Electrical double-layer capacitor

摘要

There is provided an electrical double-layer capacitor that shows only a small increase of resistance even when used under continuous application of high voltage, and has a high energy residual ratio after it is left standing for a long period of time. It includes an electrode element 3 which consists of a pair of electrodes 5 and 5 disposed opposite to each other with a separator 6 interposed therebetween and is impregnated with a nonaqueous electrolyte solution. The nonaqueous electrolyte solution is prepared by dissolving quaternary ammonium salts into cyclic carbonates. The impurities contained in the nonaqueous electrolyte solution impregnated into the electrode element 3 comprise 30 ppm or less of glycols, 30 ppm or less of primary alcohols and less than 20 ppm of tertiary amines, and the water content is 50 ppm or less. The quaternary ammonium salt is triethylmethylammonium tetrafluoroborate. The cyclic carbonate is propylene carbonate. The nonaqueous electrolyte solution has a concentration of 0.1 to 2.5 mol/liter. The electrode 5 is a polarizable electrode composed using activated carbon.