Properties of electric double-layer capacitors with various polymer gel electrolytes

Polyethylene oxide (PEO), polymethyl methacrylate (PMMA), and polyacrylonitrile (PAN) based gel electrolytes with a mixture of ethylene carbonate and propylene carbonate as plasticizer and lithium perchlorate were used to fabricate an electric double-layer capacitor (EDLC). The performance of EDLCs with these gel electrolyes was investigated by using isotropic high-density graphite electrodes. The ion conductivities of various of gel electrolytes were of the order of 10^-4 to 10^-3 S cm^-1, and they decreased in the order PAN > PEO > PMMA at ambient temperature. Capacitances approaching the value of EDLCs using organic liquid electrolyte, 20 mF cm^-2, with an isotropic high-density graphite electrode were obtained in PAN and PMMA gel electrolytes. The EDLC with PMMA-based gel electrolyte showed good charge-discharge behavior over 10⁴ cycles at a charge potential of 3.0 V.