The use of the lightweight nickel electrode, in place of the heavy-sintered state-of-the-art nickel electrode, will lead to improvements in specific energy and performance of the nickel-hydrogen cell. Preliminary testing indicates that a nickel fiber mat is a promising support candidate for the nickel hydroxide active material. Nickel electrodes made from fiber mats, with nickel and cobalt powder added to the fiber, were tested at LeRC. To date, over 8000 cycles have been accumulated, at 40 percent depth-of-discharge, using the lightweight fiber electrode, in a boiler plate nickel-hydrogen cell

Britton, Doris L.

English

NASA Technical Reports Server

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NASA Technical Memorandum 105638
_ _/__._
" Progress in the Development of
•- -- _:_Lightweight Nickel Electrode
Doris L. Britton
Lewis Research Center
Cleveland, Ohio
Prepared for the
35th International Power Sources Symposium
sponsored by the Institute of Electrical and Electronics Engineers
Industry Application Society
Cherry Hill, New Jersey, June 22-25,1992
(NASA-T_-lO563d) PROGRFSS
GEVELOPMENT OF LIGHT,FIGHT
(NASA) 8 p
IN THE
NICKEL ELECTRODE
N92-26670
Unclas
G3/25 0099212
https://ntrs.nasa.gov/search.jsp?R=19920017427 2020-03-17T11:05:05+00:00Z
significant decrease in total capacity of the Fibrex nickel electrode was observed with long term cycling but
rather a decrease in the high rate discharge capacity (refs. 2 to 5). The Fibrex nickel electrode also has an
advantage over the SOA nickel electrode due to its pore size distribution. The shift to smaller pores and
increase in the volume requirements of the SOA electrode during cycling will result in the electrode having a
greater affinity for the electrolyte. This effect can dry the separator and will lead to a high separator resistance.
This traditional increase in small pores of the cycled SOA nickel electrode is not found in the Fibrex electrode.
In addition to a two-fold increase in volume of the micropores of the cycled Fibrex electrode, the volume of the
larger pores (over 9 lam) increases two to four times as shown in figure 1 (refs. 3 to 5). This pore size distri-
bution of the Fibrex nickel electrode should improve the electrolyte management of the Ni-H 2 cell. It has been
noted that electrolyte management can have a significant effect on the cycle life and performance of the Ni-H 2
cell and should be one of the prime considerations in the overall design of the cell (ref. 6).
CELL DESCRIPTION
To verify the performance of lightweight nickel electrodes in b0iierplate hardware, a Ni-H 2 cell using a
Fibrex nickel electrode was assembled at NASA Lewis. The cycle test was conducted using a boilerplate cell
with a 5- by 5-cm active area. A sample of the cell components is shown in figure 2. It consists of a stack of
nickel electrodes, separator, hydrogen electrode, and gas screen. The nickel electrode is made from an 80-mil
thick, 90-percent porous Fibrex plaque loaded to 1.6 g/cm 3 void Volume. The separator consists of three layers
of 6-mil-thick beater-treated asbestos. The hydrogen electrode was made by Life Systems Incorporated which
consists of a mixture of platinum and Teflon applied to a gold plated nickel screen. The gas screen, located
behind the hydrogen electrode, is 60'mil-thick nickel Exmet which was compressed to 40 mil to fit into the cav-
ity designed for the hydrogen electrode and gas screen. An electrolyte reservoir plate (ERP), which is incor-
porated into the cell, is made of 125-mil-thick foam metal. The current collectors are gold plated nickel. A
graphlc representation of the unit Ceil Cross section is shown in figure 3. The components are assembled in a
stack, as shOwn in figure 4. After assembly, the entire stack is vacuum-filled with 26-percent KOH electrolyte.
The KOH electrolyte is allowed to stand in the stack overnight, then the excess electrolyte is drained out. The
stack is placed in the pressure vessel. The test chamber is evacuated and filled with hydrogen to 3.4 atm
(50 psi). The chamber is then connected to the test facility as shown in figure 5. The test facility consists of
independent cell test positions. Each test position consists of a charge/discharge controller, a dc power supply
and an ampere-hour meter. A Modicon 884 programmable controller controls the timing for the cycle tests.
The data-acquisition system is handled by an Escort 2 system developed at NASA Lewis. Current, voltage, and
the time are recorded for each cell. The Escort 2 system scans the data every 18 sec. The charge and discharge
