Linden D., Reddy T.B. (eds.) Handbook of batteries
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VENTED SINTERED-PLATE NICKEL-CADMIUM BATTERIES 27.27
FIGURE 27.19 Vented sintered-plate nickel-cadmium battery. (Courtesy of Eagle-Picker Technologies,
LLC. Power Systems Dept.)
27.28 CHAPTER TWENTY-SEVEN
FIGURE 27.20 Typical assembly of vented sintered-plate nickel-cadmium aircraft
battery.
VENTED SINTERED-PLATE NICKEL-CADMIUM BATTERIES 27.29
27.8.3 Air Cooling/ Heating
The major battery manufacturers produce some battery designs with provision for forced-air
cooling. These designs generally take the form of plenum spaces below and above the cells,
with cooling passages between the cells connecting the two plenums. The construction pro-
vides a means for the external connection of a high-volume, low-pressure air source. Sup-
plying 23
⬚C air will not only effectively cool an overheating battery, it will also rapidly
warm a cold battery. The heat transfer coefficient from the battery core is improved up to
10 times by this technique. The thermal time constant for a battery with this feature may be
as short as 10 to 20% of that of a standard non-air-cooled battery.
27.8.4 Temperature Sensors
Sensors may be provided inside the battery case which sense either typical or average cell
temperatures. They are equipped with a provision for external electrical connections. These
devices may be of the on-off type, such as thermostats, or they may be the continuous type,
such as thermistor assemblies. Continuous types have the capability of providing continuous
modulation of, for example, the regulated charging voltage of a CP charging source or of
the cutoff/ turn-on voltages of a constant-current VCO charging system.
27.8.5 Battery Cases
Although the corrosive effect of KOH on bare steel is minimal and cosmetic in effect,
additional KOH resistance in the case material is desirable. In addition to stainless steel and
steel with a protective finish, some special applications use KOH-resistant plastic materials.
It must be emphasized, however, that battery cases may require withstanding significant
rough treatment in shock and vibration without losing their KOH-containment capability.
27.8.6 Battery Electrical Termination
Aircraft batteries are normally terminated on the front case surface by a connector of the
type shown in Fig. 27.19. Special applications, however, may utilize direct cable connection
to the first and last cell terminals, as well as various other special configurations capable of
handling the high-current rates available in the event of a short circuit of the external battery
circuit.
27.8.7 Battery Heaters
Alternative to the airflow heating discussed in Sec. 27.8.3, heater blankets are sometimes
employed on the inside or outside of the battery case. These blankets may be energized with
any available electric energy source. Primarily this source will be either the DC bus of the
same voltage as the battery or an aircraft AC bus of higher potential. Heaters may also be
energized from an auxiliary ground supply. Heater blankets have the inherent poor thermal
time constant of nonair-cooled batteries.
27.30 CHAPTER TWENTY-SEVEN
27.8.8 Extensions of Vented Sintered-Plate Nickel-Cadmium Designs
To avoid costly maintenance procedures associated with vented nickel-cadmium designs and
to improve general battery reliability, the U.S. Air Force has incorporated lessons learned
from vented cell anomalies into a Maintenance Free Nickel-Cadmium Aircraft Battery. This
battery uses the same geometric cell shape as the vented nickel-cadmium design, but allows
gasses to recombine inside the cell. The cell design has a number of features found in
aerospace cell technology. It is not strictly a sealed design since the cell will vent at a high
pressure then reseal itself well above ambient pressure. To avoid excessive overcharge and
associated thermal runaway, the cell is charged and controlled by its own integrated charger
and associated electronics. This battery design is now supplied to several military aircraft
programs by Eagle-Picher Technologies, LLC, Power Systems Department, in Colorado
Springs, Colorado.
12
REFERENCES
1. J. McBreen, The Nickel Oxide Electrode, Modern Aspects of Electrochemistry, No. 21, Ralph E.
White, J. O’M. Bockris and B. E. Conway, Eds., p. 29, Plenum Press, 1990, New York.
2. D. F. Pickett and J. T. Maloy, J. Electrochem. Soc., 12:1026 (1978).
3. S. U. Falk and A. J. Salkind, Alkaline Storage Batteries, Wiley, New York, 1969.
4. A. Fleischer, J. Electrochem. Soc. 94:289 (1948).
5. G. Halpert, J. Power Sources 12:117 (1984).
6. D. F. Pickett, in Proceedings of the Symposium on Porous Electrodes, Theory and Practice, (eds.)
H. C. Maru, T. Katan, and M. G. Klein, The Electrochemical Society, Pennington, NJ, 1982, p. 12.
7. M. B. Pell and R. W. Blossom, U.S. Patent 3,507,699 (1970).
8. R. L. Beauchamp, U.S. Patent 3,573,101 (1971); U.S. Patent 3,653,967 (1972).
9. D. F. Pickett, U.S. Patent 3,827,911 (1974); U.S. Patent 3,873,368 (1975).
10. Mil-B-81757, Performance Specification, Batteries and Cells, Storage, Nickel Cadmium, Aircraft
General Specification, Crane Division, NSWC, July 1, 1984.
