In order to develop a long life nickel electrode for a Ni/H2 cell, cycle life tests of nickel electrodes were carried out in Hi/H2 boiler plate cells. A 19 test cell matrix was made of various nickel electrode designs including three levels each of plaque mechanical strength, median pore size of the plaque, and active material loading. Test cells were cycled to the end of their life (0.5v) in a 45-minute low earth orbit cycle regime at 80% depth-of-discharge. The results show that the active material loading level affects the cycle life the most with the optimum loading at 1.6 g/cc void. Mechanical strength did not affect the cycle life noticeably in the bend strength range of 400 to 700 psi. The best plaque type appears to be one which is made of INCO nickel powder type 287 and has a median pore size of 13 micron

Lim, H. S.

Verzwyvelt, S. A.

English

NASA Technical Reports Server

LONG LIFE NICKEL ELECTRODES FOR A 
NICKEL-HYDROGEN CELL: CYCLE LIFE TESTS 
H. S. Lim and S. A. Verzwyvelt 
Hughes Research Laboratories 
ABSTRACT 
In order to develop a long life nickel electrode for a 
Ni/H2 cell, cycle life tests of nickel electrodes were carried 
out in Ni/H2 boiler plate cells. A 19 test cell matrix was 
made of various nickel electrode designs including three levels 
each of plaque mechanical strength, median pore size of the 
plaque, and active material loading. Test cells were cycled 
to the end of their life (0.5~) in a 45-minute low earth orbit 
(LEO) cycle regime at 80% depth-of-discharge (DOD). This is an 
interim report of this cycle life test. The results to date 
show that the active material loading level affects the cycle 
life the most with the optimum loading at 1.6 g/cc void. 
Mechanical strength did not affect the cycle life noticeably in 
the bend strenth range of 400 to 700 psi. The best plaque 
type appears to be one which is made of INCO nickel powder type 
287 and has a median pore size of 13 pm. 
INTRODUCTION 
Nickel electrodes have been recognized as the life 
limiting components of nickel-hydrogen cells. In order to 
develop a long life nickel electrode for a nickel-hydrogen 
cell, we are engaged in a study program under a contract for 
NASA-Lewis Research Center. In this study we investigated 
the effects of various electrode parameters on the cycle life 
of the electrodes. These parameters include plaque pore size, 
plaque mechanical strength, and active material loading level 
which were varied in three levels for each parameter. The 
overall program effort is outlined in Fig. 1. Various fabri- 
cation parameters of nickel plaques including nickel powder 
type, powder density, and sintering time were studied in 
order to fabricate plaques with desired parametric variations. 1 
Selected plaques (7 types) were impregnated in three levels of 
active material loading using the standard Air Force/Hughes 
electrochemical deposition process in an alcoholic bath. 
Subsequently these electrodes were tested by a Hughes standard 
stress test procedure (200 cycles) as a part of their evaluation. 
For a cycle life evaluation of these electrodes, 19 different 
nickel-hydrogen boiler plate test cells were fabricated and 
tested for initial cell performance. These results have been 
published earlier . The present report describes interim 
results of the cycle life tests which are still in progress. 
https://ntrs.nasa.gov/search.jsp?R=19840025627 2020-03-22T10:17:46+00:00Z
TEST CELL MATRIX AND DESIGNATION OF ELECTRODES 
The nickel-hydrogen boiler plate test cells matrix 
includes 19 out of 21 various designs of electrodes as shown 
in Table 1. Each electrode was designated as follows for 
convenience of later discussions: The first two digits 
represent the nickel powder type and the median pore size, 
i.e. 55 for INCO nickel powder type 255 and 10 vm pore size, 
25 for 255 powder type and 16 vm pore size, and 87 for 287 
powder type and 13 vm pore size, respectively. The last two 
digits represent mechanical strength (band strength): 40 for 
400 psi, 55 for 550 psi, and 70 for 700 psi. For example, 
an 8755 plaque is made of 287 type powder with the bend 
strength of 550 psi and the median pore size of 13 vm. 
TEST CELLS AND CYCLE LIFE TEST 
All test cells contained three standard flig3t type 
nickel electrodes in a recirculation stack design and 
31% KOH electrolyte. The capacity of the cells were rated 
into three groups, i.e., 2.7, 3.0 and 3.3 AH, based on 
capacities measured by charging the cells for 80 minutes 
at C rate and then discharge to 1.00V at 2.74 C rate. The 
measured capacities ranged from 2.8 to 3.1 AH, from 3.1 to 
3.5 AH, and 3.5 to 3.9 AH for 2.7, 3.0, and 3.3 AH ratings, 
respectively. 
The cycle life test of all the 19 boiler plate test cells 
were carried out at 23OC by a continuous cycling to 80% depth- 
of-discharge (DOD) of their rated capacities using a 45-minute 
cycle regimes except for interruptions for periodic capacity 
measurements after approximately every 1500 cycles. The 
cycling regime included a 2.74C rate discharge for 17.5 
minutes and a 27.5 minute charge at 1.92C rate for 110% 
recharge. End-of-charge voltages (EOCV), end-of-discharge 
voltages (EODV), end-of-charge pressures (DOCP), and end-of- 
discharge pressures (EODP) of the cells were monitored daily 
(every 32 cycles). 
CYCLE LIFE TEST RESULTS 
Plots of EODV and EODP of various cells vs. number of the 
life cycles are shown in Fig. 2A and 2B. The group of elec- 
trodes made of 2540 plaques showed the lowest cycle life, as 
shown by the EODV curves, regardless of the active material 
loading level, The next lowest cycle life group included all 
electrodes with the lowest active material loadings (L-series; 
1.4 g/cc void), regardless of the plaque type. The comparison 
of the cycle life of the remaining electrodes was not as 
clear cut as the other electrodes. However, the general 
trend showed that the medium loading level (M-series; 1.55 
