Sealed nickel-cadmium batteries

Nickel-cadmium and nickel-iron are prime examples of rechargeable (secondary) batteries, invented in 1901 by Waldemar Jungner and Edison, respectively. In the 1920s and 1930s, such batteries powered radios prior to rural clectrificadnn. The sealed nickel-cadmium battery is now the most widely used battery in consumer products. 

Lead hydroxide is used in making porous glass in electrical-insulating paper in electrolytes in sealed nickel-cadmium batteries in recovery of uranium from seawater and as a catalyst for oxidation of cyclododecanol. 

Fig. 6.7 Nominal 6 V sealed nickel-cadmium battery formed by connecting five cells in scries, (By courtesy of Varta.)...

Refs. [i] Crompton TR (2000) Battery reference book, 3rd edn. Buttersworth-Heinemann, Oxford, 9/8, 30/3,47/11 [ii] Linden D (1994) Factors affecting battery performance. In Linden D (1994) Handbook of batteries, 2nd edn. McGraw-Hill, New York, pp 3.5-3.11 [Hi] Carcone JA (1994) Sealed nickel-cadmium batteries. In Linden D (1994) Handbook of batteries, 2nd edn. McGraw-Hill, New York, pp 28.1-33.35... 

Maintenance-free battery— A rechargeable - battery that does not require replenishing of water during its service life. Usually the term refers to maintenance-free -> lead-acid and sealed nickel-cadmium batteries, which, in contrary to the conventional ones, are designed to suppress water loss due to -> electrolysis (overcharging) and evaporation. 

The situation is different for sealed nickel/cadmium batteries, due to the internal oxygen cycle. Figure 1.15 illustrates the heat evolution of a sealed nickel/ cadmium battery during constant-current charging with a charge factor of 1.4 (such an amount of overcharge is usual for conventional charging methods but can only be applied to comparably small batteries < 10 Ah). 

Figure 1.15 Charging of a sealed nickel/cadmium battery with constant current 0.2 C(A). During 7 hours 140% of the nominal capacity are recharged, which corresponds with a charge factor 1.4. For comparison, all values are converted to 100 Ah of nominal capacity. Actually, batteries of this type and for such a charging schedule are only available in sizes < 10 Ah.

Various types of plastic materials are used in the different systems. In lead-acid batteries it is a must to use glass, rubber, or plastics on account of the high cell voltage that would destroy all metals. The advantage of a plastic container is that no insulation is required between adjacent cells. A general drawback of plastic materials is their permeability for gasses, water vapor, and volatile substances. Therefore, with sealed nickel/cadmium batteries and also nickel/metal hydride batteries metal is used as container material. 

In sealed nickel/cadmium batteries, oxygen evolution and oxygen reduction that form the internal oxygen cycle are the only reactions during overcharging (cf. Section 1.8.2.2). 

The internal oxygen cycle, formed by oxygen evolution at the nickel-hydroxide electrode and its subsequent reduction at the cadmium electrode, was already detected in the 1940s as a possibility to avoid gas escape during overcharging, and the sealed nickel/cadmium battery appeared on the market in the 1950s. Immobilization of the alkaline electrolyte is achieved by absorption in mats of fibers of polyamide or polypropylene. Formation of a gel, as described in Section... 

Figure 1.32 Cell balance of a sealed nickel/cadmium battery.

The characteristics of nickel/metal hydride batteries are very similar to those of sealed nickel/cadmium batteries. The cell voltage differs by only 20 mV, and charging as well as discharging performance are so alike that both battery systems can be replaced by each other in all normal applications. The discharge curves in Fig. 1.38 confirm this. 

Varta Batterie AG. Sealed Nickel Cadmium Batteries. Diisseldorf VDI Verlag GmbH, 982, p 59. 

In portable applications were batteries are exposed to temperature extremes or rough handling, nickel-cadmium batteries are used for signal lamps, hand lamps, search lights, and portable instmments. Vented spillproof batteries are used in large devices, whereas sealed nickel-cadmium batteries dominate the smaller ones (see Chap. 27). 

The major advantages and disadvantages of the sealed nickel-cadmium battery are summarized in Table 28.1. The important characteristics are described in this section. 

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. 

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. 

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