Energy enhancement of quasi-solid-state supercapacitors based on a non-aqueous gel polymer electrolyte via a synergistic effect of dual redox additives diphenylamine and potassium iodide

Enhancing redox activity at electrode-electrolyte interfaces by dispersing redox additive(s) in electrolytes is a recent approach to increase the specific energy of carbon supercapacitors. Here, we prepared a non-aqueous gel polymer electrolyte (GPE) incorporated with an ionic liquid (IL) 1-butyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide and dual redox additives (KI and diphenylamine, DPA) entrapped in a host polymer poly(vinylidenefluoride-co-hexafluoropropylene) for use in the fabrication of carbon supercapacitors. A free-standing film of the GPE with dual redox additives shows excellent flexibility, thermal stability (up to similar to 320 degrees C), high ionic conductivity (sigma(RT)similar to 4.52 mS cm(-1)) and a wide electrochemical stability window (similar to 6.2 VversusAg), indicating its suitability as an electrolyte in quasi-solid-state supercapacitors. The supercapacitor fabricated using the redox-active GPE (containing KI and DPA) and biomass-derived activated carbon electrodes exhibits superior performance over the devices with GPEs containing a pure IL or its mixture with a single additive (DPA or KI). The synergistic effect of dual redox activity at the interfaces leads to optimum specific energy (similar to 73.2 W h kg(-1)) and maximum power (similar to 34.8 kW kg(-1)), attributable to enhanced specific capacitance (similar to 337 F g(-1)) and reasonably high operating voltage (2.5 V). The optimized capacitor shows good performance for similar to 6000 charge-discharge cycles after a 20% fade in capacitance and maintains a coulombic efficiency as high as 98-100%.