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

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29.32 CHAPTER TWENTY-NINE

29.7 PROPER USE AND HANDLING

Sealed nickel-metal hydride cells and batteries can give long-term maintenance-free, safe,

and reliable service if they are used in accordance with recommended procedures and are

not abused. They are sealed and can be used in any operating position. Other than charging,

the only maintenance that should be required is to keep them clean and dry during operation

and storage.

Most important, sealed nickel-metal hydride batteries, as most battery systems, should

not be exposed to extreme temperatures for any extended period. They can be stored, in a

charged or discharged condition, at moderate temperatures without detrimental effects.

Typically nickel-metal hydride batteries are shipped in a discharged state. However, as

some residual capacity may remain, caution should be exercised to avoid short-circuiting the

cell or battery.

After storage, or periods during which the battery has not been used, the battery should

be charged before being used. Overcharging or overheating the battery should always be

avoided.

It is possible that cells may vent if the cell or battery is overcharged or otherwise abused.

The nickel-metal hydride cell releases hydrogen gas during venting, which could form po-

tentially explosive mixtures with air. (Note that this differs from the nickel-cadmium cell,

which emits oxygen when it vents.) Caution should be exercised to prevent these gases from

collecting in the battery or equipment or from exposure to a source of ignition. Airtight

compartments should be avoided.

29.8 APPLICATIONS

The characteristics of the nickel-metal hydride battery present opportunities for use over a

wide range of applications. In the portable sealed conﬁguration, it is being used in increasing

quantities in consumer electronic devices such as cellular phones, transceivers, computers,

camcorders, and other portable applications. In larger sizes, it is also one of the candidate

battery systems for use in electric vehicles, another important market for rechargeable bat-

teries in the next decade. (See Chaps. 30 and 37.)

A variation of the nickel-metal hydride cell is the silver-metal hydride cell where the

positive nickel oxyhydroxide electrode is replaced by a silver oxide electrode. The silver-

metal hydride cell has the advantage of a higher-energy density and better high-rate per-

formance, and may be useful in critical applications where its higher cost and shorter cycle

life is acceptable.

29.9 BATTERY TYPES AND MANUFACTURERS

Table 29.4(a–d ) lists some of the portable sealed nickel-metal hydride cells and batteries

that are manufactured and their physical and electrical speciﬁcations. Multicell batteries are

also manufactured using these cells or batteries in a variety of output voltages and conﬁg-

urations. Manufacturers’ data should be consulted for speciﬁc details on dimensions, ratings,

and performance characteristics as they may differ from those shown.

PORTABLE SEALED NICKEL-METAL HYDRIDE BATTERIES 29.33

TABLE 29.4a Speciﬁcations of Sealed Cylindrical Nickel-Metal Hydride Single-Cell Batteries,

Nominal Voltage: 1.2 V

Type

Capacity

(0.2C discharge)

(mAh)

Minimum Typical

Nominal dimension (mm)

Diameter

␾

Height (H) Weight (g)

Standard series

AAAA

7/ 5 AAAA

300

500

310

520

8.4

40.6

6.5

10.5

1/4 AAA

1/3 AAA

1/2 AAA

2/3 AAA

4/5 AAA

AAA

9/ 5 AAAL

120

210

280

400

550

600

1100

130

230

290

450

600

630

1130

10.3

10.5

10.3

13.7

35.9

43.5

2.4

3.3

5.3

7.3

8.5

12.5

1/3 AA

2/3 AA

4/5 AA

250

300

600

1200

600

1300

270

320

660

1250

660

1400

14.5

14.4

16.6

28.7

42.5

48.2

1/2 A

2/3 A

4/5 A

4/3A, 7/5A

600

1000

1810

2300

3500

650

1090

1870

2350

3580

17.2

28.7

50.2

66.7

1/2 N

18210

Sub-C

180

360

800

2200

4500

200

380

860

2420

4950

11.5

18.3

16.7

29.3

21.5

42.6

61.5

5.3

140

High capacity series

2/3 AAA

AAA

AAAL

7/ 5 AAAL

350

650

700

1000

380

670

720

1050

10.5

44.7

66.5

7.1

14.5

19.l5

2/3 AA

7/5 AA

750

1500

1600

1900

770

1540

1650

1960

14.5

14.4

14.5

28.7

48.2

49.2

29.34 CHAPTER TWENTY-NINE

TABLE 29.4a Speciﬁcations of Sealed Cylindrical Nickel-Metal Hydride Single-Cell Batteries,