g/cc void) gave better cycle life than the high loading level 
(H-series; 1.7 g/cc void). No noticeable trend was observed 
with the variation of plaque mechanical strength. In regard 
to the effects of pore size, the best plaque appears to be 
the 87XX series which are made of 287 type nickel powder 
with 13 pm median pore size. These series of plaques with 
M or H level loading showed slightly higher cycle life on 
the average than the 55XX series with comparable loadings. 
The 55XX are made of 255 type nickel powder with 10 vm 
median pores. The 2540 plaques with 16 vm pores were the 
worst plaques as discussed above. 
The EOCVts of the cells showed neither any appreciable 
variations with various electrode types nor any appreciable 
change during the cycle life test. 
The EOCPts and EODP's of a given cell changed parallel 
to each other as expected by the fixed quantity of charge and 
discharge. The cells with short cycle life showed overall 
lower pressure than the other cells. These short life cells, 
which include the 2540 types and all L-series, also showed 
a pressure peak. The pressure of these cells were initially 
increased with cycling along with other cells up to about 
1000 cycles and then started to decrease while the pressure 
of the other cells on the average either remains constant or 
increases with cycling. 
The cycle life of various cells to 0.5 and 0.9 v of EODV 
are plotted against active material loading level in Figs. 3 
and 4, respectively. Both curves show that the loading level 
for the optimum cycle life is about 1.6 g/cc void. These 
figures also show the effects of plaque type on the cycle 
life. The 87XX plaques on the average give better cycle 
life than the other types with comparable active material 
loading as discussed above. 
CELL PRESSURE AND ACTIVE MATERIAL UTILIZATION 
A normalized cell pressure after full charge and dis- 
charge,(P-P )/Cot where P is cell pressure, P is precharge 
pressure, aRd C is theoretical capacity of neckel electrode, 
is plotted agaiBst active material utilization of the cells 
after 1700 life cycles in Fig. 5. The term (P-Po)/CQ is a 
measure of the average oxidation state of nickel actlve 
material. The plots after full charge and full discharge of 
the cell gave straight lines, respectively. The values of 
(P-PQ)/Co at charged state were increased while the values 
at discharged state were decreased as the utilization 
increased. The values at charged state increased more 
rapidly than those at discharged state decreased when the 
utilization increased. This result appears to indicate that 
an increased active material utilization is more dependent, on 
reaching a high average oxidation state than on discharge to a 
low average oxidation state. This observation after 1700 
cycles is quite contrary to an earlier observation at the 
beginning of life on the relatiopship between (P-Po)/C and 
the active material utilization as shown in Fig. 6. O ~ h e  
earlier observation showed that the average oxidation state 
in the charge state was independent of the utilization. The 
utilization was entirely dependent on the oxidation state 
in the discharged state. This change of the relationship 
between the utilization and (P-P )/C with cycling may 
indicate the change of the mecha8ismoof the active material 
utilization. 
The plots of (P-PQ)/CQ vs. the utilization at various 
life cycles are shown In Flg. 6. An additional trend observed 
in this figure is that the overall value of (P-P )/Co is 
increased with increased number of cycles. ~his~increase 
appears to be due to either an increase in the average 
oxidation state of active material or a gradual corrosion of 
the nickel sinter to be converted to nickel oxides or hydroxides, 
or both. 
CONCLUDING REMARKS 
This report is an interim report of our studies on var- 
ious parametric effects on the cycle life of a long life 
nickel electrode for nickel-hydrogen cells. The following 
remarks are based on the combination of the results of 
presentlcycle life test and the initial performance reported 
earlier . 
e Among all parameters studied presently, the 
active material loading level affected cycle 
life of the nickel electrodes the most. The 
optimum loading level was about 1.6 g/cc void. 
e No noticeable effect of the plaque mechanical 
strength on the cycle life was found in the 
bend strength range of 400 to 700 psi. 
e Type 87XX plaques with 13 vm median pore size 
showed the longest cycle life on the average 
and slightly were better than type 55XX plaques 
which have 10 vm pore size. However, the 
active material utilization at the beginning of 
life was slightly higher with 55XX than 87XX. 
Type 2540 plaques with 16 vm median pore size 
showed the poorest life performance of all types. 
e Values of (P-Po)/Co gradually increased with 
the cycling. 
The relationship between active material 
utilization and (P-Po) /C indicated that the 
mechanism of maximum utiyization of the active 
material may be changing with cycling. 
REFERENCES 
1. H. S. Lim, S. A. Verzwyvelt, C. Bleser, and K. M. Keener, 
"Long Life Nickel Electrodes for a Nickel-Hydrogen Cell: 
I. Initial Performance", Proc. 18th IECEC, Orlando, 
Florida 1983. P. 1543, 
2. G. Holleck, "Failure Mechanisms in Nickel-Hydrogen 
Cells", the 1976 Goddard Space Flight Center Battery 
Workshop Proceedings, NASA Publication X-711-77-28, 
P. 297. 
T a b l e  1 
B o i l e r  P l a t e  T e s t  C e l l  M a t r i x  and  D e s i g n a t i o n  
o f  C e l l  Types 
PORE SIZE, 10 13 16 10 13 10 13 
*INCLUDED IN 19 TEST CELLS 
FABRICATION PARAMETER STUDIES ON PLAQUES 
(FOR MECHANICAL STRENGTH AND PORE SIZE) 
SELECTION OF PLAQUE FABRICATION PARAMETERS 
I FABRICATION AND CHARACTERIZATION OF PLAQUES (7 TYPES) I 
I IMPREGNATION OF ACTIVE MATERIAL (3 LEVELS) AND CHARACTERIZATION I 
200 CYCLE STRESS TEST 
' FAILURE ANALYSIS I L ,,,- -._.-I 
Figure 1. Outline of program. 

