Linden D., Reddy T.B. (eds.) Handbook of batteries
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25.22 CHAPTER TWENTY-FIVE
Temperature Effects. As with other alkaline battery systems, silver-iron performance can
depend on the operating temperature. Cells designed for long-life and low-rate applications
normally have a higher internal resistance than those designed for high rate and shorter life.
The two designs therefore behave differently when the discharge temperature is decreased,
as shown in Figs. 25.26 and 25.27.
Experimental Designs. Experimental tests were conducted on designs other than the mono-
polar, prismatic designs discussed so far. Hand-assembled bipolar and jelly-roll cells were
tested at the laboratory demonstration level. Results of voltage polarization tests on those
designs are compared to the prismatic design in Fig. 25.28. The voltage characteristics of
the jelly-roll design would be expected to improve considerably as assembly is refined and
automated. Designs such as these would be suited for use in smaller portable systems such
as communication devices that may require high power and energy density.
FIGURE 25.26 Effect of temperature on discharge capacity for different battery designs,
C / 10 discharge rate. (Courtesy of Westinghouse Electric Corp.)
FIGURE 25.27 Effect of temperature on discharge voltage for different bat-
tery designs; C/ 10 discharge rate. (Courtesy of Westinghouse Electric Corp.)
IRON ELECTRODE BAT TERIES 25.23
FIGURE 25.28 Voltage polarization characteristics for silver-iron system
in experimental tests on three conventional types of cell designs. - - -, bipolar;
——, prismatic; – – –, jelly roll. (Courtesy of Westinghouse Electric Corp.)
TABLE 25.6 Theoretical Capacities of Fe(VI) Compounds
Material
Molecular
weight
(g.)
Valence
change
Electrochemical Equivalence
(mAh/ g) (g /Ah)
Li
2
FeO
4
133.7 3 601 1.66
Na
2
FeO
4
165.8 3 485 2.06
K
2
FeO
4
198.1 3 406 2.46
BaFeO
4
257.2 3 313 3.19
25.7 IRON MATERIALS AS CATHODES
Iron has conventionally been used as the anode or negative active material in batteries but
iron compounds have also been used as the cathode or positive active material. The use of
iron sulfides (FeS and FeS
2
) in lithium primary and in high temperature batteries is covered
in Chapters 14 and 41.
Recently, an iron oxide, having a high valence state, has been reported for use as a cathode
active material.
24
Iron normally exists as a metal or in the valence states of Fe(II) and Fe(III).
The new cathode material is an Fe(VI)-containing compound which has a high specific
capacity due to a 3-electron change in its reduction reaction, as follows:
2
⫺⫺
0
FeO ⫹ 3H O ⫹ 3e → FeOOH ⫹ 5OH E ⫽ ⬃0.9 Volt
42
The theoretical capacity of several of these Fe(VI) compounds is listed in Table 25.6. These
values can be compared with the values given in Table 1.1 for the more conventional cathode
materials.
25.24 CHAPTER TWENTY-FIVE
FIGURE 25.29 Stability of Fe(VI) in alkaline electrolyte with various concentrations of OH
⫺
,
K
2
FeO
4
salts, and Co(II) and Ni(II) impurities. (From Ref. 24.)
The characteristics of Fe(VI) compounds have not been studied extensively in the past
mainly because of the perception that these materials are highly unstable. While Li
2
FeO
4
and Na
2
FeO
4
are soluble in alkaline hydroxide, BaFeO
4
and K
2
FeO
4
show evidence of low
alkaline solubility and high stability as shown in Fig. 25.29. Further, their stability is greater
in the more concentrated alkaline solutions that are used as battery electrolytes. This data
has been extrapolated to suggest that, over a 10-year period, there will be less than a 10%
loss of Fe(VI) in concentrated potassium hydroxide solutions using highly purified materials.
