A nickel-hydrogen cell completed 10,080 simulated low earth orbit charge/discharge cycles at depths-of-discharge ranging from 50 to 80 percent prior to failure. The cell is of the Air Force design, rated at 50 ampere-hours, 8.9 cm (3.5 inches) in diameter. Upon disassembly, the end of the polysulfone core supporting the electrode stack was found to have fractured. This allowed the electrode stack to expand. A massive short was found at the inner diameter of the electrodes centered roughly at plate set 34 to 37 from the positive end of the electrode stack. The damaged area extended through approximately one third of the electrode stack, with the effect becoming progressively less with distance from plate set 34 to 37. Measured thicknesses of the positive plates were significantly greater than the initial specification values. The postulated cause of failure is that positive plate growth caused fracture of the shoulder from the end of the polysulfone core on which the electrodes are mounted. The electrode stack relieved and pressure points were created at the area near the inner diameter of the plates at the tab attachment. A short occurred at a pressure point between opposing plates and propagated to other electrode sets due to thermal and mechanical stresses caused by the short

Mueller, V. C.

English

NASA Technical Reports Server

FAILURE ANALYSIS OF NICKEL-HYDROGEN CELL SUBJECTED 
TO SIMULATED LOW EARTH ORBIT CYCLING 
Vernon C. Mueller 
McDonnell Douglas Astronautics Company - St.  Louis Division 
ABSTRACT 
A nickel -hydrogen cel l  completed 10,080 simulated 1 ow earth orb i t  charge/ 
discharge cycles a t  depths-of-discharge ranging from 50 t o  80 percent prior 
to  fa i lure .  The cell  i s  of the Air Force design, rated a t  50 ampere-hours, 
8.9 cm (3.5 inches) in diameter., Upon disassembly, the end of the polysul- 
fonecore supporting the electrode stack was found to  have fractured. This 
allowed the electrode stack to  expand. A massive short was found a t  the 
inner diameter of the electrodes centered roughly a t  plate se t  34 t o  37 from 
the positive end of the electrode stack. The damaged area extended through 
approximately one third of the electrode stack, w i t h  the e f fec t  becoming 
progressively less  with distance from plate s e t  34 to  37. Measured thick- 
nesses of the positive plates were significantly greater than the i n i t i a l  
specification values. The postulated cause of f a i lu re  i s :  (1 ) Positive plate 
growth caused fracture of the shoulder from the end of the polysulfone core 
on which the electrodes are  mounted, (2)  The electrode stack relieved and 
pressure points were created a t  the area near the inner diameter of the plates 
a t  the tab attachment, and (3)  A short occurred a t  a pressure point between 
opposing plates and propagated to  other electrode se t s  due to  thermal and 
mechanical s t resses  caused by the short. 
INTRODUCTION 
Nickel -hydrogen cell  serial  number 148 was provided t o  McDonnel 1 Doug1 as 
Astronautics Company-St. Louis Division (MDAC-STL) by the Air Force Wright 
Aeronautical Laboratory (AFWAL) for  parametric and simulated 1 ow earth osbft  
cyclic t e s t s .  The cell  i s  rated a t  50 ampere-hours and i s  8.9 cm (3.5 inches) 
in diameter. Figure 1 shows the cell  general arrangement. This cel l  was 
constructed with asbestos separators. 
MDAC-STL mounted the ce l l s  horizontally during t e s t  in a f ix ture  which 
gripped the cel l  about the cylindrical section and permitted heat t o  flow from 
the cell  t o  the aluminum clamp and then to  the supporting aluminum plate. 