Nominal Voltage: 1.2 V (Continued )

Type

Capacity

(0.2C discharge)

(mAh)

Minimum Typical

Nominal dimension (mm)

Diameter

␾

Height (H) Weight (g)

High capacity series (Continued )

4/5 A

7/5 A

4/5 A, 7/5 A

2100

2500

3700

2170

2550

3700

3800

17.2

17.5

50.2

66.7

67.5

53.5

18650

Sub-C

550

4100

3000

3500

7000

580

4200

3150

3850

7700

11.5

18.3

25.8

29.1

65.5

42.6

61.5

9.7

78.5

170

High temperature series

4/5 AF

18650

Sub-C

1250

1600

2100

4000

2200

1270

1660

2200

4100

2310

14.4

18.3

48.2

50.2

65.5

42.6

25.5

37.5

TABLE 29.4b Speciﬁcations of Sealed Prismatic Nickel-Metal Hydride Single-cell

Batteries

Nominal

voltage

(V)

Capacity

(0.2C discharge)

(mAh)

Minimum Typical

Nominal dimension (mm)

Thickness

(T)

Width

(W)

Height

(H)

Weight

(g)

1.2

400

500

700

800

1000

1100

440

550

750

850

1100

1200

6.1

8.3

6.1

17.0

31.3

35.3

48.0

67.0

10.3

12.0

22.0

23.0

PORTABLE SEALED NICKEL-METAL HYDRIDE BATTERIES 29.35

TABLE 29.4c Speciﬁcations of ‘‘9-volt’’ Nickel-Metal Hydride Batteries

Nominal

voltage

(V)

Capacity

(0.2C discharge)

(mAh)

Minimum Typical Nominal dimension (mm) Weight (g)

7.2

8.4

150 160 17.5(T)

⫻ 26.5(W) ⫻ 48.5(H) 39

TABLE 29.4d Speciﬁcations of Button Type Nickel-Metal Hydride Batteries

Nominal capacity at 5-hr rate (mAh) 11 15 25 40 80 150 250 320

Nominal dimensions Diameter (mm)

Height (mm)

Weight (g)

9.40

2.30

0.58

2.40

0.61

11.52

3.00

1.25

5.45

1.70

15.42

16.25

3.50

7.50

4.60

24.98

6.33

11.50

8.68

14.50

Source for Tables 29.4 (a to d): GP Batteries (USA) Inc.

REFERENCES

1. T. Sakai, ‘‘Hydrogen Storage Alloys for Nickel-metal Hydride Battery.’’ Zeitschift feur Physikalische

Chemie, Bd. 183, S. 333–346 1994.

2. L. Y. Zhang, ‘‘Rare Earth-Based Metal Hydrides and NiMH Rechargeable Batteries,’’ Rare Earths:

Science Technology & Applications 3rd Symp. Orlando, Fla., Feb. 1997; Minerals, Metals & Materials

Soc.

3. D. M. Kim, ‘‘A Study of the Development of a High Capacity and High Performance ZR-Ti-MN-V-

Ni Hydrogen Storage Alloy for NiMH Batteries,’’ 279 J. Alloys and Compounds, Oct. 1998, 209–

214.

4. John K. Erbacher, ‘‘Nickel-Metal Hydride Technology Evaluation,’’ Final Report Wright Laboratories

WL-TR—96-2069, Fairborn, OH, 1996.

5. D. Friel, ‘‘How Smart Should a Battery Be?, Battery Power Products & Technology, March 1999 and

commercial literature and data books from various battery manufacturers.

6. J. Norman Allen, ‘‘The Payoff in Smart Battery Electronics’’ Battery Power Products & Technology,

July 2000.