-P
 
PA 
0
 
!=
l a, 
0
 l-i 
w
a
,
 
ACTIVE MATER IAL LOADING, glcc VOID 
Figu re  3 .  A p l o t  of c y c l e  l i f e  t o  0.5V of EODV 
vs  . a c t i v e  m a t e r i a l  l o a d i n g  l e v e l .  
ACTIVE MATERIAL LOADING, glcc VOID 
Figure  4. A p l o t  of  cycle l i f e  t o  0.9V of EDOV 
vs .  a c t i v e  m a t e r i a l  load ing  l e v e l .  
CHARGED (SLOPE = 0.53) 
87XX PLAQUES 
0 55XX PLAQUES 
2540 PLAQUES 
DISCHARGED (SLOPE = -0.19) 
@ 
I I I I I 
90 95 100 105 110 
ACTIVE MATERIAL UTILIZATIQN. % 
Figure  5 .  (P-Po)/C v s .  a c t i v e  m a t e r i a l  u t i l i z a t i o n  
a f t e r  1700 c y c l e s .  Charged f o r  16 hours  a t  0.1C 
r a t e  and d i scharged  t o  0.5V a t  0.5C r a t e .  
INITIAL* 
*0.1 C RATE CHARGE 
FOR 16 h n  AND 0.5 C 
RATE DISCHARGE 
TO 0.5 V 
"C RATE CHARGE FOR 
80 min AND 1.37 C 
RATE DISCHARGE 
TO 0.5 V 
90 100 110 
ACTIVE MATERIAL UTILIZATION, % 
Figure  6 .  (P-Po)/Co v s .  a c t i v e  m a t e r i a l  u t i l i z a t i o n  
a t  v a r i o u s  l i f e  c y c l e s .  
Q. Gross, Boeing: Based on the data you have taken so f a r  how would you 
compare the best of your combinations with the performance of the 
existing nickel electrodes used fo r  nickel hydrogen ce l l s .  
Q. Lim, Hughes Research Lab: The best combination appears to  be the 
87 excess plaques here which i s  287 powder. We d idn ' t  see any strong 
ef fec t  of the mechanical trends so the mechanical trends in the range 
of 400 to  700 PSI d idn ' t  make tha t  much of a difference. 
Q. Gross, Boeing: We11 how does tha t  material compare in other respects 
w i t h  the existing nickel electrodes commercial. 
A. Lim, Hughes Research Lab: I cannot speak i t ' s  a1 1 different  types of 
nickel electrode presently available b u t  t t i i s ' i s  very close to  the 
Hughes Air Force standard electrode which i s  madeof-287 nickel 
powder and the average pressure i s  around 550 PSI and the l'oading 
level i s  I understand Close to  1.55 to  1.6 which i s  very close to 
the optimum. 
Q. Edgar, Eagle Picher: Could you comment br ief ly  on active material 
loss from these electrodes a t  the different  cel l  s izes  you investigated. 
A. L i m ,  Hughes Research Lab: The active material loss we have reported 
ea r l i e r  a f t e r  the 200 cycle s t r e s s  t e s t  the loss was I think i t  was 
around 2% overall except 25 to  40 plaque which has a medium s ize  of 
16 microns. The plaque I think i t ' s  loss was about twice as the 
other average and a f t e r  t h i s  t e s t  we d idn ' t  measure the loss yet .  
Q. Mallory, AT&T Bell Labs: Could you remind me what impregnation method 
you were using for  these? 
Lim, Hughes Research Lab: This was Dr. Picket t ' s  method. 
Q. Mallory, AT&T Bell Labs: And do you know what level the carbonate 
was i n  the ce l l s?  
A. Lirn, Hughes Research Lab: We d idn ' t  analyze the carbonate level 
of t h i s  cel l  yet  b u t  I think we have a low i n i t i a l  carbonate content 
of the stock solution. I don't  have the number w i t h  me. Maybe my 
co-worker Scott  has i t .  
Q. Lirn, Hughes Research Lab: Scott ,  do you remember? We had a very low 
value i n i t i a l l y  b u t  a f t e r  the t e s t  we d idn ' t  measure that  yet .  


