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The vanadium redox (and redox flow) battery (VRB) is a type of rechargeable flow battery that employs vanadium ions in different oxidation states to store chemical potential energy. The vanadium redox battery exploits the ability of vanadium to exist in solution in four different oxidation states, and uses this property to make a battery that has just one electroactive element instead of two. For several reasons, including their relatively bulky size, most vanadium batteries are currently used for Grid energy storage, such as being attached to power plants or electrical grids. Building on earlier research on flow batteries,〔An earlier German Patent on a titanium chloride flow battery was registered and granted in July 1954 to Dr. Walter Kangro, but most of the development of flow batteries was carried out by NASA researchers in the 1970s.〕 the possibility of creating a vanadium battery was explored variously by Pissoort,〔P. A. Pissoort, in FR Patent 754065 (1933)〕 NASA researchers, and Pellegri and Spaziante.〔A. Pelligri and P. M. Spaziante, in GB Patent 2030349 (1978), to Oronzio de Nori Impianti Elettrochimici S.p.A.〕 The first successful demonstration of the all-vanadium redox flow battery employing vanadium in a solution of sulfuric acid in each half was by Maria Skyllas-Kazacos and co-workers at the University of New South Wales in the 1980s.〔 Their design used sulfuric acid electrolytes, and was patented by the University of New South Wales in Australia in 1986.〔 Organizations involved in funding and developing vanadium redox batteries include UniEnergy Technologies and Ashlawn Energy in the United States, Renewable Energy Dynamics Technology in Ireland, Gildemeister AG (formerly Cellstrom GmbH in Austria) in Germany, Cellennium in Thailand, (Rongke Power ) and Prudent Energy in China, Sumitomo in Japan and H2, Inc. in South Korea.〔http://www.h2aec.com/〕 The main advantages of the vanadium redox battery are that it can offer almost unlimited capacity simply by using larger storage tanks, it can be left completely discharged for long periods with no ill effects, it can be recharged simply by replacing the electrolyte if no power source is available to charge it, and if the electrolytes are accidentally mixed the battery suffers no permanent damage. The main disadvantages with vanadium redox technology are a relatively poor energy-to-volume ratio, although recent research at the (Pacific Northwest National Laboratory ) has doubled energy density, and the system complexity in comparison with standard storage batteries. ==Operation== A vanadium redox battery consists of an assembly of power cells in which the two electrolytes are separated by a proton exchange membrane. Both electrolytes are vanadium based, the electrolyte in the positive half-cells contains VO2+ and VO2+ ions, the electrolyte in the negative half-cells, V3+ and V2+ ions. The electrolytes may be prepared by any of several processes, including electrolytically dissolving vanadium pentoxide (V2O5) in sulfuric acid (H2SO4). The solution remains strongly acidic in use. In vanadium flow batteries, both half-cells are additionally connected to storage tanks and pumps so that very large volumes of the electrolytes can be circulated through the cell. This circulation of liquid electrolytes is somewhat cumbersome and does restrict the use of vanadium flow batteries in mobile applications, effectively confining them to large fixed installations. When the vanadium battery is charged, the VO2+ ions in the positive half-cell are converted to VO2+ ions when electrons are removed from the positive terminal of the battery. Similarly in the negative half-cell, electrons are introduced converting the V3+ ions into V2+. During discharge this process is reversed and results in a typical open-circuit voltage of 1.41 V at 25 °C. Other useful properties of vanadium flow batteries are their very fast response to changing loads and their extremely large overload capacities. Studies by the University of New South Wales have shown that they can achieve a response time of under half a millisecond for a 100 % load change, and allowed overloads of as much as 400 % for 10 seconds. The response time is mostly limited by the electrical equipment. Sulfuric acid-based vanadium batteries only work between about 10 to 40 °C. Below that temperature range, the ion-infused sulfuric acid crystallizes. Round trip efficiency in practical applications is around 65–75 %.〔 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「Vanadium redox battery」の詳細全文を読む スポンサード リンク
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