30.1

CHAPTER 30

PROPULSION AND INDUSTRIAL

NICKEL-METAL HYDRIDE

BATTERIES

Michael Fetcenko

30.1 INTRODUCTION

Nickel-metal hydride (NiMH) batteries are now in high volume commercial production for

small portable battery applications. The key driving forces for the rapid growth of NiMH

are environmental and energy advantages over nickel-cadmium and the explosive growth of

portable electronic devices such as communication equipment and laptop computers. Because

of its technical advantages over other rechargeable systems, this system is currently being

developed for large batteries, including industrial and electric vehicle applications.

The ﬁrst introduction of electric vehicles began at the turn of the century, but was short-

lived after losing the competition to the Internal Combustion Engine (ICE). In the mid-

1970s, electric vehicles emerged again due to what turned out to be temporary gasoline

shortages. In the early 1990s, electric vehicles reemerged due to environmental air quality

concerns in urban areas. In particular, the California Air Resources Board (CARB) gave

electric vehicles tremendous attention by mandating that 2% of all vehicles sold in California

must be zero emission vehicles by 1998 and 10% of all vehicles by 2003. While the original

CARB mandate has changed, low and zero emission vehicles are still a high proﬁle devel-

opment focus for vehicle manufacturers.

The California mandate led to the formation of the United States Advanced Battery Con-

sortium (USABC), an unprecedented cooperation between the major U.S. automakers, the

U.S. Department of Energy, and the electric utility companies. Besides providing a central

funding source for a multitude of competing technology development organizations, USABC

provided the battery performance targets shown in Table 30.1 along with a comparison to

current NiMH status.

More recently, there has been a signiﬁcant shift by the automotive manufacturers from

electric vehicles toward hybrid electric vehicles (HEVs) due to several factors including

relaxation of the CARB mandate from zero to low emissions, customer reaction to initial

low range lead-acid electric vehicles, and the lack of geographically widespread EV charging

and fast charging stations.

30.2 CHAPTER THIRTY

TABLE 30.1 Primary USABC Midterm Performance Goals for the EV Battery and Actual

Performance of the Commercial and Advanced NiMH Battery

Property USABC

NiMH

Commercial Prototype

Speciﬁc energy (Wh kg

⫺

) 80 (100 desired) 63–75 85–90

Energy density (Wh per liter) 135 220 250

Power density (W per liter) 250 850 1000

Speciﬁc power (W kg

⫺

) (80%

DOD in 30 s)

150 (⬎200 desired) 220 240

Cycle life (cycles) (80% DOD) 600 600–1200 600–1200

Life (years) 5 10 10

Environmental operating

temperature

⫺30⬚ to 65⬚C ⫺30⬚ to 65⬚C ⫺30⬚ to 65⬚C

Recharge time

⬍6 hours 15 min (60%)

⬍1 hour (100%)

15 min (60%)

⬍1 hour (100%)

Self discharge

⬍15% in 48 hours ⬍10% in 48 hours ⬍10% in 48 hours

Ultimate projected price

(dollars per kWh) (10,000

units at 40 kWh)

⬍$150 $220–400 $150

30.2 GENERAL CHARACTERISTICS

Nickel-metal hydride batteries have become the dominant advanced battery technology for

EV and HEV applications by having the best overall performance to meet the requirements

set by USABC. In addition to the essential performance targets of energy, power, cycle life

and operating temperature, the following features of NiMH

1,2

have established this technol-

ogy in this market:

•

Flexible cell sizes from 0.3 to 250 Ah

•

Safe operation at high voltage (320⫹ V)

•

Excellent volumetric energy and power, ﬂexible vehicle packaging

•

Readily applicable to series and series/parallel strings

•

Choice of cylindrical or prismatic cells

•

Safety in charge and discharge, including tolerance to abusive overcharge and overdis-

charge

•

Maintenance free

•

Excellent thermal properties

•

Capability to utilize regenerative braking energy

•

Simple and inexpensive charging and electronic control circuits

•

Environmentally acceptable and recyclable materials

Examples of EV NiMH battery packs for the General Motors EV1 and S-10 pickup truck

are shown in Fig. 30.1. In addition, nickel metal-hybride batteries are being used in industrial

applications, replacing nickel-cadmium batteries and are being considered as a replacement

for lead-acid batteries in SLI applications.

