Over 6,9000 Low Earth Orbit cycles were accumulated at 30% Depth of Discharge on twelve INTELSAT-design nickel-hydrogen cells. Physical equipment and cells are described. Performance characteristics are seen to be uniform. Further testing is planned to seek a failure mode, and also to investigate the effects of a new additive for nickel-hydrogen cells. Initial results indicate improved performance at higher temperatures and diminished swelling of positive nickel plates

Coates, D. K.

Wheeler, J. R.

English

NASA Technical Reports Server

NICKEL-HYDROGEN CELL LIFE TEST 
James R. Wheeler and Dwaine K. Coates 
Eagle-Picher I n d u s t r i e s ,  Inc. 
ABSTRACT 
Over 6,900 LEO cyc le s  have been accumulated a t  30% DOD on twelve 
In t e l sa t -des ign  nickel-hydrogen c e l l s .  Phys ica l  equipment and c e l l s  
a r e  descr ibed .  Performance c h a r a c t e r i s t i c s  a r e  seen  t o  be  uniform. 
Fur ther  t e s t i n g  is  planned t o  seek a  f a i l u r e  mode, and a l s o  t o  inves- 
t i g a t e  t h e  e f f e c t s  of a  new a d d i t i v e  f o r  nickel-hydrogen c e l l s .  I n i t -  
i a l  r e s u l t s  i n d i c a t e  improved performance a t  h ighe r  temperatures and 
diminished swel l ing  of p o s i t i v e  n i c k e l  p l a t e s .  
INTRODUCTION 
Nickel-hydrogen b a t t e r y  c e l l s  a r e  now i n  gene ra l  use f o r  geo-syn- 
chronous (GEO) s a t e l l i t e s .  Five s a t e l l i t e s  wi th  nickel-hydrogen bat- 
t e r i e s  have been s u c c e s s f u l l y  launched i n  t h e  l a s t  two years  and over 
a dozen a r e  scheduled f o r  t h e  near  fu tu re .  A l l  of t hese  use t h e  I n t e l -  
s a t  design.  However, t h e  use  of t h i s  design f o r  low e a r t h  o r b i t  (LEO) 
has not  been widely explored.  
To i n v e s t i g a t e  t h e  e f f i c a c y  of t he  In t eSsa t  des ign  f o r  LEO appl i -  
ca t ions  twelve s t anda rd  product ion c e l l s  (RNJ3-30-1) wi th  nominal 30 
ampere-hour c a p a c i t i e s  each a r e  be ing  cycled i n  a  LEO regime. The 
r e s u l t s  to-date a r e  descr ibed  he re in .  Futur-e p lans  a r e  a l s o  discussed.  
CELL DESCRIPTION 
The twelve c e l l s  were cons t ruc ted  a s  p a r t  of s tandard  product ion 
c e l l  l o t s .  A t y p i c a l  RNH-30-1 c e l l  i s  shown i n  F igure  1. Eight c e l l s  
were of completely normal cons t ruc t ion .  Two (numbers 2 and 4 i n  accom- 
panying f i g u r e s )  con ta in  negat ive  p l a t e  s u b s t r a t e s  of a unique pa ten ted  
design and two (numbers 1 and 3) con ta in  s p e c i a l  p o s i t i v e  p l a t e s .  How- 
ever ,  t h e  l a t t e r  four  c e l l s  a r e  normally cons t ruc ted  i n  every o t h e r  
r e spec t  and were processed and given acceptance t e s t i n g  with a  produc- 
t i o n  c e l l  l o t .  
The new nega t ive  p l a t e  s u b s t r a t e s ,  Figure 2 ,  a r e  designed t o  en- 
hance e l e c t r i c a l  e f f i c i e n c y  by minimizing the  e l e c t r i c a l  cu r r en t  path 
length t o  t he  tab .  A t  t h e  same time, t he  t ab  a r e a  i s  considerably 
https://ntrs.nasa.gov/search.jsp?R=19850023090 2020-03-20T17:23:38+00:00Z
strengthed s t r u c t u r a l l y  i n  comparison with previously-used designs 
by a concentrat ion of r a d i a l  r i b s  near  the  tab-rib and by taper ing  
of the  tab-r ib i t s e l f .  The o v e r a l l  geometric design provides 
roughly-rectangular s t r u c t u r a l  s e c t o r s  which a r e  e s s e n t i a l l y  iden- 
t i c a l  i n  su r face  a rea ,  thus providing a r e l a t i v e l y  homogenous su r face  
f o r  adhesion of platinum c a t a l y s t .  
