Linden D., Reddy T.B. (eds.) Handbook of batteries

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NICKEL-HYDROGEN BATTERIES 32.23

32.7.3 Capacity as a Function of Electrolyte Concentration

The effects of electrolyte concentration on capacity were determined experimentally. Air

Force positive electrodes and the Air Force 50-Ah Ni-H

cells from the INTELSAT VI

program were used for this investigation. The Air Force positive electrodes were impregnated

with active material by the alcoholic electrochemical impregnation process. The plaque was

manufactured using the dry-powder process.

For the Air Force standard 50-Ah Ni-H

cell, the electrolyte concentration was determined

to be 26% KOH in the charged state and 31% KOH in the discharged state.

Cells were

activated with three different levels of electrolyte concentration: 25, 31, and 38 wt% con-

centration of KOH. The electrolyte concentration in these cells was determined by analyses

in both the charged and the discharged conditions. Table 32.2 presents cell capacity, elec-

trolyte concentration, and average discharge voltage.

TABLE 32.2 Cell Capacity and Voltage vs. Electrolyte

Concentration at 10

⬚C

Parameter

Electrolyte concentration

38% 31% 25%

Cell capacity, Ah 64 56 43

Number of positive plates 40 40 40

Capacity per plate, Ah 1.60 1.40 1.08

Electrolyte concentration:

Charged, wt% KOH 32* 26 21*

Discharged, wt% KOH 38 31 25

Average discharge voltage, V 1.247 1.268 1.290

*Estimated.

32.7.4 GEO Performance

The Ni-H

batteries on the INTELSAT V satellites have completed up to nine years in orbit.

Voltage Performance in Orbit. In-orbit performance of the INTELSAT V batteries is

judged by the minimum end-of-discharge voltage observed during an eclipse season. The

minimum battery voltage requirement is 28.6 V, or 1.10 V per cell average with one cell

failed short-circuited. The actual minimum battery voltages and the corresponding load cur-

rents and depths of discharge for each of the 14 batteries on the F6 through F15 satellites

are presented in Table 32.3 for the Fall 1990 eclipse season.

Also presented are the min-

imum cell voltages within each battery and the corresponding average cell voltage per battery.

After up to 7 years in orbit, the minimum end-of-discharge battery voltages on the longest

eclipse day ranged from 31.2 to 32.4 V for all 14 batteries. The cells within the batteries

were well matched at their minimum end-of-discharge voltages during the Fall 1990 eclipse

season (maximum deviation is

Ⳳ20 mV between cells within the same battery). The one

exception is cell 22 in battery 1 on the F-6 spacecraft. This cell was 40 mV below the

average cell voltage. These battery voltages are well above the minimum voltage require-

ment.

32.24

TABLE 32.3 Battery Loads and Minimum Voltages for Fall 1990 Eclipse Season

DOD, %

Battery 1 Battery 2

Current, A

Battery 1 Battery 2

Voltage, V

Battery 1 Battery 2

Cell voltage, V

Batt. 1 av. Batt. 1 min. Batt. 2 av. Batt. 2 min.

F-6 55.8 53.1 14.2 13.5 32.0 32.4 1.20 1.16 1.20 1.19

F-8 54.0 54.4 13.7 13.8 32.0 32.0 1.20 1.18 1.20 1.18

F-10 56.9 55.7 14.4 14.3 31.8 32.0 1.19 1.18 1.20 1.18

F-11 55.3 60.0 14.1 15.4 32.0 32.0 1.20 1.18 1.20 1.19

F-12 53.5 58.0 13.6 14.8 32.0 31.8 1.20 1.18 1.18 1.18

F-13 67.0 59.0 16.9 15.0 31.2 31.8 1.17 1.15 1.19 1.17

F-15 67.0 62.3 16.9 15.8 31.2 31.8 1.17 1.16 1.18 1.16

NICKEL-HYDROGEN BATTERIES 32.25

Pressure Data. INTELSAT V batteries are reconditioned prior to each eclipse season. The

reconditioning capacity and pressure data for INTELSAT V F-6 battery 2 are presented in

Table 32.4.

The pressure data were measured during the reconditioning discharge. The

EOC pressure and the EOD pressure are the pressure at the start and the pressure at the end

of the reconditioning discharge, respectively. The pressure constant is

⌬P per measured

capacity.

The data in Table 32.4 show the following:

1. The strain-gauge bridge circuit provides useful pressure data.

2. No change occurred in the reconditioning EOD pressure with time for these INTELSAT

V battery cells. The EOD pressure in Fall 1991 was almost the same as the EOD pressure

at the beginning of life in orbit.

3. The signiﬁcance of these data is that no oxidation or corrosion has occurred within these

cells. Any oxidation of the cell components would result in a pressure increase at the end

of the reconditioning discharge.

