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NASA Technical Memorandum 100 102 AIAA-87-9257

Effect of Component Compression on the Initial Performance of an IPV Nickel-Hydrogen Cell

(hASA-2H-100102) E i P I C l Ch CCB€CbrEIT N87-24E 38 CCBPRESSICN C Y ISE IBII!K;CBL E E E E C L B A L C E OF A N IEV # I C K E L - H Y D P C G E E CELL ( E A E A ) 17 p A o a i l : BIIS HC ACZ/!lF A01 CSCL 1oc Unclas

G3/JU GO83764

Randall F. Gahn Lewis Research Center Clevetand, Ohio

Prepared for the 22nd Intersociety Energy Conversion Engineering Conference cosponsored by the AIAA, ANS, ASME, SAE, IEEE, ACS, and AIChE Philadelphia, Pennsylvania, August 10- 14, 1987

https://ntrs.nasa.gov/search.jsp?R=19870015405 2018-06-17T08:49:15+00:00Z

EFFECT OF COMPONENT COMPRESSION ON THE INITIAL PERFORMANCE OF AN IPV NICKEL-HYDROGEN CELL

0 Q, In 0 I w

.

Randall F. Gahn National Aeronautics and Space Administration

Lewis Research Center Cleveland , Ohio 441 35

SUMMARY

An experimental method was developed for evaluating the effect of compo- nent compression on the charge and dlscharge voltage characteristics of a 3.5-in.-diameter boiler plate cell. A standard boiler plate pressure vessel was modified by the addition of a mechanical feedthrough on the bottom of the vessel which permitted different compressions to be applied to the components without disturbing the integrity of the stack. Compresslon loadings from 0.94 to 27.4 psi were applied by suspending weights from the feedthrough rod. Cell voltages were measured for 0.96C, 55-min charge and for 1.37C, 35-min and 2C, 24-min discharges. An initial change in voltage performance on both charge and discharge as the loading increased was attrlbuted to seating of the cornDon- ents. Subseauent variation of the comression from 2.97 to only minor changes in either the charge or the discharge vo one month open-circuit voltage stands and 1100 cycles under the maximum loadlng have produced no change in performance.

INTRODUCTION

27.4 psi caused' tages. Several LEO conditions at

IPV nickel-hydrogen cells have been developed to a lev-1 of confidence that they are being considered for energy storage on the proposed space sta- tion. The desired life of storage batteries for the Space Station and other satellites in low Earth orbit is 5 years. A 5-year life is anticipated If the cells are cycled at less than 40 percent depth-of-discharge. depth-of-discharge would reduce the number of batteries required for a mission, but cycle life is then shortened to approximately 1 to 2 years.

nickel electrode. One factor limiting the electrode life has been its tendency to swell. All nickel electrodes have been observed to expand in thickness to varying degrees during charge-discharge cycling in cells. increases the amount of compression on the components and can cause electrical shorting, separator drying, and mechanical failure of the cell core (ref. 1). Recent modifications (ref. 2) of the design to include compression washers on each end of the core have allowed the electrode to expand within limited dis- tances and minimized the consequences of the expansion. However, the compres- sion washers do not maintain a specific compression on the components but operate over a specific range of force determined by their design. Thus in an operating cell the pressure on the stack components is changing continuously. Presented in this paper is a study to experimentally evaluate the effect of compression on the cell performance.

tionships of a 4 A-h, 3.5-in.-diameter cell as a function of the compression loading on the components.

