Selective Effect of Gel Polymer Electrolytes on Suppressing Decomposition and Evaporation of Electrolyte in Acetonitrile-Based Supercapacitors at Elevated Temperature

Acetonitrile-based liquid electrolytes have been used in supercapacitors due to their high ionic conductivity, but they have drawbacks when operated at elevated temperature. The electrochemical performances of acetonitrile-based activated carbon (AC) supercapacitors are improved by two gel polymer electrolytes (GPEs) functionalized in a bulk electrolyte and at the AC interface. A GPE with poly(ethylene glycol) suppresses the evaporation of acetonitrile at the bulk electrolyte during resting and cycling at 80 °C effectively. A GPE with an isocyanate group obtained by curing after impregnated into AC has an exceptional effect on suppressing the anodic decomposition of the liquid electrolyte even at elevated temperature. This parallel effect is verified through investigations of electrolytic decomposition at specific potentials of positive and negative electrodes, cycling stability of the assembled supercapacitors at 3.0 V, and change in the impedance parameters during cycling. In addition, a mechanism for the stabilization of electrolyte by an isocyanate is suggested.