Electrical double-layer capacitor

摘要

An electrical double-layer capacitor showing a sleight increase of resistance when used under continuous application of high voltage and maintaining high energy residual ratio after standing for a long time includes an electrode element including a pair of electrodes disposed opposite to each other with a separator interposed therebetween, and is impregnated with a nonaqueous electrolyte solution prepared by dissolving quaternary ammonium salts into cyclic carbonates and containing impurities of 30 ppm or less of glycols, 30 ppm or less of primary alcohols and less than 20 ppm of tertiary amines. The water content may be 50 ppm or less. The quaternary ammonium salt may be triethylmethylammonium tetrafluoroborate. The cyclic carbonate may be propylene carbonate. The nonaqueous electrolyte solution may have a concentration of 0.1 to 2.5 mol/liter. The electrode may be a polarizable electrode composed of activated carbon.