Figure 2 shows three c e l l s  in the t e s t  f ixture .  The aluminum baseplate was 
cooled by a circulating 1 iquid coolant bath to  permi t temperature control of 
the t e s t  ce l l s .  Insulation was applied around the c e l l s  such tha t  a l l  heat 
removed from them was by conduction through the mounting clamp t o  the temp- 
erature controlled baseplate. 
https://ntrs.nasa.gov/search.jsp?R=19840025632 2020-03-22T10:24:17+00:00Z
The cel l  was cycled by discharging into a fixed res i s tor  such tha t  25 
ampere-hours were removed over a 35-minute period, followed by charging a t  
approximately 50 amperes to  a voltage 1 imi t ,  which was then held constant 
while the current tapered for  the balance of the 55-minute charge interval.  
Nominal cel l  temperature was 23OC. Cycl ing was controlled automatically to  
permit unattended operation. In order to  prevent cel l  damage due t o  equip- 
ment malfunction, alarms were provided to  shut down the t e s t  (open-circuit 
the cell  ) fo r  over/under vol tage, excessive discharge current, overtemperature, 
overpressure, and loss  of f a c i l i t y  power. Approximately 5 minutes into the 
charge period of cycle 10,080, the ce l l  exceeded the temperature 1 imit, and 
on the next data-scan a few seconds l a t e r  the voltage dropped below 0.5 volts. 
The system automatical 1 y shut down, open-ci rcui t ing the cell  . Eighteen 
minutes l a t e r  when the fiext data se t  was recorded, the highest temperature 
was 89.6OC, measured a t  the top of the cylindrical section fur thest  removed 
from the coolant bath. Intermediate data points were not recorded, and the 
peak temperature excursion i s  not known. After about an hour, the cel l  
voltage dropped to  zero. Later in the day, a charge current of 5 amperes was 
applied f o r  one hour b u t  the voltage did not exceed 8.3 mill ivolts.  The cel l  
was then disconnected e lec t r ica l ly  from the t e s t  system b u t  physically l e f t  in 
the f ix ture  for  approximately 11 months before the f a i lu re  analysis was done. 
FAILURE ANALYSIS RESULTS 
The cell  was cut open with a la the just  below the weld toward the 
negative terminal (See Figure 1 ) . Before any cutting operations, something 
loose could be heard r a t t l i ng  within the pressure vessel. When the negative 
end of the pressure vessel was removed, exposing the electrode stack, the 
ceramic insulating washer a t  the negative terminal was found broken into 
four pfeces which accounts for  the ra t t l ing  noise. A1 so, the end plate,  
be1 l e v i l l e  washer, and the end of the polysulfone core were loose. These 
parts were captured by the negative leads, however, and not f ree  to  move 
within the pressure vessel. Figure 3 i s  a sketch of the electrode stack 
assembly showing component parts in greater de ta i l .  The end of the poly- 
sulfone core had fractured a t  the shoulder completely around the intersection 
with the central part of the core. Also, a plast ic  washer with a square 
opening and 2.69 cm (1.06 inches) outside diameter which was not identified 
on the drawing available to  us, was found broken inside the ce l l .  Figure 
4 i s  a photograph of the shoulder of the core, broken ceramic insulating 
washer, end plate,  unidentified washer, and be1 l e v i l l e  washer shown clock- 
wise from the upper l e f t .  The electrode stack had relieved w i t h  the f i r s t  
negative roughly flush with the broken end of the polysulfone core. The 
reservoir had melted completely across the annular section in the area of 
the negative tab. Also, the electrode stack was indented in the area of the 
negative tab extending across the annular section of the plate. This may 
have been caused by the negative tabs which applied forces to  the plates when 
the electrode stack relieved. Figure 5 i s  a photograph of the electrode stack 
prior to  fur ther  disassembly, showing these features. 
Referring t o  Figure 3, for  purposes of identification the electrodes are  
numbered consecutively from the positive end (weld ring end). Therefore, 
negative plate number 41 i s  the f i r s t  electrode encountered when disassembly 
proceeds from the fractured end of the polysulfone core. I t  was discovered 
during disassembly tha t  t h i s  particular cell  had been constructed with an 
additional reservoir between each se t  of plates rather than one a t  each end 
of the stack as shown in t h e a r t i s t ' s  sketch of Figure 3. Mr. Don Warnock 
of AFWAL confirmed tha t  some early ce l l s  had been constructed in t h i s  manner. 
