate
or battery.
4. No data have yet been generated on the corrosion resistance of rein-
forced thermoplastics in F^SO,. Literature information suggest that this is generally as
good as that of the unreinforced plastics.
- 77 -
-------
VI. TASK V. DEVELOPMENT AND MECHANICAL TESTING OF STRUCTURES
A. Factors Influencing Choice of Design Materials and Techniques
The additional aspects of plate development not already considered in previous sections
were examined here. Due to corrosion problems, structures involving metals other than Pb or
Pb alloys were not considered further. Emphasis was placed on those alternative designs out-
lined in Section III of this report. The selection of materials and techniques for further study
was closely controlled by the results of corrosion and other parameters influencing design
which are described in earlier sections. Literature surveys of material performance capa-
bilities were carried out and, where necessary, these were backed up by laboratory tests.
The following specific factors were considered: -
1. Strength
2. Ease of fabrication
3. Cost and availability
4. Bonding of the plastic to Pb or Pb alloys
5. Adhesion of active mass to the plastic
6. Oxidation of the plastic by PbO,
7. Temperature and corrosion resistance
8. Ease of handling (e.g., brittleness) and sealing (plastic to plastic)
in a battery case.
Only plastic materials were investigated since it was clear by this stage that the maxi-
mum chance of success lay in the use of plastic substrate materials as active mass support in
the grid.
1. Strength
Both thermoplastics and thermosets were considered for use as a substrate
material. Whereas it was thought that thermoplastics might not require any additional rein-
forcement (particularly the engineering thermoplastics such as Lexan, Noryl, Polysulfone
etc.) to achieve the necessary structural stability, in contrast, when using thermosets, some
type of reinforcing medium is required. Also, in the event that a substrate thickness of 10 mil
was desired in the final design (to minimize the weight of passive battery components) even the
engineering thermoplastics must be reinforced. We have therefore considered reinforcement
- 79 -
-------
types, techniques and problem areas, together with literature data on the strength of unrein-
forced plastics.
Plastics are generally reinforced in one or other of two ways, namely: (1) using woven
cloth, or (2) using chopped fibers. The reinforcement may be either glass based or carbon or
graphite based. Glass cloth reinforcements were available in various types from three main
suppliers: (1) Clark-Schwebel Fiber Glass Corp., 245 Park Ave., New York, N.Y., (2)
Burlington Glass Fabrics Company, 1345 Ave. of the Americas, Nsw York, N.Y., and (3)
J. P. Stevens and Co., Inc., Glass Fabrics Division, 1185 Ave. of the Americas, New York,
N.Y. During the weaving of the fabrics, oils and starches are added as binders, Fabrics to
which additional finishes are applied go through a heat cleaning process to remove these
binders (or sizing). Fabric no. 112 is an example of a heat cleaned material which is not
treated further. The various possible additional finishes which are applied to the fabrics
serve to improve bonding between the glass and the plastic to be reinforced. The most com-
mon of these is the Volan A finish which is suitable for reinforced structures with polyester
and epoxy plastics (and also phenolic). Here a treatment with methacrylate chromic chloride
enhances bonding to the cleaned glass surface giving a Cr-O-Si bond. Chloride salts formed
during the treatment are washed out afterwards. The chromium content of the fabric is
0.03 - 0.06%. Other finishes such as A-1100 are compatible with polyester and epoxy, phenolic,
melamine and polyimide resins, respectively. All of these treatments simply improve bonding
of the resins to the glass. (We did not anticipate that the finishes would impair battery per-
formance in any way particularly since they would not in any case be exposed directly to the
acid.) As is clear from the above, commercial finishes are applied with a view to future
applications with thermosetting plastics, for example, in laminated structures for printed
circuit boards. Similar finishes can also be applied to chopped glass fibers for use as a
reinforcing medium for the above plastics. Glass cloth however is the more usual reinforcing
medium for thermosets. The glass cloth syles used vary widely. Typical styles are 108, 128,
7628, and 181 and some properties of these materials are given in Table XI. Style 181 is the
strongest of these materials. The prices are also included in the table. Choice of material
and finish is governed by many factors such as cost, thickness, resin content desired, lay up
technique of the laminante (wet or dry), and strength of final laminate. All of these factors
are important in plate design.
It is possible to use carbon or graphite materials as a reinforcement for thermosetting
plastics and one further advantage of this is that both of these materials are conductors. The
possibility of developing a structurally sound and conducting substrate is thus realized. As
will be seen, however, there are other difficulties inherent in such a structure. Two major
suppliers of graphite and carbon materials are Union Carbide Corporation (Carbon Products
Division, New York) and the Carborundum Company, Graphite Products Division (Brookfield,
Ohio). Cloths, yarns, and chopped fibers are available from both companies. The availability
of material for structural applications, e.g., laminates, is more limited than for glass rein-
forcements. However, carbon and graphite materials are available and are treated with sizings
- 80 -
-------
Table XI. Properties of Glass Fabrics
Style
108 900-1/2 900-1/2 0.0020
1.45
128 225-1/3 225-1/3 0.0075
6.10
181 225-1/3 225-1/3 0.0090
8.90
7628
75-1/0 75-1/0 0.0070
5.80
70x40
350x340
250x200
625
250x200 250
125
250
500
750
Plain
Plain
8 Sh.
Satin
Plain
Width,
in.
19
38
40
50
33
44
50
60
38
44
50
60
38
39
44
50
Un-
treated
0.25
0.49
0.515
0.645
0.62
0.72
0.82
0.98
0.865
1.005
1.14
1.37
0.35
0.36
0.41
0.46
Typical
Finish Prices*
. — • ' *•« " • •
112 Volan
0.31
0.55
0.575
0.705
0.68
0.78
0.88
1.04
0.925
1.065
1.20
1.43
0.41
0.42
0.47
0.52
0.38
0.62
0.645
C.795
0.75
0.85
0.97
1.13
0.945
1.085
1.22
1.47
0.43
0.44
0.49
0.54
Tensile Strength - Minimum Average breaking strength,
Ibs. per inch (ASTM method 579-49).
Property values herein are based on untreated fabric,
are approximate guides only, and are not guaranteed
values.
Strength, thickness and weight values will change when cloth
is finished.
*For quantities of under 5,000 yards, add $0.03 per yard to the
listed price
(Burlington Glass Fabrics Co. Sales Data)
-------
compatible with epoxy, polyimide, phenolic, and polyester resins. Union Carbide Corporation
manufacture a "Thornel" 75S structural graphite yarn in a broadgood form with B-staged epoxy
resin. This material contains unidirectional two-ply graphite filaments and is used for high
elastic modulus and tensile strength. Its price is $2.65/lb at up to 1000 Ib with a nominal
yield of 8000 yd/lb. Of more direct interest to us were the carbon and graphite cloth
materials which impart high compressive, flexural, and tensile strengths to laminates.
Typical data on these materials are given in Tables XII and XI1L
It is clear that a wide range of structural reinforcement materials is available for the
present applications. To reinforce structures using woven glass or carbon fabrics (or unidi-
rectional yarn) , materials are generally laid up to the desired thickness and then simply hot
pressed. This method is generally applied to thermosetting resins, e.g., for printed circuit
boards, but we have recently used a similar technique successfully to reinforce thermo-
plastics - by hot pressing a thin glass cloth (~3 mil) between two 10-mil plastic sheets.
With the thermosetting resins, a wide range of structural laminates are commercially
available from, e.g., Mica Corporation and New England Laminating Company in prepreg
(or stage B) form. In the latter, the cloth or fiber reinforcement is treated with a suitable
resin compatible finish, if this is desired, and then impregnated with the resin of choice.
Finally the resin impregnated material is partically cured. Sheets of such material are com-
mercially available in various thickness and with various resin contents and types. The
reinforcing medium can also be varied and the final materials are classified as high flow,
low flow and no flow prepregs.
The latter are used mainly for adhesive purposes. All of these prepregs are shipped
in the partially cured state and have the advantage that they can be laid up to the required
thickness simply by using a combination of sheets. The prepreg is then polymerized by the
application of heat (~340°F for 30 min), pressed to size simultaneously (~25 - 200 psi) and
finally cooled tos 140°F under pressure. During the initial stages of preparation, a precure
stage can be applied to the prepregs at the curing temperature for 3-4 min at 10 psi. This
stage is crucial and controls resin flow. In a further technique to achieve the same result,
total pressure is applied immediately and the temperature then raised at a controlled rate.
The resin viscosity drops sharply on first application of heat and then increases again as
polymerization occurs. By varying the precure time, it is thus possible to vary resin content
in the final structure. Properties of typical prepregs are given in Table XIV for epoxy
materials.
In the alternative reinforcement procedure which applies mainly (but not soley) to
thermoplastics, chopped fibers are employed. A wide range of thermoplastics is available
in the pellet form with 20 to 40% fiber reinforcement. Final reinforcement content is achieved
by blending the pellets with various amounts of the basic plastic. The drawback here is that
injection molding is required to form the final shapes. In the thicknesses we are dealing with,
inadequate filling of the mold would be achieved with such reinforced plastics (or even
- 82 -
-------
Table XII. Technical Data for Carbon and Graphite Cloth
Typical Data*
Grade Designation
Type
Weave
Weight (oz/yd2)
Thickness (in.)
Width (in.)
Length, Maximum (yd)
Breaking strength, rr
Elongation, ultimate
Electrical resi
Carbon content
Type of yarn
Yarn count warp
fill
Plys per yarn
Filaments per ply
Yarn filament diai
Yarn denier
GSCC-2
GSGC-2
GSCC-8
GSGC-8
yd)
nin (Ib/in.) warp
fill
(%)
2 (ohms/sq)
ter (in.)
Carbon
Plain
7.5
0.0175
42
75
64
64
5
0.54
99.0
Continuous
27
23
2
720
37 xio"5
1200
Graphite
Plain
7.5
0.0175
42
75
50
40
5
0.55
99.9
Continuous
27
23
2
720
37 X10~5
1200
Carbon
8-harness
7.9
0.0175
30
80
64
64
5
0.51
99.0
Continuous
51
51
1
720
37 xlO"5
600
Graphite
8-harness
7.5
0.0175
30
80
50
40
5
0.54
99.9
Continuous
51
51
1
720
37X10"5
600
General Cloth Data*
Density (gm/cc)
Specific heat (BTU/lb/°F)
Heat of combustion
Heat of sublimation
Sublimation point
Emissivity
( BTU/lb)
(BTU/lb)
1.5
0.15
14,370
25,740
6600° F
> 0.9
< 1.0
* This data does not represent a specification.
(Technical Data, Graphite Products Division, The Carborundum Co.)
- 83 -
-------
Table XIII. Pricing Schedules for Carbon and Graphite Fabrics
CARBON FABRICS
Grade GSCC-2 Carbon Cloth
Type of Weave - Plain
Width of Fabric - Approx. 42 in.
Weight - Approx. 7.5 oz/sq yd
Maximum Roll Length One Piece - 75 yd
1 - 9 Ib $39.00 /lb
10 Ib and over 31.30/lb
Grade GSCC-8 Carbon Cloth
Type of Weave - 8 harness satin
Width of Fabric - Approx. 35-1/2 in.
Weight - Approx. 7.4 oz/sq yd
Maximum Roll Length One Piece - 75 yd
1 - 91b. ....'. $39.00/lb
10 lb and over 31.30 /lb
GRAPHITE FABRICS
Grade GSGC-2 Graphite Cloth
Type of Weave - Plain
Width of Fabric - Approx. 42 in.
Weight - Approx. 7.5 oz/sq yd
Maximum Roll Length One Piece - 75 yd
1 - 9 lb. . . $39.00 /lb
10 lb and over 31.50 /lb
Grade GSGC-8 Graphite Cloth
Type of Weave - 8 harness satin
Width of Fabric - Approx. 35-1/2 in.
Weight - Approx. 7.4 oz/sq yd
Maximum Roll Length One Piece - 75 yd
1 - 9 lb $39.00 /lb
10 lb and over 31.50/lb
(Technical Data, Graphite Products Division, The Carborundum Co.)
- 84 -
-------
Table XIV. Properties of Prepreg
00
en
Glass
Micaply ' Cloth
Grade Type
High Flow (Class HI) Prepreg
102-18 108 G-10
High Flow Medium Gel Prepreg
102-13 128 G-10
Nema
Grade
Mil Spec
Type
Nominal
Prepreg
Thickness,
in.
Nominal
Cured
Thickness,
in.
Resin
Content.
%
Resin
Flow,
%
Volatile
Content,
%
Tack
Time
(grade)
.Gel.
Time,
set-
Price,
(per sq. ft)
PC-GE
0.0035
PC-GE 0.0085
0.0025
0.0065
60±5 40±5
0.5
C/D 225±30
40±5 20±5 0.5 B/C 150±30
0.40
0.35
Low Flow (Class II) Prepreg
102-418 108 G-10 PC-GE
0.0035
0.0025
60±5 25±5
0.5
250±30 0.45
(Micaply Corp. Sales Literature)
-------
unreinforced plastics in < 20 mil thickness). The "sandwich" technique with cloth between
sheets of plastic is thus of major interest.
In terms of strength measurements, we have measured tensile strengths of epoxy, poly-
ester, phenolic, and Dapon resins laminated as discussed in the corrosion section and tested
on an Instron Tensometer. We used samples 2 in. long by 0.25 in. wide along a 1-in. section
and stress was applied parallel to the direction of the minimum number of fibers. Strain
rate was 0.05 in./min. Tensile strengths were 35, 700 psi, 45, 650 psi, 24, 000 psi, and 18, 950
psi for the epoxy, polyester, Dapon, and phenolic laminates, respectively, Variations arise
from glass cloth type and number of plies chosen. The values quoted are more than sufficient
for battery plate requirements.
We have a range of values for the thermoplastic materials in the unreinforced state.
Tensile strengths for Noryl, Lexan, PVC, polypropylene, and polysulfone are 9, 600, 8, 750,
7, 500, 4, 900, and 10, 200 psi, respectively. Lexan reinforced with 20 and 40% glass fibers
has tensile strengths of 16, 000 and 25, 000 psi, respectively. Noryl reinforced with 20 and
30% glass fibers has tensile srengths of 14, 500 and 17, OOOpsi, respectively. Polysulfone also
has extremely good properties in the reinforced form.
To summarize, it is evident that it is possible to achieve the desired mechanical
strength using plastic substrates. With some of the engineering thermoplastics, e.g., Noryl,
Lexan and polysulfone, there are indications that this may even be possible in the unrein-
forced form with ~20 mil substrate thicknesses. Further general engineering data sub-
stantiating this conclusion are given for thermoplastics and thermosets in the appendix.
2. Ease of fabrication
These details are discussed more fully later. They are based on many of the
facts and techniques outlined in this section.
3. Cost and availability*
Below, a list of the approximate large volume prices of thermoplastic materials
is given. Since the cost of battery manufacture is governed not only by the base price of the
chosen substrate but also by the constructional problems encountered when using a particu-
lar plastic, this must also be considered in the final cost estimations.
Values in Table XV refer to the unreinforced materials unless otherwise stated.
Table XV. Price Schedules for Thermoplastic Materials
Plastic Cost, jd/lb
Styrene/acrylonitrile (SAN) 26
Polypropylene 17
PVC 15
Polystyrene 14
Polyethylene . 14
Polysulfone 100
Lexan 75
Noryl 72
Noryl (reinforced with chopped glass fibers) 80
Lexan (reinforced with chopped glass fibers) 110
* A complete cost analysis of a battery is given in Section VIII of this report.
- 86 -
-------
The cost of thermosetting resins in large volume is more difficult to estimate and
varies from resin to resin (in the laminated form). A price of 30-45 4/sq ft is reasonable
for epoxy prepregs. in these the main cost is incurred in the glass cloth style chosen. With
Dapon resins, the price may be closer to 100
-------
In general, thermosetting resins and particularly epoxy resins show much better
bonding to metals than do thermoplastics. There are, however, various techniques which may
be used to improve this bond in the latter case. Though the methods have been employed pri-
marily with Cu, A), stainless steel, brass, and zinc, there is no reason why they should not
also be applicable to lead and its alloys. Basically, to enhance bonding between metal anil
plastic, a prior surface roughening of the metal (and plastic) is desirable as, for example,
by oxidation, sand-blasting, or chemical etching. This applies equally to thermosetting and
to thermoplastics. With the latter materials, a further improvement has been to dissolve a
5-10% solution of the plastic under study in a suitable solvent and then apply this solution to
the treated metal parts requiring bonding. The solvent is then evaporated off and the metal/
plastic bond formed by a hot pressing technique. A more usual method, and one which is very
widely used, is to use an adhesive (generally an epoxy resin) which is compatible both with
the plastic and the metal in question and proceed as above (though temperature is not always
necessary). A restriction to such a technique is that if the epoxy is conventionally cured at
high temperatures, the plastic and metal to be bonded must also withstand these temperatures
and furthermore the expansion/contraction characteristics of the epoxy adhesive/metal/plastic
system must also be relatively similar. If the latter is not so, the good adhesive bond formed
at the high temperatures will simply crack on cooling. The technique of precoating the metal
with a solution of plastic in a suitable solvent has been used successfully with polysulfone
41
plastic. Table XVI gives data on the bonding of several materials to Lexan. Similar adhe-
sives are used for Noryl, vinyl and polystyrene plastics also.
With respect to thermosetting resins, the bonding problem is not so serious —particu-
larly with epoxy resins. We have measured peel strengths for Pb strips 60 mil wide by 20 mil
thick bonded to the epoxy, polyesters, phenolics, and Dapon laminates as outlined previously.
A mold of Al was cut with 60-mil-wide grooves to a depth of 20 mil so that during pressure
application, no severe squashing of the Pb occurred. Test samples were clamped into the
bottom clamp of an Instron and a 1-in. Pb strip protruding over the edge of the sample was
clamped using a "C-clamp". A chain attached to the C-clamp was held in place in the upper
clamp of the Instron. The Pb strip was then peeled from the laminate at an angle through the
normal at a peel rate of 1 in./min and the minimum observed peel strength was recorded. The
procedure was repeated for several test samples. Using this procedure peel strengths of
12 lb/in., 1.7 lb/in., 1.7 lb/in., and 9.3 Ib/in. were observed for the above four laminates,
respectively. In the testing procedure, we did not follow a set procedure such as clamping the
test specimen round the circumference of a wheel and peeling so that the peel angle was always
40
normal to the Pb/plastic interface. In this case, we anticipated that flexing the test specimen
round the wheel might weaken the plastic-metal bond. By choosing the minimum peel strength
during testing, we achieve the same result without damaging the specimen before testing. Peel
strength values on several specimens showed good agreement. In the testing, no attempts were
made to enhance bonding by prior surface treatments. We would expect a marked improvement
- 88 -
-------
Table XVL Lexan Resin Bonding Data
Solvent Cementing
Methylene Chloride
Ethylene Dichloride
One Part Systems
A. Room Temp. Curing
Eastman 910
Central Coil HB-56
Vulcalock R-266-T
G-E RTV-102
B. Hot Melt Adhesive
Terrell Corp. 10 x 104
Two Part Systems
A. Room Temp. Curing
Epon 828
. Epon 828
Epon 828 - Thiokol LP-3
Epon Adhesive IV
Epon Adhesive 913
Bondmaster M688
B. Elevated Temp. Curing
Uralane 8089
Uralane 5716
Epon 828
Epon 828
Epon Adhesive IV
Epon Adhesive 9 13
Bondmaster M688
Flexicast 4002
Pressure and Heat
Sensitive
Lepage 4050
Nafco 101
Kleen - Stik 295
Kleen - Stik 298
G-P Transmount
G -P Transmount
For Bonds To
Lexan
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Metals
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Rubber
Wood
Plastics
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Hardener
Diethylene
Triamine
Versamid 115
DMP-30
Cur. Ag. A
Part B
Ch-8
Part B
Part B
Methyl Nadic \
Anhydride
DMP-30
Phthalic 1
Anhydride (
Cur. Ag. A
Part B
Ch-8
Part B
Pro-
portions
(pph)
100-8
100-100
100-100-10
100-6
100-12
10040
10^34
10(W4-2
10040
10(K6
100-12
100-16
10035
Cure
Tempera -
ture (°F)
Room
Room
Room
Room
Room
Room
Melts at 350
Room
Room
Room
Room
Room
Room
70-80
150
70-80
150
175
250
200
180
200
212
Room
Room
120-140
120-140
150-250
150-250
Time
(Hrs)
• 48
48
2-24
4-24
Air Dry
2-24 -
Instantaneous
2-48
24-48
48
24-6 Days
3-4 Days
4-24
2 Days
3
2 Days
3
8 (min)
8 (min)
45 minutes
3
15 minutes
3
< a minute
< a minute
10-15 minutes
10-15 minutes
Adhesion
Quality
Excellent
Excellent
Excellent
Good
Good
Excellent
Excellent
Excellent
Fair
Fair
Very Good
Very Good
Very Good
Excellent
Excellent
Very Good
Very Good
Very Good
Very Good
Very Good
Very Good
Excellent
Good
Good
Excellent
Excellent
Tensile
Shear
Strength
(psi)
4500-6500
4500-6500
350
2500
600
1800
2900
2000
1200
1000
1200
1200
1800
2900
2000
600
25 psi at
point of bond
Service
Range
(°1'1
-404270
-404270
70 to 2 12
70 to 175
-75 to 350
32 to 175
-404250
32 to 160
70 to 160
-60+190
-604250
-404212
,
—
—
32 to 2 50
-404250
-604200
-604250
-404250
-904250
Room
-40 to 400
-404200
-404200
-604250
Color of
Adhesive
Clear
Clear
Clear
Red
Amber
White
Dark
Clear
Dark Amber
Dark Amber
Red -Tan
Gray - Black
Tan
Tan
Clear
Light Amber
Light Amber
Red -Tan
Gray - Black
Tan
Gray - Black
Clear
Clear
Amber
Amber
Amber :
-604250 Amber
CO
CO
(G. E, Technical Data Revised Report CDC-502)
-------
in peel values with such treatments. The results, however, give comparative values for
bonding to the four laminates. Note that we would also expect higher peel values to unrein-
forced resins since in the above case our lead strips were, in part, in direct contact with the
underlying glass reinforcing cloths. This was a result of the relatively high pressure used
(~ 200 psi) during lamination.
