unique features of a new nickel-hydrogen 2-cell cpv · unique features of a new nickel-hydrogen...

N95- 26793

Unique Features of a New

Nickel-Hydrogen 2-Cell CPV

James R. Wheeler

Eagle Picher Ind., Joplin MO

Abstract

Two-cell nickel-hydrogen common pressure vessel (CPV) units with some unusual designfeatures have been successfully built and tested. The features of interest are half-normal

platinum loading for the negative electrodes, the use of rabbit-ear terminals for a CPV unit,

and the incorporation of a wall wick. The units have a nominal capacity of 20 Ah and are3.5 inches in diameter. Electrical performance data is provided. The data support thegrowing viability of the 2-cell CPV design concept.

Cell Description

The unit described in the tests described here is a 3½ inch-diameter RNHC 20-5. It is a

two-cell common-pressure-vessel design with a nominal capacity of 20 Ah. Its constructionis identical to that of a 40 Ah tandem-stack ManTech cell, except that the two stack-halves

are internally connected in series rather than parallel. One of the units is shown in figure 1.As can be seen, this unit has rabbit-ear terminals, which has the advantage of reducingbattery height and cell-to-cell interconnection mass.

Figure 1.RNHC 20-5

1994 NASA Aerospace Battery Workshop -489- Advanced Technologies Session

https://ntrs.nasa.gov/search.jsp?R=19950020373 2018-07-15T05:04:35+00:00Z

By "ManTech" is meant an Eagle Picher design which uses pineapple-slice-shapedelectrodes and stack elements, a central polysulfone core, continuous nickel-foil leads on

electrodes, and a wall-wick to ensure a recirculating path to return and equilibrate

electrolyte throughout the cell stack. Also unlike an IPV, there is no separator/electrolytebridge provided between the cell stacks. Although not present in these units, a hydrophobicTeflon strip adjacent to the weld ring on either side is planned for future units to discourageany possible long-term ionic migration through electrolyte film between the two internalcells.

Other features include a spring washer for uniform stack compression and

separator/electrolyte contact with the cell wall to facilitate heat transfer. The positiveelectrode material is 80% slurry. The active material loading was a standard 1.65 g/ccv.

The separator material is two layers of zirconium-oxide cloth per positive electrode. Havingtwo layers was desired because the intended functions were for operation in low earth orbit

(LEO). The double separator design results in more weight for the unit, much of which is

electrolyte.

Unusual Features

These units have some unusual features which distinguish them from normal production:

The use of a wall wick in a 2-cell CPV unit.

The negative electrodes were loaded to a platinum level of 4 g. per cm2, which is half the

normal loading.

This is the first 3.5 inch-diameter CPV unit with rabbit-ear terminals to be built by EaglePicher. The third terminal on this unit is a special test terminal (center voltage tap) which is

connected internally between the two cells. It is not necessary to the unit's function and

would not be present in flight units.

The slurry plaque for the positive electrodes was manufactured in Eagle Picher's Range-

Line plant in Joplin, Missouri. This is notable since all of EP's flight production thus far hascome from its Colorado plant. The plaque design is otherwise identical however.

performance

Seven units of this design were built and tested using conventional acceptance-type testsand a 2C (40 amp) pulse test. The pulse was applied for 20 seconds after 15 minutes of

discharge at the normal rate of 10 amps (C/2). The performance of the units in testing wasessentially what would be expected for individual-pressure-vessel cells, allowing for thedouble voltage of these units. The test results are shown in table 1, and the charge anddischarge curves at 10°C and 0°C are shown in figures 2 through 5. It is noteworthy thatthe charge retention of these units, at 88% for a 72-hour open-circuit stand, is virtually thesame as for an IPV with the same separator. The cells showed no ill effects of the 2C (40

amp) pulse. Average minimum voltage at the end of the pulse was 2.36 volts (IPV

equivalent: 1.18 volts).


Table 1.

