All solid state flexible supercapacitors operating at 4 V with a cross-linked polymer–ionic liquid electrolyte†
4 V-operated all solid symmetrical supercapacitors that employ mixtures of various weight compositions with cross-linked poly-4-vinylphenol (c-P4VPh) and 1-ethyl-3-methyl imidazolium bis(trifluoromethylsulfonyl)imide (EMITFSI) electrolytes have been demonstrated and characterized. The values at 1 : 3, 3.5, 4 and 4.5 (c-P4VPh : EMITFSI) offer free-standing membranes with high ionic conductivity. In the case of 1 : 3.5, the best specific capacitance (172.44 F g−1 in a single-electrode) and energy density (72.23 W h kg−1) were obtained at symmetrical cells based on porous carbon electrodes. Every prepared SC was reliable over 1000 cycles in the range of 0–4 V. They also have excellent flexibility and maintain capacitance after completing the bending test a thousand times.