Electrochemically, the FeO
4
2
⫺
species have a high reduction potential, on the order of 0.9
V. Against an anode of zinc, the open circuit potential was found to be 1.75 V and 1.85 V
for the K
2
FeO
4
and BaFeO
4
cell, respectively. The proposed discharge reaction mechanism
is as follows:
31 1
–– –
MFe(VI)O ⫹ Zn → Fe(III) O ⫹ ZnO ⫹ MZnO
42 2 232 2
where M ⫽ K
2
or Ba
The theoretical capacities and specific energy for the two batteries are given in Table
25.7. These values can be compared with those of other batteries listed in Table 1.2. The
values for the zinc/iron oxide cells are higher than most of the other batteries with the
exception of the lithium and air-breathing systems.
IRON ELECTRODE BAT TERIES 25.25
TABLE 25.7 Theoretical Capacity and Specific Energy for MFeO
4
batteries
Couple
Open
circuit
voltage
(V)
Theoretical
specific capacity
(g/ Ah)
Theoretical
specific capacity
(Ah/ g)
Theoretical
specific energy
(Wh/ kg)
Zn/K
2
FeO
4
1.75 3.68 0.271 475
Zn/ BaFeO
4
1.85 4.41 0.226 419
150 ohm
discharge
BaFeO
4
Discharge Voltage (V)
500 ohm
discharge
BaFeO
K FeO
MnO
4
4
2
2
6000 ohm
discharge
K FeO
MnO
2
2
4
Energy (W-h/kg)
FIGURE 25.30 Capacity of several experimental button cells using Fe(VI) compounds as cathodes
and Zn as anodes, compared to conventional Zn/ MnO
2
button cells. (From Ref. 24.)
The discharge characteristics and specific energy of experimental primary alkaline button
cells, with zinc anodes and Fe(VI) compounds cathodes, were measured and compared to
those with MnO
2
cathodes. These data are plotted in Figure 25.30 and illustrate the higher
energy output of the cells fabricated with the Fe(VI) cathodes. Similar results were obtained
with cells fabricated in the conventional cylindrical construction.
The Fe(VI) compounds were also shown to be rechargeable. A button cell, using a metal
hydride anode and a capacity limited K
2
FeO
4
cathode, was cycled for several cycles to a
75% depth of discharge and for more than 400 cycles to a 30% depth of discharge. The
open circuit voltage of the cell was 1.3 V and the midpoint voltage was 1.1 V, similar to
the voltage characteristics of the nickel-metal hydride cell.
The Fe(VI) compounds are promising candidates for cathode materials for both primary
and rechargeable alkaline batteries. The reported results demonstrate their higher specific
energy compared to other cathode materials now used in alkaline batteries. The questions of
long-term stability, shelf life and other critical performance characteristics, large scale man-
ufacture, materials cost, and so on, still have to be resolved and are subject to further eval-
uation.
25.26 CHAPTER TWENTY-FIVE
REFERENCES
1. S. U. Falk and A. J. Salkind, Alkaline Storage Batteries, Wiley, New York, 1969.
2. A. J. Salkind, C. J. Venuto, and S. U. Falk, ‘‘The Reaction at the Iron Alkaline Electrode,’’ J.
Electrochem. Soc. 111:493 (1964).
3. R. Bonnaterre, R. Doisneau, M. C. Petit, and J. P. Stervinou, in J. H. Thompson (ed.), Power Sources,
vol. 7, Academic, London, 1979, p. 249.
4. L. Ojefors, ‘‘SEM Studies of Discharge Products from Alkaline Iron Electrodes,’’ J. Electrochem.
Soc. 123:1691 (1976).
5. B. Anderson and L. Ojefors, in J. H. Thompson (ed.), Power Sources, vol. 7, Academic, London,
1979, p. 329.
6. J. L. Weininger, in R. G. Gunther and S. Gross (eds.), The Nickel Electrode, vol. 82-4, Electrochem-
ical Society, Pennington, N.J., 1982, pp. 1–19.
7. D. Tuomi, ‘‘The Forming Process in Nickel Positive Electrodes,’’ J. Electrochem. Soc. 123:1691
(1976).
8. INCO ElectroEnergy Corp. (formerly ESB, Inc.), Philadelphia, Pa.
9. ‘‘Nickel Iron Industrial Storage Batteries,’’ Exide Industrial Marketing Divisions of ESB, Inc., 1966.
