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Abstract

A capacitor element (10) fabricated by winding an anode foil (1) and a cathode foil (2) via a separator (3) is impregnated with a 3,4-ethylenedioxythiophene and an oxidizing agent to form poly(ethylenedioxythiophene) by chemical polymerization. A nonwoven fabric composed chiefly of a synthetic fiber is used as a separator, enabling a solid electrolyte to be favorably formed without being reacted with the oxidizing agent. Preferably, the capacitor element is dipped in water at 80 to 100.degree. C. for 1 to 20 minutes to dissolve and remove the binder in the separator in order to preclude adverse effects on the electric characteristics caused by the binder. The oxidizing agent is used at a concentration in excess of 40% by weight with respect to the solvent, so that the degree of polymerization is high and a dense and homogeneous solid electrolytic layer is formed. To form the electrolytic layer, the capacitor element is impregnated with a monomer solution prepared by mixing 3,4-ethylenedioxythiophene and a volatile solvent at a volume ratio of 1:1 to 1:3. Then, the capacitor element is heat-treated and impregnated with a solution of oxidizing agent to form a dense and homogenous solid electrolytic layer.

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