ampere-hours and watt-hours are calculated from current and time on every scan. The pressure is measured
using a strain gauge located on the cell dome. The charge-to-discharge ratio (ampere-hours in on charge to
ampere-hours out on discharge) is calculated from the capacities. Every 60 sec, the data is saved and stored to
a data collector. The data can be retrieved for data and graphical output.
CELL TESTING
The general procedure for testing the Ni-H 2 boilerplate cell, using Fibrex nickel electrode, consists of ini-
tial characterization testing; continuous 90-min life cycle testing; final characterization testing; and failure
analysis.
_2 _
Initial Characterization Testing
Initial characterization testing of the Ni-H 2 cell, conducted before the life cycle test, consists of capacity
measurements at various charge and discharge rates to evaluate the effects of these rates on the cell capacity.
For the charge rate effect, the cell is charged at ClIO rate for 18 hr, C/2 rate for 160 min, or C rate for 80 min,
respectively, followed by discharge at C/2 to 0.5 V. For the discharge rate effects, the cell is charged at C/2
rate for 160 min followed by discharge at C/5, C/2, C, or 1.37C rates, respectively, to 0.5 V.
Continuous Cycle Testing
After the initial characterization test, the boilerplate cell is life cycle tested using a 90-min cycle regime
at 40-percent DOD. The continuous test regime consists of charging to a constant 0.48C rate for 55 min
immediately followed by discharge at a constant 0.69C rate for 35 min. Cell capacities are measured, every
1000 cycles, by charging at the C rate for 80 min followed by discharging at the 0.69C rate to 0.5 V. Failure
of the cell will occur when the discharge voltage degrades to 0.5 V during the course of the constant current
35-min discharge at the 0.69C rate.
Initial results of the lightweight Ni-H 2 cell testing are very encouraging. The cell has been cycling for
over 8000 cycles, as shown in figure 6, with an acceptable performance. Utilization is calculated by using the
ratio of the measured capacity to the theoretical capacity. The effect of cycling on the end of charge and dis-
charge voltages for the lightweight Ni-H 2 are shown in figure 7. An average end-of-discharge voltage of about
1.16 V is observed for the first 1000 cycles. The average end of discharge voltage dropped to about 1.10 V
after 7000 cycles. The end of charge voltage remained stable at about 1.54 V. The cycle testing will continue
until the end of discharge voltage reaches 0.5 V.
Final Characterization Testing
Final characterization testing will be conducted after the cell fails. Capacity measurements, similar to ini-
tial characterization testing, will be performed. Results of the cycled and uncycled cell capacity, measured at
different rates, will be compared.
Failure Analysis
Post-test cell teardown and failure analysis will be conducted to evaluate the cause for failure. Failure
analysis will consist of the following:
(1) Visual inspection of the stack components (e.g., electrodes and electrolyte);
(2) Flooded capacity measurements of the uncycled and cycled Fibrex electrode;
(3) Weight loss and electrode expansion of the cycled electrodes;
(4) Pore size distribution of the uncycled and cycled electrode using the mercury intrusion porosimeter
method;
(5) Electrolyte distribution between the nickel electrode, hydrogen electrode, and separator;
(6) Scanning electron micrographs.
CONCLUSION
Thedevelopmentandcyclelife testingof theFibrexnickelelectrodehasdemonstratedthefeasibilityof
an improvednickelelectrodegivingahigherspecificenergyNi-H2cell. Studiesindicatea48-percentimprove-
mentin weightfor thefibrousnickelelectrodeovertheSOAsinteredelectrode.
Fromtheseinvestigations,it canbeconcludedthattheFibrexnickelelectrodeisanattractiveelectrode
candidatefor a lightweightNi-H2cell. Earlycyclelife testingof a Ni-H2cell usingan80-mil-thick,90-percent
porousFibrexnickelelectrodehasshownpromisingresultswhencycledat 40-percentDOD. To date,over
8000cycleshavebeenaccumulated.
REFERENCES
1.Colucci,S.L.: Systemfor StretchCasting Filamentary Shaped Bodies. U.S. Patent 4,312,670, 1982.
2. Britton, D.L.: Electrochemical Impregnation and Cycle Life of Lightweight Nickel Electrodes for Nickel-
Hydrogen Cells. Proceedings of the 34th International Power Sources Symposium, IEEE, New York,
pp. 235-238, 1990 (also, NASA TM-103140, 1990).
3. Britton, D.L.: Performance of Lightweight Nickel Electrodes. International Power Sources Symposium,
33rd; Proceedings, Electrochemical Soc., Inc., Pennington, NJ, pp. 467-445, 1988 (also, NASA
TM- 100958, 1988).