The sequence of stack components was positive electrode, separator, negative 
electrode, gas screen, and reservoir. This sequence was repeated through- 
out the electrode stack. Another observation of general in te res t  was tha t  
many of the positive plates had irregularly shaped depressed areas randomly 
dispersed over the surface. There appeared t o  be two d is t inc t  levels of 
material similar to  looking over a broad plain with mesas protruding from 
i t .  Finally, the positive electrodes had grown in thickness considerably 
due to  extended cycling. 
Shorting of adjacent positive and negative plates was found a t  the inner 
perimeter of the plates in the area of the negative tab. In many cases, 
active material from the positive plate was embedded in the adjacent 
negative. The gas screen and reservoir between negative and positive plates 
had me1 ted and shrunk and were fused to  the teflon coated side of the negative 
electrodes. Figures 6 and 7 i l l u s t r a t e  these conditions. Figure 6 i s  a 
photograph of positive plate 36 viewed from the negative end of the electrode 
stack. Note the missing active material and the burned area a t  the core 
where the tab attachment to  the adjacent negative was located. Figure 7 i s  
a photograph of the adjacent negative plate 37 viewed from the positive side 
of the electrode stack a f t e r  removal. Note the active material from positive 
plate 36 adhering in the tab area, and the melting and shrinking of the gas 
screen and reservoir which adhere to  the plate.  Such damage was found to  
extend from the negative end of the electrode stack to  plate se t  27. The 
most massive damage appeared to  occur in plate se ts  34 to  37 with the e f fec t  
becoming l e s s  pronounced on e i ther  side. Also, the plates became more 
planar as disassembly progressed toward the positive end of the electrode 
stack. 
The heat pulse generated when the shorting occurred appeared to  discolor 
and swell the polysulfone core, such tha t  a ribbed appearance was created and 
a black deposit was l e f t  where the positive plates restr ic ted t h i s  swelling. 
Figure 8 i s  a photograph i l lus t ra t ing  th i s  phenomenon a t  the fractured end 
of the core (negative end of electrode stack).  The dimension from the end 
of the core to  the f i r s t  indentation caused by a positive plate i s  less  than 
the combined thickness of the end plate and be l lev i l le  washer, which imp1 ies  
that  the end of the core fractured prior to  the occurrence of the short. 
CONCLUSIONS 
The thicknesses of positive plates were measured during disassembly and 
are tabulated in Figure 9. As bui l t  positive electrodes have a thickness of 
of 0.762 mm (0.030 inches) to  0.813 mm (0.032 inches). Assuming tha t  each 
positive electrode was fabricated a t  the maximum dimension, the electrode 
stack heighth increased by 1 .OO cm (0.395 inches) due to  positive plate 
growth during cycling. This growth i s  believed to  have caused the fracture 
of the shoulder from the center of the polysulfone core. Examination of the 
fa i led  area shows s t r ia t ions  in the material which i s  typical of a fatigue 
fa i lure  in metals. Since the material properties of polysulfone are  differel 
a similar conclusion can not be supported. Also, the angle tha t  the tabs ma1 
with the electrodes were acute angles in the case of negative electrodes and 
obtuse angles f o r  positive electrodes. The ef fec t  i s  most pronounced a t  the 
negative end of the electrode stack where the greatest  re lat ive movement 
occurred. This i s  believed t o  have been caused when the electrode stack 
relieved, by the forces applied through the tab. The tabs are res t r ic ted  
in the center of the core and ac t  as a column pushing on the attachment poin, 
in the case of negative electrodes. In the case of positive electrodes, the 
tab pulls on the attachment point. 