These data and literature information confirm that thermosets exhibit superior bonding
to metals than do thermoplastics. Of the thermosets, epoxy and Dapon resins are superior to
phenolic and polyester resins. There are, however, several possible alternatives available
to enhance bonding to Pb, involving prior surface roughening treatments and using plastic/
solvent solutions applied to the Pb before bonding. The use of epoxy type adhesives is also
viable, the restriction being that such adhesives should be compatible with H-SO. or, at
worst, be only slowly attacked and in the final structures be as much protected from acid
attack as possible. Also, if an adhesive is employed, it should either be room temperature
cured or have similar shrinkage characteristics to the plastic and metal in question.
5. Adhesion of active mass
The grid in a conventional battery supports the active mass and also carries
current to and from the active mass. To do so efficiently there must be good adhesion between
the two, otherwise paste shedding results. It is difficult to visualize Pb and Pb oxides adhering
adequately on each side of a plastic substrate for any length of time even if there are conducting
strips laid down the surfaces of the substrates. Conventional grids are designed to have an
interlocking hold on any paste material - which is impossible to achieve when paste is applied
separately to each side of a plastic substrate (effectively, one-sided grids) . We therefore
examined alternative methods of enhancing adhesion to plastic supports.
Apart from using no surface treatment to enhance paste adhesion the alternatives
available are to deliberately roughen the plastic by sand blasting, to incorporate a glass mat
or dynel fibers on the plastic surface during preparation, or to use a substrate of thin Pb foil
(~ 4 mil) on top of the plastic. We anticipate that some surface treatment would be desirable
and, most likely, use of glass mats or dynel fiber would be best. It is probable that any Pb
foil laid on the plastic surface would increase plate preparation difficulties, increase cost and
weight requirements, and also cause excessive corrosion and positive plate buckling problems.
The use of glass retainer mats between separators and plates to enhance retention of the paste
mechanically to the plastic substrate is also an alternative which is used commercially in some
conventional batteries.
6. Oxidation by
We do not have complete information on the susceptibility to oxidation of plastic
substrates of choice. However, various separators now in use provide useful pointers to this
susceptibility. PVC separators have now been used for a long time in the lead acid industry
- 90 -
-------
43
and exhibit no degradation due to oxidation. Similarly, the Darak 2000 supplied by W.R.
27
Grace Company is a phenolic material and is also not oxidized by PbCL. A Daramic
separator supplied by the same company and made of extruded polyethylene material also
performs well and a new experimental polypropylene separator,again from W.R. Grace Com-
s showing good performance. Polystyrene separators were introduced in the second
world war and behaved satisfactorily though only up to 165 °F. Polystyrene is still being used
in Europe as separator and spacer material. Dynel fibers are used throughout the industry
to help paste retention in the positive plates. Glass mats are also used as retainers or
separators.
We have no information on Lexan, Noryl, and polysulfone plastics but we would not
expect oxidation of these materials by Pb00. SAN, ABS, epoxy, and polyester plastics are used
i
in batteries but as case or sealant material and not in direct contact with active mass. It
appears that the problem is not a serious one and can readily be circumvented by suitable choice
of plastics.
7. Temperature and corrosion resistance
All of the plastics we have discussed are stable at least up to 150° F - the
softening point for P VC . In the reinforced form, the stability to heat increases. Heat deflection
temperatures of unreinforced PVC, Lexan, polypropylene, polystyrene, Noryl, and polysulfone
are of the order 150, 250, 285, 165, 275, and 300 °F, respectively. Polysulfone in the unfilled
form can be used at temperatures up to 300° F even under a stress of 1000 psi. Its heat de-
flection temperature is 345 ° F at 264 psi and 358 ° F at 66 psi. Long term thermal aging at
300 - 340° F has little effect on the physical properties of polysulfone. Its physical properties
are also good down to -150° F. The heat deflection temperature of Lexan 500 under stress at
264 psi is 288 ° F. The equivalent value for Noryl at 264 psi is 265 ° F. Polypropylene has
values of 220 °F and 140 °F under 66 psi and 264 psi load, respectively.
The heat deflection temperature of reinforced Lexan at 264 psi stress is 295 °F, and at
66 psi it is 300° F with 20% glass. For 40% glass, the corresponding temperatures are 295 ° F
and 310° F. The heat deflection temperature of Noryl reinforced with 20% glass at 264 psi is
270 °F compared to 275 ° F with 30% glass reinforcement. Polypropylene has heat deflection
temperatures of 305° F (68 psi) and 230 °F (264 psi) when filled with 20% glass fibers (327 °F
at 264 psi with 40% reinforcement) . SAN reinforced with 40% glass fiber has a deflection
temperature of 250 °F under 264 psi load. Polysulfone has superior properties to all of the
above. More complete details are included in the Appendix.
In the thermosetting series of resins, the materials are not softened by heat once
polymerized but are degraded at higher temperatures. Loss in tensile strength and chemical
resistance and increase in tensile elongation and flexibility occur above the heat deflection
temperature. The temperature stability depends on the choice of starting material. Table
XVII gives heat deflection temperatures of Epon resin systems. The lowest value is 320 °F.
- 91 -
-------
Table XVIL Heat Deflection Temperatures of EPON Resin Systems
Typical Value Range
Type of System
Aliphatic Amine Cured 1
Anhydride (except dianhydrides)
Aromatic Diamines (except DOS)
Cure Cycle
7 days at 23°C + 1 hr at 100°C
2 hrs at 90°C +4 hrs at 150°C
2 hrs at 80°C +2 hrs at 150°C
Heat Deflection
Temperature, °C
100-125
120-150
150-160
catalyzed with 1 phr BDMA or DMP-30
Values for Systems Designed to Provide High HOT
Resin System
EPON 826/EMI-24
EPON 826/CL
EPON 826/DDS/BF3-MEA
EPON 826/NMA/EMI-24
EPON 154/CL
EPON 826/BF3-MEA
EPON 826/ EPON 1031/NMVEMI-24
EPON 826/EPON 1031/EMI-24
EPON 154/BF3-MEA
EPON 1031/NMA/BDMA
Material Ratio
(parts by wt)
100/4
100/14.6
100/20/1
100/90/1
100/15
100/3
50/50/90/1
50/50/2
100/3
100/90/1
Cure Cycle Required,
hrs/°C
2/80 +2/150
2/80 +2/150
2/125 +2/200
4/125 +2/200 +2/260
2/80+16/150
3/120 +48/150
2/120 +2/200 +2/260
4/70 +48/150
2/80 +4/150 +16/200
4/120 +18/200 +7/260
Heat Deflection
Temperature, °C
160
160
175
176
178
184
185
202
245
280
The performance of an EPON resin system at a given temperature is governed by the glass
transition temperature of the cured resin system and the rate of oxidative or thermal degradation
occurring at that temperature.
Amine cured systems generally are not suitable for long-term service at temperatures
greater than approximately 375°F, since rapid oxidative degradation of these systems occurs at
400°F (except for DDC-cured systems which do not degrade noticeably below 450°F). With cer-
tain specific anhydride curing agents, good long-term performance can be achieved at tempera-
tures as high as 650° F.
(Shell Epon Resins for Casting, 1967)
- 92 -
-------
Our data on phenolic, Dapon, and polyester resins are not so extensive. However, the
pH-500 series of phenolic resins from Fabricon Products is based on a Monsanto SO 100 8
phenolic resin and has short term capabilities at up to 900 °F.
Based on the foregoing, we do not anticipate any problem from retention of physical
properties in any of the piastic substrates investigated, as a result of estimated increases in
temperature during battery operation. We have given information earlier on the acid stability
of various plastics — both thermosetting and thermoplastic. Additional data on stability and
changes in physical properties on exposure to HgSO. are given in the Appendix. The results
indicate that no severe plastic degradation problems will be observed particularly with thermo-
plastics. With thermosejs we have suggested that the weak point is in reinforced laminates
at the resin/glass'or carbon bond. Phenolics, epoxies, and polyesters have all been used
successfully in lead-acid systems before in bulk form (see earlier corrosion section and the
Appendix). At worst we can still employ epoxies as sealants at localized points to prevent
short circuit losses through the bipolar plates.
In regard to metal corrosion, pure lead seems to be the best choice due to its more
uniform attack compared to Pb/Sb and Pb/Ca alloys. It is also adequate in terms of expansion
28
characteristics. From a practical viewpoint the design of the plate is probably more im-
portant in relation to provision for expansion of the Pb conducting strips.
8. Ease of sealing
By this, we refer to sealing of each individual bipolar plate within the battery
case. .Many techniques arc available and various difficulties are encountered. The most
interesting techniques are heat sealing, ultrasonic bonding, solvent cementing and adhesive
bonding. Most thermoplastic materials can be solvent bonded and adhesive bonded (using
epoxies, for example) while the technique of heat sealing and ultrasonic bonding has been
applied to Lexan and Noryl plastics. The majority of the thermoplastics we have discussed
can be made to soften and flow under the influence of heat and pressure, e.g., PVC, polypro-
pylene, polysulfone, and the above two plastics. We would thus expect to be able to heat seal
the latter plastics also. We would not then anticipate problems in sealing these materials
within equivalent case materials. Thermosetting resins can best be sealed using the basic
resin/curing agent as an adhesive bonding agent. We anticipate that the major problem is not
in providing an adequate seal but rather in handling the prepared plates. In this respect, for
example, PVC tends to be rather brittle and we are informed by local plastic company per-
sonnel that, while Lexan is easy to seal, polyethylene and polypropylene are more difficult.
The inherent stiffness of unreinforced Lexan in any event makes it an ideal material to employ
rather than polypropylene. Though the latter can be reinforced, it is more difficult to seal
such reinforced structures within a case material.
- 93 -
-------
B. Conclusions
The following specific conclusions were drawn as a result of this study:
1. Both thermoplastics and thermosets have adequate mechanical strength to
support the active mass in practical design configurations. With thermosets a reinforcement
medium is required for this purpose especially for substrates of == 20 mil thickness. Engineer-
ing thermoplastics may be suitable as support material in the unreinforced form especially when
strengthened by the incorporation of a thicker plastic rim surrounding the main substrate area.
For substrates of <20 mil thickness, the thermoplastics also require reinforcement.
2. A wide range of reinforcement techniques is available using glass, carbon
and graphite cloths or chopped fibers as reinforcing media. Suitable surface treatments are
applied to these materials to enhance their compatibility with the thermoset of choice.
3. Whereas thermosets are most usually reinforced with cloth material,
thermoplastics generally use chopped fibers. Hot press techniques are used to form structural
laminates with thermosets. Reinforced thermoplastics are formed to shape by injection molding
methods. The latter technique is not suited to the thin plate structures desired here because of
inadequate mold filling.
4. A therrnoforming technique is suggested when fabricating plates from thermo-
plastics. The latter may be reinforced if desired by hot pressing a suitable cloth between thin
sheets of the plastic in question.
5. Mainly because of H?SO. corrosion stability, thermoplastics are preferred
to thermosets as substrate material.
6. Thermosets form superior bonds with Pb than do thermoplastics. The former
may then be used to provide seals in plates at localized points if desired. Careful choice of
the resin and its curing technique and curing agent are, however, necessary.
7. Because carbon and graphite can be used as reinforcement, a means of
obtaining conductive plastic substrates is offered if concurrent problem areas can be solved.
8. Lexan thermoplastic is an ideal starting material for substrate fabrication.
It is relatively low cost, is thermoformable, stable in H-SO., light weight/medium strength
and is easy to handle.
9. There are techniques available to enhance sealing of thermoplastics to Pb.
Also, paste adhesion to such substrates may be enhanced by suitable surface treatments.
C. Preliminary Plate Development
The following describes the practical application of the information presented in pre-
vious sections. Only bipolar designs are considered and these are all based on the concepts
outlined earlier. Both the information given up to this point, and also information generated
- 94 -
-------
as a result of these practical fabrication experiments, are used subsequently in the develop-
ment of the final design structure and techniques for its fabrication. In the absence of any
extensive H_SO. stability data, early plates were fabricated from epoxy laminates sinc'e these
were readily available, easy to handle and readily fabricated in the desired plate geometry.
The following fabrication techniques were used: Grooves were milled across both faces
of an aluminum mold to depths of 15-21 mil and in widths of 1/32 in. up to 1/16 in. A border
20 mil deep and 3/32 in. wide was also drilled around the mold enclosing an area 5 1/2 in. by
4 7/16 in. Down the mold additional grooves 3/32 in. wide and 15-18 mil deep were also
drilled. Three to five sheets of epoxy Micaply No. 102-13 were then cured between the faces
of the mold by the application of heat and pressure as outlined earlier. During the curing, good
resin flow into the grooves cut in the faces of the mold was obtained. The cured plate was
approximately 22 mil thick except around the edges where the resin flow into the groove drilled
round the mold (and down and across the mold at localized points) resulted in an additional
~ 20 mil border thickness o-n each side of the structure. This border also served to add flexural
rigidity to the structure which was, in fact, sufficiently rigid to begin with. When Pb strips
(22-27 mils thick by 3/32 in. wide) were laid in the grooves drilled down the mold prior to lay
up of the laminates and the hot press curing cycle then applied, good adhesion of the Pb to the
complete laminate was obtained and each Pb strip protruded above the surface of the plastic
by 16-18 mil. i.e., corresponding to the depth of the mold groove. We also made electrical
connection through the plate between the Pb strips laid in grooves on opposite sides of the
plastic prior to layup. For this purpose, holes were drilled in the substrate at the desired
connection points before curing. Structural tests, corrosion data and peel strength measure-
ments were carried out on samples from such plates and the results of these have been out-
lined earlier. The following useful information was obtained from these experiments.
a. It is possible to manufacture a structurally sound thermosetting plastic
substrate which has Pb strips as conductors on either side and with electrical connection
through the plate at desired points. Fabrication is relatively simple.
b. Plastic ribs can be incorporated across the plate simply by extruding the
resin from the prepreg sheets during the fabrication operation. These ribs can help active
mass adhesion to the plate (mechanically).
c. The plastic border also extruded round the structure during lamination
adds further flexural rigidity to the plate.
Bearing in mind that the experiments were preliminary in nature and that no major
attempt was made to optimize the resin content on the surface of the laminate (protecting the
underlying glass/plastic bonds from acid attack) the following major problem areas were
observed or anticipated with this structure.
- 95 -
-------
a. The plate was extensively attacked in acid solution. Rapid loss in structural
stability was observed and Pb strips bonded to the underlying plastic surface, became separa-
ted from that surface.
b. As a result of corrosion but also because of excessive stresses induced
by expansion of the Pb strips on the positive electrode, it was anticipated that this method
of holding the strips rigidly to the underlying plastic would not survive die rigors of extended
cycling and lifetime. An alternative design permitting rib expansion without complete separa-
tion of the ribs from the underlying substrate or causing substrate buckling, is desirable.
With these views in mind the fabrication techniques outlined below were developed.
D. Second Design Plate
Again, this design was not considered to be final but rather was chosen to rapidly test
further fabrication techniques and ideas. The mold for fabrication was made from wrought
jig-plate Al, which was machinedon both sides. Dimensions are shown in Fig. 35. For
plate fabrication we now used PVC or Lexan, both in the unreinforced form. A thermoforming
technique, given in detail subsequently, was used to fabricate the plates. A further essential
difference from the first design was that a plastic grid was now used to hold me unidirectional
Pb conductors to the plastic substrate. This allows conductor expansion down the plate without
plate buckling or conductor separation from the substrate. The separation of adjacent Pb
strips laid down the plate was held at 0.29 in. in this design. Without going into exact fabri-
cation techniques and advantages inherent in the design (there are all noted below) the following
basic problems were observed with bipolar plates made in this mold:
1. The Pb conductor strips were too widely separated (0.29 in.) and contributed
to inadequate formation of the active mass.
2. During plate preparation, plastic was extruded along the edges of the Pb
ribs laid down the base plate. This reduced the formation rate and capacity of the plates.
3. Plates with no base plate treatment or with sand-blasting only to enhance
adhesion were not satisfactory. The paste tended to shed during operation. Those plates with
glass backing or dynel fibers showed good paste adhesion properties.
4. There were problems in early test cells using these plates which were caused
by gas bubble retention in the glass mats and/or thin separators first used. (10 mil separators
and 10 mil glass mats).
Basically however, the fabrication technique worked smoothly and the final plate design
and fabrication techniques, with suitable modifications, were based on the above concepts.
- 96 -
-------
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- 97 -
-------
Ii. Final Plate Design
The concept is basically that denoted as number (1) in Task II, section A of this report
and is defined here as a "quasi-bipolar" plate. It is based on the use of a flat, insulating plastic
substrate. On each of the sides of this substrate there is a parallel array of vertical lead strips
which are held to the substrate surface at several points using a plastic grid with horizontal
strips. The lead strips are placed in such a way that each strip on the face of the substrate
has a corresponding one directly underneath on the other face of the substrate. Electrical con-
tact between one strip and the corresponding one on the other face is made at the top end of the
strips via a section cut through the plastic substrate close to its upper edge. This contact is
located above the electrolyte level and, in addition, is covered with the frame of the plastic
grid to minimize chances of electrolyte leakage. (The two strips in contact can be obviously
substituted by a U-shaped strip riding on each side of the plastic substrate over the top of the
cut section.) On one side of this structure, the positive mass is pasted, with the negative
active mass on the other side. After pasting, the plate is formed by a simple modification of
the conventional formation process.
A photograph of such a quasi-bipolar plate prior to pasting is shown in Fig. 36. The most
important aspects of this plate are summarized below:
1. It is approximately 1/6 full-size and may be scaled up to full size directly.
Final plate dimensions (pasting area) are 8 by 4 in. The 4-in. dimension is in the vertical direc-
tion. Relatively long and shallow plates result. The reason for this can be seen from the current
conduction paths which in this plate are over the top of the plate only. By making the plate rela-
tively shallow, resistance losses down the plate are minimized.
2. The materials of construction are Lexan as substrate and pure Pb as current
conductors. Lexan is a light weight/high strength plastic which permits relatively easy handling
of the plate with sufficient flexural strength capabilities. Pure Pb has minimal corrosion problems
and also is quite good from an expansion viewpoint.
3. The current conductors of Pb have been held at 20-mil thickness.
4. The conductors are separated by 0.15-in. intervals along the plate. This sep-
aration permits easy charge and discharge of active mass without introducing excessive resistive
losses. The separation is equivalent to that of horizontal grid members in conventional lead
acid batteries, but since each lead strip carries only the current generated around it, the add-
itional leads used in conventional plates to collect the current at the terminal are not necessary
here.
- 98 -
-------
Fig. 36. Typical photograph of an impasted "quasi-bipolar" plate newly
thermoformed (the pasting area is 2.55 in. x 2.04 in.)
- 99 -
-------
5. A plastic rim is provided to facilitate sealing of each plate within a case
(lexan). Lexan is an extremely easy material to handle from this aspect.
6. Paste thickness is held at 20 mil per positive and negative electrode with a
plastic substrate thickness of 20 mil also. Pasting thickness is governed by the plastic border
round the circumference of the plate (as is the case with the outside rim in conventional plates).
The rim also adds rigidity to the structure.
7. Paste adhesion to the plastic substrate is enhanced using glass mats or dynel
fibers attached to the substrate surface in a prior step. Very good paste adhesion has been ob-
served so far.
8. Current is removed from each electrode over the top of each plate only, using
Pb conductors looped over the baseplate prior to layup. The points where each conducting strip
make contact with its equivalent strip on the opposite face of the substrate are not directly im-
mersed in electrolyte. The problem of intercell leakage is thus minimized significantly. ,
9. The Pb conductors are held mechanically to the plastic substrate by a plastic
overlying grid only at those points where the, plastic and the Pb intersect down and across the
plate. During cycling, this setup permits expansion of the Pb down the plate without introduction
of any stresses resulting in plate buckling and poor paste adhesion.
10. As discussed, production of the entire plate is relatively easy. It appears that
it can be carried out on a large scale basis.
11. There is scope in the design for both thinner base plates and also thinner
pastes. No substantial changes are required. The plastic base plate can easily be reinforced
with glass cloth to provide sufficient flexural rigidity in < 20 mil thicknesses. Paste thicknesses
< 20 mil also give superior paste utilization and "reduce weight requirements.
The principal advantages of this quasi-bipolar plate are that a serious problem area in
bipolar plates, namely intercell leakage, is minimized by not immersing in acid those points
where conduction is made through the plastic. The leakage paths are also substantially lengthened.
Any corrosion product formed on the Pb conductors would expand under the sealing plastic
"cocoon" and tend to close any electrolyte leakage paths. By virtue of the unidirectional Pb con-
ductors, the design also reduces plate expansion and buckling problems which we have shown to
seriously limit successful operation of conventional battery positive plates under high rate cycling
conditions. The light weight of the substrate material further adds to the plate attractiveness and
this, together with the basic advantages of a bipolar plate design which were outlined previously,
makes the whole concept very attractive.
