High energy density solid-state supercapacitors based on porous carbon electrodes derived from pre-treated bio-waste precursor sugarcane bagasse

Abstract

Supercapacitors with hierarchical porous carbon electrodes and ionic liquid incorporated quasi-solid-state gel polymer electrolyte are of the current area of interest as environment friendly and cost-effective power sources. Herein, we report hierarchical porous activated carbons (ACs) derived from a waste-bioresource sugarcane bagasse, prepared following hydrothermal and solvent (ethanol) soaking pre-treatments, followed by chemical/physical activations. AC-powders obtained from hydrothermal and ethanol-soaking pre-treatments show an increase in microporosity with optimum mesoporous interiors suitable to use as supercapacitor electrodes. The ACs have been electrochemically tested as supercapacitor electrodes with flexible quasi-solid-state gel polymer electrolyte comprising 0.5 M sodium triflate (NaTf) in an ionic liquid 1-ethyl-3-methylimidazolium trifluoromethane-sulfonate (EMITf) incorporated in poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP) with high ionic conductivity (~8.5 mS cm−1) and high electrochemical stability (~4.7 V versus Ag/Ag+). The supercapacitor based on AC-electrodes obtained after ethanol soaking pre-treatment i.e., ESB-electrodes show optimum charge-discharge performance in terms of specific capacitance (~193 F g−1), specific energy (~32 Wh kg−1) and maximum power density (~55 kW kg−1). The ESB-based supercapacitors also illustrate relatively high rate-performance as compared to other AC-electrodes, studied in this report. The high energy storage in the supercapacitor is evident from the glow of LED for substantial duration. The device shows stability up to ~10,000 charge-discharge cycles with ~20 % initial fading in specific capacitance and ~100 % Coulombic efficiency.