TABLE 32.4 Reconditioning Capacity and Pressure Data for INTELSAT V F-6 Battery 2

Eclipse

season

Measured

capacity,

Max EOC

pressure,

lb/in

Min EOD

pressure,

lb/in

⌬P,

lb/in

Pressure

constant

⌬P / measured

capacity,

lb/in

/Ah*

F83 38.1 No pressure data in database

S84 35.4 No pressure data in database

F84 37.7 516.39 13.87 502.62 13.33

S85 37.6 518.49 17.90 500.59 13.31

F85 37.5 515.14 17.23 497.9 13.27

S86 37.9 519.34 15.32 504.02 13.29

F86 37.6 519.73 22.03 497.70 13.23

S87 38.3 519.34 13.87 505.47 13.19

F87 37.2 519.73 22.03 497.7 13.37

S88 38.3 525.78 16.20 509.58 13.30

F88 37.8 521.86 17.90 503.96 13.33

S89 36.9 526.91 18.67 508.24 13.77

F89 40.2 534.22

⫺0.57 534.79 13.30

S90 38.6 551.73 19.22 532.51 13.79

F90 36.0 530.87 38.04 492.83 13.68

S91 39.5 546.52 17.23 529.29 13.39

F91 39.0 545.30 17.90 527.40 13.52

Average 13.37

*1 lb / in

⫽ 6895 Pa.

32.7.5 LEO Performance Data

The HST was launched on April 24, 1990, with six 88-Ah Ni-H

batteries as the primary

energy storage subsystem. This was the ﬁrst reported nonexperimental mission to use Ni-H

batteries in an LEO application.

The batteries are being charged to a temperature-

compensated voltage limit as described in Sec. 32.6.2. The batteries are discharged to 7 to

10% of depth of discharge. As reported at the 1991 IECEC, ‘‘To date (April 1991) the

performance of the batteries has been ﬂawless.’’

32.26 CHAPTER THIRTY-TWO

32.8 ADVANCED DESIGNS

32.8.1 Advanced Designs for IPV Ni-H

Cells

A number of advanced concepts for IPV Ni-H

cells are being used to improve cycle life at

deep DOD

mitigating failure modes commonly found in Ni-H

cells. They include: (1) the

use of alternative methods for recombination (that is, the catalyzed wall wick), (2) the use

of serrated-edge separators to facilitate the movement of gas within the stack while main-

taining physical contact with the cell wall, (3) the incorporation of Belleville washers to

yield an expandable stack capable of accommodating some of the nickel electrode expansion

that is known to occur with cycling, and (4) the use of lower KOH concentrations to improve

cycle life.

Cells utilizing the catalyzed wall wick are now in use. This concept offers an improved

thermal design with recombination taking place on the pressure vessel wall. The heat from

recombination is removed immediately through the pressure vessel wall to the cell thermal

sleeve. This design also mitigates damage from internal stack popping since the recombi-

nation site is outside the cell stack.

The use of serrated edges for the separator is usually employed in designs utilizing as-

bestos. The irregular edge allows the unrestricted passage of oxygen along the edge of the

cell stack while maintaining contact with the wall wick of the pressure vessel for recovery

of electrolyte and removal of heat from the stack.

The Belleville washer acts as a spring, allowing further compression to accommodate any

plate expansion during cycling.

The effects of KOH concentration on the cycle life of Ni-H

were investigated.

A break-

through in the LEO cycle life of individual pressure-vessels cells was reported and cell cycle

life was improved by greater than a factor of 10 when KOH concentration was reduced from

31% to 26% in the fully discharged state. The lower concentrations, while enhancing the

cycle life, result in a slightly higher mid-discharge operating voltage with a lower available

capacity to the 1.00 V per cell limit.

32.8.2 Advanced Battery Design Concepts

The common pressure vessel (CPV) Ni-H

battery and the bipolar Ni-H

battery are two

advanced battery design concepts investigated to improve the gravimetric and volumetric

energy densities as compared to the IPV cell and battery Ni-H

technology.

Common Pressure Vessel. Conceptually a CPV Ni-H

battery consists of a number of

individual cells connected together in series and contained within one common pressure

vessel.

For the IPV cell, each individual Ni-H

cell is contained within its own pressure

vessel. Potential advantages for the CPV Ni-H

batteries include a signiﬁcant increase in

volumetric energy density (a decrease in volume), a decrease in manufacturing cost, a re-

duction in the complexity associated with the wiring and interconnection of IPV cells, an

increase in speciﬁc energy, a reduction in the internal impedance of the battery, and improved

heat transfer between the electrode stack and the pressure-vessel wall.

Several dual-cell CPV designs have been developed and tested. This design utilizes the

dual-stack conﬁguration used for IPV cells. For the CPV cell, the two stacks are connected

in series, as shown in Fig. 32.23. This dual cell CPV battery offers a 30% reduction in

volume anda7to14%reduction in mass compared to an equivalent battery with IPV cells.

Batteries utilizing these cells have been used in several ﬂight programs including LEO

and interplanetary missions. Two batteries used on the Mars Global Surveyor and Mars Polar

Lander ﬂight programs can be seen in Figs. 32.24 and 32.25. These are 28 V batteries having

capacities of 23 Ah and 16 Ah, respectively.