10. F. E. Hill, R. Rosey, and R. E. Vaill, ‘‘Performance Characteristics of Iron Nickel Batteries,’’ Proc.
28th Power Sources Symp., Electrochemical Society, Pennington, N.J., 1978, p. 149.
11. R. Rosey and B. E. Tabor, ‘‘Westinghouse Nickel-Iron Battery Design and Performance,’’ EV Expo
80, EVC #8030, May 1980.
12. W. Feduska and R. Rosey, ‘‘An Advanced Technology Iron-Nickel Battery for Electric Vehicle
Propulsion,’’ Proc. 15th IECEC, Seattle, Aug. 1980, p. 1192.
13. R. Hudson and E. Broglio, ‘‘Development of the Nickel-Iron Battery System for Electric Vehicle
Propulsion,’’ Proc. 29th Power Sources Conf., Electrochemical Society, Pennington, N.J., 1980.
14. L. Carlsson and L. Ojefors, ‘‘Bifunctional Air Electrode for Metal-Air Batteries,’’ J. Electrochem.
Soc. 127:525 (1980).
15. L. Ojefors and L. Carlson, ‘‘An Iron-Air Vehicle Battery,’’ J. Power Sources, 2:287 (1977 /78).
16. J. F. Jackovitz and C. T. Liu, Extended Abstracts: 9th Battery and Electrochemical Contractors’
Conf., USDOE, Alexandria, Va., Nov. 12–16, 1989, pp. 319–324.
17. H. Cnoblock, D. Groppel, D. Kahl, W. Nippe, and G. Siemsen, in D. H. Collins (ed.), Power Sources,
vol. 5, Academic, London, 1975, p. 261.
18. O. Lindstrom, in D. H. Collins (ed.), Power Sources, vol. 5, Academic, London, 1975, p. 283.
19. The Silver Institute Letter, vol. 7, no. 3 (1977).
20. J. T. Brown, Extended Abstract No. 28, Battery Div. The Electrochemical Society, Las Vegas (NV),
pp. 76–77, (1977).
21. E. Buzzelli, ‘‘Silver-Iron Battery Performance Characteristics,’’ Proc. 28th Power Sources Symp.,
Electrochemical Society, Pennintgon, N.J., 1978, p. 160.
22. G. A. Bayles, E. S. Buzzelli, and J. S. Lauer, ‘‘Progress in the Development of a Silver-Iron Com-
munications Battery,’’ Proc. 34th Int. Power Sources Symp., Cherry Hill, N.J., June 1990.
23. G. A. Bayles, J. S. Lauer, E. S. Buzzelli, and J. F. Jackovitz, ‘‘Silver-Iron Batteries for Submersible
Applications,’’ Proc. 3rd Annual Underwater Vehicle Conf., Baltimore, Md., June 1989.
24. S. Licht, B. Wang, and S. Ghosh, Science 128:1039–1042 (1999).
26.1
TABLE 26.1 Major Advantages and Disadvantages of Industrial and Aerospace Nickel-
Cadmium Batteries
Advantages Disadvantages
Long cycle life Low energy density
Rugged; can withstand electrical and physical abuse Higher cost than lead-acid batteries
Reliable; no sudden death Contains cadmium
Good charge retention
Excellent long-term storage
Low maintenance
CHAPTER 26
INDUSTRIAL AND AEROSPACE
NICKEL-CADMIUM BATTERIES
Arne O. Nilsson and Christopher A. Baker
26.1 INTRODUCTION
The vented pocket-plate battery is the oldest and most mature of the various designs of
nickel-cadmium batteries available. It is a very reliable, sturdy, long-life battery, which can
be operated effectively at relatively high discharge rates and over a wide temperature range.
It has very good charge retention properties, and it can be stored for long periods of time
in any condition without deterioration. The pocket-plate battery can stand both severe me-
chanical abuse and electrical maltreatment such as overcharging, reversal, and short-
circuiting. Little maintenance is needed on this battery. The cost is lower than for any other
kind of alkaline storage battery; still, it is higher than that of a lead-acid battery on a per
Watthour basis. The major advantages and disadvantages of this type of battery are listed in
Table 26.1.
