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i 93- 20520DEVELOPMENT OF FIRST GENERATION
AEROSPACE NiMH CELLS
Lawrence Tinker, Dan Dell
Tony Wu, Guy Rampel
Gates Aerospace Batteries
Gates Energy Products, Inc.
Presented at the 1992 NASA Battery Workshop
November 19, 1992
1992 NASA Aerospace Battery Workshop -617- Advanced Technologies Session
PRECEDING PPlGE E,LAt',_[K NOi iqLIvi_J
https://ntrs.nasa.gov/search.jsp?R=19930011331 2019-02-03T20:20:08+00:00Z
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Program Description
O Gates Energy Products involved in NiMH development since
1987
O GAB aerospace cell development program begun in 1990 in
conjunction with GEP
O Prismatic cell testing begun in 1991
O Initial work aimed at demonstrating feasibility and
identifying problem areas
O Recent work focused on improvements to alleviate
identified problems
Gates Aerospace Batteries in con-
junction with Gates Energy Products
has been developing NiMHtechnology
for aerospace use since 1990. GEP
undertook the development of NiMH
technology for commercial cell
applications in 1987. This program
focused on wound cell technology
for replacement of current NiCd
technology.
As an off shoot of this program
small wound cells were used to
evaluate initial design options for
aerospace prismatic cell designs.
Early in 1991, the first aerospace
prismatic cell designs were built
in a 6 Ah cell configuration.
These cells were used to initially
characterize performance in pris-
matic configurations and begin
early life cycle testing. Soon
after the 6 Ah cells were on test
several 22 Ah cells were built to test
other options. The results of testing
of these cells were used to identify
potential problem areas for long lived
cells and develop solutions to those
problems.
Following these two cell builds a set
of 7 Ah cells was built to evaluate
improvements to the technology. To
date results from these tests are very
promising. Cycle lives in excess of
2,200 LEO cycles at 50% DoD have been
achieved with cells continuing on
test.
Results from these cell tests are
discussed and data presented to demon-
strate feasibility of this technology
for aerospace programs.
Aerospace NiMH Cells Gates Aerospace Batteries
1992 NASA Aerospace Battery Workshop -618- Advanced Technologies Session
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Table I
NiMH Prismatic Cell Design Summary
Item 6 Ah 22 Ah 7 Ah
Positive Electrodes
Number .................. 14
Thickness (mm) ............. 0.71
Capacity (Ah) theoretical ........ 7.5
Negative ElectrodesNumber .................. 15
Thickness (mm) ............. 0.32
Capacity (Ah) .............. i1.5
15 14
0.71 0.71
27.6 9.31
16 15
0.32 0.32
42.2 14.4
separator
Type ............... Nylon-2538 Nylon-2538 Nylon-2538Others
Negative to Positive
Capacity Ratio (nominal) ........ 1.5 1.5 1.5
Electrolyte
Type .................. KOH
Concentration (%) ............. 31
KOH KOH
31 31
Cell Dimensions (mm)
Overall Height ............. 69.9
Case Height ............... 59.2Width .................. 53.8
Depth .................. 20.8
112.5 70.1
101.8 58.8
75.7 54.2
22.6 21.1
Table I summarizes the design pa-
rameters for the three types of
cells tested to date. The 6 Ah and22 Ah cell sizes were initial test
bed sizes and the 7 Ah size is
planned to be used for initial
qualification testing. The 6 Ahcells were used to test three con-
figurations of positive electrodes
with two separator types. The 22
Ah cells continued these tests in a
larger cell configuration to identify
any potential problems with scaling upof the cell size.
The initial baseline separator used
was nylon 2538 and the electrolyte 31%KOH. Cell dimensions are conventional
NiCd cell dimensions although forlower rated cells.
Aerospace NiMH Cells Gates Aerospace Batteries
1992 NASA Aerospace Battery Workshop -619- Advanced Technologies Session
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17
AEROSPACE 6 AH PRISMATIC CELL
CYCLE LIFE (EOCV_ : C/O = 1.05 ; 5(_ D0D 0 RT
1.6 -
1,4 -
4-.. 3,J.