RNHC 20-5 CPV

A VERAGE PERFORMANCF

Test , 2.0 Volts 2.2 Volts Max. Chg. Volts

10°C Capacity (Ah) 22.19 21.99 3.051

0°C Capacity (Ah) i24.34 23.81 3.132

10°C High Rate (Ah) 123.61 _3.046

10°C 72-Hr. C.R.*

88.0%

23.77

20.91 20.77 3.045

Conclusions

The results of the tests support the viability of the 2-cell CPV design at a time when interestin this concept for nickel-hydrogen batteries is growing. With half as many interconnects ina 2-cell CPV battery and somewhat less pressure-vessel weight per cell, they represent a

significant potential weight-savings at the battery level 1. Fears of internal electrolytebridging in two-cell unit have proven unfounded, and now the compatibility of the wall wickwith the 2-cell CPV concept has also been demonstrated.

Two cell CPV's have already flown in the MISTI, TUBSAT and APEX programs 2, and

common use in the future seems likely. The use of single rather than double layer

separator would be appropriate for GEO applicat_, ns and would make the weight of thebattery more attractive. Had this unit been a sin31e-layer design, its weight would havebeen 1146.6g., a savings of 106.3g (computer-design projection). The cost would beimproved as well since the separator is an expensive component.

The successful manufacture and testing of the units documented here add to the growingliterature for 2-cell CPV's, and in addition show that reduced platinum loading of negativeelectrodes can be combined with the CPV concept. The compatibility of the rabbit-earterminal configuration is also affirmed with this work. The use of slurry plaque from adifferent source was shown to perform to the same standards as that from the more-usualone.

Acknowledgments

David Cooke managed the assembly and testing of the RNHC 20-5. His contributions aregratefully acknowledged.

10tzinger, B. M., and Wheeler, J. R., "Common Pressure Vessel Nickel Hydrogen BatteryDevelopment", Vol. III, p. 1381, IECEC Proceedings, 1989.2Coates, D. K., and Fox, C. L., "Current Status of Nickel-Hydrogen Battery TechnologyDevelopment", Part 1, pp. 75-80, IECEC Proceedings, 1994


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Round Table Discussion of Advanced Technology for Space Applications

Gerald Halpert, Jet Propulsion Laboratory

NASA BATTERY WORKSHOP

MARSHALL SPACE FLIGHT CENTER

HUNTSVILLE, ALABAMA

November 1994

OPEN DISCUSSION

On the Subject of

WHAT WILL IT TAKE TO GET ADVANCED BATTERY TECHNOLOGY INTO SPACE

APPLICATIONS?

Chairman: Gerald Halpert

Jet Propulsion Laboratory

Notes by Michelle Manzo, NASA LeRC

OPENING REMARKS - G. Halpert

New battery technologies have been improving over the last several years. It took almost 20

years for NASA to use a Ni-H2 battery. Even then it was used on Hubble Space Telescope as a

replacement for a Ni-Cd battery in which life limiting concerns had been raised. What do we have

to do to use Ni-MH or Li-ion batteries in space? How do we qualify cells and batteries for spacemissions?

If you ask the spacecratt Manager or project manager, he or she will ask where has it been used

previously and what is the experience with the device? Even though there may be significant test

data, and the mass and volume is lower or the mission capability can be increased, the project

manager will generally opt for a previously used battery system. The philosophy is "Not on myspacecraft."

The subject is open for discussion to all attendees. I hope you will participate. The first speaker isDave Pickett from Hughes.

ATTENDEE PARTICIPATION

Pickett - It took 8 years to fly modern Ni-Cd and 11 years to for Ni-H2. A compelling reason is

needed for implementation of new technology, whether it be economics, or other. It takes time,

and someone willing to take the risk. Usually, commercial needs lead the way.

The new technologies are Ni-MH, Li-ion, and CPV Ni-H2. Larger IPV are being considered as

well as CPV. Predictions for spaceflight ofNi-MH, 5 years, and Li Ion 8-10 years. This is the

time it takes from cell test to battery integration.

E. Darcy - Safety issues with Li make Ni-MH more of a near term option.

1994 NASA Aerospace Battery Workshop -559-Advanced Technologies Session

J. Firmin - Safety tests have been conducted. Requirements need to be defined and tech must

meet the requirements.

G. Methlie - Agreement with safety issue. Ni-MH intermediate term is needed. Difficult to

accelerate verification.

M. Klein - Ni-MH is the battery of choice for next 10-15 years. Aerospace should leverage off

commercial.