The pocket plate battery is manufactured in a wide capacity range, 5 to more than 1200
Ah, and it is used in a number of applications. Most of these are of an industrial nature,
such as railroad service, switchgear operation, telecommunications, uninterruptible power
supply, and emergency lighting. The pocket plate battery was also used in military and space
applications.
The pocket plate batteries are available in three plate thicknesses to suit the variety of
applications. The high-rate designs use thin plates for maximum exposed plate surface per
volume of active material. They are used for the highest-rate discharge. The low-rate designs
26.2 CHAPTER TWENTY-SIX
use thick plates to obtain maximum volume of active material per exposed plate surface.
These types are used for long-term discharge. The medium-rate designs use plates of middle
thickness and are suited for applications between, or combinations of, high-rate and long-
term discharge.
Developmental work has been conducted almost continuously since the introduction of
the pocket-plate nickel-cadmium battery to improve the performance characteristics of the
battery and reduce weight. The sintered plate, which can be constructed in a thinner form
than the pocket plate, was developed during the 1940s and has a lower internal resistance
and gives superior high rate and low temperature performance compared to the pocket plate.
It is used in high-power applications, such as engine starting, and in low-temperature envi-
ronments. The sintered-plate battery is covered in Chap. 27. Further development of the
sintered plate led to the design of smaller batteries for portable equipment and subsequently
to the sealed, maintenance-free nickel-cadmium battery covered in Chap. 28.
The sintered-plate battery was found to be too expensive and complex to manufacture. It
used a large amount of nickel and was impractical for medium-rate thick electrodes or for
cells larger than 100 Ah. The pocket plate battery was too heavy for many applications.
Recent developmental work has been directed to more effectively use the costly materials—
nickel and cadmium—and toward simplified manufacturing processes. The design philoso-
phy was to develop a high-surface-area, conductive-plate structure that would be light, easy
to manufacture, inexpensive and to eliminate the troublesome aspects of sintered plate tech-
nology, namely, the sintering process and the chemical impregnation of the active materials.
Taking advantage of new polymer materials and plating techniques, this work has resulted
in a new electrode structure, the fiber-structured electrode (the Fiber Nickel Cadmium
Battery—FNC) developed by Deutsche Automobilgesellschaft mbH (DAUG).
The fiber plates are manufactured from either a mat of pure nickel fibers or more com-
monly nickel-plated plastic fibers. To make the plastic fiber conductive, a thin layer of nickel
is applied by electroless plating and thereafter a sufficiently thick layer of nickel for good
conductivity is applied by electroplating. The plastic is then burned off, leaving a mat of
hollow nickel fibers. The nickel fiber plaque is welded to a nickel-plated steel tab. Figure
26.1a shows the structure of a nickel fiber plaque before impregnation and Fig. 26.1b shows
an unformed positive electrode.
This fiber electrode technology, while originally developed for EV applications, was first
used for industrial low and medium rate vented cells. It is now being used in all types of
nickel-cadmium as well as nickel-metal hydride batteries, including high-rate batteries for
engine-cranking and sealed cells with oxygen recombination. Details of this technology are
covered in Sec. 26.6.
A more recent design that has shown significantly improved performance characteristics
is the plastic-bonded or pressed-plate electrode. This new development of electrode materials
in industrial batteries is a spin-off from the development of electrode materials for use in
aircraft and sealed portable consumer batteries. In the plastic-bonded plate, which is mainly
used in the cadmium electrode, the active material cadmium oxide is mixed with a plastic
powder, normally PTFE, and a solvent to produce a paste. The paste is isotropic and the
materials are manufactured at the final density for the active material. As a result, dust
problems are eliminated during manufacturing. The paste is extruded, rolled, or pasted onto
a center current collector normally made of nickel-plated perforated steel. The plate structure
is welded to nickel-plated steel tabs.
INDUSTRIAL AND AEROSPACE NICKEL-CADMIUM BATTERIES 26.3
FIGURE 26.1a Nickel-fiber electrode structure be-
fore impregnation. (Courtesy Acme Electric Corp.)