F. Construction of the Battery Using Quasi-Bipolar Plates
In construction, the bipolar battery with quasi-bipolar plates is relatively simple and each
plate is connected in series in a module to give the required voltage. To increase capacity, in-
dividual modules are connected in parallel. Sealing of each individual plate within a module may
most readily be affected by preforming a case (~l/8 in. thick) with side and bottom slots. Each
- 100 -
-------
plate is then fitted into the slots in the case and sealed by application of heat and pressure
around the rim surrounding the plate pasting area. A simple heat sealing technique has been
developed by Bell Telephone where plastic components to be heat sealed are treated with an in-
44
frared absorbing material. On exposure to infrared light, those areas in contact with each
other and treated beforehand in this manner are adequately heat sealed. The method has been
used commercially and has the advantage that it is simple and that the heated zone is very local-
ized. It may be more applicable than a conventional heat-sealing process.
The terminal plates in each module are simply thick conventional plates or, to reduce
weight requirements, lead coated Al plates. To allow for electrolyte equalization, we have in-
corporated an "upper rim" in each bipolar plate in which an equilization slot is cut. When the
module is turned partially to one side, electrolyte added through a single filling hole can flow
into each cell compartment. In the normal horizontal position, the electrolyte level is below
the level of these slots. The upper "rim" on the plates also minimizes any possible intercell
leakage problems from electrolyte splashing over the top during charge for example. A crude
schematic of an individual module is shown in Fig. 37.
Within each cell, we at present incorporate 3-mil glass mats as paste retainers together
with commercial Daramic separators with 45-mil ribbing and 30-mil backing. The final require-
ments as regards separators have not been fully established but these separators do permit
trouble free operation with minimal gas bubble retention characteristics.
G. Method of Construction of the Quasi-Bipolar Plate
The design of the bipolar plate has been kept deliberately simple to facilitate large scale
fabrications. The various steps in the process are outlined and scale diagrams and photographs
are included to ease understanding. Basic test plate dimensions are shown in Fig. 38 where we
show one face of the mold in which the final structure is thermoformed. The four basic compon-
ents of the plates are pure Pb, Lexan plastic, and dynel fibers or glass mats. Plate preparation
is as follows:
1. Lead conductor preparation
Strips of Pb were cut from a 20-mil-thick sheet and then bent U-shaped. The length
of the strips was tailored to meet the requirements of the final plate. The tops of each strip (the
"U") were etched in a H-CL/acetic acid solution, washed in H-O, dried and then painted lightly
with a solution of 5% Lexan in methylene chloride. The painted portions are shown in Fig. 39a.
The solvent was then permitted to evaporate off at room temperature. The "painted" portions of
the Pb conductors were those sections to be encased in plastic during layup. In this way, the bond
between Pb and plastic is made as strong as possible. The possibility of cell short circuits by
acid leakage at the points where the conductors extend through the plate, is thus minimized.
Exactly similar tasks v/ere performed when the conductors were made from Pb wire of
20 mil diameter.
- 101 -
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ELECTROLYTE-
MAKEUP
AND VENT
ELECTROLYTE /
EQUALIZATION /
CHANNEL
•©
LEXAN COVER
ELECTRODE SEAL
LEXAN BATTERY CASE
BIPOLAR PLATES
LEAD PLATE (TERMINAL)
Fig. 37. Schematic of an individual module
- 102 -
-------
C
i
1
ir
-j u2^.25"
vl/
/T\
•\XT
— <
•»
-^
— -
2.812"
2.550"
2.400"
2.275"
1.975"
4-
Tl
o c
- 00 t
CVJ 'S
.
>'c
fj
.
3 u
r n
3 r
ij C
u
T 0
n u
? P
vi
•) If
0 «
I 0
j c
•)
1
•J
—^^
D
0.5"
f
1
1
1
—
0.005'
0.004'
^0.020'
AB
B
CD
! !
1
o
CM
O
C)
o
ci
Fig. 38a. Dimensions of aluminum mold for quasi-bipolar plate manufacture
- 103 -
-------
Fig. 38b. Photograph showing one face of the mold used to thermoform
the final quasi-bipolar plate
- 104 -
.
.
-------
•
lll'tl
B.
to. STtastie Base
•
Fig. 36. Rrepar^ticm sequence for quasi-bipolar plate manufacture
-«
.
-------
c. Base plate with layup of
some Pb conductors
d. Plastic Grid
-
Fig. 39. Preparation sequence for quasi-bipolar plate manufacture
- 106 -
-------
I IIVH
e. Plastic Border
Fig. 39. Preparation sequence for quasi-bipolar plate manufacture
- 107
•
-------
2. Lexan preparation
A sheet of Lexan 20 mil thick* was cut with a metal die to the shape shown in
Fig. 39b. This is the "base plate" and the Pb strips are laid over the small cuts at the top of the
plate as illustrated in Fig. 39c.
Two further plastic shapes were cut using special dies. Fig. 39d shows the 5-mil Lexan
"grid" whose main purpose is to mechanically hold the Pb conductors to the base plate at local-
ized points. Around its circumference, it also combines with a 15-mil "border" to control
paste thickness at 20-mil total. The 15-mil Lexan "border" shown in Fig. 39e helps to control
paste thickness and also enhances plate rigidity. Note that the border is wider at the top of the
plate to minimize acid leakage by splashing over the top of each cell.
3. The plate mold
This is shown in Fig. 38 and is self-explanatory. It was made from wrought jig-
plate aluminum which was machined on both sides'. Grooves cut in the mold permit incorporation
of the plastic and Pb grid structure on the surface of the base plate during the hot pressing. A
photograph of one side of the mold is shown in Fig. 38b,
4. Layup technique
The sequence for this is quite simple and after preparation of the various compon-
ents is as shown in Fig. 40. When layup-.is complete,/suitable stops (generally > 18 mil) are
inserted between the faces of the mold to prevent excessive squashing of the desired structure.
A hot press is then carried out at a temperature governed by the plastic employed. This is close to
300°F for Lexan. Finally, the mold is watercooled under pressure and the plate removed from
the press. A typical plate manufactured in this way is shown in Fig. 36. We see no restriction
to performing these operations rapidly and on a large scale.
Following observations of poor paste adhesion on early plates several techniques were
developed to overcome this defect. These involved prior treatments of the base plate surface.
Thus, we now use glass mats, (112 style with Volan finish, Clarke-Schwebel Corp.}, or dynel
fiber (an acrylonitrile/vinyl chloride copolymer) backings to enhance paste adhesion. The mats
are 3 mil thick. They are cut to a size corresponding to the pasting area of the plates and are
then soaked in a 1-2% Lexan solution in methylene chloride. The solvent on the soaked mats is
then permitted to evaporate partially on a glass plate before the mats are attached to the plastic
base plate of the final structure which is to be made. At this point, Pb strips are etched, treated
with Lexan as outlined before, and then laid up over the glass mat on the base plate. The solvent
is again allowed to evaporate off this time completely for > 6 hr. The plate is then laid up con-
* Photographs of the plastic shown here have been taken on sections sprayed with black paint
so that they can be more easily seen.1
- 108 -
-------
LEXAN
GRIDS
LEXAN BORDER
\
3
/
V •
;\
1 l_l_^»-«l» UV^ItLS(_»
: ANTI -SPLASH RIM
PASTING
i
AREA
^LEAD CONDUCTOR EXTENDING
THROUGH THE BASE PLATE
LEXAN
BASE PLATE
Fig. 40. Section through the various components of the bipolar plate
prior to thermoforming
- 109 -
-------
ventionally in the mold and the entire structure oven dried for > 1 hr at 225°F. If all the sol-
vent is not evaporated off prior to this step, bubbles are formed on the Lexan surfaces. The
heated mold is then transferred to the hot press and thermoformed conventionally. One deviation
from the norm in this latter step is that 21-mil stops are now used to prevent excessive squashing
of the glass mat into the base plate during the forming operation. If this is not done, too much
plastic extrusion occurs. The Pb strips tend to become covered with plastic and there is also a
tendency towards plate buckling. Additionally, the glass mat becomes completely immersed in
the Lexan base plate and loses its effect as a paste-retaining surface. With the 21-mil stops, a
1-2 mil glass surface "sits" on top of the Lexan after layup and is well bonded to the plastic on
its underside. In practice, we also deliberately "roughen" this glass surface by scraping it with
a metal probe after layup (though this may not stricly be necessary). The Lexan "grids" used to
hold the Pb strips to the base plate at localized points also bond well to the Lexan coated (the
1-2% Lexan solution) glass mat surface between the Pb strips.
The preparation of plates with Dynel fiber backing to enhance adhesion of paste is simpler
and proceeds in the conventional manner completely through the bipolar plate preparation. When
completely manufactured, those portions of the plate between the Pb strips are lightly painted with
methylene chloride. Immediately after this, chopped dynel fibers are applied to the surface and
the plate is then left until all the solvent has evaporated off. Excess fibers are brushed off the
surface. The only care required is to avoid smearing methylene chloride over the Pb conducting
strips since the solvent may contain some Lexan dissolved off the base plate. Fig. 41 shows a
plate prepared in this manner.
5. Pasting
This was entirely conventional with the exception that ~0.2% Dynel fibers were
added to the positive paste and the negative paste to enhance mechanical stability during cycling.
Normally such additions are made only to the positive paste. The paste material was Universal
Grenox Oxide containing 25% free Pb and a balance of orthorhombic PbO. Curing and formation
schedules were conventional and are given in Appendix V.
H. Modifications to the Final Design Structure
The modifications involved the incorporation of further conduction paths through the plates
as proposed in numbers (2) and (3) of the preliminary design concepts. For the first modifica-
tion only two small changes in the entire fabrication procedure are required. Thus, the base plate
is cut also at the bottom of the pasting area to the shape shown in Fig. 39b, at the top. The 15 mil
Lexan border shown in Fig. 39e is also made equally wide at its top and bottom edges. This serves
to give an adequate sealing rim along the bottom edge. In layup, the Pb strips are now completely
circled round the base plate via the sections cut out for this purpose (Fig. 39b with the additional
bottom cut) and overlapped slightly. The overlap may be located at the top of the plate beneath
the plastic border in the final fabricated plate. Both the top and bottom sections of the Pb strips
- 110 -
-------
.
Fig. 41. Photograph of a quasi-bipolar plate prior to pasting with a surface
treatment of Dynel fibers to enhance paste adhesion
- Ill -
-------
are treated with plastic solution beforehand to enhance bonding. In the design, the conductor
paths are doubled and, therefore, the probability of intercell leakage is increased. The
advantage of better paste utilization is also expected by the modification.
In the third modification whose layup is more complex, electrical contact is obtained at
the top and bottom of each plate and also at the localized points where the Pb strips and plastic
grid intersect in the final layup. The laboratory technique is to drill holes through the plastic
at these latter points and to place 15-mil Pb squares on either side of the holes with a smear of
methylene chloride between to soften the plastic around the hole. The Pb squares are then
mechanically squashed through each hole and at the same time the softened plastic extrudes
along the underside of the squashed buttons, coating them. .The latter serves to provide good
leak-free seals at each point. In addition, after this step, a 5% Lexan solution is pointed around
the outside circumferences of each button to further prevent leakage problems. The centers of
the buttons are left free, however, to provide electrical contact with Pb strips which are then
laid down the plate and over the top of each button. The various steps in this process are shown
in Fig. 42. The remainder of the layup process is conventional. As before, corrosion problems
may ensue but if corrosion is prevented, there may be significant improvement in plate per-
formance as a result of the changes.
In summary, small scale prototype type plates have been developed which are considered
to be suitable for use in a high power density/long life battery. The fabrication techniques are
relatively simple and may be readily extended to full size plates on commercial production scale.
The complete range of plates which we have fabricated to date (including the preliminary design
plates) are tabulated in Table XVIII. Our'major operating experience has been with the quasi-
bipolar plate described first, which has a plastic substrate with Pb strips as conductors con-
nected only over the top of the plate. Performance data on these are described later (Section VII.B.).
Preliminary evaluations of the effects of the changes incorporated in initial quasi-bipolar plates
(Fig. 36) on subsequent performance are also discussed. As will be seen, the performance of the
first design is such as to negate the necessity for using the latter two if so desired.
I. Design in Which the Plastic Substrate is Conductive
This corresponds to number (4) in the preliminary design concept. In practice we had
little hope for its successful application after the conclusion of the evaluations of the acid stability
of reinforced thermosetting systems (which were found to lose structural stability as a result of
acid attack of the reinforcement/plastic bond). We also found that at the positive plate potential
and more particularly at the negative plate potential, O_ and H- gas are rapidly evolved on
graphite or carbon in HgSO, electrolyte. Since we anticipated using the latter materials as con-
ducting medium ( and as reinforcement) in plastic substrates, this obviously left no choice but
to isolate the materials from the acid (with plastic). The acid stability tests did not suggest
that the latter was possible without extended experimentation with the structures. However, we
attempted to fabricate some structures and the results of this are outlined below:
-112 -
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METHYLENE CHLORIDE
SOFT
Y777//A PLASTIC
PLASTIC-
Y////)A
MIL
Pb
SQUARE
^•60MIL WIDE
Y/////A
Pb
AREA OF PLASTIC
^EXTRUSION
\
-------
r.iblc XVlll. ConHimciion l\'tails on RipoUr riau's- \viih l'la.-stic Substraio .HK| Pb Conductors
Firs! I'latc Design Second PI art- fX\sipi l-YeanoJised Pb Conductors Second (
Cell
Number
Plastic '
Conduction
Path
Pb Conductor
Width, mil
Pb Conductor
Thickness, mil
Base Plate
Treatment
Paste
Weight, gm
Formation
Charge, Ahr
initial C5
Capacity. Ahr
Capacity After
HgPO Addition,
Ahr
Cycles Before
Failure
12 2 3456 6
repastfd ri-pastod
L 1, 1. L L L PVC i'VC
T T T T T I' T T
B
60 60 60 60 60 60 60 60
88 8 8 8 8 15 15
N N N N G G SB SB
D
13.6 14.7 13.7 13.6 12.4 14.3 16.5 16.5
.j pnnr t i R 10 0 7 0
, p^r r 1 f" 07? 11"
1.05
1000
7 8
FYC pve •
T T
20 60
mil
wire
20 !5
mil
wire
D N
16.4 17.9
9.0 5.0
poor pooi"
8
repasted
PVC
r
60
15
SB
D
17.8
7.35
1.25
1.06
1000
9 10
L L
T T
60 60
25 20
D G
17.1 16.4
9.35 9.75
1.0 1.06
0.6 1.0
730
11
1,
T
60
20
G
16.5
6.3
1.12
1.06
1000
12
\.
T
20
mil
wire
20
mil
wire
G
16.5
7.6
1.2
1.04
1005
13
L
T
B
60
20
D
14.0
6.5
0.98
0.84
560
14 15
1.. L.
T r
B B
1
60 60
20 20
D 0
15.4 14.0
7.2
0.52
< 0.1
16 17 18 19 20
L L 1. 1. i.
T T T T 1'
B B B B li
1
60 60 60 60 60
20 20 20 20 20
D LD LD G G
15.1 17.1 15.9 15.9
8.2 7.2
0.96
21 22
1. 1,
T T
It
60 60
20 20
G c;
17.4 15.5
6.6
1.09
0.65
200
23
L
T
B
1
60
20
D
18.0
6.2
1.08
0.92
1158
Key: L — Lexan; PVC — Polyvinyl Chloride; T—Top; T, B — Top and Bottom; T, D, 1—Top, Bottom and Pb/Plastic Intersection Points; N — No Treatment;
G — Glass Mat or Cloth; SB — Sand Blasted; SBD — Sand Blasted and Dynel Fiber; D — Dynel Fiber; LD — Lead Dust.
-------
A prepreg from Union Carbide was used. The material is designated as "Thornel" 75S
structural graphite and is B-staged with X-2544 epoxy resin. The material contains unidirectional
two-ply graphite filaments. Ply thickness is 7.5 mil. In layup, three plys were used with the
middle ply at right angles to i.he other two. Pb strips were simply laid along the surface of both
sides of the laminate at 0.15-in. spacing. It is not necessary ro loop the Pb over the top of the
structure to provide conduction since this is achieved through the underlying graphite filaments
in contact with the Pb strips. Apart from this, layup was as before and Lexan borders and Lexan
grids were used to hold the Pb to the base plate (the prepreg) surface at localized points. Where
no Pb adhesion to the base plate was desired, the underside of the strips were sprayed with a
suitable release agent beforehand. The entire package was placed in the hot press and subjected
to the curing shedule below:
Curing schedule (1) 15 psi at 203° F for 30 min
Bring to ( 2) 90 psi at 203° F and hold for 30 min
Heat to ( 3) 239° F and hold for 30 min at 90 psi
Bring to (4) 338° F at 90 psi for 2 hr
Cool to (5) 122° F at 90 psi in not less than 20 min.
(After 1 hr of air cooling, the temperature
was down to 150°F: The mold was then
water cooled and removed from the press.)
The plate prepared in this manner had the following characteristics:
1. Bonding of the Lexan borders and grid to the laminate base plate was poor.
2. Interply bonding in the base laminate was not good along the outside edges.
3. Resin flow tended to be nonuniform, resulting in some exposed graphite
surfaces.
4. There was good conductivity through the plate via the Pb strips.
5. The laminate was bowed and rather brittle.
A phenolic prepreg from Fiber Materials, Inc., (Westford, Mass.) was also used. It
had the following properties:
1. It was made from a graphite loaded phenolic resin B-staged on graphite cloth.
2. The cloth thickness was 15 mil and the prepreg thickness 20 mil. The prepreg
density was 1.45 g/cc and the cost was 35 dollars per sq yd (for very small volume).
The layup technique was the same as above and the curing schedule was as follows:
1. Bring to 225° F at contact pressure.
2. Increa?e pressure in 20 psi increments every 5-110 min at 225° F up to
200 psi.
3. Apply total pressure (200 — 2000 psi) which depends on requirements of final
laminate, elg., total thickness desired. [This step was omitted when preparing our laminate
which was cured at 200 psi (since the desired laminate thickness was only 20 mil)].
- 115 -
-------
4. Bring to: (1) 250° F for 0.5 hr
then: (2) 215° F for 1 hr
(3) 300°Fforlhr
(4) 325°Ffor2hr
5. Cool to < 250° F at pressure and then remove the mold from the press.
The plate prepared in this manner had the following characteristics:
1. There was nonuniform resin flow on parts of the surface of the laminate base
plate, resulting in some exposure of graphite cloth at the surface.
2. Those areas which were covered by resin showed reduced conductivity.
3. Conductivity through the plate via the Pb strips was good.
4. Bonding of the Lexan border and grid to the phenolic laminate base plate
was poor.
5. The plate bowed slightly.
In summary, our preliminary results with these new designs showed both good and bad
features. Conductivity was very good through the plate via the Pb strips and underlying graphite.
Good conductivity was also achieved through the plate via a Pb strip on one side and on the right
hand edge of the plate, and a Pb strip on the reverse side and on the left hand edge of the plate,
i.e., along the cloth underneath the resin. Of the two plates, the phenolic with graphite cloth was
less bowed and much less brittle and also showed less exposed graphite after preparation. We
believe that all these points can be adjusted, however, by adjustment of the various experimental
variables, e.g., time of curing and temperature. There is more chance of success with the cloth
reinforced prepreg, however. In regard to bonding of the Lexan border (which controls paste
thickness) and Lexan grid (which holds the Pb strips to the base plate at localized points), the
problem is less easily solved. The best approach would probably be to experiment with other
materials, e.g., polysulfone or, if available, thin sheets of the thermosetting resin actually
used in the prepreg itself. These problems are not necessarily insurmountable but would
require a reasonable time period in which to experiment with the above mentioned materials
and techniques.
- 116 -
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VII. LIFE TESTING OF NEW DESIGN PLATES
A. Test Cell and Test Procedure
The test configuration and test procedure were held constant for all of the bipolar plates
studied. Plexiglass holders were made in which each individual bipolar plate was held between
Viton rubber gaskets at the two sides and bottom edge of the plastic rim surrounding the pasting
area of the plate. This provided leak-free operation around the plate. Head plates of approxi-
mately four times the capacity of each bipolar plate (~5 Ahr total) were inserted in the test
holders on either side of the bipolar plate. The head plates were made from antimony free grids.
Industrial Daramic separators (extruded polyethylene) from W. R. Grace with 30-mil backing
and 45-mil ribbing were used in each cell and a 3-mil glass mat (from W.R. Grace) was used
as paste retainer on both positive and negative side of each bipolar electrode. Total electrolyte
4
volume in each cell was ~ 18 ml of 1.28 sp gr H^SO.. This is a large excess of acid and cycling
tests reported here were carried out using this excess. Recently, we have reduced the acid
volume per cell to 6 ml without any apparent degradation in cell performance. The theoretical
volume of electrolyte required for high rate/shallow discharge cycles is less than the latter
value.* In our battery weight calculations (based on full size plates of the quasi-bipolar design),
we have incorporated an allowance for 100% excess of acid. Even with this excess, electrolyte
weight is only 10% of total battery weight. Clearly there is adequate scope for varying practical
electrolyte requirements without overstepping final battery weight specifications. Additions of
1.8 vol% of 85% HJPO. were made to the electrolyte after formation of each plate and after initial
21
C/5 capacity evaluations. The capacity evaluations before HgPO. additions were minimized
to reduce any plate degradation prior to cycling performance tests.
Table XVIII shows the plates we have prepared to the above specifications. The exact
details of individual plate construction are given therein. Plate area was held constant at ~ 34
o
cm per positive or negative electrode. Initial capacity data are given also. Photographs of
typical pasted and formed bipolar plates are shown in Fig. 43a and 43b, respectively.
The steps leading up to cycling evaluations after the initial capacity measurement in
1.28 sp gr HgSO. were as follows:
1. Add 1.8% H,PO. to the electrolyte and recharge the plate.
2. Reevaluate the capacity at the C/5 rate.
* See page 137 in the text with respect to this point.
