Performance of Capacitors Using Organic Electrolytes
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T.Morimoto, M.Tsushima and Y.Che Asahi Glass Co. Ltd., Research Center Hazawa-cho, Kanagawa-ku Yokohama 221-0863, Japan ABSTRACT Electric double-layer capacitors(EDLC) based on charge storage at the interface between a high surface area activated carbon electrode and an electrolyte solution are characterized by their long cycle life and high power density in comparison with batteries. However, energy density of electric double-layer capacitors obtained at present is at most 1Wh/kg at a power density of 600W/kg and smaller compared with that of batteries, which limits the applications of the capacitor. Therefore, new capacitors which show larger energy density than that of electric-double layer capacitors are proposed. The new capacitors are hybrid capacitors consisting of activated carbon cathode, Li-doped graphite anode and an organic electrolyte. Maximum voltage applicable to the cell becomes over 4.OV which is larger than that of the electric double-layer capacitor. As a result, discharged energy density of the cell becomes 4Wh/kg at a power density of 600W/kg. 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]. New applications for electric double-layer capacitors have been proposed in recent years. The popularity of these devices is due to their long cycle life and high power density relative to batteries. Electric double-layer capacitors exhibit in principle 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 applications. The pulse power source provides the peak power during acceleration and recovers energy during braking using a generator. Redox capacitors, Ni-hydrogen battery and Li-ion battery have been proposed as pulse power sources besides electric double layer capacitor. However, they are not so stable in cycle life performance as the electric double-layer capacitor, because they
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Mat. Res. Soc. Symp. Proc. Vol. 575 02000 Materials Research Society
store charge by faradaic process. On the other hand the energy density of electric double-layer capacitor is smaller than that of redox capacitors and batteries. Accordingly, high cell voltage is required to obtain high energy density. This condition may not be suitable for practical application of electric double-layer capacitor. To obtain the new device which shows high energy density at moderate cell voltage and stability in cycle life performance, we studied new hybrid capacitor composed of an activated carbon cathode, a Li-doped graphite and an organic electrolyte. In this paper, the performance, the material and the construction of the electric double-layer capacitor and the hybrid capacitor are described. ELECTRIC DOUBLE-LAYER CAPACITOR
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