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T.Morimoto, M.Tsushima, M.Suhara, K.Hiratsuka, Y.Sanada and T.Kawasato, Asahi Glass Co. Ltd., Research Center Hazawa-cho, Kanagawa-ku Yokohama 221, Japan ABSTRACT Electric double-layer capacitors based on charge storage at the interface between a high surface area activated carbon electrode and a propylene carbonate solution are widely used as maintenance-free power sources for IC memories and microcomputers. New applications for electric double-layer capacitors have been proposed in recent years. The popularity of these devices is derived from their high energy density compared with conventional capacitors and their long cycle life and high power density relative to batteries. The performance of the capacitor depends not only on the materials used in the cells but also on the construction of the cells. The performance of power capacitors for large power sources as well as materials and construction of these capacitors are described. INTRODUCTION Electric double-layer capacitors based on the charge storage at the interface between a high surface area activated carbon electrode and an organic electrolyte solution have been developed, and are widely used as maintenance-free power source for IC memories and microcomputers [1]. The achievement of excellent performances of capacitors requires an electrode fabricated with high surface area activated carbon of suitable surface property and pore geometry, an electrolyte solution which provides high conductivity over a wide temperature range and good electrochemical stability to allow the capacitor to be operated at higher voltage, and a cell construction material which does not corrode electrochemically during anodic polarization. New applications for electric double-layer capacitors have been proposed in recent years. The popularity of these devices is due to their high energy density relative to conventional capacitors, and their long cycle life and high power density relative to batteries. Electric double-layer capacitors exhibit in principle provide unlimited cycle life and maintenance free operation as an alternative to batteries in power circuits. A new promising application for electric double-layer capacitor is a pulse power source in electric and hybrid vehicle application. The pulse power source provides the peak power during acceleration and recovers energy during braking 627

Mat. Res. Soc. Symp. Proc. Vol. 496 ©1998 Materials Research Society

using a generator. In this paper the performance of the electric double-layer capacitor for power sources as well as the material and the construction of the capacitor are described. MATERIAL Electroyte As the breakdown voltage of the capacitor is strongly related to the decomposition voltage of the electrolyte, it is important to use organic electrolytes having a high decomposition voltage to obtain a capacitor of both stable performance and high energy density [2],[3]. It is also important to use an electrolyte of high conductivity to obtain a capacitor of high power density. Therefore electrolyte solutions obtained b