11. J. J. Lander, personal communication.
12. T. M. Kulin, 33rd Intersociety Engineering Conference on Energy Conversion IECEC-98-145, Col-
orado Springs, CO, August 2-6, 1998.
28.1
TABLE 28.1 Major Advantages and Disadvantages of Seated Nickel-Cadmium Batteries
Advantages Disadvantages
Batteries are sealed; no maintenance
required
Long cycle life
Good low-temperature and high-rate
performance capability
Long shelf life in any state of charge
Rapid recharge capability
Voltage depression or memory effect in
certain applications†
Higher cost than sealed lead-acid battery
Poor charge retention
Sealed lead-acid battery better at high
temperature and float service*
Environmental concern with the use of
cadmium
Lower capacity than other competitive
batteries
* High-temperature nickel-cadmium batteries are available (see Sec. 28.6.3).
† See Sec. 28.4.11.
CHAPTER 28
PORTABLE SEALED NICKEL-
CADMIUM BATTERIES
Joseph A. Carcone
28.1 GENERAL CHARACTERISTICS
Sealed nickel-cadmium batteries incorporate specific battery design features to prevent a
buildup of pressure in the battery caused by gassing during overcharge. As a result, batteries
can be sealed and require no servicing or maintenance other than recharging. These unique
characteristics for a secondary battery have created wide acceptance for use in a variety of
applications, ranging from lightweight portable power (photography, toys, housewares) to
high-rate, high-capacity power (electronic devices such as phones, computers, camcorders,
power tools) and standby power (emergency lighting, alarm, memory backup). Some nickel-
cadmium batteries are now incorporating smart battery control circuitry to give state-of-
charge indication and to control overcharge and overdischarge (see Chap. 5).
The major advantages and disadvantages of the sealed nickel-cadmium battery are sum-
marized in Table 28.1. The important characteristics are described in this section.
28.2 CHAPTER TWENTY-EIGHT
Maintenance-free operation: The batteries are sealed, contain no free electrolyte, and
require no servicing or maintenance other than recharging.
High-rate charging: Sealed nickel-cadmium batteries are capable of recharge at high rates
within 1 h under controlled conditions. Many batteries can be charged in 3 to 5 h without
special controls, and all can be recharged within 14 h.
High-rate discharge: Low internal resistance and constant-discharge voltage make the
nickel-cadmium battery especially suited for high-rate discharge or pulse-current appli-
cations.
Wide temperature range: Sealed nickel-cadmium batteries can operate over the range from
about
⫺40 to 50⬚C and are particularly noted for their low-temperature performance.
Premium performance batteries extend this range to 70
⬚C.
Long service life: Over 500 cycles of discharge or up to 5 to 7 years of standby power
are common to sealed nickel-cadmium batteries.
28.2 CHEMISTRY
The active materials of the sealed nickel-cadmium battery are the same as for other types
of nickel-cadmium batteries, namely, in the charged state, cadmium for the negative elec-
trode, nickel oxyhydroxide for the positive, and a solution of potassium hydroxide for the
electrolyte In the discharged state, nickel hydroxide is the active material of the positive
electrode, and cadmium hydroxide that of the negative.
During charge, nickel hydroxide, Ni(OH)
2
, is converted to a higher-valence oxide,
⫺
Ni(OH) ⫹ OH → NiOOH ⫹ HO⫹ e
22
At the negative electrode, cadmium hydroxide, Cd(OH)
2
, is reduced to cadmium,
Cd(OH)
⫹ 2e → Cd ⫹ 2OH
2
The overall discharge/ charge reaction is
discharge
—
Cd ⫹ 2NiOOH ⫹ 2H O Cd(OH) ⫹ 2Ni(OH)
—
222
charge
During operation, the active materials undergo changes in their oxidation states but little
change in their physical states. Similarly, there is little if any change in the electrolyte
concentration. The active materials of both electrodes, in both charged and discharged states,
are relatively insoluble in the alkaline electrolyte, remain as solids, and do not dissolve while
undergoing changes in their oxidation states. Because of these and other properties, nickel-
cadmium batteries are characterized by long life in both cyclic and standby operation and
by a relatively flat voltage profile over a wide range of discharge currents.
The operation of the sealed battery is based on the use of a negative electrode having a
higher effective capacity than the positive. During charge, the positive plate reaches full
charge before the negative and begins to evolve oxygen. The oxygen migrates to the negative
electrode, where it reacts with and oxidizes or discharges the cadmium to produce cadmium
hydroxide,
1
–
Cd ⫹ O ⫹ HO→ Cd(OH)
22 2 2
A separator permeable to oxygen is used so that oxygen can pass through the separator to
the negative electrode. Also, a limited amount of electrolyte is used (starved electrolyte
system) as this facilitates the transfer of oxygen. This process is illustrated in Fig. 28.1.
PORTABLE SEALED NICKEL-CADMIUM BATTERIES 28.3
FIGURE 28.1 Oxygen recombination process. (Courtesy of Sanyo Energy Corp.)