Long Life Nickel Electrodes for a Nickel-hydrogen Cell:  Cycle Life Tests

In order to develop a long life nickel electrode for a Ni/H2 cell, the cycle life of nickel electrodes was tested in Ni/H2 boiler plate cells. A 19 test cell matrix was made of various nickel electrode designs including three levels each of plaque mechanical strength, median pore size of the plaque, and active material loading. Test cells were cycled to the end of their life (0.5v) in a 45 minute low Earth orbit cycle regime at 80% depth-of-discharge. It is shown that the active material loading level affects the cycle life the most with the optimum loading at 1.6 g/cc void. Mechanical strength does not affect the cycle life noticeably in the bend strength range of 400 to 700 psi. It is found that the best plaque is made of INCO nickel powder type 287 and has median pore size of 13 micron

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LONG L I F E  NICKEL ELECTRODES FOR A 
NICKEL-HYDROGEN CELL: CYCLE ' L I F E  TESTS 
H.S. L i m  and S.A. Ve rzwyve l t  
Resea rch  L a b o r a t o r i e s  
301 l e > a l i b u  Canyon Road 
Mal ibu ,  CA 90265 
INTRODUCTION 
N i c k e l  e l e c t r o d e s  have  been  r e c o g n i z e d  a s  t h e  l i f e -  
l i m i t i n g  components  o f  n i cke l -hyd rogen  ce l l s .  I n  o r d e r  
to  d e v e l o p  a  l o n g  l i f e  n i c k e l  e l e c t r o d e  f o r  a  n i c k e l -  
hydrogen  c e l l ,  w e  are engaged i n  s t u d i e s  of v a r i o u s  
p a r a m e t r i c  e f f e c t s  on t h e  e l e c t r o d e  c y c l e  l i f e .  These  
p a r a m e t e r s  i n c l u d e  p l a q u e  pore s i z e ,  p l a q u e  mechan ica l  
s t r e n q t h ,  and a c t i v e  m a t e r i a l  l o a d i n g  l e v e l .  T h r e e  
l e v e l s  of v a r i a t i o n  were used f o r  each  p a r a m e t e r .  
S e v e r a l  f a b r i c a t i o n  p a r a m e t e r s  o f  n i c k e l  p l a q u e s ,  
i n c l u d i n g  n i c k e l  powder t y p e ,  powder" d e n s i t y ,  and 
s i n t e r i n g  t i m e  were s t u d i e d  i n  o r d e r  to  f a b r i c a t e  
p l a q u e s  w i t h  d e s i r e d  p a r a m e t r i c  v a r i a t i o n  ( 1 ) .  S e l e c t e d  
p l a q u e s  ( 7  t y p e s )  were impregna t ed  i n  t h r e e  l e v e l s  o f  
a c t i v e  m a t e r i a l  l o a d i n g  u s i n g  t h e  s t a n d a r d  A i r  Force/ 
Huqhes e l e c t r o c h e m i c a l  d e p o s i t i o n  p r o c e s s  i n  an  
a l c o h o l i c  b a t h .  S u b s e q u e n t l y ,  t h e s e  e l e c t r o d e s  were 
t e s t e d  by a  Hughes s t a n d a r d  test  p r o c e d u r e  (200  c y c l e s )  
a s  a  p a r t  o f  t h e i r  e v a l u a t i o n .  F o r  a  c y c l e  l i f e  
e v a l u a t i o n  of  t h e s e  e l e c t r o d e s ,  19 d i f f e r e n t  n i c k e l -  
hydrogen  b o i l e r  p l a t e  t e s t  ce l l s  were f a b r i c a t e d .  T h i s  
i n i t i a l  c e l l  pe r fo rmance  h a s  been d e s c r i b e d  e a r l i e r  ( 1 ) .  
The p r e s e n t  r e p o r t  p r e s e n t s  t h e  r e s u l t s  of t h e  c y c l e  
l i f e  tests  of  t h e  b o i l e r  p l a t e  ce l l s .  D e t a i l s  o f  t h e  
f a i l u r e  a n a l y s e s  of t h e s e  t e s t  cel ls  w i l l  be p r e s e n t e d  
l a t e r  ( 2 ) .  
TEST CELL MATRIX AND ACCELERATED CYCLE LIFE TEST 
The n i c k e l - h y d r o g e n t b o i l e r  p l a t e  test  c e l l  m a t r i x  
i n c l u d e s  19 o u t  o f  t h e  21 v a r i o u s  d e s i g n s  of  e l e c t r o d e s ,  
a s  shown i n  T a b l e  1 .  Each e l e c t r o d e  t y p e  was d e s i g n a t e d  
a s  f o l l o w s  f o r  conven ience  of  l a t e r  d i s c u s s i o n s :  The 
f i r s t  t w o  d i g i t s  r e p r e s e n t  t h e  n i c k e l  powder t y p e  and 
t h e  median p o r e  s i z e ,  i .e . ,  55 f o r  INCO n i c k e l  powder 
t y p e  255 and 10 p m  p o r e  s i z e ,  25 f o r  255 powder t y p e  and 
16 p m  p o r e  s i z e ,  and 87 f o r  287 powder t y p e  and 13 pm 
p o r e  s i z e ,  r e s p e c t i v e l y .  The l a s t  t w o  d i g i t s  r e p r e s e n t  
https://ntrs.nasa.gov/search.jsp?R=19860015575 2020-03-20T15:31:42+00:00Z
of t h e s e  ce l l s  i n i t i a l l y  i n c r e a s e d  w i t h  c y c l i n g  a l o n g  
w i t h  o t h e r  cel ls  up to  a b o u t  1000 c y c l e s  and t h e n  
s t a r t e d  to d e c r e a s e ,  w h i l e  t h e  p r e s s u r e  of  t h e  o t h e r  
