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 (72.23Wh 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.