At a steady state, the recombination reaction rate during overcharge must be no lower
than the rate of oxygen generation to prevent buildup of pressure. The internal pressure is
sensitive to charge current, the reactivity of the negative electrode, the electrolyte level, and
the temperature. Solid cadmium, gaseous oxygen, and liquid water must coexist in mutual
contact for the recombination reaction to occur. If, for example, the electrolyte level is too
high (the electrodes are in a flooded state), the oxygen is prevented from contacting the
electrode, and the reaction rate at a given temperature and pressure is substantially lowered.
A safety venting mechanism is used in the battery design to prevent rupture in case of
excessive pressure buildup due to a malfunction, high charge rate, or abuse.
28.3 CONSTRUCTION
Sealed nickel-cadmium cells and batteries are available in several constructions. The most
common types are the cylindrical shaped batteries (see Table 28.3). Smaller button batteries
and rectangular batteries are also manufactured.
28.3.1 Cylindrical Batteries
The cylindrical battery is the most widely used type because the cylindrical design lends
itself readily to mass production and because excellent mechanical and electrical character-
istics are achieved with this design. Figure 28.2 shows a cross section of the cylindrical
battery.
The positive electrode is a highly porous sintered, foam or fibered nickel structure into
which the active material is introduced by embedding or impregnation with a molten nickel
salt, followed by the precipitation of nickel hydroxide by immersion or electrochemical
deposition in an alkaline solution. The negative electrodes are made by several methods:
using a sintered-nickel substrate similar to the positive, by pasting or pressing the negative
active material onto a substrate, or by a continuous electrodeposition process.
After processing, the positive and negative electrodes are cut to size and wound together
in a jelly-roll fashion with a separator material between them. The separator material, usually
unwoven nylon or polypropylene, is highly absorbent to the potassium hydroxide electrolyte
and permeable to oxygen. The roll is inserted into a rugged nickel-plated steel can, and the
electrical connections are made. The negative electrode is welded or press connected to the
28.4 CHAPTER TWENTY-EIGHT
can and the positive to the top cover. The very small amount of the electrolyte, enough for
efficient operation, is absorbed by the separator. There is no free liquid electrolyte. The cover
assembly incorporates a fail-safe vent mechanism to prevent rupture in case of excessive
pressure buildup, which could result from extreme overcharge or discharge rates.
FIGURE 28.2 Construction of sealed nickel-cadmium
cylindrical battery.
28.3.2 Button Batteries
Nickel-cadmium button cells and batteries usually have electrodes made from ‘‘pressed’’
plates. The active materials are compressed in molds into disks or plates, and the electrodes
are assembled in a sandwich configuration, as shown in Fig. 28.3.
In some cases the electrodes are backed with expanded metal or screen to enhance elec-
trical conductivity and mechanical strength. The button battery does not have a resealable
fail-safe device, but its construction allows the battery to expand, either breaking the elec-
trical continuity or opening the seal to relieve excess pressure caused by an abnormal cir-
cumstance. Button batteries are very suitable for low-current, low-overcharge-rate applica-
tions.
PORTABLE SEALED NICKEL-CADMIUM BATTERIES 28.5
Cap (–)
Contact spring
Cell cup (+)
Gasket
Negative electrode
Separator
Positive electrode
FIGURE 28.3 Nickel-cadmium battery, button configuration.
28.3.3 Slim Rectangular Batteries
The slim or flat rectangular batteries are designed to meet the needs of lightweight and
compact equipments. The rectangular shape permits more efficient battery assembly, elimi-
nating the voids that occur with the assembly or cylindrical batteries. The volumetric energy
density of batteries can be increased by a factor of about 20%.
Figure 28.4 shows the structure of the slim rectangular battery. The plates are manufac-
tured as described in Sec. 28.3.1, but the finished electrodes are cut to predetermined di-
mensions and placed in the metal casing. These are then hermetically sealed in place to the
cover plate. All sides of the casing and cover-plate assembly are laser-welded together to
prevent electrolyte leakage. A resealable safety venting system is built into these batteries
similar to the ones used in the cylindrical designs.
FIGURE 28.4 Construction of sealed slim rectangular battery. (Cour-
tesy of Sanyo Energy Corp.)
28.3.4 Rectangular Batteries
The rectangular battery is housed in a nickel-plated steel can using a construction similar to
the vented battery, but incorporating the features needed for sealed-battery operation. This
construction is particularly suited for high discharge rates because of the large electrode area.
Figure 28.5 is an illustration of a sealed rectangular battery, in this case using fiber-structured
electrodes (see Sec. 26.6).
28.6 CHAPTER TWENTY-EIGHT
FIGURE 28.5 Sealed rectangular nickel-cadmium battery using fiber-structured
electrodes. (Courtesy of Hoppecke Batteries.)
28.4 PERFORMANCE CHARACTERISTICS
28.4.1 General Characteristics
A typical charge-discharge cycle for the sealed nickel-cadmium cylindrical battery, at 20⬚C,
is shown in Fig. 28.6. The voltage increases slowly but steadily at the C /10 charge rate to
a steady-state condition, decays slightly during the 1-h rest, and is relatively flat during the
1-h discharge to 1.0 V. The voltage recovers rapidly over the next hour, while at rest, to
near 1.2 V.