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COMMON - PRESSURE-VESSEL NICKEL-HYDROGEN
BATTERY DEVELOPMENT
Burton M. Otzinger
Rockwell Internatinal
Space Systems Division
Seal Beach, CA
and
James R. Wheeler
Eagle-Picher Industries
Joplin, MO
Introduction
Abstract
The dual-cell, common-pressurevessel, nickel-hydrogen configuration
has recently emerged as an option for
small satellite nickel-hydrogen battery
application. An important incentive is
that the dual-cell, CPV configured
battery presents a 30 percent
reduction in volume and nearly 50
percent reduction in mounting
footprint, when compared with an
equivalent battery of individualpressure-vessel (IPV) cells. In
addition energy density and cost
benefits are significant. Eagle-Picher
Industries and Rockwell International
have collaborated on the
development and test evaluation of a
40 Ampere-hour, nickel-hydrogen,
dual-cell, CPV battery module. The
module was committed to a cycle life
test in Rockwell's advanced battery
test facility. Performance and cycle
life data for this first proof-of-concept
module, collected over more than 6
years and 15,000 cycles of testing is
presented.
A two-cell, series-connected,
common-pressure-vessel (CPV)
battery has been successfully
designed, produced, and tested in a
joint effort by Rockwell and EaglePicher. The prototype unit is of 40
Ampere-hour size. In comparison
with two 40 Ampere-hour individual
pressure vessel (IPV) cells to which it
is equivalent in power, it offers a 19pe~eMimprovemeMinene~y
density. Perhaps more significantly.
the CPV module offers a 30-percent
reduction in volume and a nearly 50percent reduction in the battery
mounting footprint on the thermal
radiator of a communications satellite.
This smaller footprint may be of
particular advantage for those
applications requiring smaller
capacity batteries (5 to 25 Amperehour) with a limited thermal radiator
area.
A physical description of the prototype
module is provided in Table 1. Note
that the energy density is particularly
good at 61.8 Watt-hours per kilogram.
A summary of Rockwell's efforts in the
development of the CPV concept is
given in Table 2.
Development History
A common-pressure-vessel
configuration in nickel-hydrogen
batteries consists of two or more
series-connected cells in a singlepressure vessel, where the available
hydrogen gas is common to all the
cells. The electrolyte of each cell
must, however, remain isolated from
the other cells to prevent shorting or
open-circuit dry out due to vapor
transfer and/or electrolyte
redistribution.
Prototype Development
By using proven production
technology from IPV programs, EaglePicher constructed a 40 Ampere-hour,
proof-of-concept dual-cell module and
delivered it to Rockwell in June 1984
as part of a joint proprietary
development effort. This battery
module was then committed to a
modified low-earth-orbit (LEO) life
cycle test, at approximately 45%
depth-of-discharge. The battery
module is still performing well as of
August 1, 1991 with over 15,280
cycles completed. There has been no
evidence of electrolyte problems nor
any significant voltage degradation
noted.
Early appreciation for the problems
and advantages of the CPV
configuration was acquired by
building and testing a four-cell CPV
boilerplate unit in 1978. Rockwell
reported the apparent feasibility of the
technology and problems needing
resolution to the Goddard Space
Flight Center battery workshop that
year.
Prototype Test Details
Feasibility of the CPV concept was
further confirmed by EIC Laboratories
between July 1979 and February
1982 under a contract with Air Force
Wright Aeronautical Laboratory
(AFWAL). Work on a CPV
development program by Hughes
under an AFWAL contract was
redirected in Late 1982 to larger IPV
cell development because "larger IPV
cells represented a nearer-term
technology with fewer development
risks and costs involved."
The performance of the prototype
module during its initial acceptance
tests is tabulated in Table 3. These
tests included a capacity retention
cycle during which the capacity was
measured after the module was left
fully charged on open circuit for 72
hours. The results of this test were
equivalent to those for flight-quality
IPV·s.
The module has continued to perform
well during life-cycle testing. Capacity
retention results have ranged from 80
to 88 percent, (Table 4). The capacity
has been measured occasionally
during the life test and has increased
and then decreased somewhat.
However, the latest capacity to 2.0 volt
cut-off is still excellent at 48.7
Ampere-hours, somewhat greater
than the initial acceptance test value.
In FY 1983 Rockwell concluded that a
series-connected, two-cell CPV could
be constructed in a tandem
arrangement on either side of a nearly
solid weld ring (with one bus-bar
aperture) to form a module with all of
the multicell advantages and virtually
none of the problems.
