Polymer and Ionic Liquid Electrolytes for Advanced Lithium Batteries
Lithium-ion secondary batteries have the advantages of high energy density and long cycle life and, thus, are expected to serve as energy storage devices for electric vehicles (EVs) and in devices of renewable energy (wind power, solar power, and so on).
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Polymer and Ionic Liquid Electrolytes for Advanced Lithium Batteries Shiro Seki and Masayoshi Watanabe
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Introduction
Environmentally benign energy generation methods, for example wind and photovoltaic power, are extremely valuable in terms of not only their contributions to improving the self-sufficiency ratio in energy supply and preventing global warming but also for their advantage of being energy-dispersive systems. However, these new energy generation methods are affected by nature (particularly, the weather and seasons), resulting in the instability of their output performance. For example, if electric power systems were supplied with a large amount of energy generated by these methods, not only the maintenance of operation frequency but also the power supply would become more difficult to maintain compared with systems based on thermal power generation. Therefore, when a large amount of energy supplied by such methods is introduced, output smoothing by storage control and the accumulation of energy are required during times of light loads such at night. Given such a background, lithium-ion secondary batteries have significant advantages, such as a high energy density and a long cycle life, and are used in laptop personal computers, cellular phones, and in household electronics and appliances [1, 2]. Furthermore, in recent years, investigation of the use of high-power lithiumion secondary batteries for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and electric vehicles (EVs) has been widely promoted on a
S. Seki (*) Materials Science Research Laboratory, Central Research Institute of Electric Power Industry (CRIEPI), 2-11-1, Iwado-kita, Komae, Tokyo 201-8511, Japan e-mail: [email protected] M. Watanabe Department of Chemistry and Biotechnology, Yokohama National University, Yokohama, Kanagawa 240-8501, Japan e-mail: [email protected] T. Osaka and Z. Ogumi (eds.), Nanoscale Technology for Advanced Lithium Batteries, Nanostructure Science and Technology 182, DOI 10.1007/978-1-4614-8675-6_6, © Springer Science+Business Media New York 2014
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Fig. 6.1 Cross-sectional images of highly safe lithium secondary batteries using solid polymer electrolyte and room-temperature ionic liquid
global scale [3–6]. Certainly, current lithium-ion secondary batteries are also attractive from the viewpoint of large-scale energy storage such as in electric power load-leveling systems [7, 8]. However, many accidents caused by the electrical short circuit of commercially available cells used in portable systems have been reported, and safety management and performance are now recognized as an important problem. Furthermore, when battery systems are enlarged, for example to megawatt-class battery systems, safety becomes a much more important issue. Given such a background, solid polymer electrolytes and room-temperature ionic liquids (room-temperature molten salts) have been attracting attention as safe lithium secondary battery electrolytes for large-scale
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