battery

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Any chemical energy-storage device allowing release of electricity on demand. It is made up of one or more electrical cells. Electricity is produced by a chemical reaction in the cells. There are two types of battery: primary-cell batteries, which are disposable; and secondary-cell batteries, or accumulators, which are rechargeable. Primary-cell batteries are an extremely uneconomical form of energy, since they produce only 2% of the power used in their manufacture. It is dangerous to try to recharge a primary-cell battery.

Primary cell
The dry cell is the most common type of primary-cell battery, based on the Leclanché cell. Dry cells are used in batteries to power, for example, torches, electronic toys, and compact stereo systems. Dry cells consist of a zinc case used as a negative electrode, and a carbon rod as a positive electrode suspended in the centre of the case and immersed in a paste of manganese dioxide and ammonium chloride acting as an electrolyte.

The cell depends on the difference in electronegativity between the zinc and carbon to produce electricity. Carbon strongly holds onto its electrons; it is more electronegative. Zinc weakly holds onto its electrons; it is less electronegative. Zinc dissolves in the ammonium chloride and loses two electrons for each atom of zinc. The electrons move towards the carbon electrode:

Zn ® Zn²⁺ + 2e^-

A small amount of charge is produced and zinc becomes negatively charged and carbon becomes positively charged. When a connection is made externally between the positive carbon terminal and the negative zinc terminal, electrons flow to the carbon from the zinc. The charge is neutralized on both electrodes and more of the zinc metal dissolves in the electrolyte to produce more electrons. A dry cell provides a current until the zinc electrode is completely used up.

Secondary cell
A storage battery of secondary cells gives large amounts of power for a short time and can be recharged. The lead–acid car battery is a secondary-cell battery. The electrolyte is sulphuric acid (battery acid), the positive electrode is lead peroxide, and the negative electrode is lead. A typical lead–acid battery consists of six lead–acid cells in a case. Each cell produces 2 volts, so the whole battery produces a total of 12 volts.

Hydrogen cells and sodium–sulphur batteries were developed in 1996 to allow cars to run entirely on battery power. The introduction of rechargeable nickel–cadmium batteries has revolutionized portable electronic news gathering (sound recording, video) and information processing (computing). These batteries offer a stable, short-term source of power free of noise and other electrical hazards.

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