c e l l s ,  on a v e r a g e ,  e i t h e r  remained c o n s t a n t  o r  i n c r e a s e d  
w i t h  c y c l i n g .  
PARAMETRIC EFFECTS OF CYCLE LIFE 
Rated  and t h e o r e t i c a l  c a p a c i t i e s  ( c h e m i c a l  
c a p a c i t y )  dep th-of  - d i s c h a r g e  (DOD) o f  c y c l i n g  w i t h  
r e s p e c t  t o  t h e  t h e o r e t i c a l  c a p a c i t y ,  and t h e  c y c l e  l i f e  
t o  0,9 V of EODV a r e  summarized i n  T a b l e  2. Al though  
t h e  r a t e d  c a p a c i t y  was based  on t h e  i n i t i a l  measured 
c a p a c i t y ,  t h e  t h e o r e t i c a l  c a p a c i t y  was used  i n  t h e  
a n a l y s i s  o f  t h e  r e s u l t s .  T h i s  is b e c a u s e  t h e  measured 
c a p a c i t y  v a r i e d  w i t h  t h e  measurement c o n d i t i o n s  and 
showed a  memory e f f e c t  o f  p r i o r  c y c l i n g .  The c y c l e  
l i f e  o f  n i c k e l  e l e c t r o d e  depends  s t r o n g l y  on t h e  DOD of 
c y c l i n g .  T h e r e f o r e ,  it is n e c e s s a r y  to  compare t h e  
c y c l e  l i f e  o f  v a r i o u s  ce l l s  a t  a  g i v e n  v a l u e  of  DOD i n  
o r d e r  to  e v a l u a t e  t h e  e f f e c t s  o f  t h e  e l e c t r o d e  
p a r a m e t e r s .  A q u a n t i t a t i v e  r e l a t i o n s h i p  between c y c l e  
l i f e  and DOD of a  n i cke l -hyd rogen  c e l l  o r  a  n i c k e l  
e l e c t r o d e  is no t  a v a i l a b l e .  However, t h e  f o l l o w i n g  
q u a n t i t a t i v e  r e l a t i o n s h i p  between t h e  DOD and an 
e x p a n s i o n  r a t e  of t h e  n i c k e l  e l e c t r o d e  a c t i v e  m a t e r i a l  
h a s  been e s t a b l i s h e d  ( 4 ) .  
where k is t h e  e x p a n s i o n  r a t e  and A is a c o n s t a n t .  F o r  
t h e  p r e s e n t  d a t a  a n a l y s i s  it h a s  been assumed t h a t  t h e  
c y c l e  l i f e  o f  t h e  n i c k e l  e l e c t r o d e  is i n v e r s e l y  
p r o p o r t i o n a l  t o  t h i s  r a t e ,  k. The measured c y c l e  l i f e  
was n o r m a l i z e d  to  70% DOD of t h e  t h e o r e t i c a l  c a p a c i t y  
u s i n g  t h e  r e l a t i o n s h i p  i n  E q u a t i o n  ( 1  ) ,  combined w i t h  
t h i s  a s s u m p t i o n .  
The n o r m a l i z e d  c y c l e  l i f e  v a l u e s  a r e  summarized i n  
T a b l e  2 and p l o t t e d  a g a i n s t  t h e  median p l a q u e  p o r e  s i z e ,  
t h e  p l a q u e  bend s t r e n q t h ,  and t h e  a c t i v e  m a t e r i a l  
l o a d i n g  i n  F i g u r e s  3, 4 and 5 ,  r e s p e c t i v e l y .  The 
optimum p o r e  s i z e  a p p e a r s  to  be a b o u t  12 pm, r e g a r d l e s s  
o f  t h e  l o a d i n g  l e v e l  ( F i g u r e  3 ) .  The 16-pm p l a q u e s  
showed much s h o r t e r  c y c l e  l i f e  t h a n  t h e  o t h e r  p l a q u e s .  
m e c h a n i c a l  s t r e n g t h  (bend  s t r e n g t h ) :  40 f o r  400 p s i ,  55 
f o r  550 p s i ,  and 70 f o r  700 p s i .  Fo r  example ,  an  8755 
p l a q u e  is made of  287 t y p e  powder w i t h  a bend s t r e n g t h  
o f  550 p s i  and a  median p o r e  s i z e  o f  13 p m ,  The l e t t e r s  
L, M ,  and H i n d i c a t e  t h e  nomina l  a c t i v e  material  l o a d i n g  
l e v e l s  o f  1 .4 ,  1 .55,  and 1.7 g / c c  v o i d ,  r e s p e c t i v e l y ,  
A l l  test  cel ls  c o n t a i n e d  t h r e e  s t a n d a r d  f  l i g h t - t y p e  
n i c k e l  e l e c t r o d e s  i n  a r e c i r c u l a t i o n  s t a c k  d e s i g n  ( 3 )  
and 31% KOH e l e c t r o l y t e .  The ce l l  c a p a c i t i e s  were 
r a t e d  i n  t h r e e  g r o u p s :  2 .7 ,  3.0 and 3.3 A-hr, based  on 
c a p a c i t i e s  measured by c h a r g i n g  t h e  c e l l s  f o r  80 m i n u t e s  
a t  C r a t e  and t h e n  d i s c h a r g i n g  them t o  1.00 V a t  2.74 C 
r a t e .  The i n i t i a l  measured c a p a c i t i e s  r anged  f rom 2 , 8  
t o  3.1 A-hr, from 3.1 t o  3.5 A-hr and 3.5 to  3.9 A-hr 
f o r  t h e  2.7,  3.0,  and 3.3 A-hr r a t i n q s ,  r e s p e c t i v e l y .  
The c y c l e  l i f e  tests of  a l l  of  t h e  19 b o i l e r  p l a t e  
t e s t  ce l l s  were c a r r i e d  o u t  a t  2 3 " ~  by a c o n t i n u o u s  
c y c l i n g  to  80% d e p t h - o f - d i s c h a r g e  o f  t h e i r  r a t e d  
c a p a c i t i e s  u s i n g  45-minute c y c l e  r eg imes .  These  were 
i n t e r r u p t e d  p e r i o d i c a l l y  f o r  c a p a c i t y  measurements  a f t e r  
