Flexible electric double-layer capacitors fabricated with micro-/mesoporous carbon electrodes and plastic crystal incorporated gel polymer electrolytes containing room temperature ionic liquids

Abstract

Novel configuration of symmetrical electric double-layer capacitors (EDLCs) comprising plastic crystalline succinonitrile (SN)-based gel polymer electrolytes, incorporated with ionic liquids 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMPTFSI) and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMITf) immobilized in a host polymer poly(vinylidine fluoride-co-hexafluoropropylene) (PVdF-HFP), have been fabricated and characterized. The cost-effective activated carbon powder containing a large proportion of mesoporosity has been derived from coconut shell to use as the capacitor electrodes. The high ionic conductivity (∼10−3 S cm−1 at room temperature) and good electrochemical stability render the gel polymer electrolyte films suitable candidates for the fabrication of EDLCs. The performance of the EDLCs has been tested by electrochemical impedance spectroscopy, cyclic voltammetry, and charge–discharge studies. Performance of the capacitor cell with EMITf-based gel electrolyte in terms of specific capacitance, specific energy, pulse, and continuous power densities (which are respectively ∼254 F g−1, 35 Wh kg−1, 10.3 kW kg−1, and 12 kW kg−1) is found to be better than the EDLC fabricated with BMPTFSI-based gel electrolyte. The superior performance of the EMITf-based cell is correlated with smaller sizes of EMITf component ions, responsible for easy ion migration and switching through even smaller pores of activated carbon.