Ionic liquid-based polymer gel electrolytes for symmetrical solid-state electrical double layer capacitor operated at different operating voltages

• The blend GPE contain 7.5 wt.% of [bdmim]BF4 exhibits highest ionic conductivity.
• The GPE reveals low Tg and wide range of electrochemical stability.
• The electrical double layer capacitor (EDLC) based GPE-IL give high capacitance.

In this work, 1-butyl-2,3-dimethylimidazolium tetrafluoroborate ([bdmim]BF4) ionic liquid is introduced into poly(vinyl pyrrolidone)/poly(vinylidene fluoride-co-hexafluoropropylene) (PVP/PVdF-HFP) blend host to prepare a gel polymer electrolyte (PVP/PVdF-HF-Mg(CF3SO3)2) system for a symmetrical solid-state electrical double layer capacitor (EDLC). Ionic liquid-incorporated gel polymer electrolyte (GPE) containing 7.5 wt.% [bdmim]BF4 exhibits the optimum room temperature ionic conductivity of (2.92 ± 0.02) × 10−3 S cm−1 and is electrochemically stable up to +2.4 V. The specific capacitance (Cs) of the optimised GPE at 100th cycle with porous carbon as electrode delivers 95, 133, 108 and 117 F g−1 at operating voltage of 0.8, 1.0, 1.6 and 2.0 V, respectively, under a constant current density of 100 mA g−1. The solid-state displays the highest energy and power density of 14 W h kg−1 and 21 W kg−1, respectively, at an operating potential of 1.0 V, which qualifies the GPE-IL for symmetrical solid-state EDLC application.