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The capacity trend data are displayed
in Table 5.
As a follow-on to the proof-of concept
module, Eagle-Picher delivered four
flight-quality modules to Rockwell.
These embody zirconium-oxide
separators and high-porosity nickel
electrodes. The specification sheet
for this design is provided in Table 6.
The initial test results appear to
confirm those from the prototype.
The life-cycle testing is, at this writing,
in excess of 15,280 cycles. A typical
capacity verification cycle (Le.,
temperature, voltage, etc.) is shown in
Figures 1 and 2 (charge and
discharge, respectively). These data
are for cycle No. 15,200.
Conclusjons
The difficulties in developing the
nickel-hydrogen, dual cell, commonpressure-vessel concept are less
severe than had at first been feared.
Excellent results have been obtained
with no apparent problems in internal
shorting or electrolyte imbalance.
The concept provides definite,
measurable benefits in energy
density. When used in a larger
battery, the two-cell CPV will result in
lower voltage drop because the
internal connection between the two
cells of each module are shorter than
if the pressure vessels were separate,
and because only half the number of
external connections are required.
But more importantly, only half the
number of thermal mounting sleeves
are required.
The dual-cell CPV concept embodied
here entails minimum risk because
almost all the technology is flight
proven. The same concepts that
appear to offer improvement to the
standard IPV design can be equally
applied to the CPV module. These
include fiber-mat nickel plates,
reduced platinum catalyst electrodes,
and alternative separator designs.
One area that does need more study
is the effect of variations in the thermal
environment in the CPV vis-a-vis the
IPV design.
3
TABLE 1. 40 Ahr PROTOTYPE CPV MODULE PHYSICAL DESCRIPTION
TWO 40 Ahr STACKS IN SERIES
BACK TO BACK
ASBESTOS
9.00 IN
1,849.6 g
61.8 W-hr/kg (28.0 W-hr/lb)
950 psig
DESIGN
PLATE SEQUENCE
SEPARATOR
PV LENGTH
WEIGHT
ENERGY DENSITY
OPERATING PRESSURE
TABLE 2. ROCKWELL CPF NICKEL-HYDROGEN TECHNOLOGY EFFORT
1975
Nickel-hydrogen technology search
Report SD75-SA-Q171
1976-77
Two IPV cells and a dual cell CPV module
evaluated
Reported in IR&D
1978
Four-cell CPV bOilerplate tested to
synchronous eclipse season parameters
Paper presented at GSFC battery
workshop
1979-1980
Two AFWAL-furnished 50 Ahr cells
characterized
Paper presented at IECEC 1980
1981-1982
AFWAL cells evaluatedj CPV battery sized for
SC-90 study
Reported in IR&D brochure-results
in 1982. Project 394
1983
Advantages of dual cell, CPV, configuration-for
GPS noted in battery options study
Reported in IR&D brochure-results
in Project 285
1984-1991
Accelerated cycle life evaluation test
continuing on a dual cell, CPV module
Reported in IR&D brochure-results
in 1984. 1991 more than 15,000
charge/discharge cycles
completed
TABLE 3. 40 Ahr PROTOTYPE CPV MODULE ACCEPTANCE DATA SUMMARY
Capacity
CHARGE TIME (HR)
CHARGE RATE (AMPS)
EOCVOLTS
EOC PRESSURE (PSIG)
DISCHARGE RATE (AMPS)
CAPACITY TO 2.0 VOLTS (Ahr)
Overcharge
Charge
Retentlon*
2.O.::.c
lIr:C
~
lIr:C
lIr:C
16
4.0
2,982
1,020
20.0
41.7
16
4.0
3,027
1,050
17.92
45.4
16
4.0
3,118
1,110
17.92
47.2
72
2.0
3,013
1,160
17.92
53.8
16
4.0
3,032
1,090
17.92
36.6
*CELL ALLOWED TO STAND OPEN CIRCUIT FOR 72 HOURS BEFORE DISCHARGING
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TABLE 4. CAPACITY RETENTION RESLILTS FOR 40 Ahr PROTOTYPE CPV MODULE
DATE
MONTH/YEAR
6-84
8-87
10-87
4-89
6-89
12-89
7-91
CYCLE NO.
