Nickel-cadmium cells sealed

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. 

To complete the assembly of a cell, the interleaved electrode groups are bolted to a cov er and the cover is sealed to a container. Originally, nickel-plated steel was the predominant material for cell containers but, more recently plastic containers have been used for a considerable proportion of pocket nickel-cadmium cells. Polyethylene, high impact polystyrene, and a copolymer of propylene and ethylene have been the most widely used plastics. 

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. 

Fig. 14-6 Circuit diagram for a dc decoupling device with nickel-cadmium cell. (KE) insulated cable end sealing, (E) grounding installation, (1) grounding side bar (2) NiCd cell, 1.2 V (3) breakdown fuse (4,5) isolating links.

The manufacture of secondary batteries based on aqueous electrolytes forms a major part of the world electrochemical industry. Of this sector, the lead-acid system (and in particular SLI power sources), as described in the last chapter, is by far the most important component, but secondary alkaline cells form a significant and distinct commercial market. They are more expensive, but are particularly suited for consumer products which have relatively low capacity requirements. They are also used where good low temperature characteristics, robustness and low maintenance are important, such as in aircraft applications. Until recently the secondary alkaline industry has been dominated by the cadmium-nickel oxide ( nickel-cadmium ) cell, but two new systems are making major inroads, and may eventually displace the cadmium-nickel oxide cell - at least in the sealed cell market. These are the so-called nickel-metal hydride cell and the rechargeable zinc-manganese dioxide cell. There are also a group of important but more specialized alkaline cell systems which are in use or are under further development for traction, submarine and other applications. 

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

Fig. 6.10 Battery for Viking Mars orbiting spacecraft, comprising 26 sealed 30 Ah nickel-cadmium cells, which was placed in Mars orbit in 1976. (By courtesy of Jet Propulsion Laboratory,)...

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. 

Button, cylindrical and prismatic sealed cells are similar in design to the starved-electrolyte configuration of nickel-cadmium cells. A schematic diagram of a six-cell battery is shown in Fig. 6.11. Because of the slightly... 

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

Note The letter K always indicates a nickel/cadmium cell or a battery conforming to the specihcations of lEC Standard 60285, sealed nickel/cadmium cylindrical... 

Because rapid oxygen recombination eliminates the pressure buildup normally associated with sealed nickel cadmium cells, high charging rates can be sustained even in the overcharge mode. Also, it is possible to use conventional nylon cell construction to produce prismatic sealed cells rather than the cylindrical design required for high pressure cells. The sealed... 

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. 

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