|
battery, electric, device that converts chemical energy into electrical energy. A dry-cell flashlight battery consists of an electric cell, but larger batteries are made up of a group of cells that are connected to act as a source of direct electric current at a given voltage. A cell consists of two dissimilar substances, a positive electrode and a negative electrode, that conduct electricity, and a third substance, an electrolyte, that acts chemically on the electrodes. A group of several such cells connected together is called a battery. The two electrodes are connected by an external circuit (e.g., a piece of copper wire); the electrolyte functions as an ionic conductor for the transfer of the electrons between the electrodes. The voltage, or electromotive force, depends on the chemical properties of the substances used, but is not affected by the size of the electrodes or the amount of electrolyte. Batteries consisting of carbon-zinc dry cells connected in various ways (as well as batteries consisting of other types of dry cells) are used to power such devices as flashlights, portable computers, and pocket-sized CD players.
A battery called the storage battery is generally of the wet-cell type; i.e., it uses a liquid electrolyte and can be recharged many times, unlike the ordinary dry-cell battery, which uses a paste electrolyte and can be recharged few times, if at all. The storage battery consists of several cells connected in series. Each cell contains a number of alternately positive and negative plates separated by the liquid electrolyte. The positive plates of the cell are connected to form the positive electrode; similarly, the negative plates form the negative electrode. In the process of charging, the cell is made to operate in reverse of its discharging operation; i.e., current is forced through the cell in the opposite direction, causing the reverse of the chemical reaction that ordinarily takes place during discharge, so that electrical energy is converted into stored chemical energy. The storage battery's greatest use has been in the automobile where it was used to start the internal-combustion engine. Improvements in battery technology have resulted in vehicles : some in commercial use : in which the battery system supplies power to electric drive motors instead.
In the United States the lead storage battery is commonly used; the nickel-cadmium battery, although far more costly, is also in wide use. The cell of the lead storage battery consists of alternate plates of lead (negative electrode) and lead coated with lead dioxide (positive electrode) immersed in an electrolyte of sulfuric acid solution; when fully charged, it produces a voltage of between 2.0 and 2.5 volts. In the discharging process lead sulfate is deposited on both the negative and the positive electrodes, while the sulfuric acid electrolyte becomes weaker. Another type of storage cell, called the Edison cell, has a nickel oxide positive plate and an iron negative plate suspended in a solution of potassium and lithium hydroxides.
See also electric circuit; fuel cell; solar cell.
The Columbia Electronic Encyclopedia Copyright © 2009, Columbia
University Press.
Licensed from Columbia University Press. All rights reserved.
|