PROPULSION AND INDUSTRIAL NICKEL-METAL HYDRIDE BATTERIES 30.3

FIGURE 30.1 GM Ovonic NiMH battery packs for General Motors

EV1 (30 kWh) and Chevrolet S-10 pickup truck (30 kWh).

30.3 CHEMISTRY

The chemistry and chemical reactions for large propulsion NiMH batteries are the same as

in small portable applications, as discussed in Chap. 29.

The active material in the positive electrode is nickel hydroxide. Usually, the nickel

hydroxide has a conductive network composed of cobalt oxides and a current collector which

commonly is a nickel foam skeleton, but may alternately be a nickel ﬁber matrix or may be

produced by sintering ﬁlamentary nickel ﬁbers.

The active material in the negative electrode is an alloy capable of storing hydrogen, and

usually of the AB

(LaCePrNdNiCoMnAl) or AB

(VTiZrNiCrCoMnAlSn) type, where the

‘‘AB

’’ designation refers to the ratio of the A type elements (LaCePrNd or TiZr) to that of

the B type elements (VNiCrCoMnAlSn). In either case, the materials have complex micro-

structures that allow the hydrogen storage alloys to operate in the aggressive environment

within the battery where most of the metals are thermodynamically more stable as oxides.

The metal hydride materials are conductive, and are applied to a current collector usually

made of perforated or expanded nickel, or nickel foam substrate. Copper current collectors

have recently emerged for extremely high rate discharge applications.

30.4 CHAPTER THIRTY

The electrolyte is also similar to small portable NiMH batteries, predominantly 6 Molar

KOHinH

O with a LiOH additive. Practically all NiMH batteries are sealed and use the

‘‘starved electrolyte’’ design, allowing for fast gas transport through the separator that is vital

for gas recombination. The separator itself is usually a highly porous permanently wettable

polypropylene, or it may be a polypropylene/ polyethylene composite made by either wet

laying of the ﬁbers or by the ‘‘melt blown’’ process. In either case, the separator is usually

made wettable by a grafting process that bonds a material such as acrylic acid to the base

ﬁbers by an energetic process such as radiation grafting. There are many variations within

the separators used by manufacturers and the processing details are proprietary.

30.4 CONSTRUCTION

30.4.1 Cylindrical Versus Prismatic Conﬁguration

NiMH batteries are versatile in that both cylindrical and prismatic constructions can be

utilized. Each type of construction has advantages and disadvantages, and a particular end

use can determine which conﬁguration is used. For NiMH applications below about 10 Ah,

cylindrical construction dominates due to low cost and high speed of manufacture. Above

20 Ah, cylindrical construction is extremely difﬁcult and the prismatic conﬁguration domi-

nates. In the 10 to 20 Ah cell size range, manufacturers are offering both cylindrical and

prismatic designs although prismatic designs are more common.

Cylindrical cells for industrial and propulsion applications are similar to high volume

production consumer batteries in that the well-known ‘‘jelly roll’’ construction is used. How-

ever, most small portable cylindrical cells require only low to moderate discharge rate ca-

pability and electrode terminal connections are usually quite simple. Conversely, since in-

dustrial and propulsion NiMH applications require high to ultra-high discharge rate capability

and low internal resistance, multiple tab current collection is used. This type of construction

is termed edge welding and requires each electrode to have a current collecting strip on one

side of the electrode. The current collecting strip for the positive and negative electrodes are

on opposite sides of the jellyroll. After coil winding of the jellyroll, the edge current collector

is welded in multiple locations to each electrode. Other aspects of cell assembly are virtually

identical to small consumer batteries. The net result of the enhanced current collection is a

reduction in cell speciﬁc energy and an increase in speciﬁc power due to decreased cell AC

impedance (usually around 8 to 12 m

⍀ for small portable batteries and around 1 to 2 m⍀

for industrial cylindrical cells). For industrial applications such as HEV, motorcycle and

electric bicycle applications, the most popular cylindrical cell sizes are standard C and D

sizes, although a multitude of height changes within those diameters are also used. Some

work on larger size cells such as the F size has also been reported.