- 117 -
-------
a. Pasted Plate
b. Formed Plate
Fig. 43. Photographs of a pasted and cured quasi-bipolar plate and of a
formed quasi-bipolar plate
- 118 -
-------
3. Charge at the C/5 rate to full capacity (based on the initial capacity).
4. Partialiy discharge the plate to 80% total capacity [based on the value in
(2) above].
At the end of this sequence, testing is started with exactly the same procedures as out-
lined previously for commercial plates (page 8, point 4). Temperature was also held at 30°C
_4_ 1°C. Charge and discharge currents were those required to obtain the power ratings of
55 KW and 30 KW within the weight (550 Ib maximum) and voltage (150 V minimum) limita-
tions using a battery system based on these quasi-bipolar plates. Based on this, an operat-
ing point of 150 mA/cm was chosen. Note that this is lower than the current density re-
quired from commercial plates to achieve the same power ratings. Superior life-time on
cycling would thus be expected. As before, discharge time was 25 sec. Charge time was
held at 67 sec giving a < 10% overcharge on each cycle. It is difficult to measure individual
positive or negative electrode potentials in a bipolar battery since there are no current take-
off terminals. Therefore, complete cell voltages are given for each bipolar plate plus head
plates. However, the head plates were shown to vary in voltage during charge and discharge
in a characteristic manner which did not change throughout the cycling. Changes in voltage
characteristics during cycling are thus a function of bipolar plate performance only. The
capacity retained as shown in the data is also that retained by the bipolar test plates only.
Because of the difficulty in determining individual positive or negative electrode potentials
it has not yet been possible to evaluate which electrode is actually failing as a result of the
cycling.
B. Test Results
Test results are recorded in Table XVIII (page 107) and in Figs. 44-52. A synopsis of
the relatively poor performance of plates based on the first design has been given already. A
major problem was that the Pb strips were too widely separated (0.29 in.) in the design to permit
adequate plate charging. Plates numbered 6, 7, 8 and 9 in the final design also did not per-
form well at first. Thus, paste adhesion was poor in 6, where only sand blasting was used
to improve adhesion. Though it formed well initially, the paste rapidly shed from the plastic
base plate on subsequent cycling. The same was true for plate number 8 which had no prior
surface treatment. Plate number 7, which had Pb wires as conductors, had plastic extruded
over many of the wires during fabrication and thus did not form well. Plate number 9 had
relatively thick (25 mil) Pb strips as conductors and on plate fabrication, some of these cut
completely through the substrate causing short circuit paths when immersed in acid. We
overcame these defects by adjusting the fabrication techniques as outlined earlier and were
able to salvage plates number 6 and 8 for repasting. These are thus denoted as 6"repasted"
and 8 "repasted" in the table. These two plates subsequently showed superior formation
characteristics compared to further plates made in exactly the same way and avoiding the
defects noted above. We attributed this to better contact between paste and conductors
caused, in turn, by the prior surface roughening which the conductors had undergone in the
plates during their initial pasting and testing. Subsequently, we now deliberately pre-
anodize all the strips on the fabricated plates at 0.5 A for 10 min before pasting. This is
noted also in the table.
- 119 -
-------
to
o
6 1
47
w
0
•- 5 J
O
>
4.»
4.3
too
X
O
CMAROt PORTION Or CYCLE
_
-
-
-
1
trstr.
,
1
_
-
-
-
'
PERCENT TIME ON CHARGE
PERCENT CAPACITY RETAINED
DISCMADGE PORTION Or CYCLE
iniiiiiiiiitliiiiiiiiiiiiiiifiiniinniiiininiiiiii^iiiiiiiinij'n,
503A 25SEC ' i I I *' * 1 I 1 I
PERCENT TIME ON DI8CMAHOE
53 48
too
400
CYCLE NUMBER
aoo
Fig. 44. Performance of quasi-bipolar plate no. 6 "repasted" under severe cycling
conditions (two cell voltage)
-------
si- ' '
s-
49
« 3
0
-
r
2 BA 61 SEC
It 1 1 1 :
P
1
.RCENT TIM
E 0
N C
H
an
G
1
1
?r
1
«« 61 SIC
i
1 ».* SfSK
1
-
. _
PERCENT CAPACITY RETAINED ~
DISCHARGE PORTION Of CYCLE
»04t 88 SCC
PERCENT TIME ON DISCHARGE
'II
1 I 1 I
300 «OO
CTCLE NUMBER
Fig. 45. Performance of quasi-bipolar plate no. 8 "repasted" under severe cycling
conditions (two cell voltage)
-------
CHARGE PORTION OF CYCLE
1
6.1 -
5.7
UJ
13
•a 5.3
O
4.9
4.5
100
iTX—tTT^ PERCENT CHARGE TIME BEFORE CUT-OFF
^ 2.06A 61 SEC .2.1 A 67 SEC ,
0 -
PERCENT CAPACITY RETAINED
100
105
17
82 70
60
50
42
4.6
DISCHARGE PORTION OF CYCLE
5.1 A 25 SEC
5.06 A 25 SEC
UJ
o
4
4.2
3.8
3.4 -
3.0
100
PERCENT DISCHARGE TIME BEFORE CUT-OFF
0-
i
j r
100
200 300
CYCLE NUMBER
400
50O
600
700
Fig. 46. Performance of quasi-bipolar plate no. 10 under severe cycling
conditions (two cell voltage)
-------
4.S
-M» 67 SEC . .?O6A 67 SEC
CHARGE PORTION OF CYCLE
PERCENT TIME ON CHARGE
PERCENT CAPACITY RETAINED
CO
co
3.8
bJ
O
2 M
_*
O
>
3.O
100
9.03A 29 SEC
DISCHARGE PORTION OF CYCLE
PERCENT TIME ON DISCHARGE
200
300 400
CYCLE NUMBER
500
600
roo
800
900
Fig. 47. Performance of quasi-bipolar plate no. 11 under severe cycling
conditions (two cell voltage)
-------
XKJ -
0 -
I
h-A
to
1!
CiUIICi KMTiM Of CHC1.C
1
>ti»cmr TIM OH
MIKOT C*MCIT< HfTMCO
OttCMMM rMTiON 0* CVCU
1!
PfUCCNT TIM ON DIICMWU
Fig. 48. Performance of quasi-bipolar plate no. 12 under severe cycling
conditions (two cell voltage)
-------
CHARGE PORTION OF CYCLE
UJ
o
O
>
UJ
o
o
>
6.
5.7
4.9
4.5
100
%
0
1C
4.2
3.8
3.4
3.0
100
0
-
-
-
2JI
D6
A(
55
sec
: 2.5A 65 se
9
2.
06
A
6
5 sec
PERCENT TIME ON CHARGE
•
— PERCENT CAPACITY RETAINED * '
)0
86 58
DISCHARGE PORTION OF CYCLE
—
>\
—
]
5.03A 25 sec
*~ PERC
-
EN
T
I
TIME ON DISCHARGE
•
i
' 1
KDO
CYCLE NUMBER
200
Fig. 49. Performance of quasi-bipolar plate no. 22 under severe cycling
conditions (two cell voltage)
- 125 -
-------
6.1
17
5.3
4.S
IOO
0
K
—
-
-
CHARGE
:
.1
A
PORTION
57
S
FC
PERCENT TIME ON
-
X)
9S 93
PERCENT
OF CYCLE
-
-
-
-
CHARGE
CAPACITY RETAINED
DISCHARGE
-
3.8
34
3.O
100
0
'
-
11 I I ... 5.03A
1
II
1
III
1
81
a
PORTION
OF
77
69
57
48
CYCLE
25 SEC
- PERCENT TIME
-
1 1
100
200
1
ON
CYCLE
]
,
1
DISCHARGE
300
NUMBER
•
400
1
1
I
soo
1
1
-
-
-
r
60
Fig. 50. Performance of quasi-bipolar plate no. 13 under severe cycling
conditions (two cell voltage)
- 126 -
-------
CHABGC PORTION Vf < :.E
206& *?SEC
3.O3A 25 S£C
PERCENT TlMt ON OlSCM*B-,£
I 1
CYCLE NUMBER
Fig. 51. Performance of quasi-bipolar plate no. 23 under severe cycling
conditions (two cell voltage)
-------
110 -
100
* 70 -
2
O
I 1 1 1
I ..... I .3 _l I 1. I
£ 60 -
UJ
1C
t- 50 -
0-
4
u
20 -
10 -
100 2OO 300 4OO 500 600 700 800
NUMBER OF CYCLES
900 1000 1100 1200
Fig. 52. Capacity retention (C/5) for the limiting electrode of quasi-bipolar test
plates as a function of the number of prior high rate cycles undergone.
The dotted curves show the equivalent data for three conventional positive
plates tested under slightly less severe conditions (cf pages 10 and 113).
- 128 -
-------
The maximum data have been recorded on plates 6 repasted, 8 repasted, 10-12, 22
which all have conduction only over the top of the plate. Other details of the plates are indicated
in Table XVIII. They all exhibited good characteristics requiring an average 7.37 Ahr for forma-
tion. Visually, they could be seen to form well and evenly over the entire surface. The initial
C/5 capacity values were also high, averaging at 1.09 Ahr prior to H,PO. addition. The average
paste weight was 16.1 g total and assuming that the positive and negative sides of each bipolar
plate have equal weights, this gives a value of 8.05 g/positive or negative paste. The expected
fi 0
capacity for the plates based on Berndt's value of 0.125 Ahr/g (at 2.5 mA/cm discharge
current) is 1.01 Ahr. The observed value of 1.09 Ahr is 8% greater than this and was in addition
measured at a current density approximately two-and-a-half times greater than the value on
which Berndt's figure was based. The plates thus perform well based on this simple evaluation.
An interesting observation, and one which we have no real explanation for as yet, was that the
addition of H^PO. to the electrolyte caused on average only a 10% drop in capacity of these
plates. This is less than the average 25% capacity drop following H,PO. additions to the iR-free
21
plates containing no Sb. (Tudor, et al. also observed a fall in capacity of up to 50% following
H,PO. additions to Sb-free cells.) It has been suggested elsewhere that if battery plates are
left to sit for an extended period of time after H«PO. addition, the decrease in capacity is not
so large. In practice, we did leave all the bipolar plates for more than 6 hr in the discharged
state after HJPO. additions. The iR-free plates, in contrast, were immediately recharged after
HnPO. additions to the cell. This may or may not be the important difference. For whatever the
« 4
cause, the observation is important since minimum reductions in plate capacity following HoPO
additions are desirable. Here, it was not deemed necessary to "work" the phosphate into the
21
paste by cycling as recommended by Tudor, et al. to minimize capacity losses in the paste.
(That is, the latter authors found that the initial capacity loss could be minimized by subjecting
the paste to a number of deep cycles after HgPO. additions).
Results of the cycling on these plates are shown in Figs. 44-52. Apart from plate 22
(Fig. 49) in which some conductors had cut through the substrate during fabrication, all the
plates tested stood up extremely well to the cycling regime. The plates are much superior to
commercial plates tested under similar circumstances, and four plates which have conduction
only over the top of the plate have successfully completed 1000 cycles before onset of failure.
Conventionally, due to time limitations, results were terminated after the completion of 1000
successful cycles. It is apparent that each plate underwent capacity degradation as a result of
cycling (Fig. 52) and that towards the end of the ninth and tenth groups of 100 cycles, that is,
after close to 900 complete cycles and 1000 complete cycles, the voltage of the test cells
generally started to decrease sharply towards the 3.0 V cutoff point. However, in each case
where such a decrease was observed, the good performance characteristics of each plate were
re-attained on re-charging the plates (after the usual capacity evaluations). It is thus antici-
pated that on these plates, particularly plates numbered 8, 11, and 12, in excess of 1000 cycles
could be successfully completed if time permitted. With plate number 10, which also had
- 129 -
-------
conduction only over the top of the plate, 730 complete cycles were obtained prior to failure.
Time again did not permit an investigation of the failure mode here, but no severe paste shedding
was observed on this plate. The negative electrode paste, however, was softened and severely
blistered.
The completion of 1000 successful high rate cycles with these plates compares very
favorably with the 350 cycle maximum of commercial positive plates. The capacity retained by
these bipolar plates is also well in excess of that retained by the commercial plates after equiva-
lent numbers of cycles (see Fig. 52). Thus, for example, after 300 complete cycles, the
capacity retained by bipolar plates 6, 8, 10-12 was 87%, 102%, 90%, 91% and 89%, respectively
(the maximum capcity retained by the commercial positive plates after 300 cycles was 57%). The
voltage on discharge of the bipolar plates is also high when compared to that of the commercial
plates (for example, compare Fig. 2). During charge, the voltage of the bipolar plates is quite
high, reaching ~ 3 V/cell, but this does not appear to accelerate plate degradation. The differ-
ence is due to the absence of Sb in the bipolar plates, and also due to the fact that the plates also
receive overcharge at rates up to 40 KW, e.g., in some cycles on plates 8 repasted and 10. Sb
46
lowers the polarization of the positive plate and also lowers H0-evolution on the negative plate.
a
Because we are able to eliminate Sb from the plates and yet still maintain cycling life, the advantage
of maintenance-free performance is thus realized with these bipolar plates.
The results were extremely encouraging. The capacity retained by plates 6 repasted, 8
repasted, 10, 11, and 12 was 47%, 61%, 42%, 51% and 48%, respectively, on completion of
1000, 1000, 730, 1000 and 1005 cycles (Fig. 52). Even at this stage the appearance of the plates
was quite good, as can be seen in Figs. 53 and 54, which are of plates 8 "repasted" and 12 after
the above number of cycles. Little shedding was observed and the positive electrode paste
appeared to undergo less physical changes than the negative. The negative electrode paste was
somewhat softened in a manner similar to that observed in commercial negative paste material
after cycling (cf. Fig. 10). Note also the whitish tinges (probably due to phosphate) on the
positive electrode paste of plate 8 "repasted." Insignificant buckling of the plates was observed
and no degradation of the plastic substrate was found. Though some corrosion product was ob-
served on the Pb conducting strips under the plastic border at the top of the plate on the positive
electrode, no leakage paths were apparent. After removing the paste from all these plates, the
Pb conductors were examined for corrosion attack. Even with 20 mil wires (in plate number 12),
no excessive corrosion was observed.* Taken together, the results indicate that the above plates,
without further modification, are extremely promising for use in a high rate/long life battery.
Though only quasi-bipolar in nature, they apparently are sufficiently well designed to stand up
to the rigors of high rate cycling and still exhibit good performance after extended periods.
Nevertheless, we also tested two plates, numbered 13 and 14, in which the Pb conduct-
ors were connected through the substrate at the top and bottom of the plate, and one plate
* An examination of the minimum conductor cross-section which is compatible with desired life-
time is one of the factors proposed to further characterize these plates on a more realistic time
basis.
- 130 -
-------
Rg. S3. Photographs of the positive (a) and aegpcive (b) electrodes of plate
no. 8 after extended (1000) high rate/shallow discbarge cycles
- 131 -
-------
Pl.ltc V
*
Fig. 54. Photographs of the positive (a) and negative (b) electrodes of plat;
no. 12 after extended (1000) high rate/shallow discharge cycles
,
- 132 -
.
•
-------
number 23, in which connection was made also at multiple points down and across the plate.
Plate number 14 did not perform well and some conductors were found to have sliced through
the substrate during plate fabrication. Plate number 13 lasted for 595 complete cycles, and the
capacity retention was 47%. As can be seen from Fig. 50, its voltage characteristics are not
excessively different from that of the unmodified quasi-bipolar plates. Plate number 23 (Fig. 51)
was tested for 1158 complete cycles and after these, its capacity retention was 74%. On the
last 123 of these cycles the plate was operated successfully in the starved electrolyte condition,
that is, with electrolyte in the paste and a slight excess outside the paste (approximately 6 mil
compared to 18 mil per cell in all the other tests).. The data plotted for this plate are shown in
Fig. 51. Though the voltage characteristics on cycling are again not markedly changed from
those of the above plates, the plate does appear to stand up somewhat better to the high rate
cycling as evidenced by the higher final capacity retention figures (after a greater number of
cycles). Note also that testing was terminated with this plate after 1158 cycles, not because of
failure, but due to time limitations. More so than with the previous plates discussed, an ex-
tended cycling lifetime beyond 1158 cycles is anticipated.
Obviously, no exact conclusions may be drawn from the last results since not enough
test data are available. However, it is apparent that if sufficient care is taken in fabrication,
plates with plastic substrates and multiple connections through the plate between Pb conducting
strips placed on either side, can be made and operated successfully. The performance of such
a plate suggests that superior life time on cycling may ensue due to better paste utilization,
compared to plates where connection is made only over the top of the plate.
- 133 -
-------
VIII. BATTERY DESIGN AND PRELIMINARY COST ANALYSIS
In this section, derails of the design, operation, and characteristics of full-scale battery
systems made from the quasi-bipolar plates are given. Since the actual experimental test pro-
gram and design concepts were based on the Preliminary Power Profile specified by EPA (pages
1 and 2), the specifications of a full-scale battery operating at .the minimum permissible limits
given in this profile, i.e., at 100 W/lb, are discussed first. The maximum power density demon-
strated in the program period for a full-sized battery system based on the plates is then calculated.
Also, the energy density of the battery operating at 100 W/lb and at a moderate rate (C/5) is in-
cluded and contrasted with that of an equivalent battery constructed from thin conventional SLI
plates operating at the same power densities. Finally, the modifications to the above battery
system which are necessary to make it conform to the Final Power Profile specified by EPA (Fig. 1
and pages 2 and 4) are then discussed. In this respect, the specifications are given first for such
a modified battery operating at the minimum permissible limits given in the profile, i.e., 128 W/lb.
Then, the specifications are given for operation at the final preferred goal of 156.6 W/lb (the latter
is the average power density over a 25 sec period - at the 70.5 KW rate). Finally, the specifica-
the average power density over a 25 sec period - at the 70.5 KW rate). Finally, the specifica-
tions of the battery operating at the maximum desired power output (92.5 KW for 10 sec) of
205.5 W/lb are given; and here the preferred changes to the basic (Fig. 36) quasi-bipolar plate
design, which are considered desirable to enable a system constructed from the plates to con-
form to the latter limits, are also detailed.
Of necessity, several assumptions were made in all these calculations and they are
rationalized below. Where possible, however, projected full-scale battery performance is based
on actual test results and calculations have been based on the use of those materials which have
been shown here to be suitable for use in lead acid batteries.
A. Design, Operation, and Characteristics of a Quasi-Bipolar Battery System
Based on the Preliminary Power Profile Specified by EPA
The design of the system is based on the same modular approach discussed in Section III
Concept I and in Appendices I and II for Preliminary Bipolar Concepts A and B. The basic plate
design is exactly as discussed in Sections VI (E, F, and G) for the small scale quasi-bipolar
plates, with conduction only over the top of the plate. The pasting area is approximately six
- 135 -
-------
times that of the small scale quasi-bipolar plates and is made relatively long (8-in.) and shallow
(4-in.) to minimize resistance losses. As before, each module consists of a series arrangement
of 100 such plates, with rwo conventional head plates (~ 80 mil thick) pasted in Pb or Pb/Ca grids
and placed at each <..-nd of the module to remove the current. The modules are placed in parallel
to provide the necessary capacity, In this design, the total plate dimension is held at 9-in. long
x 5.3-in. deep. Thus, approximately 0.37-in. is available on each side of the plate for sealing
within the case and approximately 0.5-in. is available at the bottom for sealing in the case. The
additional space at the bottom of each module also tends to prevent short circuits in each cell due
to accumulation of paste which may shed from the plates during operation. Sealing is accomplished
within the case (such as that shown in Fig. 37), preferably in the manner used by Bell Telephone,
which is outlined on page 97 of this report. At the top of the plate, the 0.55-in. rim prevents acid
splashing over the plate. In each module an acid equalization slot is also cut in each plate, as
shown in Fig. 37. The following specific points rationalize the choice of design parameters for the
full-scale battery:
1. Choice of Pb conductor dimensions
For calculation purposes, these were taken as 20 mil Pb wires. Pb has a minimal
corrosion rate in HJSO.. In effect, the minimum cross-section through the conductor governs
its life due to corrosion. In some test plates, the minimum dimension was actually 15 mil per
conductor, and plates with such conductors performed very well on cycling. Within the short
time scale (~ 1 mo.) of the tests, there was no recorded instance in which severe corrosion
of these strips (e.g., complete corrosion through of any strip) was observed. On the contrary,
the conductors in all of the plates after 1000 cycles, though corroded somewhat on the positive
side, still looked very good. Plate number 12, which was made using 20 mil Pb wires as conduc-
tors, also performed very well. In addition, the minor change in conductor separation across
the plate, affected by using conductors of thinner cross-section, also did not limit plate per-
formance. Nevertheless, in any subsequent development of the battery system, a more exten-
sive evaluation of the minimum conductor dimension necessary to maintain a 5 yr lifetime under
the specified operating conditions is required.
2. Electrolyte weight
The electrolyte weight was a calculated value for the final design battery, and the
calculations are exactly as shown for the preliminary bipolar concepts (A) and (B). As before,
this electrolyte weight was based on the two consecutive 55 KW, 25 sec power pulses. An acid
utilization factor of 0.5 was selected, and this has been shown to have only a minor effect on
overall battery weight (Fig. 16). In practice, we doubled the calculated amount of HJ5O. to
allow for the volume of electrolyte required physically to soak the retainer and separator in the
intervening space between adjacent electrodes. In fact, the volume of electrolyte required for
the most severe high rate discharge cycles can be incorporated totally in the volume of the paste.