1.3 - APE- IAP6,- ;2AD6- 3AP6-4AP6- 5AP6- 6
1.2 I 1 I0 6
AEPIO POS 1 SEP IAE_O POS I SEP 2AEP_) POS 2 SEP 1AERO POS 2 SEP 2AEI::IO I::E)S 3L; SEP IAEI:=IOPOS 3H; SED 1I I I !
2 4CThoulanc_)
CYCLE
Figure I Performance of 6 Ah Cells in Initial Configuration
Cycling of all cells included in
this paper was performed in a LEO
simulation regime using an integra-
tor controlled cycler. Each cell
is monitored using a FLUKE scanning
multimeter interfaced to a PC based
data collection system. Cell pres-
sures are monitored by direct read-
ing of gauges (Ashcroft AIS1) at-
tached to the cells. Pressure data
is manually entered into the cor-
rect data file.
This figure illustrates the EOCV per-
formance for the initial build of 6 Ah
NiMH prismatic cells. One cell of
this group provided greater than 6,000
LEO cycles at 50% DoD. Three primary
failure modes were observed in these
cells, end of charge pressure increas-
es, shorts, and declining EODV. These
cells included three types of positive
electrodes with one alloy type and two
separators.
Aerospace NiMH Cells Gates Aerospace Batteries
1992 NASA Aerospace Battery Workshop -620- Advanced Technologies Session
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1.4
AEROSPACE 6 AH PRISMATIC CELL
CYCLE LIFE (E-ODV'J : ClO = 1.05 ; 505; DOO 0
1.3 -
1.1 -
,5
I -
i
i A0. g -- AP_-2 : AEI:_O POS I SEP 2
AP6-3 : AEI:_O POS 2 SEP I
: AP6-4 : AER0 POS 2 SEP 2i APtS-5 : AE;:_O POS 3L,; 5EP I
I AP6-_ : AEl:lO POS 3H; SEP I
0,8 L l I 1 I I I
0 2 4 6CThousancte)CYCLE
Figure 2 EODV Performance for 6 Ah Cells in Initial Configuration
This figure illustrates the EODV by the substrate in use and this prob-
performance trend for the same lem has been corrected for future
cells identified in Figure i. As cells. Three cell configurations were
can be seen from the curves the terminated due to low EODV and high
earliest failures were at about EOCP and the last cell was terminated
3500 cycles due to shorts. These due to high EOCP (Figure 3).
shorts were identified to be caused
Aerospace NiMH Cells Gates Aerospace Batteries
1992 NASA Aerospace Battery Workshop -621- Advanced Technologies Session
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kJ
I.
150
AEROSPACE 6 AH PRISMATIC CELL
CYCLE LIFE (EOCI_ : C/O = 1.05 ; 50_ OOO O RT
I1413 -
130 -
120 -
110 -
100 -
90 -
80 -
70 -
60 -
50 -
40 -
30 -
20 -
10 -
oo
AP6- 1AP6- 2AP6- 3AP6-4APCl-AP6-6
4
I I I I2 4 6
CThousa nets)CYCLE
5
Figure 3 EOCP Performance of 6 Ah Cells in Initial Configuration
This figure shows the increase in
EOCP as a function of cycle life
for the initial 6 Ah cell configu-
rations. Initially, the recharge
ratio was 1.10 and the pressures
appeared to rise rapidly early in
life. The ratio was reduced to
1.05 at about 500 cycles and the
performance improved. However, the
cells exhibited a steady increase
in pressure with cycling that even-
tually led to termination of the
tests. The increase in pressure has
been attributed to a slow degradation
of the metal hydride alloy and low
negative to positive ratio in the
cells. These issues have been addres-
sed in recent cell designs and are
reflected in lower EOCP performance
with cycle life.
Aerospace NiMH Cells Gates Aerospace Batteries
1992 NASA Aerospace Battery Workshop -622- Advanced Technologies Session
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20
1.8
AEROSPACE 22 AH PRISMATIC CELL
CYCLE LI!=E (EODV'j : C/O = 1.05 ; 55 DO0 Q, RT
1,7 -
1.6 -
1.5 -
1,4 -
1.3 -
I.;2 -
1.1 - _ ..... -"- !