An 80 percent

The life of an IPV nickel-hydrogen cell appears to be a function of the

This expansion

The purpose of this study was to measure the initial voltage-current rela-

~~~

EXPERIMENTAL

A photograph o f t he exper imental hardware used t o determine t h e e f f e c t o f component cornpression on the c e l l performance i s shown i n f l g u r e 1. A sche- mat ic diagram o f the c e l l assembly and component l oad ing mechanism i s shown i n f i g u r e 2.

An A i r Force b o i l e r p l a t e pressure vessel w i thou t a w a l l wick was sup- por ted i n a v e r t i c a l p o s i t i o n . A 1/8- in. O-ring sealed male connector was threaded i n t o the bottom o f t h e pressure vessel . A l /B- in.-diameter s t a i n l e s s s t e e l rod attached t o the compression p l a t e a t t he top o f t h e stack extended through the O-ring f i t t i n g . A T-shaped weight ho lder was suspended f rom t h e feedthrough rod. S tee l weights were l a i d on t h e ho lder t o t h e des i red loading.

The c e l l stack consis ted o f f o u r u n i t c e l l s i n the back-to-back design. The n i c k e l e lectrodes were obtained from the A i r Force and t h e hydrogen e lec- t rodes from Eagle-Plcher. Previous eva lua t lon o f n i c k e l e lec t rodes f rom t h e same l o t ind ica ted they d i d no t have long c y c l e - l i f e c h a r a c t e r i s t l c s . Th is c h a r a c t e r i s t i c , however, d i d n o t a f f e c t t h e i r cyc le - to -cyc le performance r e p r o d u c i b i l i t y over a sho r t eva lua t i on per iod. The n i c k e l e lec t rodes were nominal ly 0.028 In . t h i c k and had a capac i ty o f about 1 A-h. The hydrogen e lect rodes were nominal ly 0.006 i n . t h i c k . The separator was one l a y e r o f beater - t rea ted asbestos approxlmately 0.010 I n . t h i c k .

The c e l l stack was assembled w i t h d ry components. The s tack was sa tur - a ted w l t h 31 percent KOH by vacuum b a c k f i l l i n g . Excess KOH was dra ined and the stack placed i n the pressure vessel. The c e l l assembly res ted on p l a s t i c spacers i n the bottom o f t he pressure vessel . The 1/8- in. feedthrough rod went through the center o f t he stack core and was threaded i n t o t h e 1/8-in.- t h i c k s t a i n l e s s s tee l compression p l a t e r e s t i n g on t o p o f t h e c e l l s tack. Fol lowing evacuation t o about 1 t o r r t he vessel was pressur ized w i t h approx i - mately 50 p s i o f hydrogen.

Compression on the components was increased as weights were app l i ed t o the holder. The pressure app l ied by the hydrogen gas on t h e 1/8-in.-diameter feedthrough rod added about 1-ps i load ing t o t h e components i n t h e discharged s t a t e (H2 = 100 p s i ) and about 3 p s i a t f u l l charge (HZ = 250 p s i ) . compresslons stated i n the r e p o r t r e f e r t o the ac tua l weight app l i ed on the holder .

Component

RESULTS AND DISCUSSION

I n i t i a l l y the uncompressed stack loaded a t 0.94 p s i underwent t h r e e forma- t i o n cyc les using a C/10 t o 16 h r charge and a C/4 discharge. charge capac i ty t o 0.9 V was 4.2 A-h. Cyc l ing parameters f o r t h i s study were based on a 4 A-h capac i ty stack ( 1 A-h/nickel e lec t rode ) . Vol tage performance and amp-hour capaci ty f o r the second and t h i r d cyc les were i d e n t i c a l . c y c l i n g regime t o study the e f f e c t o f i nc reas ing compression on t h e c e l l per- formance was begun on the f o u r t h cyc le . Four cyc les a t a s p e c l f l c compression were run on the same day.

Heasured d i s -

The

The stack was cyc led a t 80 percent DOD us ing a 10 percent overcharge. Two cycles were performed w i t h a 0.96C, 55-min charge and a 1.37C, 35-min

2

.

.

discharge followed by two cycles at the same charge rate but with a 2C, 24-mln discharge.

The various compression loadings evaluated are given in table I as the total weight applied to the holder and as the pressure per square inch of electrode/separator area.

c

Performance curves for the 2C and the 1.37C discharges of the stack taken during the initial compression are shown in figure 3 and 5, respectively. At both discharge rates the performance improved with increasing compression. A 3 0 mV increase was measured at the 2C rate between the minimum compression of 0.94 psi and the maximum cornpression of 27.4 psi. Voltage curves at 0.94, 5.68, 11.1, 19.2, and 27.4 psi are shown in figure 3 and illustrate the steady voltage increase. The 1.37C discharge voltages improved about 20 mV as the compression was increased from 2.97 to 27.4 psi.