A chronological history of the fa i lure  can be postulated as  follows: 
o Positive plate growth during cycling causes fracture of the shoulder 
from the polysulfone core. 
o Forces applied to  the electrodes when the stack expands create 
pressure points between adjacent pairs of electrodes, most pro- 
nounced a t  the tab attachments. 
o A short occurs a t  a pressure point a f t e r  some period of time. 
o The heat pulse and mechanical forces generated by the short cause 
the f a i lu re  t o  propagate to  adjacent plate sets .  
WELD RING ELECTRODE 
POSITIVE 
- -
ASSEMBLY STACK ASSEMBLY BELLEVILLE 
/ WASHER I 
LEADS 
Figure 1. 50 ampere-hour nickel-hydrogen cell. 
- - 
Figure 2. Nickel-hydrogen cells mounted in test figure. 




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PLATE 
IDENTIFICATION 
THICKNESS 
CENTIMETERS ( INCHES) 
PLATE 
IDENTIFICATION 
THICKNESS 
CENTIMETERS 
-- (INCHES) 
TOTAL THICKNESS OF ALL POSITIVES 4.255 CM (1.675 IN.) 
Figure 9. Measured positive plate thicknesses-Cell S/N 148. 
Q. Pickett ,  Hughes Aircraft: Could you t e l l  me what year the ce l l s  were 
made? 
A. Mueller, McDonnell Douglas Astronautics Company: No I can't .  The 
ser ia l  number is 148 i f  tha t  h e l ~ s .  I think we aot them i n  about 
COMMENT 
Pickett ,  Hughes Aircraft: I jus t  wanted to  comment that  these don't  
have the plates tha t  we are  currently making now. 
Muel l e r ,  McDonnell Douglas Astronautics Company: No these have the 
old plates. I don't know. I talked t o  different  people about this 
plate expansion problem or the plate expansion I saw they have told 
me tha t  there i s  some t e s t  data available. I think they ci ted some 
a t  Lewis and one other location that  shows tha t  the plates, that  you 
have now expansion rates of less  than 10% of what we see here. 
Q. Lim, Hughes Research Lab: Do you have the plate  loading data for  
th is?  
A. Muel 1 e r ,  McDonnel 1 Doug1 as Astronautics Company: No I have not. 
Q. Unidentified: You didn ' t  mention much about the broken ceramic 
washer which i s  something tha t  would concern me because i t ' s  going 
to  be representative of ce i l  fa i lure .  Did you find anything t o  
t e l l  you why tha t  broke? Whether i t  broke ea r l i e r  or a t  the same 
time as the core? 
A. Muel l e r ,  McDonnell Douglas Astronautics Company: No. I theorized 
tha t  broke a t  the same time and mv theorv i s  tha t  i t  broke due to  
the mechanical shock which creat& the ~ m e l y  shorting. We had no 
indication we were leaking hydrogen and I do think t h a t ' s  a good 
indication tha t  the end of the core broke before the cell  shortage. 
I might mention also that  the ce l l  continued t o  work relat ively 
well up until  the cycle before the f a i lu re  occurred. 
Q. Green, RCA-Astro: Could you t e l l  us anything about the history of 
the ce l l s ,  what was done before you yourself put them on t e s t .  
A. Mueller, McDonnell Douglas Astronautics Company: Yes we got them 
from the Air Force and I assume tha t  a l l  that  was done to  them was 
normal exceptance testing. We did some characterization t e s t  where 
we t r ied  different  charge schemes and different  charge rates  
probably about a month in duration. Then we went on to  cycling 
and we did 10,000 cycles on th i s  particular cel l  - 90 minute cycles. 
COMMENT 
Rogers, Hughes Aircraft: Jus t  a comment on the ceramic washer. Had 
that  fa i led  prior to  your main fa i lure  you would undoubtedly l o s t  the 
hydrogen. 
Muel l e r  , McDonnell Douglas AstronauLics Company: I would think so. 