1.0 -
0.9 -
0.8 -
0.2 -
0.G -
0.5 -
0.4 -
0.3 -
0,2 - AP22-1 : AERO POS 2; 5EP 1
0. I - ,aJ:)22-'_ : AERO PO5 2.; SEP "1
0.0 I I I X l0 1 2
CThousonds)CYCLE
z
1
I I I
3 4
Figure 4 EODV Performance for 22 Ah CelZs
The second set of test cells eval-
uated were 22 Ah cells. These
cells were built in 15 Ah equiva-
lent NiCd cases using one type of
alloy and one type of positive and
separator. This figure illustrates
the EODV performance for the cells
in 50% DoD LEO cycling. As can be
seen from the curves the voltage was
stable at about i.i0 V over the cycle
life with minor dispersion appearing
at about 3600 cycles and continuing
until termination of the test.
Aerospace NiMH Cells Gates Aerospace Batteries
1992 NASA Aerospace Battery Workshop -623- Advanced Technologies Session
Page 8
17
AEROSPACE 22 AH PRISMATIC CELL
CYCLE LIFE (E-OCV') : C/O = 1.05 ; 50% OOO 0 RT
1.6 -
I .4 -
1.3 -
£
/I,1:'22-1 : AERO POS 2; SEP IAP22-2. : AERO POS 2_ SEP "1
1.2 I I I I I0 I 2
CThousen<:_)CYCLE
I I I I
3 4
Figure 5 EOCV Performance for 22 Ah Cells
Shown here is the EOCV performance
for the 22 Ah cells tested. The
data shows an increasing trend over
the 4,236 cycles tested. This
trend is not desirable for long
cycle life. Improvement of the EOCV
trend was one of the primary issues
addressed in subsequent cell designs
that are being tested.
Aerospace RiHH Cells Gates Aerospace Batteries
1992 NASA Aerospace Battery Workshop -624- Advanced Technologies Session
Page 9
v
W
_sn
AEROSPACE 22 AH PRISMATIC CELL
CYCLE LIFE (EOCP_ : C/D = 1.05 ; 50_ 13OO • RT
140 -
130 -
1 _ 0 I
110
9o
Bo
7o
so
50
4o
30
2O
lO
0 I I ! I
3 4
Figure 6 EOCP Performance for 22 Ah Cells
This figure illustrates the EOCP
performance for the 22 Ah cells.
The trend of increasing EOCP has
been the limiting factor in the
testing of these cells. Although
there have been increases observed
in the EOCV the primary reason for
termination of the testing of these
cells was EOCP. The changes have been
attributed to the slow degradation of
the alloy being tested combined with
a low negative to positive ratio.
Aerospace NiMH Cells Gates Aerospace Batteries
1992 NASA Aerospace Battery Workshop -625- Advanced Technologies Session
Page 10
Table II
7 Ah NiMH Capacity Performance
Cell Type
AP7-5
Discharge Mid-Point Capacity
Rate Voltage Ah
C/2 1.201 7.47
C 1.133 6.04
Alloy Sep
MH-2 Sep 1
AP7-6 C/2 1.198 7.33
C 1.131 5.75
MH-2 Sep 2
AP7-7 C/2 1.199 7.25
C 1.132 5.62
MH-2 Sep 2
AP7-8 C/2 1.209 7.34
C 1.149 6.62
MH-2 Sep 3
AP7-9 C/2 1.202 7.31
C 1.135 5.91
MH-2 Sep 3
This table illustrates the capacity
performance of the 7 Ah cells in
initial testing. All tests were
performed at room temperature.
Mid-point Voltages were similar at
both the C/2 and C rate with the
best performance seen in the AP7-8
cell configuration.
Capacity delivery was similar also
with the best C/2 performance seen inthe AP7-5 cell and the best C rate
capacity in the AP7-8 cell. All cells
tested were from one alloy of the AB 2type. The AP7-6,7 cells are the same
configuration and the AP7-8,9 cells
are of the same configuration.