During the initial compression process, loading was increased in 20-lb increments until the 19.2 psi compression was reached. At this point the com- pression was reduced in one step to 2.97 psi. After the standard four cycle regime was performed, the compression was increased in one step to 27.4 psi.

As can be seen in figure 5 the performance for the 2.97 psi compression (cycle 43) following the 19.2 psi loading was about 12 mV higher than the inl- tial performance at 2.97 psi (cycle 15). Increasing the compression to 27.4 psi improved the discharge voltage by an additional 5 mV over the 19.2 psi loading. 2.97 psi) the stack performance decreased only 5 mV.

It is also significant that with a decrease in cornpression (19.2 to

The 0.96C charge curves for the 2C and 1.37C rate discharges are shown in figure 4 and 6, respectively. An unexpected decrease in charging perform- ance, 1.e.. higher voltage, was observed as the compression was Increased from 0.94 to 27.4 psi. In figure 4 the charge voltage reached a maximum value at 19.2 psi. The charge curve at 27.4 psi loadings was essentially the same as at 19.2 psi. The maximum difference between the 0.94 and 27.4 psi loadings was about 25 mV. The charge performance given in figure 6 for the 1.37C dis- charge shows the voltage increase from the 2.97 to 19.2 psi cycle. However, when the compresslon was then reduced to 2.97 psi the charge curve did not change. Increasing the compression from 2.97 to 27.4 psi in one step also had no effect on the charge performance.

Following testing at the maximum loading the stack was removed from the pressure vessel and vacuum backfilled with 31 percent KOH to resaturate the asbestos separators. Although the components were loosened during saturation, their positioning on the core was unchanged.

The stack was returned to the pressure vessel. The ampere hour capacity for two cycles at C/10 to 16 hr charge and C/4 to 0.9 V discharge was 4.58 A-h compared to the initial capacity of 4.20 A-h.

The standard cycling regime was repeated with increasing compressions of 0.94, 5.68, 1 1 .l, 16.5, 21.9, and 27.4 psi. Voltage curves for the 1.37C discharge cycles at 5.68, 16.5, and 27.4 psi are shown in figure 7. An improvement in performance of about 10 mV was observed as the compression was increased from 5.68 to 27.4 psl. However, the performance appears to

3

s t a b i l i z e a t t h e 16.5 p s i loading. i n f i g u r e 8. was observed a t any o f t he loadings.

The charge performance r e s u l t s a r e g iven Only curves a t 5.68 and 27.4 p s i a re shown because no d i f f e r e n c e

The c e l l was a l so evaluated f o r t he e f f e c t s o f sho r t term load ing a t t he maximum compression. resu l ted i n a vol tage increase o f about 10 mV f o r bo th t h e d ischarge and charge. i n performance dur ing an open-c i rcu i t stand.

Standard c y c l i n g a f t e r 36 and 78 days on open-c i r cu i t

This change was no t considered s i g n i f i c a n t bu t i s a t y p I c a l v a r i a t i o n

Fol lowing the open-c i r cu i t stand a LEO (0.96C. 55-min charge and 1.37C, 35-mIn discharge) c y c l i n g pe r iod was i n i t i a t e d a t maximum loading. charge/dlscharge cycles some changes occurred i n t h e o v e r a l l performance when compared t o t h e i n i t i a l vo l tage c h a r a c t e r i s t i c s . no t s i g n i f i c a n t or a f a c t o r o f t he compression. about 10 mV. t h e standard cha rac te r i za t i on c y c l i n g regime t h e vo l tages were w i t h i n 10 mV o f t he vo l tages before t h e extended c y c l i n g .

A f t e r 1100

This was expected and was

Discharge vo l tages decreased about 30 mV b u t a f t e r undergoing Charge vo l tages increased

The e f f e c t o f component compression on the performance was determined again f o l l o w i n g t h e 1100 continuous cyc les. Three compressions, 0.94, 11.1, and 27.4 p s i were evaluated us ing the standard c h a r a c t e r i z a t i o n cyc les. charge r e s u l t s are shown i n f i g u r e 9. 0.94 p s i t o es tab l i sh performance r e p r o d u c i b i l i t y . Voltage c h a r a c t e r i s t i c s f o r t h e discharges were near l y i d e n t i c a l a t t h i s loading. then run a t 11.1 and 27.4 p s i . than a t 0.94 p s i . The 11.1 p s i cyc le was between t h e o ther two.

D i s - Two 1.37C discharge cyc les were run a t

S ing le cyc les were Voltages a t 27.4 p s i were about 10 mV g rea te r

Charging performance a t 0.96C f o r t he th ree compressions i s shown i n f i g u r e 10. formance was unaffected by t h e changes i n compression.

Except for some vo l tage d i f f e rences e a r l y i n t h e charges, t h e per-

CONCLUDING REHARKS

