Electric double-layer capacitor and method of making a separator therefor

Abstract

An electric double-layer capacitor includes a casing, a pair of porous electrodes disposed within the casing, a permeable separator sandwiched between both the porous electrodes, and an electrolytic liquid formed of an organic solvent, injected into the casing and permeating the porous electrodes and the separator. The separator is formed from an aggregate of cellulose fiber having a surface modified by an organic solvent thereby. A method of making a separator for an electric double-layer capacitor includes producing a cellulose fiber aggregate, forming a sheet of the cellulose fiber aggregate, modifying a surface of the cellulose fiber aggregate sheet by immersing the sheet in an organic solvent for a predetermined time period, drying the modified sheet, and cutting the dried sheets to form the separator of a desired size and shape. The cellulose fiber aggregate sheet may also be pretreated by immersing the sheet in an amphipathic solvent. Since the wettability of the cellulose fiber to the electrolytic liquid is improved, the permeation of the electrolytic liquid into the separator is improved, whereby a reduction in internal resistance of the electric double-layer capacitor is achieved.