Even with the above allowances, electrolyte contributes only 10% to total battery weight,
leaving scope for further incorporation of more electrolyte if desired. In practice, though the
- 136 -
-------
majority of the tests reported here were carried out with excess of electrolyte, in one instance
with cell 23, we used a starved electrolyte condition (6 mil cell compared to 18 mil normally)
and observed no degradation in plate performance during the high rate cycling. It is, neverthe-
less, true that even in^this starved condition the electrolyte volume (converted to a volume per
full size cell) is still twice that used for calculation purposes. Therefore, further development
work in this field is required. We re-emphasize, however, that in actual fact there is scope for
more than doubling the acid volume without exceeding battery weight requirements.
3. Separators and retainers
A major problem area anticipated was that of gas bubble retention, particularly
during charging. In the latter experiment, outlined above, we used a 3 mil glass mat and a
Daramic separator with 10 mil backing and 10 mil ribbing. No severe gas retention problems
were observed. Note that with the latter separators and retainers, the total weight contribution
per battery is only 1.5% and 1.0%, respectively. Therefore, no weight restrictions are found
with these two components, nor apparently is gas bubble retention a problem with such materials.
However, at the electrolyte volume chosen per cell for calculation purposes, the calculated
spacing between adjacent electrodes is only 0.011-in. Therefore, a compromise is required
between the retaining mat thickness, separator thickness, and configuration and the desirability of
reducing the acid volume (weight component) per cell. In such a tightly packed cell configuration
as that proposed in a module, it is questionable if retaining mats are necessary, or even desirable,
but we have included their weight in the final calculations. We have considered the use of 10 mil
flat sheet separators for calculation purposes, but this is another area requiring further develop-
ment work. An ideal compromise may be to use a ribbed separator with 10 mil backing and 5 mil
ribbing (which can be made available from W. R. Grace Co.) and with a retainer only on the
positive electrode side. Alternatively, the desired approach may involve modifications to the
electrode structure incorporating channels for gas bubble release in conjunction with the use of
a flat sheet separator.
4. Choice of paste thickenss
The paste thickness necessary to supply the required capacity during the most
severe energy transfer cycle of 760 Whr was initially calculated as 7-mil (for a 8-in. x 4-in.
plate or 5-in. x 3-in. plate - see Appendices I and II). These calculations were based on paste
O
utilization factors taken from Berndt's data and assuming a decay allowance (F in Section III
and in Appendices I and II) of 0.5. The values assumed were recognized as being conservative
since they referredjto conventional thick plate designs (see for example, Fig. 21, and the re-
lated discussion). Nevertheless, the paste thickness was held at 20-mil per electrode during
plate development and also for the present calculation purposes. The reason for the choice of
this large excess of active material was simply to ease any plate fabrication and handling
problems. In fact, as discussed, there were no problems, and the quasi-bipolar plates with
20-mil paste thickenss all behaved very well (see Section VII). Moreover, the capacity of these
- 137 -
-------
full-size quasi-bipolar plates is 6.4 Ahr at the C/5 rate and is ~ 3 Ahr/plate at a power density
2
of 135 W/lb (150 mA/cm discharge current). On discharging at 55 KW for two consecutive
25 sec pulses, 4.25 Ahr/battery (or 0.425 Ahr/plate with 10 parallel modules) are consumed.
Clearly, with the present design, there is a very large excess (sevenfold) of capacity available
even at the highest discharge rates. This excess of active mass is also very desirable in view
of the more extreme power ratings recently specified by EPA (Fig. 1).
The calculations for the preliminary bipolar concept A (see Fig. 16) also revealed the
significant impact on battery weight of the reserve capacity in the plates, suggesting that a
marked reduction in overall battery weight can be achieved simply by reducing the paste thick-
ness to 15 mil per electrode. Finally, it is normal practice to make a conventional positive
electrode slightly thicker than the negative since the former is usually limiting at high rates.
Possibly then, the negative electrode in the present quasi-bipolar plates may be made even
thinner than 15-mil with further optimization in power density. For the present purposes, how-
ever, it is sufficient to reiterate that the battery weight was calculated on the basis of a 20-mil
paste thickness per electrode and that the plates in the battery have consequently more than
adequate reserve capacity after extended cycling at high rates.
5. Paste adhesion
For the calculations, no Pb plate was incorporated to prevent corrosion through
the substrate and enhance paste adhesion. In fact, this is a desirable omission. Final battery
cost and weight are reduced and expansion on the positive electrode (with plate buckling) is
minimized (see Preliminary Concept A in Section Tl and particularly Fig. 15). We observed very
good adhesion to the substrate using dynel fibers or glass mat, and, because of the design of
the plate, no corrosion probelms are evident.
The design values used for power density calculations of a battery system based on the
above discussion are summarized below in Table XIX. The values (not the current density) are
also the same in a battery conforming to the final power profile.
Table XX gives a summary of the weight requirements for each module designed to oper-
ate under the preliminary power profile specified by EPA, and Table XXI is a comparison of the
4
component weight distribution in a conventional battery (ex. Vinal ) and the module above.
- 138 -
-------
Table XIX. Basic Assumptions and Design Parameters of a Full-Size
Battery Based on the Quasi-Bipolar Plate with Conduction
Over the Top (Concept I)
Average Discharge Voltage
Pasted Are.:)
Total Plate Area
Operating Current Density
Lexan Density
Plastic Base Plate
Plastic Grid
Plastic Border
Plastic Border Surrounding the
Active Mass
Lead Conductors
Paste Thickness
Case Material
Separator Thickness
Retainers
Inter-Module Wiring
Electrolyte
1.8 V/cell
32 sq in./positive or negative electrode
48 sq in.
o
150 mA/cm
1.2 g/cc
20 mil thick
5 mil thick
15 mil thick
Same dimensions as in small scale
test plate
20 mil Pb wire
20 mil per electrode
0.2 in. thick
10 mil (0.9 g/cc)
3 mil (1.9 gm/cell)
= 1 ft/module of heavy gauge aluminum
at 59:gms/ft
1.28 sp gr
Table XX. Summary of Weight Requirements for Each Module Based
on the Quasi-Bipolar Plates (Concept I) and Operating Under
the Preliminary Power Profile
1. Paste/module
2. Head plates/module
3. Plastic components (grid) in the
Plate/module
4. Lead conductors (grid)/module
5. Glass retainers/module
6. Separators/module
7. Case material/module
8. Inter-module wiring
9. Electrolyte/module (double the
calculated requirement)
Total, wt/module
Number of modules/battery
Total wt/battery
Ib
22.50
0.79
5.22
4.50
0.43
0.60
2.88
0.11
3.92
40.95
10
409 Ib
%of
Total Wt
55
2
13
11
1
1.5
7
0.3
9.5
- 139 -
-------
'['able XXI. Percentage Weight Distribution Comparison in Conventional
and Quasi-Bipolar Batteries
Active materials (Pb +PbO0)
Lt
Electrolyte
Pb grid
Case
Connectors
Separators
Plastic grid
Retainers
Conventional
37
23
25
6
6
1
-
-
Bipolar
55
9.5
11 -i
7.
0.3
1.5
Equivalent
to a
Conventional
grid
13-
1
The above module weighs only 40.95 Ib, and the quasi-bipolar plates in it have been
2 2
demonstrated to operate successfully at 150 mA/cm on discharge and up to 83 mA/cm on
charge for 1000 cycles. Concurrently, conventional lead plates in each test cell which incorp-
orated Universal Grenox oxide pasted in 50 mil Pb or Pb/Ca grids did tend to shed somewhat but
still readily withstood the same cycling regime. This is not surprising since the effective current
2 2
density for these conventional plates is only 75 mA/cm and 41.5 mA/cm on discharge and
charge, respectively. Under a small drain, the voltage of such a module is close to 200 V and
o
is, on average, close to 180 V at a discharge current of 150 mA/cm . To obtain the minimum
power density of lOOW/lb originally specified by EPA, 14 such modules can be used in parallel
2
and the operating current density is only 110 mA/cm . Since 1000 cycles were performed
2 2
successfully at 150 mA/cm , it is inferred that even more could be performed at 110 mA/cm .
Alternatively, an exact calculation of the maximum power density of a full-size system
which has been experimentally demonstrated using these quasi-bipolar plates is instructive.
2
Thus, based on the maximum discharge current examined of 150 mA/cm , a power density of
136 W/lb is calculated. To achieve the maximum 55 KW discharge rating initially specified,
only 10 modules are required and the total battery weight is 409.5 Ib.
The modifications to the above design which are necessary to achieve the more recent
power profile (Fig. 1) specified by EPA are discussed below.
B. Design, Operation and Characteristics of a Quasi-Bipolar Battery System
Based on the Final Power Profile Specified by EPA
There are basically no design changes, as such, required to conform to the more severe
power profile. Thus, the same modular approach is followed and the plate design and sealing
techniques are exactly as before. The plates are still mounted in series in a module and the
modules are placed in parallel also. However, the number of plates required per module is
changed and so also is the operating current density.
- 140 -
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The most pertinent changes in the power profile are as follows:
1. The minimum working voltage is increased from 150 V to 200 V.
2. The average maximum power over a 25 sec pulse is 70.5 KW (compared to
55 KW previously).
3. The mosi severe power pulse called for is 92.5 KW for 10 sec (compared to
55 KW previously).
4. The maximum total energy output during two consecutive 25 sec pulses at an
average power of 70.5 KW is 980 Whr. This is ~ 30% more than the previous 760 Whr during
two consecutive 55 KW pulses for 25 sec each, as specified in the preliminary power profile.
Because of (1) and the specified minimum voltage per cell of 1.5 V, an additional 33
plates per module are now required. Thus, the module weight is increased from 40.95 Ib to
54.5 Ib. Fortunately, however, no further changes in the module are necessary, for example,
in the amount of paste or electrolyte required, due to the higher power ratings specified in (2)
and (4). The latter points are illustrated in the comparative calculations given below.
a. Operation at 55 KW with a maximum energy output of 760 Whr for a
system using 100 cells per module (and assuming 1.8 V/cell discharge).
2 2
The active plate size is 8-in. x 4-in. = 206 cm .
For the entire battery, the highest discharge current at 55 KW and 180 V is
305 A.
The current per module is 0.206 X (amperes), where X = operating current
2
density (mA/crn ).
The number of modules required in parallel is:
305 _ 1480
0.206 X ~ X
Deepest depth of discharge over two 25 sec consecutive pulses is:
760 Whr
180V
= 4.25 Ahr, or
= 0.00287 X Ahr/plate
The amount of acid required is calculated from the value 0.103 Ahr/gm of 1.28 sp gr
0 00287 X
Therefore, the weight of acid per cell is 'n'ln* . ,
4
acid.
V
where A = fraction of acid to be used (0-1) = 0.0278 -r- gr H SO./cell.
- 141 -
-------
b. Operation at 70.5 KW with a maximum energy output of 760 Whr for a
system using 133 cells per module (and assuming 1.8 V/cell on discharge)
2 2
The active plate size is Sin. x 4 in. = 206 cm .
For the entire battery, the highest discharge current at 70.5 KW and 239 V
is 295 A.
The current per module is 0.206 X(amperes), where X = operating current
o
density (mA.cm ).
The number of modules required in parallel is:
295 _ 1432
0.206 X "• X '
Deepest depth of discharge over two 25 sec consecutive pulses is:
980 Whr , ,„ .,
23QV = 4'10 Ahr' °r
= 0.00286 X Ahr/plate
4
assuming 0.103 Ahr/gm of 1.28 sp gr acid.
The weight of acid per cell is again °X°?n*6AX = 0.0278 £ gm H0SO ./cell.
—** U. 1U*5 A A & 4
Thus, no more paste or excess electrolyte are required for the modified system. Exact
operating characteristics for the full-scale battery are given below for a series of possible power
densities. A summary of the weight requirements of a modified module conforming to the final
power profile is given in Table XXII.
Table XXII. Summary of the Weight Requirements for Each Module Based on
the Quasi-Bipolar Plates (Concept I) and Operating Under the Final
Power Profile
%of
Ib Total Wt
1. Paste/module . 30.0 55
2. Head plates/module 0.79 1.5
3. Plastic components (grid) in the
plate/module 6.96 13
4. Lead conductors (grid)/module 6.00 11
5. Glass retainers/module 0.57 1
6. Separators/module 0.80 1.5
7. Case material/module 3.84 7
8. Inter-module wiring 0.11 0.2
9. 1.28 sp gr electrolyte/module 5.23 9.8
Total wt/module 54.3
- 142 -
-------
1. 70.5 KW rate, 128 W/lb power density
The above is the maximum average rate desired over 25 sec pulses, and the power
density is a minimum desired value from a 550 Ib system. Tne battery is constructed from the
same quasi-bipolar plates and the modules are modified as above to include 33 more plates in
series (133 total). To obtain the 70.5 KW discharge rate, 10 parallel modules are employed and
2
the operating current density per plate is 143 mA/cm . This is within the limit at which the
o
plates were already successfully tested in the present program (150 mA/cm , and so no extra-
polations are required to predict successful performance on cycling.
2. 70.5 KW rate, 156.6 W/lb
The system is exactly the same as above, but the preferred final battery weight is 450 Ib
maximum. Since the module weight is 54.3 Ib, only 8 parallel modules could be used giving a
2
system weight of 436 Ib. The operating current density per plate is increased to 178.6 mA/cm
and the exact power density is 161.6 W/lb. Though this current density is somewhat higher than
2
the 150 mA/cm value actually used to test the plates, it is still anticipated that no severe
degradation on cycling would occur.
3. 92.5 KW rate, 205.5 W/lb
This corresponds :o the maximum power required only over a 10 sec period. With 8
parallel modules (212 W/lb), the current density per plate to achieve this power density from a
2
full size battery, (450 Ib desired weight) is increased to 234 mA/cm for those 10 sec.
It is clear that to project battery performance at the power densities specified in (2) and
( 3) above, some further test data are desirable. The depth of discharge per plate is increased
at these higher operating current densities. Fortunately, however, there is already a seven-
fold excess of active mass in each plate to compensate for this, so we anticipated no problems
in this respect. The question arises as to whether or not repeated cycling at these higher
rates would adversely affect performance. Though it is believed that the plates would perform
well under such circumstances, further tests are required to demonstrate this.
Rather than raise the operating current density to achieve the power densities specified
in (2) and (3), a more feasible approach would be to reduce, by 25% say, the active mass thick-
ness for electrode (to 15 mil) since this is present in such excess anyway. Such a reduction
would still leave a large excess (about five times) of active material in the plates over the
required amount. The utilization of active mass would also be increased in the thinner plate and
2
the operating current density of the full-size system would be < 190 mA/cm even at the
92.5 KW rate. From our test results, there are no design restrictions involved in such a pro-
cedure. It is possible that the Pb conductors may have to be kept at 20 mil (even though the
paste thickness is reduced to 15 mil) from a corrosion aspect, but our plates with 15 mil Pb
conductors have, in fact, shown very good performance capabilities to date.
In summary, a modular high power density battery system incorporating quasi-bipolar plates
with conduction only over the top of each plate (Concept I) is promising. Each module contains 133
plates in series, and there are 8 modules in parallel (436 Ib total) in the final battery. The
2
plates must operate at close to 180 mA/cm to achieve a power density of 161.6 W/lb (the 70.5 KW
- 143 -
-------
rate). To operate at 92.5 KW for 10 sec periods (212 W/lb), the required operating point is
2
234 mA/cm . There is more than adequate paste and electrolyte in the present design to achieve
t\
these rates, but the plates have not been tested on extended cycling above 150 mA/cm . A pre-
ferred approach is to reduce the amount of active mass per plate by 25%, and thus the operating
2
current density per plate may be reduced to < 190 mA/cm even at a power density of 212 W/lb.
C. Energy Density of a Full-Size Battery System Based on the Quasi-Bipolar Plates (Concept I)
A calculation of the energy density of the battery built with the quasi-bipolar plates and
operating at 100 W/lb is instructive. Additional allowance is required for the excess electrolyte
used to discharge the plates to 100% of available capacity at this high rate. Initially, there were
no data available on paste utilization at high rates for the quasi-bipolar plates. Therefore, we
abstracted the data from Fig. 21 using the performance of the iR free one sided 20 mil pasted
positive electrode. The operating current density at 100 W/lb and with excess acid is > 110
2 2
mA/cm and is estimated as 130 mA/cm for these calculations. Paste utilization in Fig. 21 is
~ 42% at this point (for the positive paste). No data were available for utilization of the nega-
tive electrode at high rates. However, because the negative uses less electrolyte, it would be
expected to perform as well as, if not better, than the positive, at high rates. Also, when we
recently discharged quasi-bipolar plate number 23 to test paste utilization, we recorded a 63%
2
utilization factor at the 150 mA/cm operating point. This was even better than expected and,
in addition, is a measure of the utilization of the limiting electrode at high rates - whether this .
is the positive or negative electrode is not known, nor does it matter for these calculation
purposes. The measured capacity of the small scale quasi-bipolar plates is 1.04 Ahr and is,
therefore, 6.4 Ahr for the full size plate. Effective capacity for the plate at 100 W/lb is, con-
servatively, 42% of this, i.e., 2.7 Ahr. Taking an acid utilization factor of 50% and assuming,
as before, a value of 0.103 Ahr/gm hLSO., the total module weight is recalculated as 49.3 Ib.
Thus, 11 parallel modules can be taken to conform to the specified 550 Ib weight maximum.
Total battery capacity is 29.7 Ahr and the calculated energy density is 9.7 Whr/lb. This compares
favorably with the calculated value of 5.9 Whr/lb for a conventional battery discharged at 100 W/lb.
Also, positive plates from the conventional battery did not meet the cycle life requirements at
this rate. For the conventional battery calculation, allowance was also made for the reduced
volume of acid needed at high discharge rates.
At medium discharge rates (C~5), even more acid is required for both conventional and
bipolar batteries (29 Ib/module in the latter case). Total bipolar module weight is recalculated
as 66 Ib. At medium discharge rates, the effective capacity of the quasi-bipolar plate is 6.4 Ahr,
and using 8 parallel modules in the full-size battery, the energy density is close to 20Whr/lb. The
4
conventional battery with the excess acid required can be rearranged in 100 parallel cells with 4
positives (and 5 negatives) in parallel per cell. Total weight is 550 Ib in this configuration. At
the C/5 rate, the capacity of each conventional plate is 11.9 Ahr and the energy density of the
complete 200 V battery is 17.3 Whr/lb, i.e., 13.5% less than the complete bipolar battery.
Interestingly, whereas the bipolar battery exhibits 48.5% of its medium rate energy density at
- 144 -
-------
100 W/lb, the conventional battery exhibits only 34.1% at 100 W/lb. That is, the bipolar battery,
which has an improved energy rating at medium rates, is even more superior to the conventional
system at high discharge rates.
D. Preliminary Cost Estimate for the Quasi-Bipolar Battery (Concept I)
No detailed analysis has been carried out here, but the respective large volume cost
estimates for the component parts of the system are given below in Table XXIII, and the cost
of an individual module is estimated from these figures.
Table XXIII. Preliminary Large Volume Material Costs and Individual
Component Cost Estimates for a Module Conforming to the
Final Power Profile and Incorporating the Quasi-Bipolar Plates
Outlined in Concept I
1. Paste/module
(Universal Grenox)
2. Head plates/module
(plus Dynel fiber)
[ (Lead grid 4-paste)/module]
3. Plastic components (grid) in
f
the plate/module
Plus Dynel fiber
4. Lead conductors (grid)/module
5. Glass retainers/module*
6. Separators/module**
(Daramic)
7. Case materials/module
8. Inter-module wiring
9. 1.28 sp gr electrolyte/module
Large Volume
15. 1 gf/lb
or
16
2.50 $/lb
75 «f/lb (Lexan)
or
2.50 $/lb
17 izVlb
4 $/1000
20 $/1000
75 i/Vo (Lexan)
15«
-------
IX. SUMMARY OF ACHIEVEMENTS, EVALUATION OF THE MAIN AREAS REQUIRING
FURTHER DEVELOPMENT, AND PRELIMINARY PROPOSED WORK PLAN
A. Summary of Achievements
1. A new quasi-bipolar plate has been developed in which the active material
support is plastic, and conduction through the plate is achieved by parallel Pb strips laid verti-
cally over the top of each plate and along it. The conduction paths through the support are so
arranged as to be not immersed in electrolyte during normal cell operation. The possibility of
short circuits via intercell electrolyte leakage is thus minimized.
2. The Pb conductors are held at fixed points to the plastic substrate via a plastic
grid with horizontal cross-members. Expansion is thus permitted in a vertical direction without
introduction of excessive strains resulting in plate buckling.
3. The plate uses dynel fiber or glass mat backing to enhance paste adhesion.
Pure Pb strips act as conductors and no Sb is used in the plate components. Cycling life is main-
tained using H,PO, additions to the electrolyte.
o 4 2
4. On operation at high rates of charge and discharge (150 mA/cm ), the bipolar
plates show very good performance characteristics. They last typically for 1000 high rate/
shallow discharge cycles, and capacity retention at the C/5 rating is also extremely good. Com-
paratively, fresh commercial battery positive plates degrade excessively after < 350 cycles and
capacity retention is relatively poor.
5. In the preliminary power profile, the maximum discharge rate specified is
55 KW and the minimum desired power density is 100 W/lb. In a full-size system using the above
quasi-bipolar plates, 14 parallel modules may be used, each with 100 bipolar plates in series
2
and weighing 40.9 Ib/module. The required operating current density per plate is only 110 mA/cm .
A modular system constructed from the above plates operating to the limits of their tested cycling
2
capabilities, i.e., at 150 mA/cm incorporates 10 parallel modules and exhibits a power density
of 136 W/lb.
6. To conform to the specifications given by EPA in their final power profile
(Fig. 1), the only change required in the above modular system is to incorporate 133 quasi-
bipolar plates in series per module instead of 100 plates/module. Module weight is recalculated
at 54.3 Ib. At the 70.5 KW average maximum discharge rate and the minimum required power
__ 2
density of 128 W/lb, the operating current density per plate is 143 mA/cm (10 parallel modules).