a p p r o x i m a t e l y  e v e r y  1500 c y c l e s .  The c y c l i n g  r eg ime  
i n c l u d e d  a  2.74 C ra te  o f  d i s c h a r g e  f o r  17.5 m i n u t e s  and 
a 27.5-minute c h a r g e  a t  1.92 C r a t e  f o r  110% r e c h a r g e .  
End-of - c h a r g e  v o l t a g e s  (EOCV) and end-of - d i s c h a r g e  
v o l t a g e s  (EODV) , and end-of -charge  p r e s s u r e s  (EOCP ) and 
e n d - o f - d i s c h a r g e  p r e s s u r e s  (EODP) o f  t h e  ce l l s  were  
m o n i t o r e d  d a i l y  ( e v e r y  32 c y c l e s  ) . 
CELL VOLTAGE AND PRESSURE DURING LIFE TEST 
P l o t s  o f  EODV and EODP o f  v a r i o u s  ce l l s  v e r s u s  t h e  
number o f  l i f e  c y c l e s  are shown i n  F i g u r e s  1 and 2. The 
EODV d e c r e a s e d  g r a d u a l l y  w i t h  c y c l i n g  u n t i l  n e a r  t h e  end 
o f  l i f e  where  t h e  v o l t a g e  d e c r e a s e  a c c e l e r a t e d ,  e x c e p t  
i n  t w o  anomalous  c e l l s ;  i , e . ,  8770H ( F i g u r e  1 )  and 
5 5 5 5 M  ( F i g u r e  2 ) .  The end o f  l i f e  was d e f i n e d  a s  0 , 9  V 
of  t h e  EODV. The EOCVPs of  t h e  c e l l s  showed n e i t h e r  any  
a p p r e c i a b l e  v a r i a t i o n s  w i t h  v a r i o u s  e l e c t r o d e  t y p e s  no r  
any a p p r e c i a b l e  change  d u r i n g  t h e  c y c l e  l i f e  t es t .  
The EOCP" and EODP's o f  a g i v e n  ce l l  changed i n  
p a r a l l e l  t o  each  o t h e r  a s  e x p e c t e d  by t h e  f i x e d  q u a n t i t y  
o f  c h a r g e  and d i s c h a r g e .  The cel ls  w i t h  s h o r t  c y c l e  
l i f e  showed o v e r a l l  lower p r e s s u r e  t h a n  t h e  o t h e r  cel ls .  
These  s h o r t  l i f e  ce l l s ,  which i n c l u d e  t h e  2540 t y p e  and 
a l l  L - s e r i e s ,  a l s o  showed a  p r e s s u r e  peak ,  The p r e s s u r e  
N o  d e f i n i t e  e f f e c t  of  t h e  bend s t r e n g t h  on t h e  
c y c l e  l i f e  was i d e n t i f i e d ,  due  to t h e  s p r e a d  d a t a  
p o i n t s ,  a s  shown i n  F i g u r e  4 .  
The a c t i v e  m a t e r i a l  l o a d i n g  l e v e l  a f f e c t e d  t h e  
c y c l e  l i f e  s t r o n g l y ,  a s  shown i n  F i g u r e  5, i f  t h e  v a l u e s  
of t h e  2540 p l a q u e s  were d i s r e g a r d e d  because  of t h e i r  
e x c e p t i o n a l l y  s h o r t  l i f e .  The optimum l o a d i n g  l e v e l  
a p p e a r s  to  be a t  a b o u t  1.6 g / cc  vo id .  The p r e c e e d i n g  
c o n c l u s i o n s  on t h e  p a r a m e t r i c  e f f e c t s  on t h e  c y c l e  l i f e  
d i d  n o t  change when t h e  d a t a  were a l t e r n a t i v e l y  a n a l y z e d  
u s i n g  t h e  c y c l e  l i f e  v a l u e s  of  0.5 V f o r  t h e  end of  
l i f e ,  or w i t h o u t  u s i n g  t h e  DOD c o r r e c t i o n .  
CELL PRESSURE AND ACTIVE MATERIAL UTILIZATION 
A n a l y s e s  of  t h e  c e l l  p r e s s u r e s  d u r i n g  t h e  i n t e r i m  
c e l l  c a p a c i t y  measurements  r e v e a l e d  a  r e l a t i o n s h i p  
between t h e  c e l l  p r e s s u r e  and t h e  a c t i v e  m a t e r i a l  u t i l i -  
z a t i o n .  T h i s  u t i l i z a t i o n  is d e f i n e d  a s  t h e  r a t i o  of  t h e  
measured v s  t h e  t h e o r e t i c a l  c a p a c i t i e s ,  A no rma l i zed  
c e l l  p r e s s u r e  a f t e r  f u l l  c h a r g e  and d i s c h a r g e ,  
(P-Po)/Co, (where  P is t h e  cel l  p r e s s u r e ,  Po is t h e  
p r e c h a r g e  p r e s s u r e ,  and Co is t h e  t h e o r e t i c a l  c a p a c i t y  
of n i c k e l  e l e c t r o d e ) ,  is p l o t t e d  a g a i n s t  a c t i v e  m a t e r i a l  
u t i l i z a t i o n  of  t h e  ce l l s  a f t e r  1700 l i f e  c y c l e s  
( F i g u r e  6 ) .  The term (P-P,)/C, is a  measure  of  t h e  
a v e r a g e  o x i d a t i o n  s t a t e  of  t h e  n i c k e l  a c t i v e  m a t e r i a l .  
A f t e r  f u l l  c h a r g e  and f u l l  d i s c h a r g e  of  t h e  c e l l ,  t h e  
p l o t s  gave  s t r a i g h t  l i n e s ,  r e s p e c t i v e l y .  The v a l u e s  o f  
(P-Po)/CQ a t  cha rged  s t a t e  i n c r e a s e d ,  w h i l e  t h e  v a l u e s  
a t  t h e  d i s c h a r g e d  s t a t e  d e c r e a s e d  a s  t h e  u t i l i z a t i o n  
i n c r e a s e d .  The v a l u e s  a t  t h e  cha rged  s t a te  i n c r e a s e d  