FIGURE 26.1b Unformed, pasted nickel positive
electrode. (Courtesy Acme Electric Corp.)
26.4 CHAPTER TWENTY-SIX
FIGURE 26.2 Pocket plate cells.
26.2 CHEMISTRY
The basic electrochemistry is the same for the vented pocket plate, sintered plate, fiber and
plastic-bonded plate types as well as for other variations of the nickel-cadmium system. The
reactions of charge and discharge can be illustrated by the following simplified equation:
discharge
—— —
2NiOOH ⫹ 2H O ⫹ Cd 2Ni(OH) ⫹ Cd(OH)
———
2
22
charge
On discharge, trivalent nickel oxy-hydroxide is reduced to divalent nickel hydroxide with
consumption of water. Metallic cadmium is oxidized to form cadmium hydroxide. On charge,
the opposite reactions take place. The electromotive force (EMF) is 1.29 V.
The potassium hydroxide electrolyte is not significantly changed with regard to density
or composition during charge and discharge, in contrast to the sulfuric acid in lead-acid
batteries. The electrolyte density is generally approximately 1.2 g /mL. Lithium hydroxide
is often added to the electrolyte for improved cycle life and high-temperature operation. A
more detailed description of the cell reaction on overcharge is found in Sec. 26.6.
26.3 CONSTRUCTION
A cutaway view of a modern pocket-plate cell is shown in Fig. 26.2. The active material for
the positive electrodes consists of nickel hydroxide mixed with graphite for conductivity and
INDUSTRIAL AND AEROSPACE NICKEL-CADMIUM BATTERIES 26.5
additives such as barium or cobalt compounds for improved life and capacity. The active
material for the negative electrodes is prepared from cadmium hydroxide or cadmium oxide
mixed with iron or iron compounds and sometimes also with nickel. The iron and nickel
materials are added to stabilize the cadmium, prevent crystal growth and agglomeration, and
improve conductivity. Typical active material compositions are shown in Table 26.2.
TABLE 26.2 Typical Composition of Active Materials for Pocket Plate Cells in the Discharged State
Positive active material
Substance Weight %
Negative active material
Substance Weight %
Nickel (II) hydroxide 80 Cadmium hydroxide 78
Cobalt (II) hydroxide 2 Iron 18
Graphite 18 Nickel 1
Graphite 3
The positive and negative electrodes of pocket-plate nickel-cadmium batteries are made
using the same basic design to hold the active materials. The pocket plates are built up of
flat pockets of perforated steel strips holding the active materials. The thin steel strips are
perforated by hardened steel needles or by a technique using profiled roller dies. The specific
hole area is between 15 and 30%. The strips are nickel-plated to prevent ‘‘iron poisoning’’
of the positive active material.
The active mass is either pressed into briquettes, which are fed into the preshaped per-
forated strip, or fed into the preshaped strip as a powder. The upper and lower steel strips
are folded together by rollers. A number of these folded strips are arranged to interlock with
each other to form long electrode sheets, which are then cut to electrode blanks. Electrodes
are made from these blanks by providing them with steel frames for mechanical stability
and for current takeoff.
The electrodes are made with different thicknesses (1.5 to 5 mm) to provide cells for
high, medium and low-rate discharge rates. The negative plate is always thinner (30 to 40%)
than the positive.
The electrodes are bolted or welded to electrode groups. Plate groups of opposite polarity
are intermeshed and electrically separated from each other by plastic pins and plate edge
insulators, Sometimes separators or perforated plastic sheets or plastic ladders are used be-
tween the electrodes. The distance between plates of different polarity in an element may
vary from less than 1 mm for high-rate cells to 3 mm for low-rate cells.
The elements are inserted into cell containers of plastic or stainless steel. Plastic containers
are made from polystyrene, polypropylene, or flame-retardant plastics. Important advantages
of plastic containers over steel containers are that they allow visual control of the electrolyte
level and they require no protection against corrosion. Also, they have lower weight and
they can be more closely packed in the battery. The main drawbacks are that they are more
sensitive to high temperatures and they require somewhat more space than steel containers.
A plastic-bonded plate cell in a plastic container is shown in Fig. 26.3.