Sealed nickel cadmium

The aimual production value of small, sealed nickel—cadmium cells is over 1.2 biUion. However, environmental considerations relating to cadmium are necessitating changes in the fabrication techniques, as well as recovery of failed cells. Battery system designers are switching to nickel —metal hydride (MH) cells for some appHcations, typically in "AA"-si2e cells, to increase capacity in the same volume and avoid the use of cadmium. 

Lower cost and lower weight cylindrical cells have been made using plastic bound or pasted actwe material pressed into a metal screen. Tliese cells suffer slightly in utilization at high rates compared to a sintered-plate cylindrical cell, but they may be adequate for most applications. Tlie effect of temperature and discharge rate on the capacity of sealed nickel-cadmium cells is illustrated in Figure 8 and Table 3. 

Fig. 8. Discharge capacity of small sealed nickel—cadmium cells where the hiitial charge is 0.1 C x 16 h at 20°C and the discharge is 1 C at temperatures of...

A number of manufacturers started commercial production of nickel—MH cells in 1991 (31—35). The initial products are "AA"-size, "Sub-C", and "C -size cells constmcted in a fashion similar to small sealed nickel —cadmium cells. Table 6 compares the Ovonics experimental cell and a similar sized nickel—cadmium cell. Ovonics also deUvered experimental electric vehicle cells, 22 A-h size, for testing. The charge—discharge of "AA" cells produced in Japan (Matsushita) are compared in Figure 22. 

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.)...

Fig. 6.8 Schematic cross-seciion of spiral wound cylindrical sealed nickel-cadmium cell...

The sealed nickel-metal hydride cell (more consistently metal hydride-nickel oxide cell) has a similar chemistry to the longer-established hydro-gen-nickel oxide cell considered in Chapter 9. In most respects (including OCV and performance characteristics), it is very similar to the sealed nickel-cadmium cell, but with hydrogen absorbed in a metal alloy as the active negative material in place of cadmium. The replacement of cadmium not only increases the energy density, but also produces a more environmentally friendly power source with less severe disposal problems. The nickel-metal hydride cell, however, has lower rate capability, poorer charge retention and is less tolerant of overcharge than the nickel-cadmium cell. 

Sealed nickel-cadmium and nickel-metal hydride sealed cells for consumer equipment now generally employ charge control circuits which permit fast charging. A number of methods are used to detect the onset... 

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. 

Fig. 13.1 Cell balance for vented and sealed nickel cadmium cells. It is important to avoid hydrogen gas evolution in the sealed cell...

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