INITIAL
CAPACITY
AFTER 72-HR
STAND
RETAINED
EPI ACCEPTANCE TEST
8,201
8,303
9,592
10,003
11,546
13,425
45.4
54.7
54.5
46.1
47.3
45.6
41.7
36.6
46.3
48.2
39.7
40.4
39.2
35.5
CAPACITY
RETAINED TEMPERATURE
(OC)
(%)
10.0
10.0
5.0
12.5
10.0
8.6
9.7
80.4
84.7
88.4
86.1
85.4
86.0
85.1
TABLE 5. CAPACITY TREND DATA FOR 40 Ahr PROTOTYPE CPV MODULE
DATE
MONTH/YEAR
8-84
8-85
11-85
3-86
6-86
9-86
11-86
12-86
4-87
8-87
4-88
4-89
6-89
7-90
6-91
CYCLE NO.
DISCHARGE
CAPACITY
(Ahr)
TEMPERATURE
(OC)
EPI ACCEPTANCE TEST
4
1,215
2,414
3,244
4.038
4,811
5,004
6,016
6,208
6,459
9,591
10,003
13,428
15,266
45.4
44.8
44.5
47.5
48.4
50.5
50.7
51.6
48.7
55.6
48.3
46.1
47.3
46.2
48.7
10.0
11.4
11.3
9.6
10.6
11.4
10.4
14.6
9.3
7.6
20.3
12.5
10.0
11.9
7.9
5
TABLE 6. 40 Ahr FLIGHT QUALITY CPV MODULE SPECIFICATION SHEET
PART NO.
EAGLE-PICHER IND. RNH-40.3
CONFIGURATION
TWO TANDEM, SERIES-CONNECTED CEllS IN A COMMON 3.5 IN.
DIAMETER INCONEl PRESSURE VESSEL WITH HEMISPHERICAL ENDS;
PLATE STACKING IS BACK-TO-BACK
SEPARATOR
POSITIVE PLATES
DESIGN PRESSURE
ELECTROLYTE ISOLATION
CAPACITY
NOMINAL MIDVOlTAGE
PRESSURE SENSOR
WAll GAP
NEGATIVE PLATES
ELECTROLYTE
ZIRCONIUM-OXIDE CLOTH, DOU BlE lAYER
82% POROUS SLURRY NICKEL
900 PSIG (MAXIMUM: 1,000 PSIG)
CLOSED-WEB WELD RING, TEFLON-COATED INTERNALS
40 Ahr AT 10°C TO 2.0 VOLTS AT THE C/2 (20 AMP) RATE
2.5 VOLTS
STRAIN GAGE
0.80 in.
PlATINUMITEFlON CATALYST OVER PATENTED NICKEL GRID GEOMETRY
26% KOH IN H2 0
SIZE
• MAXIMUM lENGTH:
• DIAMETER:
• MASS:
6
13.0 in .
3.520 in.
1,980 g
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30.0
3.4
1,000
CYCLE 15266
CHARGE RATE: 4 Amps
3.3
900
.
3.2
C)
'in
c.
UJ
a:
BOO
700
600
::::)
en
en
500
UJ
~
en
3.0
0
2.9
~
-0
UJ
.-cs:
::::)
••
...d
2.7
2.6
300
25.0
a:
>
>
Il.. 2.B
400
~
. . ·0 .. . "
20.0
0
a:
Il..
•• ••
3.1
•• ••
.D
•
2.5
•••
•••
•
•.[J
a:
UJ
Il..
:iE
.-UJ
•
10.0
>
Il..
0
200
5.0
2.4
100
2.3
0
2.2
0.0
2.0
4.0
B.O
6.0
10.0
12.0
14.0
0.0
16.0
TIME (hr)
Ni H2 CPV CHARGE
FIGURE 1.
30.0
3.2
1,000
CYCLE 15266
DISCHARGE RATE: 20 Amps
3.1
900
3.0
.~
I/)
2.9
700
S:
UJ
a:
600
en
en
UJ
500
::::)
>
0
en
2.B
0
2.7
~
,
25.0
,,
0
400
300
a:
.-cs:
>
>
Il.. 2.6
15.0
a:
UJ
Il..
:iE
.-UJ
2.5
10.0
2.4
23
o DISCHARGE VOLTAGE
l:1 TEMPERATURE
2.2
0
UJ
::::)
200
100
-0
20.0
0
a:
Il..
'0
BOO
5.0
o CPV PRESSURE
2.1
0.0
2.0
0.0
0.5
1.0
1.5
TIME (hr)
FIGURE 2.
Ni H2 CPV DISCHARGE
7
2.0
2.5
>
Il..
0
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