more r a p i d l y  t h a n  t h o s e  a t  t h e  d i s c h a r g e d  s t a t e  
d e c r e a s e d  when t h e  u t i l i z a t i o n  i n c r e a s e d .  T h i s  r e s u l t  
a p p e a r s  to  i n d i c a t e  t h a t  an i n c r e a s e d  a c t i v e  m a t e r i a l  
u t i l i z a t i o n  is more dependen t  on r e a c h i n g  a  h i g h  a v e r a g e  
o x i d a t i o n  s t a t e  t h a n  on d i s c h a r g e  t o  a  l o w  a v e r a g e  
o x i d a t i o n  s t a t e .  T h i s  o b s e r v a t i o n  a f t e r  1700 c y c l e s  is  
q u i t e  c o n t r a r y  to an e a r l i e r  o b s e r v a t i o n  a t  t h e  
beg inn ing  of l i f e  on t h e  r e l a t i o n s h i p  between (P-Po)/Co 
and t h e  a c t i v e  m a t e r i a l  u t i l i z a t i o n  which showed t h a t  
t h e  a v e r a g e  o x i d a t i o n  s t a t e  i n  t h e  c h a r g e  s t a t e  was 
independen t  of  t h e  u t i l i z a t i o n  ( I ) ,  The u t i l i z a t i o n  was 
e n t i r e l y  dependen t  on t h e  o x i d a t i o n  s t a t e  i n  t h e  
d i s c h a r g e d  s t a t e .  I t  is s p e c u l a t e d  t h a t  t h i s  change o f  
t h e  r e l a t i o n s h i p  between t h e  u t i l i z a t i o n  and (P-Po)/C 
w i t h  c y c l i n g  may i n d i c a t e  a  change  of  t h e  mechanism 09 
t h e  a c t i v e  m a t e r i a l  u t i l i z a t i o n .  The v a l u e  of (P- 
P,)/Co g r a d u a l l y  i n c r e a s e d  w i t h  an i n c r e a s e d  
number of  c y c l e s .  T h i s  i n c r e a s e  a p p e a r s  to  be d u e ' t o  
e i t h e r  an i n c r e a s e  i n  t h e  a v e r a g e  o x i d a t i o n  s t a t e  o f  
a c t i v e  m a t e r i a l  or a g r a d u a l  c o r r o s i o n  o f  t h e  n i c k e l  
s i n t e r  to  be c o n v e r t e d  to  n i c k e l  o x i d e s  or h y d r o x i d e s ,  
or b o t h .  
CONCLUDING REMARKS 
o The a c t i v e  m a t e r i a l  l o a d i n g  l e v e l  s t r o n g l y  
a f f e c t s  t h e  c y c l e  l i f e  o f  t h e  n i c k e l  elec- 
t r o d e s ,  showing t h e  optimum l o a d i n g  l e v e l  a t  
a b o u t  1.6 g / cc  v o i d .  
e The p l a q u e  p o r e  s i z e  a f f e c t s  t h e  c y c l e  l i f e  
s i g n i f i c a n t l y ,  showing t h a t  t h e  optimum p o r e  
d i a m e t e r  w a s  a b o u t  1 2  urn .  
a N o  n o t i c e a b l e  e f f e c t  of t h e  p l a q u e  m e c h a n i c a l  
s t r e n g t h  on t h e  c y c l e  l i f e  was found i n  t h e  
bend s t r e n g t h  r a n g e  o f  400 to  700 p s i .  
CD A s  t h e  test  cells were c y c l e d ,  t h e  a v e r a g e  
v a l u e s  of  (P-Po)/C g r a d u a l l y  i n c r e a s e d ,  and 
t h e  r e l a t i v e  depen8ence  o f  t h e s e  v a l u e s  a t  t h e  
c h a r q e d  and d i s c h a r q e d  s t a t e s  on t h e  a c t i v e  
m a t e r i a l  u t i l i z a t i o n  was changed ,  i n d i c a t  i n q  a 
p o t e n t i a l  change  of t h e  u t i l i z a t i o n  mechanism 
of  a c t i v e  m a t e r i a l .  
ACKNOWLEDGMENTS 
T h i s  work was s u p p o r t e d  by NASA-Lewis R e s e a r c h  
C e n t e r  under  C o n t r a c t  N o ,  NAS 3-22238 _ ( C o n t r a c t  Manager, 
John  S m i t h r i c k ) ,  The a u t h b r s  w o u n  l i k e  to  acknowledge  
D r .  J . D .  Margerum and D r .  R.C. K n e c h t l i  f o r  many h e l p f u l  
d i s c u s s i o n s  d u r i n g  t h e  c o u r s e  of t h i s  work, and M r .  S.T. 
T a y l o r  for h i s  m o n i t o r i n g  of  t h e  l i f e  tes t ,  
REFERENCES 
1 .  H.S. L i m ,  S.A. Ve rzwyve l t ,  C. Bleser, and K.M. 
Keener ,  "Long L i f e  N i c k e l  E l e c t r o d e s  f o r  a N i c k e l -  
Hydrogen C e l l :  T. I n i t i a l  Pe r fo rmance" ,  P roc .  1 8 t h  
I E C E C ,  O r l a n d o ,  F l o r i d a  1983, p, 1 5 4 3 .  
2. H,S. Lim and S,A. V e r z w y v e l t ,  s u b m i t t e d  f o r  
p u b l i c a t i o n  a t  t h e  1 9 t h  I E C E C ,  San F r a n c i s c o ,  CA, 
August  1984. 
3 .  G. H o l l e c k ,  " F a i l u r e  Mechanisms i n  Nickel-Hydrogen 
C e l l " ,  1976 Goddard Spaee  F l i g h t  C e n t e r  B a t t e r y  
Workshop P r o c e e d i n g s ,  p  297, 
4. H.S. Lim, "Expans ion  o f  t h e  N i c k e l  E l e c t r o d e " ,  1980 
Goddard Space  F l i g h t  C e n t e r  B a t t e r y  Workshop 
P r o c e e d i n g s ,  p, 175,  and r e s u l t s  to  be p u b l i s h e d .  
Table 4, Boiler Plate Test Cell Matrix and ~esignation 
of Cell Types, 
Table 2. Summary of the Boiler Plate Cell Cycle Test 
13858-4 

