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Nickel-cadmium accumulators (Glossary) |
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| Although NiCd rechargeable batteries display excellent qualities such as a high energy density, ruggedness, resistance to cold and service life as well as a favourable price and long storage life, their days are numbered on account of the toxicity of the cadmium they contain. In some countries corresponding bans are already in effect and the replacement of this type of accumulator has begun, primarily through nickel-metal hydride accumulators. Nevertheless, the production of NiCd-accumulators in 2003 still accounted for the largest share of cadmium consumption in Germany with around 600 tones p.a. See also: Ban on cadmium and mercury In nickel-cadmium cells containing a basic electrolyte (caustic potash solution), metallic cadmium is oxidised to cadmium hydroxide at the anode and at the same time trivalent nickel-oxide hydrate is reduced to its bivalent form at the cathode. The overall reaction, greatly simplified, is as follows:  Typical performance data and uses  Cell terminal voltage: 1.2 volts Service life in charge cycles: 1,000 to 1,500 (2,000) For use in ambient temperatures: (-40°C) -30°C to +50°C (+70°C) Typical energy density: 50 - 70 Wh/kg (theoretically approx. 240 Wh/kg) Typical volumetric energy density: 130 Wh/l Typical power density: 150 - 200 W/kg Typical spontaneous discharge: to 20% residual capacity within 3 monthsDisadvantageous are the relatively high spontaneous discharge, relatively high susceptibility to the so-called memory effect and the toxicity of the cadmium. NiCd cells have extremely diverse fields of use: millions of individual small cells can be found in a wide variety of devices such as torches, portable phones or CD players. Assembled into battery packs (Power-Packs) they are used as energy sources in mobile phones, notebooks or cordless screwdrivers. As plate accumulators with peak currents of 500-1,000 amperes they are used, for example, in the aerospace industry, as traction batteries for industrial trucks or as starter batteries in very cold environments. Historical development The nickel-cadmium accumulator was the first system that was able to establish itself on a large scale after the earlier lead accumulators. What was new at that time was not only the choice of electrode materials but above all the principle of the alkaline electrolyte. Since this type of electrolyte only serves as an ion conductor and does not take part itself in the chemical reactions within the cell it is subject to hardly any change, which has a positive effect on the ageing process of the accumulator. Since 1950, nickel-cadmium accumulators have also been produced in a gas-tight design, making them maintenance-free and also prolonging their service life. A safety valve is integrated in the gas-tight Ni-Cd cells as an overcharge protection. The nickel-cadmium secondary cell was developed around 1899 by the Swede Waldemar Jungner (1869 - 1924). © Marc Stenzel |
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