Rogers, Hughes Aircraft: I t ' s  c lear  that  was associated with the 
other f a i lu re  in the ce l l .  
Muel 1 e r ,  McDonnell Dougl as Astronautics Company: As I was saying 
before there was no indication of performance degradation other 
than normal graceful degradation before the f a i lu re  occurred. 
Q. Ritterman, Comsat: You had no pressure indicator on the ce l l s  as I 
saw. 
A. Muel 1 e r ,  McDonnell Dougl as Astronautics Company: Yes we did. 
Q. Ritterman, Comsat: You did have pressure? 
A. Mueller, McDonnell Douglas Astronautics Company: And we saw no loss 
of pressure. 
COMMENT 
Milden, Aerospace Corporation: I was a t  Hughes Aircraft when these 
were bu i l t  and I was actually the guy who was building them and f i r s t  
the good news i s  the cel l  went 17,500 cycles a t  23 degrees centigrade 
which i s  astounding. 
Muel 1 e r ,  McDonnell Dougl as Astronautics Company: That i s  the one 
tha t  just fai led yes th i s  one went 10,000. 
Milden, Aerospace Corporation: Considering t h a t ' s  a f i r s t  generation 
of the f i r s t  f i f t y  tha t  were produced in any quantity, i t ' s  
astounding tha t  they went tha t  fa r .  There have been a number of 
changes made in the design as a resu l t  of the learning experiences. 
One of them i s  tha t  the positive electrode tabs a re  performed now so 
that  there ' s  not quite a sharp a edge there so tha t  shorting path 
would be a l i t t l e  b i t  different .  Also in one program that  area 
has been redesigned and improved significantly.  The electrodes were 
an early attempt and very very f a r  from optimum i n  terms of lower 
orb i t  electrodes. And i t ' s  amazing that  they went that  fa r .  So fo r  
f i r s t  generation a i r  force design production cel l  s actual ly pre- 
production since they were advanced development i t ' s  astounding. 
Kunigahall i , Bowie State College: Could you please tell me what was 
the volume of the electrolyte in the cell? 
Muel 1 er, McDonnel 1 Dougl as Astronautics Company: I 'm sorry I can ' t 
tell you any details about the cell construction. 
Kunigahall i, Bowie State College: What was the condition of the 
separator? 
Muel 1 er, McDonnel 1 Douglas Astronautf cs Company: The separators toward 
the end of the stack were actually in very good condition and in fact 
they were not, did not adhere to the positives very much. In some 
cases they did adhere to the positives, but we were able to get them 
off usually in one piece, some shredding some adherence. But really 
not bad at all. 
Kunigahalli, Bowie State College: Because my experience of nickel 
cadmium cells you know most of the time the separator would be verv 
strongly sticking to the negative due to the cadmium migration. 
I was wondering what is the situation in nickel hydrogen? 
Muel 1 er, McDonnel 1 Dougl as Astronautics Company: I 'rn always sticking 
to the positives. The negatives have teflon coating on them. 
Kunigahall i ,. Bowie State College: Excuse me one last question. By 
any chance did you take the same pictures of the positives? Were 
there any crystal growth or anything like that? 
Mueller, McDonnell Douglas Astronautics Company: All we did was a 
tear down of visual inspection. We did do a chemical analysis of 
the separator to verifym it was asbestos. It was kind of amazing 
to us that it was hanging together so well if it was asbestos, 
Kunigahall i , Bowie State College: Thank you very much. 
Unidentified: Vern, you did mention that they had a reservoir in the 
building stack. Did it have a wall wick also? 
Muel 1 er, McDonnel 1 Dougl as Astronautics Company: We1 1 it had one the 
standard wick on wall .yes- As I mentioned it was wet thev must have 
had very good electrolyte ' retention. 
" 


Failure Analysis of Nickel-hydrogen Cell Subjected to Simulated Low Earth Orbit Cycling

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