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An electric battery is a device consisting of two or more electrochemical cells that convert stored chemical energy into electrical energy. Each cell has a positive terminal, or cathode, and a negative terminal, or anode. The terminal marked positive is at a higher electrical potential energy than is the terminal marked negative. The terminal marked positive is the source of electrons that when connected to an external circuit will flow and deliver energy to an external device. When a battery is connected to an external circuit, electrolytes are able to move as ions within, allowing the chemical reactions to be completed at the separate terminals and so deliver energy to the external circuit. It is the movement of those ions within the battery which allows current to flow out of the battery to perform work.〔(【引用サイトリンク】title=Battery - Definition of battery by Merriam-Webster )〕 Although the term ''battery'' technically means a device with multiple cells, single cells are also popularly called batteries. Primary (single-use or "disposable") batteries are used once and discarded; the electrode materials are irreversibly changed during discharge. Common examples are the alkaline battery used for flashlights and a multitude of portable devices. Secondary (rechargeable batteries) can be discharged and recharged multiple times; the original composition of the electrodes can be restored by reverse current. Examples include the lead-acid batteries used in vehicles and lithium-ion batteries used for portable electronics. Batteries come in many shapes and sizes, from miniature cells used to power hearing aids and wristwatches to battery banks the size of rooms that provide standby power for telephone exchanges and computer data centers. According to a 2005 estimate, the worldwide battery industry generates US$48 billion in sales each year,〔(Power Shift: DFJ on the lookout for more power source investments ).''Draper Fisher Jurvetson''. Retrieved 20 November 2005.〕 with 6% annual growth. Batteries have much lower specific energy (energy per unit mass) than common fuels such as gasoline. This is somewhat offset by the higher efficiency of electric motors in producing mechanical work, compared to combustion engines. == History == (詳細はBenjamin Franklin, who in 1748 described multiple Leyden jars by analogy to a battery of cannon〔Bellis, Mary. (History of the Electric Battery ). ''About.com''. Retrieved 11 August 2008.〕 (Benjamin Franklin borrowed the term "battery" from the military, which refers to weapons functioning together〔(【引用サイトリンク】title=Quiz: What You Don't Know About Batteries )〕). Alessandro Volta built and described the first electrochemical battery, the voltaic pile, in 1800.〔Bellis, Mary. (Alessandro Volta – Biography of Alessandro Volta – Stored Electricity and the First Battery ). ''About.com''. Retrieved 7 August 2008.〕 This was a stack of copper and zinc plates, separated by brine-soaked paper disks, that could produce a steady current for a considerable length of time. Volta did not appreciate that the voltage was due to chemical reactions. He thought that his cells were an inexhaustible source of energy,〔Stinner, Arthur. (Alessandro Volta and Luigi Galvani ) (PDF). Retrieved 11 August 2008.〕 and that the associated corrosion effects at the electrodes were a mere nuisance, rather than an unavoidable consequence of their operation, as Michael Faraday showed in 1834.〔(Electric Battery History – Invention of the Electric Battery ). ''The Great Idea Finder''. Retrieved 11 August 2008.〕 Although early batteries were of great value for experimental purposes, in practice their voltages fluctuated and they could not provide a large current for a sustained period. The Daniell cell, invented in 1836 by British chemist John Frederic Daniell, was the first practical source of electricity, becoming an industry standard and seeing widespread adoption as a power source for electrical telegraph networks.〔(Battery History, Technology, Applications and Development ). ''MPower Solutions Ltd''. Retrieved 19 March 2007.〕 It consisted of a copper pot filled with a copper sulfate solution, in which was immersed an unglazed earthenware container filled with sulfuric acid and a zinc electrode. These wet cells used liquid electrolytes, which were prone to leakage and spillage if not handled correctly. Many used glass jars to hold their components, which made them fragile. These characteristics made wet cells unsuitable for portable appliances. Near the end of the nineteenth century, the invention of dry cell batteries, which replaced the liquid electrolyte with a paste, made portable electrical devices practical. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Battery (electricity)」の詳細全文を読む スポンサード リンク
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