The two c e l l s  with s p e c i a l  p o s i t i v e  p l a t e s  were designed t o  inves- 
t i g a t e  performance c h a r a c t e r i s t i c s  of a p a r t i c u l a r  nickel-oxide s i n t e r  
l o t .  
TEST FIXTURING 
The test f i x t u r e  is  shown i n  Figure 3. Each c e l l  is  mounted i n  
an aluminum thermal f lange  which is bonded t o  i t  with RTV-560 and which 
is  e l e c t r i c a l l y  i s o l a t e d  by a l a y e r  of photo-etched mylar. The c e l l s  
a r e  mounted i n  a common v e r t i c a l  aluminum f i x t u r e  which is 0.8 inches 
th ick .  Its l a r g e  mass enables i t  t o  se rve  e f f e c t i v e l y  a s  a s t a b i l i z i n g  
hea t  r e se rvo i r .  
The e n t i r e  f i x t u r e  is contained i n  a r e f r i g e r a t e d  chamber which is 
ab le  t o  r egu la te  temperature t o  4 + 3'~. Each c e l l  is  mounted horizon- 
t a l l y .  Some add i t iona l  c e l l s  may ce seen i n  Figure 3 alongside the  
ver t ica l ly-s tanding f ix tu re .  These a r e  p a r t  of another l i f e  test being 
run concurrently with t h i s  one. 
A s  s a f e t y  f ea tu res  the  test chamber contains a c a t a l y t i c  hydrogen 
gas sensor and a temperature-sensitive switching element. These a r e  
wired t o  a faul t - re lay  which w i l l  terminate cycling and t r i g g e r  an 
audible alarm i n  the  event of a hydrogen l eak  o r  excessive hea t  build-  
up. Overlunder vol tage  protec t ion  is  a l s o  provided, 
Ancil lary equipment includes a small  computer which contro ls  
cycl ing automatical ly,  a power supply, and a monitor f o r  recording 
voltage.  
CYCLE REGIME AND PERFORMANCE 
The c e i l s  have, a s  of November 1984, completed over 6,900 LEO 
cycles a t  a 30% depth-of-discharge (DOD) , i.e., 55 minutes of charge 
a t  C/3 and 35 minutes of discharge a t  C/2 f o r  16 cycles per  day. 
The i n i t i a l  chargeldischarge (c/D) r a t i o  of 1.08 was reduced t o  
1.04 a f t e r  3,300 cycles t o  maintain an EOC V near  1.57 v o l t s  per  c e l l .  
C/D was f u r t h e r  reduced t o  1.02 a t  6,000 cycles and then re-adjusted 
t o  i .03  a t  6,400 cycles. 
EOC and EOD vo l t ages  have remained q u i t e  uniform throughout cycl ing.  
Data r e p r e s e n t a t i v e  of  t h e  lowest  and h ighes t  c e l l  a t  each measurement 
a r e  d isp layed  i n  Figures  4 and 5. 
Discharge c a p a c i t i e s  are measured a t  i n t e r v a l s  t o  monitor c e l l  per- 
formance. This t y p i c a l l y  c o n s i s t s  of a C/2 d ischarge  t o  1.0 v o l t  which 
is preceded by a C/10 charge f o r  16  hours.  Capac i t ies  are shown i n  Fig- 
ure  6. Note t h a t  c a p a c i t i e s  increased  s i g n i f i c a n t l y  a t  cyc l e  4200. A 
mechanical f a i l u r e  occurred a t  t h a t  time which caused t h e  unintended 
r e v e r s a l  of a l l  twelve c e l l s  t o  an average of -0.25 v o l t s  pe r  c e l l .  
Charge r e t e n t i o n  is a l s o  measured a t  i n t e r v a l s .  The c e l l s  a r e  
charged at C/10 t o  knee-over ( t y p i c a l l y  e ighteen  hours)  and EOC vo l t ages  
obtained.  Af t e r  a f o u r  t o  twelve day open-circui t  s t and  another  OCV is  
obtained.  Capacity a f t e r  one such s t and  is  shown i n  t h e  l a s t  column of 
Figure 6. Charge-retention v o l t a g e  d a t a  a r e  t abu la t ed  i n  Figure 7. 
FUTURE PLANS FOR LIFE TESTING 
It is planned t o  cont inue  l i f e - t e s t i n g  of t h e  twelve c e l l s  indef-  
i n i t e l y  wi th  t h e  i n t e n t i o n  of even tua l ly  determining a. f a i l u r e  mode. 
I n  add i t i on ,  l i f e  t e s t i n g  of two a d d i t i o n a l  RNH-30-1 c e l l s  i s  planned. 