C. Lurie - High cost for qualification of Ni-Cd to Ni-MH. Not clear that it offers significant

advantages at battery level. Li-Ion will probably ultimately replace Ni-MH. Probably cannot

justify costs.

G. Dudley - Wh efficiency less for Ni-MH than Ni-Cd.

C. Lurie - Ni-MH advantage is improved round trip efficiency, thus, smaller array.

W. Tracinski - Possible use for all technologies to optimize for all applications.

G. Methlie - Project forward by looking backward. If end up with one system, you better be

right. Also need multiple vendors.

D. Maurer - Need all technologies. Li-Ion a long way off. Need several technologies going at

once. The mechanism for demo in space will be in small s/c.

A. Dunnett - Cheaper and faster, not better. No new battery systems seen without compelling

reason. Ni-MH will not be qualified with Ni-Cd and Ni-MH available. Li-Ion is the next step.

G. Halpert - What is the necessary incentive to go Li-Ion? Does your company support R&D on

Li-Ion?

A. Dunnett - Lower battery weight, more propellant, increase in payload. My organization does

not support Li-Ion or other R & D.

E. Darcy - The time line is long without terrestrial applications. Ni-MH make sense in todays

environment.

C. Lurie - Small satellites are new visions for aerospace. They become the platform for new

technology.

M. Anderman - Ni-MH advantages depend on DOD capability and life as a function of DOD.

V. Kennedy -Responding to a question on Na-S, acceptance and abuse tests are being worked.

Johnson -Go on to far term technologies. Let other Intermediates develop in commercial


technology. Sponsor research in space for space applications.

G. Methlie - Commercial base does not guarantee success in space.

J.Firmin - Same battery as EV commercial? Need to begin improvement at early stages to

influence development.

P. O'Donnell - Need dual-use drivers. Can't take terrestrial alone. Need to work on parallel

paths.

J. Firman - Limit documentation for qualification of new technologies for space. Documentation

is costly.

C. Lurie - Dual answer. Small satellites, Yes, DOD/NASA, no.

C. Lurie - On the capacity fade issue - It still exists but we have an understanding. TRW prefers

to deal with Ni precharge issues.

G. Halpert - Managers want low cost but also want guarantees that product will work. Thus,

costs will remain high. However, we are careful. Not always battery failures, e.g., Magellan -

failure was arrays not battery.

S. House - Phillips Lab will not support development of Ni-Mh. Lithium-ion possible substitution

to Na-S and Ni-H2. 7 year test is required.

M. Tof_ - To get new technology into orbit, which product has been shown to be best understood.

Elimination of documentation and visibility is the wrong way to go. Vendor data is valuable. It

holds clues to success. If you show understanding, customers will be willing to pay.

C. Bennett - There is a large database for Ni-H2. Varied parameters, no consistent production.Need to use a model.

G. Halpert - Why do we have all these variations in product? (No response)

J. Armantrout - Historically we have used database for decisions. Develop a standard for a 5Kw

satellite. Need more standardized designs.

J. Wheeler - The process is: The manufacturer recommends to the customer, then customer has

strong preferences including plate and cell designs. The manufacturer is at the customer's mercy.

There are multiple paths to success. Let the customer make the selection.

C. Garner - Cooperative efforts work well.

G. Methlie - Commercial look at products.


S. Surampudi - Technology is driven by customer. Customer was leader. Leader disappeared

replaced by managers. They want the best products without supporting costs.

G. Halpert - Are there any planned Ni-Mh flights?

B. Bragg - Shuttle orbiter GFE. Ni-MH flown in IBM think pad. To be flown in helmet light.

NASA/JSC approves specific designs and specific applications - no blanket chemistry approval.

OSHA and EPA have environmental concerns. Japanese Ni-MH flight in 1998 will follow

European's and Amercians.

A. Dunnett - The delta performance improvement does not warrant development of Ni-Mh over

Ni-Cd.

G. Halpert - Are there any planned Li-Ion flights?

S. Surampudi - JPL use in 1997. Small spacecraft 5-10 Ah cells. 45 new technologies evaluated

for new spacecratt. Li-Ion was selected. Looking at Li-Ion instead of Ni-MH because no

apparent payoff over Ni-H2. The fallback is Ni-Cd compelling reason is size.

Session adjourned

Many thanks to Michelle Manzo for taking these notes


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