Prismatic construction is conventional in that electrode stacks of alternating positive and

negative electrodes with intermediate separators are used (Fig. 30.2). The main design al-

ternatives involve the thickness and number of each electrode and the aspect ratio (relative

proportions of cell height to width to thickness). Key design variations include the ratio of

active materials to inactive components such as the cell can and terminal, and current col-

lectors. In all cases, the cell designer has the objective of emphasizing one or more properties

of performance such as energy vs. power, while maintaining a minimum threshold of other

performance factors such as cycle life. One example is that for EV NiMH prismatic cells,

a speciﬁc power of about 200 W/kg is acceptable for most vehicles and consequently,

relatively thick positive and negative electrodes can be used to increase the ratio of active

material to inactive cell components, allowing speciﬁc energy in the 63 to 80 Wh /kg range.

Alternately, HEV prismatic NiMH batteries typically must deliver greater than 500 W /kg

speciﬁc power and therefore electrode thickness must be lower than that for EV use. NiMH

batteries for HEV use have a typical speciﬁc energy ranging from about 42 to 68 Wh /kg.

PROPULSION AND INDUSTRIAL NICKEL-METAL HYDRIDE BATTERIES 30.5

Negative Terminal

Safety Vent

Positive Terminal

Electrode Tab

Positive

Electrode

Negative

Electrode

Cell Case

Separator

FIGURE 30.2 GM Ovonic 90 Ah Prismatic Cell and 13 V module.

30.4.2 Metal Versus Plastic Cell Cases

NiMH cylindrical cells exclusively use metal cell cases. One important reason is that the

can itself is electrically connected to the metal hydride negative electrode and serves as the

negative terminal. Another important reason is that many applications require fast charge

where gas recombination rates permit considerable internal pressure where only a metal

container would sufﬁce without signiﬁcant volumetric penalties. Finally, the metal crimp seal

to the cover plate assembly with a polysulfone seal ring is inexpensive, readily manufactur-

able, and reliable.

Both metal and plastic cell cases are common for the prismatic NiMH batteries used in

automotive applications such as electric vehicles. Unlike cylindrical cells where the can itself

is the negative terminal, prismatic design cells have both a positive and negative terminal at

the top cover plate. Key criteria for selecting metal cell cases include excellent thermal

conductivity, inexpensive prototyping costs for changing cell dimensions, and small volu-

metric penalties.

Advantages to plastic cell cases are cost and electrical isolation in the 320 V and higher

battery packs common to today’s electric vehicles, where even high resistance leakage cur-

rents to other vehicle components must be considered. Further design considerations for

plastic cell cases include development costs for permanent molds, gas permeation, thermal

conductivity, and sufﬁcient plastic thickness for gas pressure containment without can wall

bulging. NiMH battery modules using plastic cell cases are shown in Fig. 30.3.

30.6 CHAPTER THIRTY

FIGURE 30.3 Plastic cell case NiMH module designs of SAFT (93 Ah,

64 Wh / kg) and Matsushita (95 Ah, 63 Wh / kg).

30.4.3 Sintered Versus Pasted Nickel Hydroxide Positive

Positive electrodes for use in NiMH batteries for industrial and transportation application,

whether cylindrical or prismatic, can be of the sintered or pasted type also common to NiCd

batteries.

Sintered electrodes have the best rate and power capability,

but sacriﬁce capacity on a

weight and volume basis and are more expensive to manufacture. Sintered electrodes involve

an expensive and complicated sequence of manufacturing steps, and consequently only com-

panies with an existing capital investment for this process would manufacture sintered elec-

trodes. Sintered positives begin with the pasting of ﬁlamentary nickel onto a substrate such

as perforated foil, where the nickel ﬁbers are then ‘‘sintered’’ under a high temperature

annealing furnace in a nitrogen /hydrogen atmosphere and binders from the pasting process

are burned away to leave a conductive skeleton of nickel having a typical average pore

size of about 30 microns. Nickel hydroxide is then precipitated into the pores of the sinter

skeleton using either a chemical or electrochemical impregnation process. The impregnated

electrode is then formed or preactivated in an electrochemical charge/discharge process.