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In recent years, the number of practical applications for electrochemical power sources has increased dramatically, so that what was seen up to the 1980s as a relatively mature industry, has now become one with significant growth.
This renaissance has been led largely by the development of microelectronics-based high value consumer products which need easily portable primary or secondary batteries - for example, 'smart' cards, electric watches, calculators, mobile telephones, 'camcorders', personal CD players and 'lap-top' computers. At the other end of the capacity scale, developments in industrial traction, military and stationary applications, and especially in the electric vehicle market, are demanding greatly improved power sources which have both high power and energy densities.
While the number of chemical reactions which can be successfully harnessed to provide electrical energy is limited, the range of energy requirements for particular applications extends over many orders of magnitude: from 100mWh for a button cell to 20kWh for an electric vehicle battery. The same is true for power: from 25-100µW for a cardiac pacemaker to 50kW for a military thermal reserve battery. The diversity of use also requires many specific electrical characteristics which in turn call for different battery chemistry, materials and cell .
The past few years have seen significant developments both in 'traditional' aqueous electrolyte-based batteries and in high energy density cells based on lithium or sodium anodes. So far as zinc carbon and alkaline zinc cells are concerned, probably the most significant advance has been the reduction and now elimination of mercury. A further important innovation has been the commercialization of the nickel-metal hydride cell in which the cadmium negative plate in sealed nickel-cadmium cells is replaced by hydrogen absorbed in a metal alloy. Such metal hydride electrodes have a higher energy density and a reduced problem with disposal.
Perhaps the most significant recent change has been the rapid advance of lithium battery technology. The excellent electrical characteristics and outstanding performance of such cells now make them the normal choice for primary applications where cost is not the overriding consideration. Some research is continuing on improving high-rate solid cathode cells and on thin laminated cells for 'smart' card and similar applications. In contrast, research and development of secondary lithium batteries both for consumer products and for electric vehicle application is now seen to be the most important activity in the battery field.
