ELECTRIC DOUBLE-LAYER CAPACITORS WITH NEW GEL ELECTROLYTES

Polymer gel electrolytes consisting of poly(acrylonitrile) (PAN), propylene carbonate(PC) as a plasticizer and tetraalkylammonium salts such as tetrabutylammonium perchlorate, tetraethylammonium perchlorate and tetraethylammonium tetrafluoroborate have been investigated for electric double-layer capacitors with activated carbon fiber cloth electrodes. The PAN, PC and tetraalkylammonium composites showed high ionic conductivity (above 10(-3) Scm(-1) at 298 K). The ionic conductivity increased with an increase in the salt concentration and a decrease in the size of each ion. The composites were electrochemically stable over a wide potential range (ca. 5.O V). The application of the PAN and tetraethylammonium tetrafluoroborate composites to the electric double-layer capacitors with activated carbon fiber cloths as polarizable electrodes resulted in large values of capacitance and high coulombic efficiency. The low leakage current at constant voltage floating (2 V) and the long voltage retention in the self-discharge test were obtained in the capacitor with tetraethylammonium tetrafluoroborate.