- 147 -
-------
At the preferred operating point of 156.6 W/lb, the operating current density is close to 180 mA/
2
crn_ , while to achieve the maximum discharge rate of 92.5 KW for 10 sec (205.5 W/lb)the rate
must be increased to 234 mA/cm . In the latter two cases, only 8 parallel modules are used.
Also, though cycling behavior is not demonstrated in the latter cases, the plates with 20 mil
thickness of paste per electrode do contain an adequate excess of active mass (sevenfold).
7. In the preferred mode, it is anticipated that the best module design for opera-
tion under the final power profile would be one incorporating 133 quasi-bipolar plates in series,
but on each plate the paste thickness would be reduced by at least 25% to 15 mil per electrode.
More than sufficient capacity is still available in the plates to meet the most extreme capacity
demands (980 Whr on two consecutive cycles for 25 sec at an average 70.5 KW rate). In this
manner, the op
of 205.5 W/lb.
2
manner, the operating current density can be reduced to < 190 mA/cm even at a power density
8. A battery built from 11 parallel modules, each with 100 quasi-bipolar plates
2
in series and with incorporation of sufficient acid, can operate at ~ 130 mA/cm , and its energy
density is 9.7 Whr/lb at this rate. Under the same circumstances, a. battery constructed from
2
conventional plates must operate at > 200 mA/cm , and its energy density is 5.9 Whr/lb.*
9. At medium discharge rates (C/5-rate), the respective energy densities for
the bipolar and conventional systems are 20 Whr/lb and 17.3 Whr/lb, respectively. The bipolar
battery clearly retains more of its energy density (48.5%) at high rates compared to the con-
ventional battery (34%).
10. A modification of the quasi-bipolar plate in which multiple Pb conduction paths
are made across and down the plate has also been constructed, and an initial plate exhibits
superior performance on extended cycling (compared to the initial quasi-bipolar plate above).
B. Areas Requiring Further Development
The most important areas requiring further study to develop the quasi-bipolar plate and
battery discussed above are as follows:
1. Extend cycling data on a large number of quasi-bipolar plates under a range
of conditions and at higher rates as specified in the more recent EPA requirements. This will
establish plate reliability on a more realistic basis.
2. Construct full scale plates to demonstrate structural stability and feasibility
of large scale fabrication techniques.
3. Extend evaluations of long term plate corrosion resistance, particularly of
the thin cross section Pb conductors but also of the plastic substrate. This will establish a
realistic value for the minimum cross-section per conductor, which is compatible with cell
performance, weight, and reliability.
4. Establish the exact volume of electrolyte and electrode gap separation nec-
essary to permit successful operation of the plates under high rate/shallow discharge cycling.
Here the dimensions of separator and retainer are crucial regariding their effect on interelec-
trode volume and also gas bubble retention between electrodes.
* In such an operating mode, the conventional battery does not perform satisfactorily on
extended cycling.
- 148 -
-------
5. Construct prototype modules to develop technology in this area and isolate
any plate sealing problems.
6. Complete a more thorough cost analysis, particularly with relation to manu-
facturing and assembly costs.
7. Identify alternate applications for such a system.
8. Investigate the behavior of the bipolar plates under two consecutive high rate
power pulses for 25 sec within a 60 sec interval and followed by high rate recharge.*
C. Work Plan
A suggested plan of approach to further develop the quasi-bipolar plate and battery is
outlined as follows: (1) .scaleup the plate to a practical size, (2) build a battery using the
scaled-up version of the plate developed up-to-date, (3) test this battery to determine its
characteristics, including its more probable failure mechanisms, (4) study the further optimi-
zation of the plate, and (5) build and preliminary test a battery based on optimized configuration.
Task I: The primary purpose of this task would be to develop a technology for
the construction of a corr.plete quasi-bipolar battery based on the final design discussed in this
report. Two 25 V prototypes would be made, one using plates described here (1/6 full size)
and the other with full-size plates ( 8-in. x 4-in.) of exactly the same design. Since time is
always a limiting factor in evaluating the performance (expecially cycle life) of novel batteries,
a significant advantage could be gained by starting this at the beginning of the contract period.
Possible constructional and operational problems could then be isolated and overcome at an
early stage leaving maximum time for optimization work.
For the above task, we would employ the technology so far gained during the present
program. That is, plate design, retainers, separators, etc., would be "frozen" and incorporated
in the prototypes. The small scale prototype would be constructed within the first 1.5 months
followed by the large scale prototype development. Testing of prototypes would proceed through-
out the contract period.
Task II: Taking into consideration problems uncovered in Task I and theoretical
analysis of the system, experimental work aimed at the optimization of the plate design and the
battery would be performed. This optimization would include the following factors.
* In a one time test with plate number 6, which had already been cycled successfully under the
stated mode for 770 cycles, we did carry-out two consecutive pulses for 25 sec each, with a
1 sec interval, at a current (150 mA/cm ) corresponding to the 55 KW rate for a full scale
system constructed from the plates. After this the plate was re-charged at a current correspond-
ing to the 36.8 KW rate for 120 sec. The latter corresponds to a 20% overcharge. The plate per-
formed well for the 6 cycles examined in this mode. The test cell exhibited a final discharge
voltage of 3.2 V(i.e., bipolar plate plus head plates) and a final charge voltage of 6.2 V. No failure
was observed which is encouraging for future battery development, particularly since the plate had
already undergone severe testing prior to the above.
- 149 -
-------
1. Conductor rib thickness: A realistic examination of the cross-sectional
area per conductor required to maintain a balance between cell performance, weight, and
reliability will be undertaken.
2. Conductor rib separation: As it affects paste formation, cycling capabili-
ties, etc.
3. Electrolyte gap separation: We have calculated, but not yet established
experimentally, the volume of 1.28 sp gr electrolyte necessary to supply the energy required at
high power ratings. Since the concentration and volume of electrolyte affect both battery life
(by corrosion) and weight requirements, this aspect would be of major interest.
4. Glass retainer type: That is, as it affects paste retention and gas bubble
retention during charging of the plates.
5. Separator type: That is, the minimum thickness and type of separator
(weight and ribbing geometry) which are consistent with electrolyte volume, gas bubble retention,
and how they effect the voltage characteristics of the cells.
6. Paste microstructure: The effect of microstructure of the positive elec-
trode paste will be studied in the "quasi-bipolar plates" with three additional paste formulations
on the positive face: (a) N.L. Industries Barton VLY oxide, (b) Barton VLY oxide plus 15%
Pb,O4, and (c) Bell Telephone Laboratories tetrabasic lead sulfate. The performance of these
plates would be analyzed to decide whether or not a significant advantage is to be gained by using
one or the other of these rather different formulations.
7. Optimum end plate construction would be briefly investigated.
8. Paste thickness: The performance of plates with paste thickness per
electrode of the order of 15 mil would be investigated.
A time scale of approximately 8.5 months is estimated for the above.
Task III:
1. Construction of further 25 V prototypes: Based on the above tasks, further
prototypes would be constructed, and their performance evaluated. Initial prototypes would
again be on the small scale version, with expansion to full plate size as performance demanded.
2. Prototype specifications: Complete performance specifications would be
detailed for prototypes of choice with detailed analysis of weight requirements, constructional
procedures, estimated lifetime capabilities, and cost.
This phase of the program would commence after approximately 6 months of the contract
and continue for the remaining period.
- 150 -
-------
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Aerospace Corporation, June 1971.
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- 152 -
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43. F. Booth, "Comparative Study on Battery Separators for Lead-Acid Starter Batteries,"
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- 153 -
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Appendix I: CALCULATION DETAILS FOR A FULL SIZE BATTERY BASED ON THE PRELIM-
INARY BIPOLAR CONCEPT A, WITH PLASTIC SUBSTRATE AND Pb CONDUCTORS,
USING THE PRELIMINARY POWER PROFILE
o
The active plate size is 5 in. x 3 in. = 96.75 cm .
For the entire battery, the highest discharge current at 55 KW and 180 V is 305 amperes.
2
The current per module is 0.097 X (amperes), where X = operating current density (mA/cm ).
The number of modules required in parallel is:
305 _ 3150
0.097 X X
Deepest depth of discharge is:
764 Whr
180V
4.25 X
= 4.25 Ahr, or
= 0.00135X Ahr/plate.
g
Or expressed as paste volume (assuming density of 4.2 g/cm ):
°-00135X * = 0.00032 =y- cm3 of paste/electrode,
FY x 4.2 g/cm
where Y = initial amperes/hour/gram of paste and F = decay factor (0 -* 1),
This corresponds to a thickness of active material on each side of
32X10"5 X oovirT7 x (^™\
„ = 33x10 (cm).
96.75 cm FY FY
For 100 cells, the active paste weighs:
200X0.00135X nitcn X
- 155 -
-------
Weight of plastic sheet:
4 in. x 6 in. X T x 16..38 X 1.4 g/cm3 = 550 T grams (where T = thickness of PVC
in inches).
Weight of lead ribs:
TL X6.45 x5 in. (0.7Tp X2.54 +100 X10~7 ^ ) x 11.3 grams
(where TT is thickness of lead ribs inside of the plastic plate in inches, the first term of the
J_>
parenthesis represents the part of the rib inside of the plastic, assumed 30% void, and the second
term represents the sum of the two outer sections of the rib with an allowance for their larger
average thickness.)
- ^ YT1
647 TT T +3.64 x 10 ° A1L grams
L P . PY~
There are 3/S lead ribs on each plate (where S = rib spacing in inches).
Weight of lead plate:
2 33
P x 15 in. x 2 sides x 16.38 x 11.3 g/cm = 5.5 x 10 P grams, (where P = lead plate
thickness, inches).
Total weight of substrate:
T
100 plates 550 T * | (647TLT + 3.64 x 10"3 x _|i) +5.5 x 103 P
5.5X104T + ^*10TLTP +1>09 XjL + 5.5 x 105 P grams
P S 3FT
Electrolyte weight:
Theoretical value is 0.095 Ahr/g of 1.26 sp gr acid, or
0.12 Ahr/cm3.
Weight of acid per cell is
= 0.0142 -r- . gr H0SO./cell, where A = fraction of acid to be used (0-1).
and
0.0113 -£- cm3 of H0SO ./cell.
A 24
y 156 -
-------
Distance between plates:
o.oiis -2L
£- = 1.17 x 10 * -£- cm
A
96.75 crn
The length of the module ( 100 cells):
1.17X10"2 -£- f 254 T + 66X10"5 -^ + 508 P cm
A p r Y
3
Case weight (assuming 0.635 cm thick wall, with 1.4 g/cm density):
Bottomandtop 2[ 0.635 X 6 x 2.54 ( 1.17 X 10"2 -^- + 254 T +66 x 10'5 ^-+ 508 P) ]
2 ends 2 x 24 x 6.45 x 0.635 = 197 cm3
2 sides 4/6 (bottom and top)
Total 0.53 -£- + 11500 T +2.98 x 10"2 ^- + 276 + 23000 P grams
A p r Y
Lead end plates:
3
Assume these are mostly aluminum wires at density of ~ 5.5 g/cm and they are
0.25 in. diick
2
96.75 cm x 0.635 cm x 5.5 x 2 grams/module
Inter -module wiring:
« 1 foot/module is needed; -^ — ft. are required for entire battery
A
Aluminum heavy gauge wire at 50 g/ft
„ . . , 50 X3150 157.5 ,„ ,
Total weight: - ^ - = — ^ — ( Kg)
Refer also to Section III for summary details on the above.
- 157 -
-------
Appendix II. NEW DESIGN EQUATIONS FOR THE PRELIMINARY BIPOLAR CONCEPT B WITH
A PLATE DIMENSION OF 8 in. x 4 in. USING THE PRELIMINARY POWER PROFILE
Component
Active Paste
Plates
Weight/Module/g
0.575 X
FY
4.12 X10 T T 2.3 XT
1.03 x 10 TD + - .
r o
c-v
or i
+ 1.18 x 10 p
Acid
PVC Case
3.02 X
_2
16058 Tp + 4'17*y° X + 32U6 p
Terminal Plates
Interelectrode Wiring
No. of Modules
Battery Weight
1442
50
1480
X
2.01
FY
.
T
TL TP
'5 T
SX
3.9 x 10 P , 12.24 . 6559
The following parameters were not varied:
5 x 9 in.
0.25 in.
4 X 8 in.
Module height and width
Plastic case thickness
Electrode size
Paste density
Acid density
Interelectrode wiring
Module terminals
4.2 g/cc
1.26 g/cc
50 g/ft wire
0.25 cm lead plated Al
- 159 -
-------
Appendix III. COMPARISON OF BATTERY SYSTEMS BASED ON THE PRELIMINARY POWER
PROFILE AND ON THE TWO DIFFERENT BIPOLAR PLATES OUTLINED IN
PRELIMINARY CONCEPTS A AND B
System Design Values
Current Density mA/cm* (X)
Coulombic Yield Ahr/g (Y)
Decay Allowance (F)
Plastic Plates in. (T_)
Lead Ribs in. (TT )
J_j
Lead Plates in. (P)
Rib Spacing in. (S)
Acid Use
Module Length, ft
No. of Modules
System Weight, Ib
3
System Volume, ft
2
Design Values for the 150 mA/cm Operating Point Using the 8-in. x 4-in. Plate
8 in. x 4 in.
Plate
(X) 150
') 0.054
0.5
0.03
0.03
0.004
0.5 -
0.5
0.55
10
364 '
1.8
5 in. x 3 in. *
Plate
150
0.054
0.5
°'03' 'See
0.03 Section III,
0 004 p 27, 28
°'UU4 for more dec
0.5
0.5
0.47
21
380
1.8
Active Paste, Ib 7.00
Plates (Pb+PVC), Ib 20.60
Acid, Ib 2.00
PVC Case, Ib 3.47
Terminal Plates, Ib 3.20
Intermodule Wiring, Ib 0.10
Total Module Weight, Ib 36.4
Distance Between Plates, in. 0.014
Active Paste Thickness, in. 0.007
Substrate Thickness, in. 0.038
Case Thickness, in. 0.25
Module Length = 0.59 for 100 cells, ft
- 161 -
-------
Appendix IV: ENERGY D2NSITY COMPARISON OF THIN PLATE CONVENTIONAL SLI AND
QUASI-BIPOLAR BATTERIES (Final Design Plates) AT HIGH AND LOW
DISCHARGE RATES
Operating Current Density
Efficiency of Paste Utilization
Effective Plate Capacity
at 100 W/lb
Average Discharge Voltage
(200 V system)
Cell Configuration
Total Capacity
Total Weight
Energy Density
At Low Discharge Rates:
Average Discharge Voltage
Total Capacity
Energy Density
Conventional
o
250 mA/cm
(100 W/lb)
-27%
3.7 Ahr
180V
100 cells in series
5 positives in parallel
per cell
18.5 Ahr
550 Ib
5.9 Whr/lb
Bipolar
~ 130 mA/cm2
(100 W/lb)
-21%
2.7 Ahr
180V
11 parallel modules
100 series cells/
module
29.7 Ahr
550 Ib
9.7 Whr/lb
200 V 200 V
47.6 Ahr 51.2 Ahr
17.3 Whr/lb 20 Whr/lb
o
For the conventional battery, the energy density at high rates is 34.1% of the low rate
energy density.
For the quasi- bipolar battery, the e'nergy density at high rates is 48.5% of the low rate
energy density.
The improved performance of the quasi-bipolar plate at increased discharge rates is,
thus, self-evident.
- 163 -
-------
Appendix V: CURING AND FORMATION TECHNIQUES
A. Universal Gre.iox Oxide (25% free Pb, balance orthorhombic PbO)
For the positive paste, 8 Ib of oxide were first dry mixed with 2.8 g (0.2%) of
Dynel fibers (to impart stability to the paste). 440 ml of distilled water were then added with
continuous mixing for a further 10 min when a uniform wet paste was obtained. Then, 340 ml of
1.4 sp g HJSO. were added ever at least a 1 min period while still mixing. Paste temperature
was not allowed to exceed 140° F during this latter process. The paste was well mixed for ~ 10 min,
resulting in a homogeneous paste structure. For the mixing, a heavy duty mixer from Charles
Ross and Sons was used incorporating a variable speed motor, planetary mixing action, and stain-
less steel mixing components. The procedure was exactly the same when preparing the negative
paste. Here, 8 Ib of oxide plus 2.8 g of Dynel fiber were again used, but 72 g of an industrial
KX expander (N.L. Industries) were also added. In addition, 412 ml HpO and 304 ml of 1.4 sp gr
H-SO. were now used in the mixing process.
The paste was applied to the grids placed on a glass plate using a wide plastic spatula.
The pasted plates were then cured by covering them with damp cloth and leaving them for ~ 80 hr
in this condition. Finally, they were air dried at ~ 150°F for at least 60 hr.
Prior to formation, each plate was soaked in 1.08 sp gr acid, generally for an overnight
period. For formation in 1.08 gravity acid, approximately 1 Ahr/g of paste was used. For the
2
bipolar plates, for example, formation was generally at 5.9 mA/cm while for the iR-free lab-
2 2
oratory test plates, formation was at 5 mA/cm and then 3 mA/cm .
The above procedures are exactly the same as emplyed by Tyco's Mule Battery Division
in commercial plate preparation, and the pasted plates so obtained performed very well.
B. Barton VLY Oxide (40% tetragonal PbO, 60% orthorhombic PbO < 2% free Pb)
The performance of this paste was generally not satisfactory, particularly after a high
temperature cure.
Our initial techniques are summarized below:
1. 45 cc H2 O/lb oxide
2. 45 cc H-SO./lb oxide: - 1.25 sp gr acid added over a 10 min period
et 4
- 165 -
-------
3. Immersion in a 100% rh chamber at 100°F followed by a temperature increase
over a 7 min period to 170-18Q°F. The paste was the n left for ~ 2-1/2 hr and finally was air
dried.
We modified the techniques as follows:
4. 30 cc and 37 cc H0O/lb oxide
-"'" T"""~ Ci
5. 45 cc H9SO./lb oxide: 1.25 sp gr acid added in 1 min
£> 4
6. Immersion in the 100% rh chamber at 100°F followed by a temperature increase
at 25° F/hr to 170-180° F. Trie paste was again left for 2-1/2 hr and finally dried in air at
150-160°F for 6 hr.
The major deviations above were in the amount of H2O additions to control paste consistency
and in the rate of H0SO. addition to control the heat evolution during the mixing process. As the
£ 4
HpO content is reduced, the paste becomes firmer, and as the HJ3O. addition rate is increased,
more heat is evolved. Thus the temperature rose to 140°F (and remained there for 5 min) after
a 1 min acid addition. On addition of the acid over a 10 min period, a maximum temperature of
134° F only was attained briefly after the first two additions. We chose also a slower heating rate
during curing to allow for the large heat capacity of our plate structures. During the curing, we
strictly controlled rh in our rh chamber since we had observed severe shrinkage of our pastes in
some instances under apparent 100% rh conditions. For this reason also, we cured some plates
separately in a simple forced convection oven containing a bowl of water. Finally, after curing,
we air dried our plates at 150°F-160°F for 6 hr, compared to a previous room temperature
drying. This was to ensure complete removal of water from the cured plates. If water is present
in the paste when it is immersed in acid, excessive heat may be generated and the gas evolved
then "pops" the paste out of the grid structure.
Formation techniques were the same as for the Grenox paste. The above paste, cured
in the relative humidity chamber, using the modified techniques, was used for some investigations
of paste performance versus paste thickness in the iR-free laboratory test structures.
- 166 -
-------
Appendix VI: ENGINEERING DATA FOR BATTERY MATERIALS OF
POSSIBLE INTEREST
- 167 -
-------
iTHERMAL PROPERTIES OF POLYPROPYLENE*
Property
Heat Deflection Temp, F
At 2G4 psi
At 66 psi
Coef of Ther Cond,
Btu/hr/sq ft/°F/in.
Coef of Linear Ther F.xp°,
in./in./°F x 10-s
Melt Point (crystalline), F
Ther Aging at 300 F, daysb
General
Purpose
140
210
1.48
6.46
333
40-80
Long-Term
Head Aging
140
210
1.48
6.46
333
40-80
Copolymers
Impact
135
215
_
8.3
333
—
High
Impact
130
205
—
10
340
—
Polyblends
Impact
125
175
1.62
7.00
-
—
High
Impact
115
145
1.72
7.23
—
—
Asbestos
Filled
200
295
1.55
2.9
333
>100
Glass Fiber
(20'b)
Reinforced
230
305
-
2.9
-
1
8 Above 86 K.
° End point defined by craving and/or discoloration.
CHEMICAL RESISTANCE OF POLYPROPYLENES"
INORGANIC CHEMICALS
Distilled Water
Sulfuric Acid (98'i)
Sulfuric Acid (2N)
Nitric Acid (fuming)
Nitric Acid (2N)
Hydrochloric Acid (30%)
Phosphoric Acid (85%)
Potassium Hydroxide (54'i)
Sodium Hydroxide (52%)
Ammonia (30%)
Sodium Hypochlorite (20%)
30 Days at 72 F
Weight
Change,
%
+0.7
-0.2
-0.3
-0.1
+0.1
-0.2
ND
-0.3
-0.2
+0.3
+0.1
Tensile
Elong
Change
0
0
0
0
0
0
0
0
0
0
0
30 Days at 140 F
Weight
Change,
%
+0.2
-0.2
+0.3
ND
+0.8
+1.2
-0.5
+1.3
+0.7
ND
-2.1
Tensile
Elong
Change
0
X
0
X
0
0
0
0
0
ND
X
a O ~ reduction in tensile strength of less than 10% and change in
elongation of lea* than 25^; X = reduction in tensile strength of
more than 10% and.-'or mo.-e than 257* change in elongation; P = a
plasticlzing effect; ND = not determined.