These a r e  i d e n t i c a l  t o  those  of a r e c e n t  product ion c e l l  l o t  except  t h a t  
they con ta in  a s p e c i a l  add i t i ve .  
The a d d i t i v e  used increased  c e l l  capac i ty  a t  h ighe r  temperatures  
and a l s o  improved charge r e t e n t i o n  a t  ~ O ~ C .  Figure 8 shows capac i ty  
comparisons between t h e  two a d d i t i v e  c e l l s  ( c e l l s  A and B )  and t h e  
product ion c e l l  l o t  i n  which they were b u i l t  and t e s t e d .  The change 
is  most s t r i k i n g  a t  3 0 ' ~  where an e i g h t  ampere-hour improvement is seen. 
The improvement i n  10°c capac i ty  a f t e r  a 72-hour charge-retent ion s t and  
is  n e a r l y  four  ampere-hours. 
F igures  9 through 19 show t ime/vol tage  comparisons between one of 
t h e  a d d i t i v e  c e l l s  ( l abe l ed  "A") and one c e l l  r e p r e s e n t a t i v e  of t h e  
product ion l o t  average. The abrupt ,  b r i e f  r i s e  i n  vo l t age  nea r  t he  end 
of some d ischarge  curves i s  an a r t i f a c t  of t h e  curve-smoothing a lgor i thm 
and should be  disregarded.  
Beyond t h e  improvements i n  capac i ty  and charge r e t e n t i o n  an i n t e r -  
e s t i n g  f e a t u r e  is a r i s e  i n  vo l t age  near  EOC f o r  t h e  a d d i t i v e  c e l l  
which i n v a r i a b l y  crosses-over t h e  non-additive c e l l ' s  vo l tage .  
A s  a check on p o s s i b l e  e f f e c t s  of t he  a d d i t i v e  used, a 1OC s t r e s s  
t e s t  was performed on s i m i l a r  p o s i t i v e  p l a t e s ,  us ing  a 12-minute charge/  
6-minute d ischarge  cycle .  S i x  p l a t e s  were immersed i n  normal KOH 
(1.300 SpG) and s i x  i n  t h e  same KOH wi th  t h e  add i t i ve .  Thickness mea- 
surements were made be fo re  t e s t i n g  and a f t e r  cyc les  55, 160, 240 and 
320. The measurements a r e  t abu la t ed  i n  F igure  20. Notably, t he  p l a t e s  
i n  t h e  a d d i t i v e  grew only 1 t o  4 m i l s  compared t o  those  i n  t h e  r e g u l a r  
KOH which thickened 4 t o  8 m i l s .  This s t r e s s  t e s t  was extremely s e v e r e  
and went f a r  beyond t h e  number of cyc les  normally employed. 
SUMMARY 
Over 6,900 LEO cycles  have been accumulated a t  30% DOD on twelve 
In t e l sa t -des ign  nickel-hydrogen c e l l s .  Although t h e  c e l l s  a r e  from 
two d i f f e r e n t  product ion l o t s ,  vo l t age  and capac i ty  performances have 
been very  uniform and charge r e t e n t i o n  c h a r a c t e r i s t i c s  remain nominal. 
Voltage r e v e r s a l  on one d ischarge  was seen  t o  have a posi- 
t i v e  e f f e c t  on capac i ty  and d id  no t  otherwise a f f e c t  performance. New 
des ign  negat ive-p la te  s u b s t r a t e s  have not  a f f e c t e d  performance a t  t h e  
low charge/discharge r a t e s  used. 
Futnre p lans  inc lude  continued t e s t i n g  of t h e  twelve c e l l s  wi th  
t h e  i n t e n t  of determining a f a i l u r e  mode. Two c e l l s  wi th  a s p e c i a l  
a d d i t i v e  w i l l  a l s o  be  t e s t e d  i n  a regime y e t  t o  be determined. I n i t i a l  
r e s u l t s  i n d i c a t e  improved capac i ty  a t  h ighe r  temperatures  and improved 
charge-retent ion c h a r a c t e r i s t i c s .  P l a t e  growth may a l s o  be  reduced 
because of t h e  add i t i ve .  
Not l e a s t  of a l l ,  t h e  e f f i c a c y  of nickel-hydrogen c e l l s  without  
wall-wicks i n  LEO cyc les  is  being shown as  s u p e r i o r  t o  previous e s t i -  
mates. A u s e f u l  l i f e - t e s t  d a t a  base  i n  t h i s  regard cont inues t o  b e  
generated. 
Figure 1. Typical RNH-30- 1 Nickel-Hydrogen Cell 

