Batteries are classified in two main divisions. In primary cells, the chemical reaction is ordinarily irreversible and the battery can yield only a finite quantity of electricity. Single primary-cell batteries are used in flashlights, shavers, light meters, etc. The most common type is the dry Leclanché cell, which has a zinc cathode, a carbon anode, and uses ammonium chloride paste as electrolyte. Manganese dioxide "depolarizer" is distributed around the anode (mixed with powdered graphite) to prevent the accumulation of the hydrogen gas which would otherwise stop the operation of the cell. The dry Leclanché cell gives a nominal 1.54V. For the higher voltage necessary to power radios, etc., batteries containing several thin laminar cells are used.
Secondary cells, known also as storage cells or accumulators, can be recharged and reused at will provided too much electricity has not been abstracted from them. The most common type, as used in automobiles, is the lead-acid type, in which both electrodes are made of lead (the positive covered with lead (IV) oxide when charged) and the electrolyte is dilute sulfuric acid. Its voltage is about 2V, depending on the state of the charge. The robust yet light nickel-iron battery (having a potassium hydroxide solution electrolyte) was widely used in telephone exchanges and other heavy-duty situations but has been displaced by the nickel-cadmium type. They give about 1.3V.
The first battery was the voltaic pile invented in about 1800 by Alessandro Volta. This comprised a stack of pairs of silver and zinc disks, each pair separated by a brine-soaked board. For many years from 1836 the standard form of battery was the Daniell cell, with a zinc anode, a copper cathode, and a porous-pot barrier separating the anode electrolyte (copper (II) sulfate) from the cathode electrolyte (sulfuric acid). The lead-acid storage battery was invented by Gaston Planté in 1859 and the wet Leclanché cell, the prototype for the modern dry cell, by Georges Leclanché in 1865.
Related category• ELECTRICITY AND MAGNETISM
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