NICKEL-HYDROGEN BATTERIES 32.27

FIGURE 32.23 EPT CPV design (2.5 volt) (Courtesy of

Power Subsystems Group, Eagle-Picher Technologies, LLC).

A lightweight CPV Ni-H

battery was designed and developed jointly by COMSAT and

Johnson Controls, Inc.

A prototype 10 inch diameter 26 cell, 24 Ah CPV battery was

fabricated and tested to demonstrate the feasibility of this lightweight design for LEO ap-

plications. This battery used two 13 cell half-stacks connected in series within the single

common pressure vessel to provide a nominal 32 V battery. The 10 inch aerospace design

used a semicircular cell with a double-tap design to enhance current distribution. The com-

ponents of the prototype CPV battery are shown in Fig. 32.26 with the ﬁxed heat-ﬁn cavity

and lightweight pressure vessel.

Johnson Controls developed a new 5 inch diameter 9.6 Ah CPV battery with loose heat

ﬁns (Fig. 32.27). The loose heat ﬁn design was designed to overcome the problems encoun-

tered with the insertion of the cells into the heat ﬁn cavity for the 10 inch CPV cell de-

scribed.

A 5 inch diameter, 28 V, 15 Ah CPV battery with the loose ﬁn design was ﬂown on the

Clementine Program. This battery was manufactured by Johnson Controls under contract

with the Naval Research Laboratory. This ﬂight was launched and ﬂown successfully in

January, 1994.

The advantages of the CPV Ni-H

battery make it a candidate for use in large multikilo-

Watthour LEO energy storage applications, such as the International Space Station or con-

stellation systems such as Iridium

威. It also appeals to the other end of the spectrum—the

small 100–400 Wh applications that need low-cost lightweight batteries.

32.28 CHAPTER THIRTY-TWO

FIGURE 32.24 Mars Global Surveyor 23-Ah CPV battery assembly.

FIGURE 32.25 Mars Polar Lander 16-Ah CPV battery assembly.

NICKEL-HYDROGEN BATTERIES 32.29

FIGURE 32.26 COMSAT / JCI CPV Ni-H

battery (10-in diameter).

FIGURE 32.27 JCI CPV Ni-H

battery (5-in diameter). (a) Cir-

cular cell and loose heat ﬁn. (b) 10-cell stack.

32.30 CHAPTER THIRTY-TWO

Eagle-Picher Technologies, LLC supplied 10 inch diameter 28 V, 50 and 60 Ah CPV

batteries for the Iridium

威 program. Over 80 satellites using these CPV batteries have been

launched to date. A 28 V, 60 Ah CPV battery manufactured for the Iridium

威 program can

be seen in Fig. 32.28. This design offered impedances less than 25 milliohm, a speciﬁc

energy of 55 Wh/kg, and an energy density of 68 Wh/L.

FIGURE 32.28 IRIDIUM威 60-Ah CPV battery assembly.

32.8.3 Bipolar Ni-H

Batteries

Studies have shown that the bipolar batteries promise saving in weight and volume as com-

pared to IPV batteries.

The research has been directed toward large energy storage require-

ments for LEO applications such as the International Space Station program. Several bipolar

Ni-H

batteries were designed, fabricated, and tested at NASA Lewis Research Center. The

second one, assembled in 1983, was a 10-cell 6.5-Ah bipolar Ni-N

battery. Useful data were

generated from tests of this 10-cell bipolar battery and results should aid the development

work needed to improve performance.

REFERENCES

1. J. Dunlop, J. Giner, G. van Ommering, and J. Stockel, ‘‘Nickel-Hydrogen Cell,’’ U.S. Patent

3,867,199, 1975.

2. S. U. Falk and A. J. Salkind, Alkaline Storage Batteries, Wiley, New York, 1969, sec. 2.5

3. R. L. Beauchamp, ‘‘Positive Electrodes for Use in Nickel Cadmium Cells and the Method for

Producing Same and Products Utilizing Same,’’ U.S. Patent 3,653,967, Apr. 4, 1972.

NICKEL-HYDROGEN BATTERIES 32.31

4. D. F. Pickett, H. H. Rogers, L. A. Tinker, C. Bleser, J. M. Hill, and J. Meador, ‘‘Establishment of

Parameters for Production of Long Life Nickel Oxide Electrodes for Nickel-Hydrogen Cells,’’ Proc.

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Cells,’’

Proc. 28th Power Sources Symp., June 1978, pp. 139–141.

13. H. H. Rogers, U.S. Patent 4,177,325, Dec. 4, 1979.

14. S. J. Stadnick, U.S. Patent 4,224,388, Sept. 23, 1980.

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32.32 CHAPTER THIRTY-TWO

30. D. Warnock, U.S. Patent 2,975,210, 1976.

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BIBLIOGRAPHY

NASA Handbook for Nickel-Hydrogen Batteries, NASA Reference Publ. 1314, September 1993.