(Materials and Processes Manual, No. 238, p89 (1966))
- 168 -
-------
8
1234567
STRAIN (%)
POLYSULFONE TENSILE STRESS-STRAIN CURVES
150 200 250
TEMPERATURE (°F)
FLEXURAL MODULUS VS.
TEMPERATURE
300 350
125
100
75
50
25
/TENSILE YIELD STRENGTH
,HEAT DEFLECTION TEMPERATURE (264PSI)
/TENSILE IMPACT STRENGTH
(SHORT SPECIMEN)
3 6 9 12 15 18 21
DURATION OF AGING, MONTHS
EFFECT OF HEAT AGING AT 300°F ON
THE PROPERTIES OF POLYSULFONE
ALL PROPERTY TESTS MADE AT ROOM TEMPERATURE
ON 1/8-IN.-THICK SPECIMENS.
24
(Union Carbide Corporation
Product Data Article)
TYPICAL PROPERTIES OF "BAKELITE" POLYSULFONE
Property
General
Melt Flow, @650°F.
(343°C.) 44 psi. dg/min..
ASTM
Method
01238
Value
6.5— P-1700, P-1710
3.5— P-3500, P-3510
Specific Gravity ............ 0792
Mold Shrinkage, in. /in ...... .007
Water Absorption,
%in24hrs ............ .0570 0.22
Mechanical
Tensile Strength at Yield, psi D638 10.200
Tensile Modulus, psi ....... D638 360,000
Tensile Elongation at
Break, % ............... 0638 50-100
Flexural Strength, psi ...... 0790 15.400
Flexural Modulus, psi ...... 0790 390.000
Izod Impact, @ 72° F., >/8"
spec., ft.-lb./in. notch ... D256 1.3
Izod Impact, @ — 40° F.. '/8"
spec., ft.-lb./in. notch ... D256 1.2
Tensile Impact, ft.-lb./in.1 . . D1822 200
Rockwell Hardness ........ 0785 M69 (R120)
Thermal
Heat Deflection Temp.,
@ 264 psi, ° F ........... D648 345
Coefficient of LinearThermal
Expansion, in. /in. /°F. ... 0696 3.1x10'
Flammability .............. 0635 Self-Extinguishing
.............. UL Self-Extinguishing
Group II
Thermal Conductivity,
BTU/hr./sq.ft./°F./in. .. 1.8
Electrical Properties
Dielectric Strength, ya"
spec., ST, v/mil ......... 0149 425
Arc Resistance, sec.
(Tungsten Electrodes) . . . D495 122
Volume Resistivity,
@ 72° F., ohm-cm ....... D257 5x10"
Volume Resistivity,
@ 347° F.. ohm-cm ...... 0257 1x10"
Dielectric Constant,
@72"F.. 60cps-l Me .... D150 3.07-3.03
Dielectric Constant,
@ 347° F., 60 cps-1 Me... D150 2.82-2.73
Dissipation Factor,
@ 72°F., 60 cps-1 Me .... D150 0.0008-0.0034
Dissipation Factor,
@ 347°F., 60 cps-1 Me ... D150 0.006-0.003
Chemical Resistance
Inorganic Acids ............ No effect
Alkalies ................... No effect
Alcohols ........ ........... No effect
Esters ..................... Partly soluble, swells
Ketones ................... ParWy soluble, swells
Aliphatic Hydrocarbons ____ No effect
Aromatic Hydrocarbons ____ Partly soluble, swells
Chlorinated Hydrocarbons . Dissolves
- 169 -
-------
I LEX AN SHEET
A Comparison with
Other Metals and
Plastics
The strength of LEXAN sheet compares favor-
ably with other plastics and the more comrnonly
used metals. Having one of the lowest specific
gravities, LEXAN sheet offers a particular ad-
vantage in having a high strength-to-weight ratio
and a low cost per finished part.
o
I
1 — •
Specific Gravity
Impact Strength —
notch.el izod —
'.* " specimen
Heat Deflection Temp.
66 psi
264 psi
Flammability
ASTM 0-635
Tensile Yield Strength
Tensile modulus.
10' psi
Fiexural Yield
Strength
Flexural Modulus
H.O Absorption. %
Thermolorming
Shrinkage in/ in.
Rockwell Kirancsa
Elonganon
Clarity
1.20
16.0
285
275
SE
8000-
9500
3.5
13.500
3.4
o.ts
.005-
.007
M70-
R11B
100%
Trans-
parent to
Opaque
1.09
6.0
220
SE
7800-
9600
3.55-3.8
12.800-
13.500
3.6-4.0
0.06
.005-
.007
R119
35%
Opaque
1.19
.4
225
205
Slow
Burning
8000-
11.000
3.5-4.0
12.000-
17.000
3.9-4.75
0.30
M80-
M100
5%
Trans-
parent to
Opaque
. ...,
1.27
1.3
358
345
SE
10.200
3.6
15.400
3.7-3.9
0.22
.0076
M69-
R120
50%
Trans-
parent to
Opaque
1.24
1.6-3.5
180
SE
3000-
5500
2.2-3.!
6000-
7500
2.2-3.0
0.30
.003-
.008
H75-
R90
20%
Opaque
1.18
0.8-6.3
130-227
113-202
Slow
Burning
2600-
6900
2.0-J.5
4000-
9000
-
1.50
_
H30-
R115
50-100%
Trans-
parent to
Opaque
,
1.35
12.0-15.0
177
160
SE
6500
3.35
10,700
4.0
0.06
.006-
.001
I'luS
100%
Opaque
-rSu,.'
D-792
D-356
D-648
ASTM
D-635
D-638
D-638
D-790
D-790
D-570
D-955
D-785
D-638
Specific Gravity
l
; Ibs/in.
!zod Impact Strength
Ib/in. notch
(V."TK Specimen)
t
1 Elongation Percent
Bending Strength
psi x 10'
1
Flexural Modulus
psi x 10'
Stillness
psi x 10'
Tensile Strength
psi x 10'
LEXAN
1.20
0.043
14-16
110
13.5
0.34
0.38
9.5
£ZZ*
1.5-1.7
0.061
4-12
1.0-1.5
45
0.8-1.8
1.8
24
Wfir-wp/rMI
1.4-1.6
0.058
10-20
1.0-1.2
28
0.8-1.8
1.2
10
Pol !••(•!
1.8-2.0
0.072
1.0-10
0.3-0.5
26
1.6-2.0
2.5
10
Aluminum
2.57-2.96
0.100
N.A.'
6-8
18
10
10
8
Etc
dl« CMl
6.6
0.240
4.3
to
-
-
-
14
-------
G.E. Product Data Sheet CDX-80A
Typical Properties
Property
Specific Gravity, 73°F
Specific Volume, cu. in./lb.
Water Absorption, 24 hrs. ,73"F, %
Heat Deflection Temperature (264 psi), °F
Thermal Conductivity, Btu/hr./ft.V°F/in.
Coefficient of Thermal Expansion, in./in./°F
(-20° to 150" F)
Mold Shrinkage, in./in. x 10'J
Flammability
Dielectric Constant (50% RH,73°F at 60 cps)
Dissipation Factor (50% RH.73°F at 60 cps)
Volume Resistivity, dry, ohm cm., 73°F
Surface Resistivity, ohm/sq.
Dielectric Strength ('/8" sample), volts/mil.
Arc Resistance (Tungsten), sec
Tensile Strength, psi at 73°F
Elongation at Break, %
Tensile Modulus, psi at 73° F
Flexural Strength, psi at 73° f
Flexural Modulus, psi at 73° F
Compressive Strength (10% Deformation), psi
Shear Strength, psi
Deformation Under Load, % at 2,000 psi, 122" F
Creep (300 hrs. 73° F at 2,000 psi), %
Izod Impact Strength, ft. Ibs./in. notch
Rockwell Hardness
Taber Abrasion, mg.
Fatigue Endurance Limit, psi, 2 x 10' cycles
Colors
Clarity
SE - Sell-Extinguishing Non-Dripping (ASTM D835)
SE-1 — Self-Extinguishing Non-Oripping Group 1 (U
' 1500 psi
ASTM
METHOD
D792
—
D570
D648
C177
D696
D1299
(see note)
D150
D150
D257
D257
D149
D495
D638
D638
D638
D790
D790
D695
D732
D621
D674
D256
D785
DI044
D671
-
-
L. Bulletin
NORVL
731
1.06
26.1
0.066
265
1.5
3.3 x 10-'
5-7
SE
2.64
0.0004
10"
10"
550
75
9,600
60
355,000
13,500
360,000
16,400
10,500
0.30
0.75
5.0
R119
20
2,500
Unlimited
Opaque
94)
NORYL
SE-1
1.06
26.1
0.066
265
1.5
3.3 x 10-'
5-7
SE-1
2.69
0.0007
10"
10"
500
75
9,600
60
355,000
13,500
360,000
16,400
10,500
0.30
0.75
5.0
R119
20
2,500
Unlimited
Opaque
NORYL
SE-100
1.10
25.2
0.07
212
1.1
3.8 x 10-'
5-7
3E-1
2.65
0.0007
10"
10"
400
70
7,800
50
380,000
12,800
360,000
16,000
6,900
0.50
0.50'
5.0
R115
100
1,850
Unlimited
Opaque
NORYL
GFN2
1.21
22.9
0.06
290
1.15
2.0 x 10-s
2-4
SE
2.86
0.0008
10"
10"
420
70
14,500
4-6
925,000
18,500
750,000
17,600
10,400
0.20
0.33
2.3
L106
35
4.000
Unlimited
Opaque
NORYL
GFN3
1.27
21.8
0.06
300
1.1
1.4 x 10-5
1-3
SE
2.93
0.0009
10"
10"
550
120
17,000
4-6
1,200,000
20,000
1,100,000
17,900
10,600
0.12
0.2
2.3
L108
35
5,000
Unlimited
Opaque
.
NORYL
SE1-GFN2
1.30
21.3
'0.06
270
1.15
2.0xlO-5
2-4
SE-1
2.98
0.0016
10"
10"
600
70
14,500
4-6
925,000
18.500
750,000
17,600
10,400
0.30
0.33
2.3
L106
-
-
Unlimited
Opaque
NORYL
SE1-GFN3
1.36
20.2
0.06
275
1.1
1.4 x 10-5
1-3
SE-1
3.15
0.0020
10"
10"
530
120
17,000
4-6
1,200.000
20,000
1,100,000
17,900
10,600
0.25
0.20
2.3
L108
—
-
Unlimited
Opaque
- 171 -
-------
TYPICAL PROPERTIES
-- - «? *-T-\ r** *•«»•"
....•Ju S L
(S3
G.F., Prndnr.r Data Article CDX-81 (20M) 2/70
I'HUl'CmY
PHYSICAL
Specific GMvily, ?3°F
Specific Volume, cu. in./lb.
Water Abscrpiioi, (?5 hrs.J, %
THERMAL
Heat Deflection Temperature (264 psi), °F
Thermal Conductivity Btu/hr./ft.!, °F/in.
Coellicient ol Thermal Expansion
in./in./-F(-20to150"F)
Mold Shrinkage, in./in. x 10 '
Flammability
ELECTRICAL
Dielectric Constant (50% FIH, 73°F @ 60 cps)
Dissipation Factor (50% RH. 73'F @ 60 cps)
Volume Resistivity, dry, ohm cm., 73°F
Surface Resistivity, ohm/sq.
Dielectric Strength ('/«" sample), volts/mil.
! Arc Resistance (Tungsten), sec.
i
MECHANICAL
Tensile Strength, psi
Elongation at Break, %
Ton:;ile Modulus, psi
Flexural Strength, psi
i Flexural Modulus, psi
Compressive Strength (10% deformation), psi
Deformation Under Load. 90 at 2.000 psi at 122°F
Creep (300 hrs.. 73'F at 2,000 psi). %
Izod Impact. Notched Va x Vz x 5" bar,
at 73"F, ft. Ib./in. notch
Rockwell Hardness
i
i Taber Abrasion, mg.
Fatigue Endurance Limit, psi at 2 x 10'
ARTM
MEtHOD
D792
0570
D648
C177
D696
D1299
(See Note)
D150
D150
D257
D257
D149
D495
D638
D638
D638
D790
D790
D695
D621
D674
D256
D785
D1044
D671
NORYL
731
1.06
26.1
0.066
265
1.5
3.3 x 10 s
. 5-7
SE
2.64
0.0004
10"
10"
550
75
9,600
20-30
355,000
13.500
360.000
16.400
0.30
0.75
' 2.5
H119'
20
2.500
NORVU
SE-I
1.06
26.1
0.066
265
1.5
3.3 x 10 •>
5-7
SE-1
2.69
0.0007
10"
10"
500
75
9,600
20-30 .
355.000
13.500
360,000
16.400
0.30
0.75
2.5
R119
20
2,500
NORVL
SE-100
1.10
25.2
0.07
212
1.1
3.8x 10"s
5-7
SE-1
2.65
0.0007
10"
10"
400
—
7,800
35
380,000
12,800
360.000
16,000
0.50
0.50'
2.5
R115
100
1.850
NORYL.
GFS2
1.21
22.9
0.06
290
1.15
2.0x10-s
2-4
SE
2.86
0.0008
10"
10"
420
70
14,500
4-6
925.000
18.500
750.000
17,600
0.20
0.33
2.3
L106
35
4,000
NOnvt.
GFN3
1.27
21.8
0.06
300
1.1
1.4 X10'1
1-3
SE
2.93
0.0009
10"
10"
550
sen. i
SEVUfN.'
1.30
21.3
006
?rii
1.15
2.0 x 10'1
2-^
SE-t
2.93
0.0016
10''
10"
600
120 70
I
17.000
4-6
14.500
4-6
1.200,000 S250CO
NORYL
SEl-GrNJ
1 36
20.2
006
275
1.1
1.4x10-'
1-3 .
SE-1
3.15
0.0020
10"
10"
530
120
17.000
4-6
1.200,000
20.000 I 13.500 20.000
1,100.000
17,900
0.12
0.20
2.3
L108
35
5.000
750 000
17.600
0.30
0.33
2.3
L10£
1.100.000
17,900
0.25
0.20
2.3
L108
~ L~
1 (ASTM DC3&)
n^ Croup 1 (U.L. Bulletin 94)
-------
G.E. Thermoplastic Resins Data Article CDX 81 (20M) 2/70
PRICE. PROPERTIES COMPARISON
NQRYL
CO
I
COST COMPARISON
Nylon 8/ft
LEXAN
on NORYL
QRNyion
CM LEXAN
'SS
ZB
za
HOLD SHRINKAGE
3
0 9 tO tS 10
Mold Snrlnhig* In7ln,
14
FATiGUC ENDURANCE
rooo 3000
TENSILE STRENGTH
J
T«nt>>* Slrvngth i 10'
'.J
WATER ABSORPTION
IZOD IMPACT STRENGTH
AC«UI
Nylon 6/6
LEJCAN
J
TENSILE CREEP-NOHTL GFN3
HEAT OEFLEC/tON TCMKPATURU
FLAMMABILITY COMPARISONS
6E-1
SE-2
BURNS
ABS
•
*
NO«VL
SE-100,
SE-t.
Stl-GfNl
°;sr
crm.
CFNl
ACETAL
•
IE* »M
wV1
KB.lii
Ondt*
'00.
"1?"
0
MELT FLOW VS. TEMPERATURE
100 ioo xn 400
-------
,,-r- nc rr-,1 r roper*, i"S
The largest selection of engineering plastics comes from GENE!
PTOPWtl
PKYilCAL
Vn..-cun>.:< ,. ;) 1
>v;,,«r....". •>.•<»>• •!.„:)( .
HwDrlMMnltfnrojiiminiii.) T
,...-.,,,,,.,.:, •
^T:;':^1'01""""'"'1
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C-'j-i
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MECHANICAL
V..'.-S-;.-.... - .n
-,-•.'. -.M-rrOJ. ;x
f .•-:.!-.-" ;: !:«• ' i 7] F
T-.V.VV •''•••• "•' .; 73 F
FwfMV.Jji .-!'•> 7] F
:.-.*«: .r:vr,-.iii(f'.Mc-«lo«r1
Sr«'S::*\1i EH
;•«;,« f.-! ;J ? M 7.000 91.1. -, Swin
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ri;:\'!:«;'K>K'T:H>
ELECTRICAL
1!., "•:;•- .-,-:.!•? WU1 fi;s::;.il
?-,.Bf .--•-!• ' :; .='I7JF,!SO.»>
... .- '-. -, •.«"" 7M
t . • :• •'"•- • .' j.'-:'el •.£ :s .T.I
.'. -••• -.'f - '-' .'"I! U'.:
MSI!
U1U
IIST
UtlHOO
VIV
•wo
OMS
n//
Of*
D!2'J9
f,r,W
P633
Dn3>.
0:90
07*1
D695
0<*32
0674
01044
0671
o;w
PIW
W',7
PK9
W95
NORIL
RESIN
731
1 It.
Ort*
265
1 'iO
33.10 *
Sf
UniiiMfd
"7
(VIS 007
9.™
noun.
Bum
Sl-l
NOHTL
RESIN
U100
,* i :,o
OMi [ 0070
265
1 50
3 3 . 10 l
St-l
fieenole)
linlimiirt
Owque
005-007
9 TOO
JO 30 ?0 3)
3SVOOO
13500
360000
16100
IO.MO
063
3119
JO
.1.500
;w
OOOW
n-1
550
75
355.000
13.MO
360.000
16400
10.500
0.63
25
R1J9
20
2.50G
269
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!0;;
500
7i
212
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38.10 %
Si 1
Unlinked
Oiuque
005 007
7.snn
2030
380,000
12.800
360000
16.000
6,900
080
100
1,350 '
265
00007
I01'
NORTL
RtSIN
via
1 21
PMO
no«n
fit SIN
OfNJ
Noun
Rtsm
SCIGIW
i :; | : :v
-'LW i 'I'VI
^ALE
NOW
HtSIN
1 .it.
OtXV
:«? .-a w \ ;«
1 15 ! 1 10 i 1 15 ; ; it}
20.10 *
Sf
Unlimited
Opjque
NA
002 004
14 500
45
925000
750.000
17600
10,400
033
LJ06.
35
4,000
2'6b
ooooa
II):-
400 420
-
70
M,W :?o,W- j M.10-
Si i if 1
SL i
UnbmiM | U^m,!M Urtun-Irt
'T °«"e
001 00 J Wi'-OW
170™
H500
Opjque
NA
00 i OC3
;7?oo
4.5 i<6 ! 46
i.2CG 000
20 COO .
1 100.000
17.900
10.600
020
.'3
L1M
50CO
1&500
750000
17600
l.?JO.OOO
KOOS
1. 100.000
'17.900
10.400 10.600
033
23
27*. | 2 ••&
OOOifl
OODIG
111 ' 1C"
550
173
600
70
020
23
L108
3 15
OM20
Ifl '
530
120
LECT
RESIN
Stwbtd
120
'J;J
;w
1 35
3 75. 10 '
SI
Unlimited
B5
005-007
9 10'
30 35 » 10'
-
11 36
VJMMH5
-
70 13 t
0, i4
.' ,1 1100
< 1C.
!-•« 3W
131
IMMC1
MAWS
! 36 1 tit
lid
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1 J I 7
091S
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70110
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12.500
6000
16
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M95
G.E. Product-Data Article GDP-IB
-------
POLYCARBONATE RESINS
PRODUCT DATA
LEXAN 500
Issued February 1, 1970
DESCRIPTION
LEXAN® 500 is a new member of the LEXAN family of polycarbonate resins particularly suited
to applications requiring high rigidity combined with the toughness and impact strength of LEXAN.
LEXAN 500 has the highest combination of rigidity and impact strength available in any thermo-
plastic, plus self-extinguishing characteristics, excellent dimensional stability, low mold shrinkage, and
colorability.
LEXAN 500 has these advantages:
Mechanical:
Flexural modulus increased nearly 60% over standard LEXAN, while high impact strength is
retained.
Thermal:
Self-extinguishing SE-1 per UL bulletin 94. UL approved for sole support of current carrying parts.
Molding:
Mold shrinkage is reduced to about Vz that of standard LEXAN, making production of more
precise parts possible.
PROPERTIES
The following data are typical for LEXAN 500:
Physical
Properties
Property
Specific Gravity
l>od Impact strength
Notched Bar. Vo" « W (fl-lbs/in.)
Unnotched Bar, '/8" » Vl" (fl-lbs/in.)
Falling Dart Impact, 1" dart (ft-lbs/in.)
Tensile Strength, psi
Tensile Modulus, psi
Elongation, (%)
Shear Strength
Compressive Strength, psi
Compreisive Modulus, psi
Flexural Strength, psi
Flexural Modulus, psi
Deformation under load (%)
4,000 psi 77°F
Fatigue Endurance, psi
Rockwell Hardness
Water Absarbtian (%)
24 hours
Equilibrium @ 73°F
Value
1.25
4-6
20-40
>125
9.600
450,000
10
8.500
14,000
520.000
15,000
500,000
.10
3.500
M-85
R-124
.12
.31
ASTM
Test
D 792
D 256
D 638
D 638
D 638
D 732
D 695
D 695
0 790
D 790
D 621
D 85
D 570
THERMAL
PROPERTIES
ELECTRICAL
PROPERTIES
Heal Deflection °F @ 264 psi
OF @ 66 psi
Coefficient of linear Thermal Expansion
Thermal Conductivity (cal/see/cmV°C/cm
Flammability (Ul Bulletin 94)
Flammability
Mold Shrinkage, in. /in.