4. Britton, D.L.: Lightweight Fibrous Nickel Electrodes for Nickel-Hydrogen Batteries. NASA TM-101997,
1989.
5. Britton, D.L.: Characterization and Cycle Tests of Lightweight Nickel Electrodes. Proceedings of the
Symposium on Nickel Hydroxide Electrodes, The Electrochemical Society, Inc., Pennington, NJ,
pp. 233-246, 1990 (also, NASA TM-102399, 1989).
6. Thaller, L.H.; Manzo, M.A.; and Sanabria, O.D.: Design Principles for Nickel-Hydrogen Cells and Batteries.
Intersociety Energy Conversion Engineering Conference (IECEC), 20th; Proceedings, Vol. 1, SAE,
Warrendale, PA, pp. 1.145 - 1.150, 1985 (also, NASA TM-87037, 1985).
SOA
Fibrex
TABLE [--CALCULATED SPECIFIC ENERGY OF A 48-AH NICKEL-
HYDROGEN CELL USING NICKEL ELECTRODES WITH
DIFFERENT THICKNESSES, POROSITIES,
AND LOADING LEVELS
Thickness Porosity
30 85
30 85
30 85
30 9O
30 90
30 93
30 93
80 90
80 90
Loading
level
1.6
1.8
1.6
1.6
1.8
1.6
1.8
1.6
1.8
Specific Relative
energy specific
energy
56.56 1.00
60.49 1.07
61.44 1.09
66.40 1.17
68.29 1.21
67.73 1,20
73.06 1.29
76.72 1.36
83.88 1.48
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SOA ELECTRODE
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PORE DIAMETER, um
Figure 1.--Pore size distribution curves of Fibrex and SOA
nickel electrodes.
C-86-1714
Figure 2.-- Components of the nickel-hydrogen cell,
CURRENT COLLECTOR
GAS SCREEN
HOUSING
HYDROGEN ELECTI_ODE
SEPARATOR
NICKEL ELECTROOE
ELECTROLYTE RESERVOIR PLATE (ERP]
CURRENT COLLECTOR
Figure 3.-- Cross-sectional unit of the nickel-hydrogen cell. Figure 4.-- Components of the nickel-hydrogen cell assembled
in a stack with the pressure vessel.
ORIGINAL PAGE
BLACK AND WHITE PHOTOGRA[_I_
ORIGINAL PAGE
BLACK AND WHITE PHOTOGRAP_
Figure 5.-- Nickel-hydrogen cell test facility.
120
(:3
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::3
I00
80
60 40_ DOD
1.6 g/co void loading
40 , I , I , I , I
0 2000 4000 6000 8000
NUMBER OF CYCLES
Figure 6.-- Utilization versus number of cycles of a nickel-
hydrogen cell using a Flbrex nickel electrode.
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CHARGE
D ISCHAI:IGE
2000 =4o'0o 60'o0 8ooo
..... ' - " --'__BER or- CYCLES
Figure 7.-- End of charge and discharge voltages versus number
of cycles for nickel-hydrogen cell using a FIbrex nickel electrode.
6
REPORT DOCUMENTATION PAGE FormApproved
OMB No. 0704-0188
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1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE
June 1992
4. TITLE AND SUBTITLE
Progress in the Development of Lightweight Nickel Electrode
6. AUTHOR(S)
Doris L. Britton
7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio 44135-3191
9. SPONSORING/MONITORING AGENCY NAMES(S) AND ADDRESS(ES)
National Aeronautics and Space Administration
Washington, D.C. 20546-0001
3. REPORT TYPE AND DATES COVEREDTechnical Memorandum
5. FUNDING NUMBERS
WU-506-41-21
8. PERFORMING ORGANIZATION
REPORT NUMBER
E-6984
10. SPONSORING/MONITORING
AGENCY REPORT NUMBER
NASA TM- 105638
11. SUPPLEMENTARY NOTES
Prepared for the 35th International Power Sources Symposium sponsored by the Institute of Electrical and Electronics
Engineers, Industry Application Society, Cherry Hill, New Jersey, June 22-25, 1992. Responsible person, Doris L.
Britton, (216) 433-5246.
12a. DISIH|BUTION/AVAILABILITY STATEMENT
Unclassified - Unlimited
Subject Category 25
12b. DISTRIBUTION CODE
13. ABSTRACT (Maximum 200 words) "'
The use of the lightweight nickel electrode, in place of the heavy-sintered state-of-the-art nickel electrode, will lead to
improvements in specific energy and performance of the nickel-hydrogen cell. Preliminary testing indicates that a
nickel fiber mat is a promising support candidate for the nickel hydroxide active material. Nickel electrodes made from
fiber mats, with nickel and cobalt powder added to the fiber, were tested at NASA Lewis Research Center. To date,
over 8000 cycles have been accumulated, at 40 percent depth-of-discharge, using the lightweight fiber electrode, in a
boiler plate nickel-hydrogen cell.
14. SUBJECT TERMS
Ni-H2; Lightweight; Specific energy; Nickel electrodes; Pore size; Boilerplate cell.
17. SECURITY CLASSIFICATION
OF REPORT
Unclassified
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18. SECURITY CLASSIFICATION
OF THIS PAGE
Unclassified
19. SECURITY CLASSIFICATION
OF ABSTRACT
Unclassified
15. NUMBER OF PAGES
8
16. PRICE CODE
A02
20. LIMITATION OF ABSTRACT
Standard Form 298 (Rev. 2-89)
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Progress in the development of lightweight nickel electrode

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