Figure 3. Test Fixture and Refrigeration Chamber 
495 


AVG : 
I N I T I A L  
CYCLE 
#2300 
-
CYCLE 
f 4 2 0 0  (1) 
CYCLE 
/ I4200  ( 2 )  
(1) IMMEDIATELY PRIOR TO REVERSAL 
(2) AFTER REVERSAL TO - 0 . 2 5 V  
(3)  AFTER 96 HR. OPEN CIRCUIT STAND 
CYCLE 
# 4 4 0 0  (3 )  
Figure 6.  Discharge Capacities (Ampere Hours) RNH-30-1 Life Test 
CYCLE 870 
96 HOUR STAND 
B E G I N  END 
OCV OCV 
- 
CYCLE 112500 
288 HOUR STAND 
B E G I N  END 
ocv ocv 
- 
CYCLE I1000 
120 HOUR STAND 
B E G I N  END 
OCV 
- 
OCV 
- 
CYCLE /I4200 
96 HOUR STAND 
B E G I N  END 
ocv OCV 
- 
CYCLE //2200 
288 HOUR STAND 
B E G I N  END 
OCV 
- 
0 cv 
- 
CYCLE /I4500 
96 HOUR STAND 
B E G I N  END 
ocv 
- 
OCV 
- 
Figure 7. Charge Retention, RNH-30-1 Life Test 
CYCLE 
LOT AVG. 
CELL A CELL B (80 CELLS) SIGMA 
30°c Capacity 35.5 35.3 27.0 1.4 
0 
20 C Capacity 35.4 35.4 31.7 .8 
1 0 ' ~  Capacity 36.8 36.9 34.2 - 5  
OOC Capacity 
~ O O C  Chg. Ret. 
Figure 8. Performance of Additive Cells, Capacities in Ampere-hours 



TIME (MINUTES) 
Figure 12. 20 Degree Discharge 





TIME (HOURS) 
Figure 1 8. 10 Deg Charge Ret 72 hr. OCV 

NORMAL 
KOH 
ADDITIVE 
KOH 
-- 
THICKNESS (IN.) AT: 
CYCLE - 0 
- - 
5 5 
-
160 
-
2 40 
-
.031 ,031 ,031 .035 
.031 .031 ,031 ,036 
,030 .O 30 .030 .037 
.031 .031 .031 ,039 
.031 .031 .031 .O 36 
Figure 20. Thickness of Positive Plates During Stress 


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