Representative samples of nickel hydrogen cells for the INTELSAT program were used to evaluate the effects of prolonged storage under passive conditions such as open circuit discharged at 0 C, room temperature, and -20 C, and under quasidynamic conditions such as top-off charge and trickle charge. Cell capacity declines when cells are stored open-circuit discharged at room temperature, and a second plateau occurs in the discharge curve. Capacity loss was 47 percent for a cell with hydrogen precharge and 24.5 percent for one with no hydrogen precharge. Capacity recovery was observed following top-off charge storage of cells which had exhibited faded capacity as a result of passive storage at room temperature. Cells stored either at -20 C or on trickle charge maintained their capacity. At 0 C storage, the capacity of all three cells under tests was greater than 55 Ah (which exceeds the required minimum of 44 Ah) after 7 months

Vaidyanathan, Hari

English

NASA Technical Reports Server

WN87-29921
LONG-TERM STORAGE OF NICKEL-HYDROGEN CELLS*
H. Vaidyanathan
COMSAT Laboratories
Clarksburg, Maryland 20871-9475
Representative samples of nickel-hydrogen cells for the INTELSAT VI program were
used to evaluate the effects of prolonged storage under passive conditions such as
open-circuit discharged at 0°C, room temperature, and -20°C, and under quasidynamic
conditions such as top-off charge and trickle charge. Cell capacity declines when
cells are stored open-circult discharged at room temperature, and a second plateau
occurs in the discharge curve. Capacity loss was 47 percent for a cell with hydrogen
precharge and 24.5 percent for one with no hydrogen precharge. Capacity recovery was
observed following top-off charge storage of cells which had exhibited faded capacity
as a result of passive storage at room temperature. Cells stored either at -20°C or
on trickle charge maintained their capacity. At 0°C storage, the capacity of all
three cells under test was greater than 55 Ah (which exceeds the required minimum of
44 Ah) after 7 months.
INTRODUCTION
Long-term storage of nickel-hydrogen batteries has become an important issue
since the storage requirements for the INTELSAT VI battery have been increased from
28 to 60 months as a result of launch delays. The capacity maintenance characteris-
tics of INTELSAT VI nickel-hydrogen cells were discussed in 1986 (ref. I). This
present paper continues that work by elaborating on the capacity variations observed
in these cells after extended storage under various conditions.
The nickel-hydrogen cells discussed here are of the U.S. Air Force/Hughes design,
containing 40 sets of positive and negative plates, with zircar as the separator, in
a recirculating stack configuration. There are two types of cells, positive- and
negative-limited, which are defined based on differences in the amount of hydrogen
precharge. Positive-limited cells use about 150 psi of hydrogen gas as precharge;
negatlve-limited cells use no hydrogen precharge. A cell capacity of 44 Ah is
considered sufficient to meet the load requirements of the INTELSAT VI satellites
(ref. 2).
STORAGE MODE STUDY APPROACH
A storage mode investigation was begun using selected nickel-hydrogen cells.
First, the initial capacity of the cells was determined at 10°C. The cells were then
divided into groups and stored under a variety of conditions, as follows:
• -20°C open-circuit discharged
• 0°C open-circuit discharged
• room temperature open-circuit discharged
*This paper is based on work performed at COMSAT Laboratories under the sponsorship
of the International Telecommunications Satellite Organization (INTELSAT). Views
expressed are not necessarily those of INTELSAT.
41
P ,i_.le.DING PAGE BGANF_ N0'i' iq!2_it"2)
https://ntrs.nasa.gov/search.jsp?R=19870020488 2020-03-20T10:01:53+00:00Z
• trickle charge at room temperature
• top charge
Several points must kept in mind when discussing the results of this study.
Cells are oriented vertically while in storage. Cells stored at -20°C, 0°C, and room
temperature are in the fully discharged state, which is achieved by power discharge
at 23.5 A to 0.i V, followed by draining through 1 _ for 18 to 24 hours and short-
ing for 4 hours. Top-charge and trickle-charge cells are charged at 4.8 A for
