High-Energy-Density Carbon Supercapacitors Incorporating a Plastic-Crystal-Based Nonaqueous Redox-Active Gel Polymer Electrolyte
Neetu Yadav, Nitish Yadav, S.A. Hashmi
Abstract
Addition of redox additives in electrolytes to enhance the electrochemical activity at electrode–electrolyte interfaces is one of the prime approaches these days to develop high-energy-density supercapacitors. Here, we report an investigation on a quasi-solid-state supercapacitor, fabricated with a nonaqueous, gel polymer electrolyte (GPE) based on a mixture of a plastic crystal succinonitrile and an ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethyl sulfonyl) imide, added with a redox additive hydroquinone (HQ), immobilized in a polymer poly(vinylidine fluoride-co-hexafluoropropylene). The HQ-incorporated GPE is observed to be a freestanding, easily processible, and reusable film, showing excellent flexibility and thermal stability up to ∼100 °C. The high ionic conductivity (∼4.2 mS cm–1) and wide electrochemical stability window (∼5.0 V) through linear sweep voltammetry measurements make the optimum composition of GPE a potential electrolyte for high-energy-density supercapacitors. The symmetric supercapacitor coin cells have been fabricated with peanut shell-derived porous carbon electrodes separated by GPE films. The electrochemical activity due to the presence of HQ at carbon electrode–GPE interfaces introduces additional pseudocapacitance over the double-layer capacitance, leading to enhanced overall specific capacitance (289 F g–1), and hence corresponds to the high specific energy (∼40 Wh kg–1) and maximum power (∼20 kW kg–1). The capacitor cell shows prolonged cyclic profile up to ∼10 000 charge–discharge cycles with ca. 85–93% Coulombic efficiency.