Aerospace NiMH Cells Gates Aerospace Batteries
1992 NASA Aerospace Battery Workshop -626- Advanced Technologies Session
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AEROSPACE 7 AH PRISMATIC CELL
CYCLE LIFE CEOCV'_ : C/D==I,OS .; 50% DOD @ PrF
.J
g
1,6 -
1,5 -
"I .4 -
1.3 -
1,20
APT-1 MH1 _ SEP IAPT-5 MH2 NEG SEP IAP7-6 MH2 NE'G SEP 2APT-7 MH2 NE-G SEP 2Ap7-e MH2NEG sEP 3APT-p : M_2 NEq ; SE_ 3
0.4 0.8
I I 1 i I I I I1.2 1.6 2 2.4
C Thousa ncl_OCYCLE
Figure 7 EOCV Performance for 7 Ah Prototype Cells
The 7 Ah cells described in Table
II plus one similar cell with alloy
type MH-I were placed in LEO life
cycle testing at 50% DoD at room
temperature. This figure illus-
trates the EOCV performance of
these cells with cycle life. In
general the voltage has been steady
with a very slight increase shown
for all cells. Within similar cell
configurations the EOCV is tracking
well except for the AP7-8,9 config-
urations. These two cells have dif-
ferent electrolyte levels and this is
believed to be the cause of the dif-
ference. The overall spread across
all of the cells is about 0.030 V.
Aerospace NiMH Cells Gates Aerospace Batteries
1992 NASA Aerospace Battery Workshop -627- Advanced Technologies Session
Page 12
20
18
q 7
1.8
1.5
1.,4
1.3
q.2.
1.1
1.0
0.9
0.8
0.7
0.8
0.5
0.4
0,3
0.2
0,1
0.0
AEROSPACE 7 AH PRISMATIC CELL
CYCLE LII:E CEODV"J : CJD=I.05 ; 50_ _O @
MHq NEG ; SEP 1MH2 NEG ; SEP IMH2 NEG ; SEP 2
MH2 NEG i SEP 2MH2 NEG SEP 3MH2 NEG 5EP 3
0.4 0,8 1,2
CThousancls)CYCLE
Figure 8 EODV Performance for 7 Ah Prototype Cells
This figure illustrates the EODVperformance with cycle life for the
7 Ah cells. The voltage has re-
mained steady over the cycle life
to date with only a slight disper-sion between cells. The C/D ratio
has been maintained at 1.05 during
the tests and this has maintained the
EODV. The EODV is at 1.06 V for the
lowest cell and 1.12 for the highest
cell. The performance is similar tothat seen in the 6 Ah and 22 Ah cell
designs to this point in cycling.
Aerospace NiMH Cells Gates Aerospace Batteries
1992 NASA Aerospace Battery Workshop -628- Advanced Technologies Session
Page 13
J
20
1.9
1.8
1.7
1.6
1.4
1.3
1.1
0.9
0.8
0.7
0.6
0,_
0.:3
0.2
0,1
0.0
AEROSPACE 7 AH PRISMATIC CELL
CYCLE L II:E (:MI_ : C/O=1.05 : 50_i DOO D Rlr
Figure 9 Hid-Point Yoltage Performance for 7 Ah Prototype Cells
This figure illustrate the mid-
point voltage trend over the cycles
completed to date. This voltage is
measured at the equivalent of 25%
DoD during the discharge. The MPV
is currently at 1.14 V for the worst
cell and at 1.21 V for the best cell.
Within each cell configuration the
performance is similar.
Aerospace NiMH Cells Gates Aerospace Batteries
1992 NASA Aerospace Battery Workshop -629- Advanced Technologies Session
Page 14
G
W
150
AEROSPACE 7 AH PRISMATIC CELL
CYCLE LIFE (EQCP"j : C/O =1.05 .: 5E_; DC_ @ I::IT
140 -
130
120
11o
1oo
9o
Bo
70
60
50
40
30
20
10
0
. AP7- 6:MH2 N_ ; SEP 2
AP7-7:&,IN2 NEG _ SEP 2 _ _.I_APT-B: MH2 NEG { SEP 3 _ _
- APT-9:Vii}i,iE__ ._Eh_ 5
0 0,4 0.8 1.2 1,6 2 2.4Crhousanc_)
CYCLES
Figure 10 EOCP Performance for 7 Ah Prototype Cells
Increase in pressure with cycle
life has been the primary reason
for termination of testing on ear-
lier cell configurations. This
figure shows the EOCP for all of
the 7 Ah cells on test. The data
trend shows that the pressure is
below 20 psig in all cells except
for the one with alloy MH-I. Cells
AP7-1 and AP7-5 are showing steady
increases with life, however, the four
remaining cells are maintaining level
performance at less than i0 psig. The
6 Ah and 22 AH cells were showing 20
to 70 psig (Figures 3 and 6), at this
point in life. The improvement is
very encouraging and is a result of
design adjustments made to improve the
response over time.