18 hours at 10°C prior to storage. All capacity determinations are performed at a
C/2 rate (23.5 A) at 10°C.
EFFECT OF ROOM TEMPERATURE STORAGE
Five cells were stored at room temperature, and their resulting capacity
variation is shown in figure I. (Cells with negative precharge are denoted by the
letter N, and those with positive precharge by the letter P.) In this storage mode,
the cells showed capacity loss of as much as 47 percent for a cell with hydrogen
precharge and 24.5 percent for one with no hydrogen precharge. The capacity loss
appears to level off after 94 days. One result of room temperature storage is the
occurrence of a second plateau in the discharge curves, as depicted in figure 2. The
capacity below 1 V (not all in the plateau region) increases with time in storage, as
shown in figure 3. The occurrence of the second plateau is of major concern, since
it is not known whether the plateau can be eliminated by any recovery procedure. The
capacity of the cells after almost 1 year of storage at room temperature falls short
of the amount required to fully support the spacecraft load.
STORAGE AT 0°C
Three cells were tested after storage at 0°C, and their capacity variation with
storage time is shown in figure 4. Two of the cells are maintaining capacity, and
the third shows only a negligible decline in capacity. There was no second plateau
in the discharge profiles of these cells. After 8 months of storage at 0°C, cell
capacity is above the required minimum of 44 Ah. These results appear encouraging.
TOP CHARGE AT ROOM TEMPERATURE
Four cells were used in this experiment in which the cells are recharged for
i0 hours at 4.8 A every 7 days. Figure 5 shows the capacity variation of the cells
for two periods of top charge. One of the cells showed capacity loss in the first
period. In the second period, all the cells exhibited increased capacity. Two of
the cells showed remarkable recovery, from capacities in the 30's at the beginning to
high 50's at the end of the second period.
Figure 6 gives EMF profiles of the four cells, which are of particular interest
in regard to the second plateau. Two of the cells show a capacity of about 8 Ah
below 1 V, which is much less than for cells stored at room temperature. In addi-
tion, the capacity that was in the second plateau at the beginning of the top-charge
experiment has moved to the major plateau, as illustrated by the two profiles for
cell 8-I127P.
42
TRICKLECHARGE
The trickle-charge storage modeclosely resembles that of the battery in orbit
during non-eclipse periods. Three cells were used in this experiment. One, which
had a lower capacity, was trickle charged at 0.65 A for 64 days at 10°C. The cell
gained 5 Ah, as shownin figure 7. This cell, along with the other two, was then
trickle charged at the samerate but at roomtemperature. After 184 days, capacity
determination revealed almost the samecapacity as at the beginning, with negligible
capacity below 1 V. These results show that capacity recovery initially occurs when
a faded cell is trickle charged, and capacity is maintained thereafter.
-20°C STORAGE
A group of four cells, three with hydrogen precharge and one without, were stored
at -20°C and their capacity was determined at intervals. Table 1 presents the
resulting capacity variations. Two of the cells gained capacity and the other two
maintained capacity. Thus, passive storage at -20°C appears to be an excellent stor-
age method. However, somemisgivings exist regarding the stability of the seal at
this temperature, although no cell leakage was observed in the four cells tested.
CELLPRESSURE
Pressure variation was monitored for the cells, which were instrumented with
strain gauges. Table 2 illustrates the end-of-charge and end-of-discharge (to 1 V)
pressure of the cells. As expected, cells with hydrogen precharge showhigher
pressures than those with positive precharge. The end-of-discharge pressure is
abnormally high for the cell stored at room temperature, which indicates that some
positive active material is not dischargeable at the C/2 rate.
The pressure of the cell stored in the top-charge mode is higher than expected
for a positive precharge cell. The end-of-charge pressure for this cell increased
from 740 psi at the beginning of the experiment to 781 psi at the end of the first
