A high performance flexible gel polymer electrolyte incorporated with suberonitrile as additive for quasi-solid carbon supercapacitor

We report a novel composition of a free-standing, flexible gel polymer electrolyte (GPE) film comprising a polymer poly(vinylidine fluoride-co-hexafluoropropylene) (PVdF-HFP), immobilizing a solution of lithium bis(trifluoromethane sulfonyl)imide in suberonitrile for use in quasi-solid-state carbon supercapacitor. Physicochemical properties, characterized by SEM, X-ray diffraction, FTIR, and TGA/DSC along with its high ionic conductivity (σ_RT ~1.2 × 10⁻³ S cm⁻¹) and wide electrochemical stability window (~4.23 V versus Ag) make the GPE a potential electrolyte/separator for supercapacitors. Quasi-solid-state symmetrical supercapacitor has been assembled using the suberonitrile-based-GPE and activated carbon electrodes derived from a waste-biomass (pinecone). The supercapacitors are tested by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge-discharge. The capacitor offers specific capacitance of 220–230 F g⁻¹, which corresponds to high specific energy and power (27–32 Wh kg⁻¹ and 12.5–13.5 kW kg⁻¹, respectively). The device shows excellent cyclic performance for ~20000 charge-discharge cycles with ~10% initial fading and a safe performance over a wide temperature range.