Aerospace NiMH Cells Gates Aerospace Batteries
1992 NASA Aerospace Battery Workshop -630- Advanced Technologies Session
Page 15
16
AEROSPACE -2 AH PIqlSMATIC CELL
CHARGE (CYCLE #f1850"J @ 3. 635 An_, flHR
1.4 -
13 -
1.2 -
z/±,5c,"_
q
AP'}-"I: MH'I NF=_ ; SEP IAPT-5_ MH2 NEG ._ 5EP "IAlaT-6:MH2 NEG ; 5EP 2APT-7:MH2 NEG _ SEP 2AP7-8:MH2 NEG .; SEP 3
APT-9:MH2 NEG _ 5EP 31.1 I - I I 1 I I I
0.0 1.0 2.0 3.0 4.0
C.AF_C I "r¥ £A_0
Figure 11 Charge Voltage Profile for 7 Ah Prototype Cells, Cycle 1,850
This figure shows the charge volt-
age profile for cycle number 1,850.
The voltage ranges from 1.47 to
1.49 V at EOC. The curve is rela-
tively smooth and increasing with
time and has a slight upturn at the
end of charge. This curve is similar
to those seen for NiCd cells under
similar test conditions and is further
evidence of the ability of the NiMH
system to replace NiCd cells.
Aerospace NiMH Cells Gates Aerospace Batteries
1992 NASA Aerospace Battery Workshop -631- Advanced Technologies Session
Page 16
2.0
1.9
1.8
1.7
1.6
1.5
1,4
1.3
1.2
1.1
1,0
0.9
0.8
0.7
06
0.5
0.4
0.3
0.2
0,1
0,0
AEROSPACE 7 AH PRISMATIC CELL
OlSCI.4ARGE (CYCLE #1850] @ 7.00 ArnD, 30 MIN
Figure 12 Discharge Voltage Profile for 7 Ah Prototype Cells, Cycle 1,850
This figure shows the corresponding
discharge voltage profiles for
cycle 1,850 for all cells in test.
The curves are relatively flat with
mid-point voltages of 1.16 to 1.21
V. The EODV ranges from 1.09 to
1.14 V. The highest discharge volt-
ages are seen with the AP7-8 and AP7-9
cell configurations. Again, this data
is very similar to that seen for NiCd
cells of similar design.
Aerospace NiMH Cells Gates Aerospace Batteries
1992 NASA Aerospace Battery Workshop -632- Advanced Technologies Session
Page 17
AEROSPACE 2 AH PRISMATIC CELL
NIMH LEO C5(_ 1900; CJO=I.0S'J CYCLING 0 R'I"1,7
1.8 -
1.5 HARGE : 60 MIN 0 CJ2 RATE
1.4
1.3
1.2
IoO
DISCHARGE: 30 MIN II C PATE
1.1 - I CYCLE 100
1.0 - I CYCLE 1000
CYCLE 2000
0,9 i I0.0 20.0
_-IOO O
I I I I I I I I
40,0 60.0 80.0 100.0
TIIvE_ CMIN)