period and 824 psi at the end of the second period. The increase in end-of-charge
pressure corresponded with the increase in capacity. It is unclear whether the
present selection of i0 hours at C/lO is appropriate in view of this pressure
increase. Additional experiments which use less than i0 hours of recharge are
needed. Nevertheless, recharge every 7 days appears to be a successful and practical
method for recovering and maintaining cell capacity.
CONCLUSIONS
INTELSAT VI nickel-hydrogen cells exhibit capacity fading when stored passively
at room temperature for extended periods. This loss in capacity is accompanied by a
gradual growth in capacity in the second plateau. In contrast, capacity is main-
tained when cells are stored at -20°C and at 0°C in the open-circuit discharged
condition.
Top-charge and trickle-charge storage modes also maintain cell capacity.
Preliminary results have shown a capacity recovery in the top-charge mode. The
second plateau is absent in cells stored in the trickle-charge mode at room
temperature. The common denominator in the top-charge and trickle-charge storage
modes is the overcharge, which is perpetuated continuously in one procedure and at
regular intervals in the other.
43
1,
2,
REFERENCES
Vaidyanathan, H., and Dunlop, J. D., "Capacity Maintenance for INTELSAT VI
Nickel-Hydrogen Cells," 22nd Intersociety Energy Conversion Engineering
Conference, American Chemical Society, Washington, D.C., 1986, Proc., Vol. 3,
pp. 1560-1564.
Wong, D. W., Herrin, J., and Stadnick, S. J., " INTELSAT VI Nickel-Hydrogen
Battery," 22nd Intersociety Energy Conversion Engineering Conference, American
Chemical Society, Washington, D.C., 1986, Proc., Vol. 3, pp. 1541-1546.
Table i. Capacity Variation at -20°C
Cell No.
4-II04N
5-II16N
13-1382P
1-1081N
Precharge
H2
H2
None
H2
Initial Capacity
(to 1 v)
(Ah)
Storage Period
(days)
63.6
60.7
66.7
59.9
270
270
112
112
Final Capacity
(to 1 v)
(Ah)
66.0
67.2
66.3
60.3
Table 2. Cell Pressure Variation
Cell No.
15-1110P
8-I127P
4-II04N
3-I033N
Precharge
Positive
Positive
H2
H2
Storage Mode
Trickle charge
Top-off charge
0oc
Room temperature
End-of-Charge
Pressure
(psi)
742
824
847
766
End-of-Discharge
Pressure (to 1 V)
(psi)
125
264
219
432
Cell
Capacity
(Ah)
61.9
54.5
59.5
31.0
44
7O
65
6O
55
f-
<
v
>- 5O
I-
< 45
<
o 40
35
30
25
I I I I
LIMIT
I
0 31 52 94 165
DAYS IN STORAGE
Figure 1. Capacity (to 1 V) Variation for Cells
Stored at Room Temperature
CELL NO. I
o 3-1033N q
• 11 -1337P
o 5-1116N -
• 8-1127P
o 10-1303P -
--------.o.-.._
282
1.6
1.4
1.2
_. 1.0
_ .8
w 0.6
0.4
0.2
0
0
I I I I I I
I=
I I I
I I I (_ELL'NO. I I
o 3-1033N -
• 11-1 337P
,, 5-1116N-
. • 8-1127P_
03N
5 10 15 20 25 30 35 40 45 50 55 60 65 70
CAPACITY (Ah)
Figure 2. EMF Profile of Cells Stored at Room
Temperature at 23.5-A Discharge Rate
45
30
28
26
¢-
24
>- 22
1-
20
,<
a. 18
,<
0 16
uJ 14
< 12
I-
" 10
0
> 8
6
0
4;
2
0
0
I I I I I
.-----,--0 --
m
// j _ o 3.!o33_N_
_V_ / / .11-133-{p__
LZ/ // o 5-111eN_
L // • 8- !27p_
I I I o 1 0-1303P
31 52 94 165 282
DAYS IN STORAGE
Figure 3. Variation of Additional Capacity at
Low Voltages With Storage Time
at Room Temperature
7O.O I I
67.5 --
65.0 -
60.0
0 c
57.5 i_1
55.0
52.5
0 21 64
CELL NO.
o 2-1061N
• 4-1104N
o 11-1291P
DAYS IN STORAGE
Figure 4. Capacity (to 1 V) Maintenance for
Cells Stored at O°C
0
4
O--
I
253
46
A
t--
<
>-
I.-
5
<
13_
<
0
7O
65
60
55
5O
45
40
I I CELL NO.
o 5-1116N
• 8-1127P
o10-1303P
t13-1382P
3O
0
! I
1 2
(6 WKS) (12 WKS)
PERIODS OF TOP CHARGE
Figure 5. Capacity (to 1 V) Variation in the
Top-0ff Charge Storage Mode
16
14
12
I0
>
LL 08
LLI
I I
-CELL NO.
a 5-1116N \
_ • 8-1127P**
0.6
04
o 10-1303P
02 -- • 13-1382P
0 I I I I I I I I I I I
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70
CAPACITY (Ah)
,, BEFORE TOP CHARGE
** AFTER TOP CHARGE
Figure 6. EMF Profile of Cells at 23.5-A Discharge
Rate After Two 6-Week Periods of Top-Off Charge
47
65.0 I I I
t-
<
v
>-
I-
5
<
13_
<
O
62.5
60.0
57.5
55.0
52.5
50.0
,.--------O
A
---o
/
/
/
-- /
/
/
/
-/
/
I I
0 22 64
CELL NO.
o 1-1081N
.15-1110P
,-,1 5-1 463P
----- (_b 10°C
-- _ ROOM TEMPERATURE
I
DAYS IN STORAGE
226
Figure 7. Variation of Capacity (to 1 V) for
Cells in the Trlckle-Charge Storage Mode
48


Long-term storage of nickel-hydrogen cells

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server