Throughout t h i s study t h e discharge performance o f t he c e l l improved as the compression on the components increased. A vo l tage increase o f about 30 mV was observed dur ing i n i t i a l cornpression o f the s tack f rom 0.94 t o 27.4 p s i . A f t e r 1100 LEO cycles the vo l tage increase was on ly about 10 mV. An unexpected increase i n charging vol tages was observed when t h e compression was increased. Dur ing t h e i n i t i a l compression f rom 0.94 t o 27.4 p s i , vo l tages increased about 25 mV. However, a f t e r the stack had been compressed t o 19.2 p s i f u r t h e r changes (bo th higher and lower) i n t h e component compression d i d n o t a f f e c t t h e charg ing voltages.

Although only one c e l l was evaluated I n t h i s study and t h e o v e r a l l com- press ion range was l i m i t e d , a f e a s i b l e method was developed f o r f u r t h e r i n v e s t i g a t i o n s .

REFERENCES

1. Mu l le r , V.C., I IFai lure Analys is o f Nickel-Hydrogen C e l l SubJected t o Simulated Low Earth O r b i t Cyc1ing.I' Ba t te ry Workshop, NASA CP-2331, 1984, pp. 523-538.

The 1983 Goddard Space F l i g h t Center

4

2 . S m i t h r i c k , J . J . , Manzo, M . A . , Gonzalez-Sanabria, O . , "Advanced Designs f o r I P V Nickel-Hydrogen C e l l s . " Paper 849555, Proceedings of t h e 1 9 t h I E C E C , V o l . 1 , pp. 631-634, August 19-24, 1984, San F r a n c i s c o , C a l i f o r n l a .

TABLE I . - COMPRESSION LOADINGS

APPLIED TO THE 3.5-ln.-DIAMETER.

7.38- In.z CELL

I Appl led welght . Component compresslon, I 'b PSI

6 . 9 1 1 . 9 21 .9 41 .9 61 .9 8 1 . 9

101.9 121.9 141.9 201.9

0.94 1 .61 2.97 5 .68 8 .39

1 1 . 1 0 1 3 . 8 0 1 6 . 5 0 19.20 27.40

5

FIGURE 1. - I P V NICKEL-HYDROGEN CELL COMPRESSION-TEST FACILITY.

6

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PRESSION PLATE

0 - NICKEL ELECTRODE

7 HYDROGEN /

ELECTRODE

0 - STACK CORE

\ -O-RING SEALED FEED-THROUGH

CONNECTOR

r LOAD

FIGURE 2. - CELL ASSEMBLY AND COMPONENT LOADING MECHANISM.

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Report Documentation Page

7. Key Words (Suggested by Author@))

1. Report No

18. Distribution Statement

NASA TM-100102

9 Security Classif (of this report)

Unc lass i f i ed

I 2. Government Accession No.

20. k u r l t y Classif. (of this page) 21. No of pages 22. Price' - Unc lass i f i ed I 6 A02

A I AA- 8 7 - 925 7 4. Title and Subtitle

E f f e c t o f Component Compression on the I n i t i a l Performance o f an I P V Nickel-Hydorgen C e l l

~~

7. Author@)

Randall F. Gahn

_- - --- 9 Performing Organization Name and Address

Nat iona l Aeronautics and Space Admin is t ra t ion Lewis Research Center Cleveland, Ohio 44135

2. Sponsoring Agency Name and Address

Nat iona l Aeronautics and Space Admin is t ra t ion Washington, D.C. 20546

-- __ _.___ 3. Recipient's Catalog No.

5. Rewrt Date

6. Performing Organization Code

506-41 -21 8. Performing Organization Report No.

E-3590 10. Work Unit No.

11. Contract or Grant No.

13. Type of Report and Period Covered

Technical Memorandum 14. Sponsoring Agency Code

5. Supplementary Notes

Prepared f o r t h e 22nd I n t e r s o c i e t y Energy Conversion Engineer ing Conference cosponsored by the A I A A , ANS, ASWE, SAE, IEEE, ACS, AIChE, Ph i lade lph ia , Pennsylvania, August 10-14, 1987.

6. Abstract

An exper imental method was developed f o r eva lua t i ng the e f f e c t o f component com- press ion on t h e charge and discharge vo l tage c h a r a c t e r i s t i c s o f a 3-1/2 In . dlam- e t e r b o i l e r p l a t e c e l l . A standard b o i l e r p l a t e pressure vessel was mod i f ied by the a d d i t i o n o f a mechanical feedthrough on t h e bottom o f t h e vessel which per- m i t t e d d i f f e r e n t compressions t o be app l i ed t o the components w i thou t d i s t u r b i n g the I n t e g r i t y o f the stack. Compression loadings f rom 0.94 t o 27.4 p s i were app l i ed by suspending weights f rom the feedthrough rod. C e l l vo l tages were meas- ured f o r 0.96-C, 55-min charge and f o r 1.37-C, 35-min and 2-C, 24-min discharges. An i n i t i a l change i n vo l tage performance on bo th charge and d ischarge as t h e load ing Increased was a t t r i b u t e d t o seat ing o f t he components. Subsequent v a r l - a t i o n o f t he compression from 2.97 t o 27.4 p s i caused on ly minor changes i n e i t h e r the charge o r t h e discharge vol tages. Several one month open-c i r cu i t vo l tage stands and 1100 cyc les under LEO cond i t i ons a t t h e maximum load ing have produced no change i n performance.

B a t t e r i e s N1 cke l -hydrogen ba t te r1 es Energy s torage

U n c l a s s i f i e d - u n l i m i t e d STAR Category 44

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