Figure 13Cells
Charge�Discharge Voltage Profile Over Life for 7 Ah Prototype
This figure illustrates the change
in voltage profile for one cell
during a single cycle at three
points in cycle life, i00, 1,000
and 2,000 cycles. These curves areshown to illustrate the stability
of the cells during cycle life
testing. There is very little change
observed relative to the shape of the
curve or the voltages obtained. At
the 2,000 cycle point there has onlybeen a 0.020 V increase in EOCV and a
0.010 V decrease in EODV.
Aerospace NiMH Cells Gates Aerospace Batteries
1992 NASA Aerospace Battery Workshop -633- Advanced Technologies Session
Page 18
t2
W
D_9
150
140
13O
120
110
100
9O
80
70
60
5O
40
3O
2O
I0
0
AEROSPACE 7 AH I::::)I:qlSMATIC CELL
NIMH LEO (50_ DOD; C/D:=fl.05") CYCLING @ RT
CYCLE 100
CYCLE 1000
CYCLE 2000
CHARGE : 60 MIN @ C12 RATE OISC_E 30 MIN 0 C RATE
Figure 14 Pressure Response Profiles for 7 Ah Prototype Cells
This figure illustrates the pres-
sure response profiles for one of
the 7 Ah cells on test at 100,
1,000 and 2,000 cycles. The over-
all change in EOCP has been 7 psia
over the first 2,000 cycles. As
indicated earlier, increasing EOCP
has been the primary failure mode
observed in previous cell builds. The
low pressure results seen here are a
significant improvement over the ear-
lier 6 Ah and 22 Ah cell configura-
tions. With pressure performance this
low at 2,000 cycles significantly
improved cycle life is anticipated.
Aerospace NiMH Cells Gates Aerospace Batteries
1992 NASA Aerospace Battery Workshop -634- Advanced Technologies Session
Page 19
Summary and Conclusions
Prototype 7 Ah NiMH cells have demonstrated >2,000 LEO
50% DoD cycles with excellent voltage and pressure
performance
O 7 Ah cells size to be used for initial test configuration
for qualification testing
O Designs for 24 Ah and 35 Ah cells based on scale up of 7
Ah cells in progress
O Development program continuing with goal of >I0,000 LEO
50% DoD cycles by 1995
O NiMH appears to be excellent candidate for use in aero-
space cells
Cycle life testing of prototype
NiMH cells in 6, 7, and 22 Ah sizeshas been discussed. As indicated
in the results to date the 6 and 22
Ah cell designs were used as ini-
tial test vehicles to identify
potential performance issues so
that subsequent cell configurationscould address those issues. Even
though these cells were early de-
signs, cycle lives in excess of
4,000 50% DoD LEO cycles were
achieved in both designs. The
improvements in design for the 7 Ahcells are reflected in the excel-
lent performance to date.
This 7 Ah cell design will be used to
begin initial qualification testing in1993. In addition, 24 Ah and 35 Ah
cell designs are in progress and will
also be evaluated in qualification
testing. GAB plans to continue this
development effort with a goal of
achieving >I0,000, 50% DoD, LEO cycles
in qualification hardware by mid 1995.
Based on the results achieved to date
NiMH appears to be a viable alterna-
tive to NiCd and NiH 2 cell technology
for aerospace applications.
Aerospace NiMH Cells Gates Aerospace Batteries
1992 NASA Aerospace Battery Workshop -635- Advanced Tech.ologies Session
Page 20
Future Direction
o continue evaluation of Alloy/Separator/Positive Combina-tions
AB 2 and AS s Type alloys
Other non-nylon separator materials
O Expand parametric database using 7 Ah and 24 Ah cells
Voltage and Capacity performance vs temperature
Charge retention and overcharge tolerance
O Begin qualification testing on 7 Ah and 24 Ah cells inmid 1993
O Expand available range of NiMH cell designs
Although results of NiMH cell test-
ing to date are promising, quali-
fied designs are still on the hori-zon. As such GAB intends to con-
tinue its development program in
order to establish those qualified
designs. Future work will be aimed
at evaluation of various alloy
combinations with different types
of separators to optimize the de-
signs.
Testing of current designs willcontinue in order to establish the
database needed for cell qualifica-
tion. This will include various para-
metric tests including capacity and
voltage performance at various temper-
atures, self-discharge, and overchargetolerance. It is GAB's intention to
have cells available to begin internal
qualification testing in mid-1993.
GAB will also develop an expanded
range of NiMH cell designs in 1993.
Aerospace NiMH Cells Gates Aerospace Batteries
1992 NASA Aerospace Battery Workshop -636- Advanced Technologies Session