Dielectric Constant (73°F)
50 cycles
10* cycles
Power Factor (73"F)
50 cycles
10* cycles
Dielectric Strength (73°),
s/t, volts/mil, '/a thick
s/s, volts/mil, Va thick
Volume Resistivity (ohm-cm), 73°F
Arc Resislonce (sees.)
Tungsten Electrodes
Stainless Steel
288
2?5
3.42x10-'
1.79x10-'
4.8x1 0-«
SE-1
Self- ex!.
0.002-0.003
3.10
3.05
00008
0.0075
450
450
3x10'
120
5-10
D 648
D 696
D 696
0 635
D 955
D 150
D 150
D 149
•Properties for some colors may vary slightly from the average values listed. For additional information »•» your Central Electric representative.
E-41
- 175 -
-------
POLYCARBONATE RESIN
PRODUCT DATA
Glass-Reinforced Grades
Issued February 15, 1969
DESCRIPTION
LEXAN resin reinforced by nUiss fiber is available in two standard grades. The 3412-products
contain 20% glass, the 3'f I4-producf:s 40% glass. Unreinforced LEXAN resin is outstanding among
engineering thermoplastics in the areas of impact strength, heat resistance, dimensional stability, and
creep resistance. Reinforcement with glass fiber raises performance to levels approaching those of
metals while retaining the basic plastic attributes of low cost processing, dielectric character, resistance
to corrosion, and inherent color.
The outstanding differences between reinforced (40% glass) and natural LEXAN are these:
Mechanical:
tensile modulus is as much as five times greater—
flexural, compressive and tensile strengths are nearly doubled or more than double
fatigue endurance is dramatically changed, increasing more than 7 times to permit tolerance of a
7500 psi load at 18CO cycles per minute—
deformation under load, a more than satisfactory 0.20% for unreinforced resin, drops to a mere
0.12%, even under 4000 psi.
Thermal:
coefficient of thermal expansion, reduced nearly 75%, equals that of many metals.
Molding:
mold shrinkage is reduced to about l/3rd that of LSXAN resin, making possible production of
very precise parts. >•
PROPERTIES
The following data are typical for LEXAN 3412 and 3414:
Physical
Properties
Property
Specific Oro/ity
iTod Impact strength
Notched Bor, '/| • . Vl ' (fHhi/ln.)
U.motched Bar, V, • < V, • (f>-lbt/ln.|
Trn»il« Strength, ps[
Tensile Modulus pii
Elongation, (%l
ihear Strength
Cot.ipressive Stiength, psi
CoTipressirfe Modulus, psi
fle'urot Strength, pii
Flexural Modulus, psi
Deformation under load (%)
4,000 psi 77°f
122°F.
1JB°F
2,000 psi 122°F
Fatigue Endurance, pii
Rockwell Hardness
Water Absorption |%)
24 hours
Equilibrium @ 73'F
LEXAN GR 3412
(20% glass)
1.35
2.0
19.0
16,000
860,000
4
10,000
16,000
760,000
21,000
800,000
0.04
0.04
0.10
0.03
5,000
M-91
R-113
0.16
0.29
LEXAN GR 3414
(40% fllass)
1.52
2.5
24.0
25.000
1 ,680,000
4
1 1 ,000
21,000
1.500,000
32,000
1 ,400,000
0.02
0.02
0.06
0.01
7,000
M-93
R-114
0.12
0.23
ASTM
Test
D792
D 256
0438
D 638
0 638
0732
D 695
D 695
D 790
D790
D 621
D785
0570
Thermal
Properties
Heot Deflection °F @ 264 psi
"f @ 66 psi
Coefficient of linear Thermal Expansion
m./b./°C
in./in./°F
Thermo! Conductivity (caf/sec/crnV"C/cm
Flammobility
Mold Shrinkage, in. /in.
295
300
2.68 x 10-'
1.49 x 10-'
J.O x 10-'
Self-ext. 1
0.002-3
295
310
1.68 x !0-»
0.93 x 10-'
5.2 x 10-«
Self-ext. 1
0.001-2
D 648
O696
D696
D 635
D955
Electrical
Properties
Dielect'ic Constant (73<-r'j
50 cycles
I0« cycles
Power Factor (73°FI
50 cvcles
10' cycles
Dielectric Strength (73°F),
i/t, volts/mil, !/• thick
i/if volli/mil, '/• thick
Volume Raslslivily (ohm-cm), (73°F)
Arc Resistance (sees.)
Tu'igtten Electrodes
Stafnleis Sreel
3.17
3.13
0.0009
0.0073
490
490
5 i IO-«
120
5
3.53
3.48
0.0013
0.0067
450
400
4 x !0-«
120
5
D 150
D 150
D 149
- 176 -
-------
GLASS-REINFORCED
THERMOPLASTIC RESIN
PRODUCT DATA
GRADES
PRODUCT DESCRIPTION
Self-extinguishing glass-reinforced NORYL® thermo-
plastic resin is oll'cred in addition to General Electric's
standard glass-reinforced NORYL-2 and NORYL-3.
This resin contains well dispersed, randomly oriented
short glass fibers and is rated soli-extinguishing, non-
dripping, Group I according to UL Bulletin 94. Com-
pared with the base NORYL. thermoplastics, this SH-1
filled resin oilers even better mechanical, thermal, di-
mensional and inolding-io-toleranec characteristics
while at the same time maintaining excellent electrical
properties and hydrolytic stability.
PRODUCTS AVAILABLE
SE-I glass-reinforced NORYL is available at the 20
and 30% level of glass loading, designated SE I-GFN2
and SE 1-GFN3 respectively.
These resins arc supplied in V»" diameter pellet
form in a standard gray color (designation -ISO) for
molding and extrusion. A ranac of opaque colors is
available on special order. SE 1-GFN2 and SE l-GI-'N-
3 NORYL products arc generally recommended for
applications requiring high mechanical strength, dimen-
sional stability and UL rated self-extinguishing char-
acteristics.
TYPICAL PROPERTIES OF NORYL GRADES SE 1-GFN2 and SE 1-GFN3
Property ASTM Method SE 1-GFN2
SE1-GFN3
Specific Gravity
Specific Volume
Water Absorption, 73°F, 24 hr.
Heat Deflection Temp., 261 psi,
Mold Shrinkage, in./in.
Flammability
Tensile Strength, Yield, psi at 73'F
Elongation at Break, %
Tensile Modulus, poi at 7i"'F
Fle/ural Strength, psi at 73'F
at200*F
Flexural Modulus, psi at 73'F
at200°F
Izod Impact, Notched '/a" Y V?" Bar
Ft. Lb./in. notch, at -40°F
at 73°F
Tensile Creep, 300 hrs. 2000 psi, 73'F, %
Hardness, Rockwell
Dielectric Constant, 73°F, 50% HH
at 60 cps
at 10 cps
Dielectric Constant, 150°r, at 60 cps
at 10' cps
Dissipation Factor, 73"F, 50% RH at 60 cps
at..U)° cps
Dissipation Factor, 150°F, at 60 cps
at ID6 cps
Volume Resistivity, dry, 73°F, ohm cm.
Surface Resistivity, ohm/'sq.
Dielectric Strength, volts/mil., ST, J,V sample
D792
D570
D648
D955
D635
U.L.
Bulletin 94
D638
D638
D638
D790
D790
D256
D674
D785
D150
D150
D150
D150
D257
D257
D149
1.30
21.3
0.06
270
0.002
Self-
Extine.
Non-
Dripping
Group 1
14,500
4-6
925.000
18,500
13,500
750,000
625,000
1.4
1.5
0.33
M90
L106
2.98
2.95
2.96
2.93
.0016
.0017
.0021
.0018
10"
10"
600
1.36
20.2
0.05
275
0.001
Self-
Exting.
Non-
Dripping
Group 1
17.000
4-6
1,200.000
20,000
15,000
1,100,000
1,000,000
1.3
1.4
0.2
f M93
X L108
3.15
3.11
3.14
3.10
.0020
.0021
.0029
.0022
10"
10"
530
- 177 -
-------
CURING AGENTS FOR EPON" RESINS - CASTING APPLICATIONS (1967)
C«Mitll|«ll
1. OiethvlenetriamtneiDTA).
2. irietnyienetetrarr.ine (TETA)
3. Di*ihyl«minopropyl«mine (A)
4. EPOIT Curing Agent T
b UYVCu::Oi;»«nll1
I. tPOS' Curing AEent II
7. tr-CIT Curing Agent V 25
8. (PON' Curing Agent V40
9. EPON 'Curing Agent D
10. N-Aminoclrtylpipetajine (AEP)
It. OFI-7
12. F.IW Curing Agent Z
.13. rtieta Phenylenediamine (CD
14. Metlrylene Oianiline IMOAi of Tonox
15. Oianincdipheny! Suitone IDOS)
16. BF.-MonoetliylaminelBF.'VEA)
17. Dodecenylsuccinic Anhydride (ODSAJ
18. HADIC Methyl Anhydride INMA)
19. Phthalic Anhydride (PA)'
20. Mexafiydrophthalic Anhydride (HKPA1
21; Clilorendic Anhydride (HIT)
22. Trimellilic Anhydride 1'""
23. TetiahyoiopMrulic Anhydride (THPAI
24. EJII-24
CknUllT>H
Polyline
Polyamme
"""'"""
Modified Polvamine
Mjdilicdl'dlyamme I
Mndi'ied Polyamine
Polyamide
Pofvimide
Polyamine Salt
Polyamine
Modified Polyamine
Modilied Polyamine
Polyamine
Polyamine
Polyamine
Lewis Acid Amine Complex
Anhydride
Anhydride
Anhydride
Anhydride
Anhydride
Anhydride
Anhydride
Substituted Imida/ole
Still
U'J-ij
l:c.uid
tisuid
Liquid
liquid
Liquid
'. ;ou-'d
LiQ'jid
Lie. ;d
liquid
liquid
lie's
Solid
Solid
S=i;j
Solid
Liquid
tiO>d
Solid
Solid
. Sciid
fci:d
Soiid
SuDt:-;::'ed
liquid
CtjBhjIeeV
Wtit»t
23 i
24.!
65
0 38
11.47
ca 48
ti 1(3
ca KO
-"
43
ca. 35
*i
J!
50
6:
— "
266
no
148
154
371
192
1S3
ItoraeiKu"
Caneeatritiin
•.ante, phr
101!
11-13
4>
1525
2U30
20-30
33-133
33-133
10.5-13.5
2023
16-20
19-21
13-14
28-30
2030
2-4
130-140
85 95
;oao
~~~75-85 """
100-120
3IMO
75-80
2-10
Curlaf Cunillent*
C.rf«i
TcfRperatara
Ijntt 'ICO
60-3001151501
60300115-150)
7 7 300 C5 1501
77300(25150!
(;..uwi.'i ism
603uOU5i50l
60300115-1501
60300 115 1501
150-300165150)
80-300 (25-150)
14MOOI60200)
140-400(602001
140400 160 ZOO)
140-400160-200)
240-400(115-200)
240-400(115200)
140-300160-150)
1755001802601
200-300194-1501
200400(94-200)
200400(94-200)
210400(100-200)
200-300194150)
140-300 (60 150)
Cuff ChVM
Cll lilM
11)1 mall) V I'd
Wnm. 7/n!
30n.ii.. Hirsi
3 4hr. J7i.ni
3040 min. 77C5I
.'(kill n,:.v I'M
.'0 30 mm, 77 !25)
45-60 mm. 77(25)
45 60 min. 77 (25)
2-4 hi, 77(25)
2030mm. 77(25)
8 hr, 77 (25)
8 hr, 77 (251
8 hr. 77 (251
8 hr. 7 7 125)
45 60 min. 250(120)
69 mo, 77 1251
5.6 days, 77 (25)
56 da(s. 77 125)
5 hr. 250 (1201
3060mm. 175180)
10-15 min. 250(120)
3IWO min, 250 11201
1 2 M. 2)2(100)
8-24 hr. dependinf
on concentration
ttrtltit-l' _
Comalett Cm
lljprcal tcktOll)
•fit)
Jdjvs :.":5i
7oais. 77(25!
JO mm. ?40IU5>
7 3a>;. 77 (251
.'dais. :i'JV
7d)(S, 7; 125) -
7 days. 7 71251
7davi. 7/1C5'
Ihr. 1)5(601
1 1 hr. 300 (ISO:
24 hr. 77125)
*lhr. 300(1501
2 hr. 175180)
S2hr 300(1501
2 hr. 1 15 130)
i2hr. 300i)50)
2hr. 1 75(80*
*?nr..)00fl5<»
2 hr. 175180!
S 2 hr. 300 11501
2 hi, 25011201
S 2 hr. 300(1501
Ihr. 250 (1201
t 2 hr. 300 (1501
Ihr, 2121100!
1 2 hr, 300(150)
1 hr, 750(1201* 4
hr. 400 12001 1
It hr. 500 (260)
12 hr, 250(120)
or4hr. Mil 501
Ihr, 175 ISO)
t 2 Iw, 300 (1501
Ihr, 25011201
< 2 hr. 3001150)
Ihr. 250(120)
«2Jir.300ll50)
1 hr. 200 194-
> 2 hr. 300 (150)
4nrs. 140150)
4 2 hr. 300(1501
M*lt
IhfhctM
Trapnun*
•fro
liOii'OI
?53rl2»
,>l.'it»l
180i!.'l
1ft ISUl
250:1 MI
195 (90)
240(115!
175180'
250II20!
300 (150)
300(150)
300115C!
300 (150)
250 (12C)
340(170
160 (70)
356(180)
3001150)
265(130)
356(180)
460(2501
.•50(1201
230-320(110.1601
Satnnm'
I.8.C"
1.8 C
c
R
1
«
"
1
"
B
G
II
«. f. C
A.)
0. E
F. H
R.F.K.M
«. F
C.F,
»,f
UN
P
«. F
11
ttmtiti i
Fast cure, shorl pot life, good R.r. strength. lo» initial .urc it> ;
Fast cure, short pot Me. good P..T. strength, lo* initial nw«it> . I
DTA and UIA. '
Mostly used »ilh low viscosity resins in tocfci Lj«!o>itit>. i
Sinulai lo 1 bul cures at sl'gh'lf loiei trni:-en!u'e
Fast 'ure, shwt pot hie, tow toiicity, gives strr?g iamiinled IncK
Concentration ranee with [PON rtiiris car. be vanN <*iotit without it'tctiftt pro?ert>ts al
the rurpd svstfm Utrrt lo provide lleiiMr M^tp^is
Similar to V-25 but wit.'i luwer v^cosilt ano s)i(^!'t u^iri pot i(r» . j
Requires moderate heal cure. Eiceller.t iii ;as:-i>£ LP to .^W F. seuice. ' i
Requires modfiate heat cure, fast curing Ipvt nit tisccsitv. gives castings wit> hijft :rr:ac!
strength.
Requires helt cure, gives eicelient high terperatjre properties, electi:cal progenies, i
chemicil resistance.
chemical resistance.
cnemica! resistirrce. '
Requires heat cure, imparts eicellent high temperature properties, cltctrical properties, t
chemical resistance.
Excellent high temperature properties, high mix viscosity, excellent resistance (o NO .xr ;-:v
environment.
resistance, good electrical prcoerties. c-'iv.le at roon terroera'.ure.
Long pot life at R.T.. gives excellent electrical properties ;r. castings and re'a-.-s t?-;-i axv? '
heat deflection temperature, imparts a decree pt flexibility to castings. S^'c Cf ^std |
with an accelerator.*, '•
Low viscosilv liquid at ropm tfmre'aljre. lon£ pet lile, excellent lor higti te-crri^n
applications, requires extensive post cure for maximum heat resistance. j
Insoluble below curing temp., difficult to handle, used in electrical polling, ineipers.-vt
Low melting point, gives low mix viscosity. lo~| pot lile, good electrical proce:! ;s C.>es
light-colored castings and laminates with good color stability to ultraviotel. Sno-jiJ Ot
rjSc(JwilhanKr;clr;(,i;'il.*
Short pot lite, gives castings of low flammafaility and high heat deflection temperature.
applications.
Low mix viscosity, good electrical properties, relatively inexpensive, insohiDle below melting
point.
Good high temperature strength with moderate temperature cure.
00
I
I. M tcom t*mp*fitui*
2. Amcunl rcquirtd to rcicl *>itrt one male of enaittc.
I. With EPON fifi.ns SIS. 120. 126. BII. l.id 110 ci:t0l chl.itl^ whrdriiM
(Sw Nol* •)
4. Curci cin bfl ifltclcd witti tlVti* c>.ria| iftntt it avq Tt>ffi0cri!uft mthm
(fit ipplic*0l« ttntn fttn in Hit t-Ji'f. H,fttt tt^pt^latn tl**r* I"*W
ihorttr cur* timet for * |i*a>n rcun. TM tt>i*c*! i:hMu!n jnftn aw*
inlcndcd only to iHuitf*te curmf condttient tvnocRir ntt. in prictic*.
wd* «»n»Ii04i» in cuie time CM bt acniwJ Sj <*T",t :»""• »lur*.
S. Witti EPCN Ruin i:i nccpt pMtulic tt^jti^t (Set Vie I). HtAf. TIM
trdbDl "l>" i* Ih-t columi, niau 11(8>.a-*a trf".
C. ObUrntd oilh CPOtt MB mini optimum tonctnim-o* Md cm*| tondiUoris
(not kwcnurilr UUM WKifitd btnin). MTH DMS, I** p*i.
A. Dow Cntmictl C«inp»nir
•. Mlo-ian Chunk*! Compmr
C. Union Cirtxd* Ch«nic»it C«nu>*nr
0. K* terpetttioa
I. fdjcuemtcii iriMrttorin
F. Allied Chwiftll Co.
Induitriil Crimitili Dim ion
C. L I. Oufont dt Ntmouri C«. Djn
f»*u|J(uc
Mortiawto
Haotf/ C
Cbe
Cntmicil C*.
VlltiCOl CbtmiC
Amoco CMmitil
Q. Hounttj P>K t dwm. Co.. Di*h)rM
el Air Pradixt> t ctM-ntcaihi, '«.
R. Shtli CiMmioi Co . ftetm >M
ttflM D«.
t. Uied *ith lolid nlhtr tfian Injunj tti.ni. ti'i ht:(in rttci to ujaj
EPON RKin [001.
«. Ccrtitn epmy comtioiiltant dctcr.bM in !M 6-j''(i'i *>c int tjb,*t
U.S. P»tent 3.CS7.CSO. Wf MM b»*n ..iloiTi'a ^»t w-nnnnu Win.fn
M*nul»i(tut.n| Co. i» pfcpirtq to l.cfc.* ir-wt «**"»(. «"rl •' «
tompiK'tiom covtied by IMt pclenl,
10. C*l tfiti ol lytttmi mikifit utt ol »cc«'*r*t»'i, *i. inlirdntlf c
iTittmt. n>>ll bi dfpcndint on eoi-cf«tt.iion of tcctltttlor u.M.
II. *l« coftiult manutaactufiri' boHttrni for cut:"! M»ntt not minulKt
Or Shell.
11. Cure cltflrtlcillT.
Th.t irrloimition ii bit*4 en dill obt.t.n*4 by Owl ••" t.ti'ck i
tontidtrtd Ktur»le, Mo"ev«f, "0 ,«*'«int» .» tipmtM or —pl.t* iti»
tki icciuKr ol »**• djt». tni mmu 10 bi obtained Horn ti>e ui« Uit't
Hut ony tuth v\t mil not intrinfo my pitrnl. TNK m
-------
:..U:Vi"y: :•.: :-:-;,;7if'::-.A^;- OF
ui
§
:£
z
£T
UJ
2
6.0
EPON 823 CURED AT 65°C
WITH INDICATED CURING
AGENT
200 300
TIME— MINUTES
EPON 828 CURED AT 25°C
WITH INDICATED CURING
AGENT
200 300
TIME— MINUTES
- 179 -
-------
TENSILE PROPERTIES OF "HIGH STRENGTH" EPONH RESIN SYSTEMS
(Syste.ns Providing Tensile Strength Values of Approximately 10,000 psi)
(Shell Epon Resins for Casting 1967)
fletin System
Material Ratio
i
Aliphatic Amice Cured
8?R/BTA
82S/ACP
Aromatic Oiamine Cured
S'.S'C,.
S?0/CPI-7
3,'o'Z
S.^R/CL
S28/ roNOx
815.7
Anhydride Cured
'S2Vr;M.VDVP-30
.'00/12
100/ZO
IOO/15
105.'- 8
inn/20
ICO/l'i
I no. '23
100/22-
i no: 87/i
8?6.'N.Vi'EMI-2« i 103/50/1
£.V!-'?»'30Va
•nOWl
sii TW. 3DVA ; ; on; 76/i
rttV'J'S-D-VA
Catalyizd Systems
• SJS.'BF/TO
828/0
100/75/0.'.
100/3
100/10.5
Cure Cycle' (tirsPC)
— _ ~— ____ - - - • --' •
l?rOI fZ/lHO'
RTG':I 4-1/200
• 2/80 + ?/150
2/90 + 4/160
2/80 + 2/150
2/80 -4- 2/150
2/80 + 4/150
2/EO -f 2/150
2/125 H- 2'200 + 2/245
' 2/90 + 4.' 135
2 .'90 + 4/150
3-'! 20-i 4.M50
3'i23 + !li
at23°C.Ma>. Value, psi
10,900
9,600
13,300
1 2/.00
13.0CO
12,400
12,800
15,000
8,400
7,600
12,300
10,700
11,500
8,700
11,100
I
Tensile Modulus at 2J°C. psi
410,000
400.000
440.000
430,000
Elonjatinn at 23*C, %
HDT'C
i
' 1
6.3 I 115
8.8
6.1
7.0
10, -
1lamin«
- 180 -
------- |