A Flexible Supercapacitor Based on Deep Eutectic Solvent/[EMIM][TFSI] Ionogel with High Energy Density and Wide Temperature Range

Hydrogel electrolytes have attracted wide attention because of their high ionic conductivity and anti-leakage characteristics. However, these advantages are hindered under extreme conditions. In this paper, an ionogel electrolyte for supercapacitors with a wide temperature range is constructed. It consists of a double cross-linked structure of polyacrylamide and 1-vinyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([VMIM][TFSI]), with the addition of ethylene glycol and choline chloride to form a deep eutectic solvent with a large hydrogen bonding network. On this basis, a partial ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM] [TFSI]) is innovatively added to choline chloride. The ionogel electrolyte exhibits a conductivity of up to 13.26 mS/cm at 90 °C. A flexible supercapacitor is assembled with activated carbon electrodes and has a wide voltage window of 2.4 V. The specific capacitance and energy density are 43.81 F/g and 35.1 Wh/kg, respectively, when the current density is 0.25 A/g. Remarkably, the device retains high coulombic efficiency (97.1%) and capacitance retention (94.3%) after 10 000 cycles. These excellent properties show that the ionogel electrolyte prepared in this work has broad application prospects.