-!J a 
0 w 
r l m  
Pl Cv 
- 
10,000 
0 
w 
I 
I-- 
 
a 
0 5000 a 
8 
h 
k 
W 
L 
- 
J 
u 2000 
0 
> 
0 
2 
a 
0 
1000 
10 11 12 13 14 15 16 
MEDIAN PORE DIAMETER,prn 
Figure 3. Plots of the normalized (calc, ) cycle life at 
70% DOD with respect to the theoretical 
capacity versus median plaque pore diameter, 
Curves A (A), B ( @ ) ,  and C (0) represent 
active material loading level of 1 - 4 ,  1.55,  
and 1.7  g/ce void, respectively- 
BEND STRENGTH, psi 
Figure 4. Plots of the normalized (calc.) cycle life 
vs plaque bend strength for various plaque 
types and the active material loading 
level, 
PLAQUE TYPES: 
ACTIVE MATERIAL LOADING, g/cc VOID. 
Figure 5. Plots of the normalized (calc. ) cycle life 
vs the active material for various types of 
electrodes, 
13530-3 
CHARGED (SLOPE = 0.53) 
DISCHARGED (SLOPE = -0.19) 
90 95 100 105 110 
ACTIVE MATERIAL UTILIZATION, % 
87XX PLAQUES 
@ 55XX PLAQUES 
2540 PLAQUES 
F i g u r e  6.  (P-Po)/C v e r s u s  a c t i v e  m a t e r i a l  u t i l i z a t i o n  
a f t e r  1700 c y c l e s .  Charged f o r  16 h o u r s  a t  
0.1 C ra te  and d i s c h a r g e d  to  0.5 V a t  0.5 C 
r a t e ,  


Long Life Nickel Electrodes for a Nickel-hydrogen Cell: Cycle Life Tests

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