Effect of the progressive addition of 1-ethyl-3-methylimidazolium tetrafluoroborate as ionic liquid solvent for designing potassium ion conducting polymer gel electrolyte

A novel polymer gel electrolyte (PGE) system containing potassium perchlorate (KClO₄) and poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) incorporated with various concentrations of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF₄) and tetraethylene glycol dimethyl ether (TEGDME) as molecular solvents is reported. Impedance measurements revealed that the PGE film with higher content of EMIMBF₄ ionic liquid provides an excellent room-temperature ionic conductivity of ~ 2.36 × 10⁻² S cm⁻¹, relatively low activation energy of ~ 0.18 eV, and notably higher electrochemical stability window of ~ 3.5 V. The optimal PGE demonstrates gel-phase retention for a wide temperature range and maintains thermal stability up to 112 °C. The infrared spectroscopy studies reveal the interactions of electrolyte ions with the polymer matrix. The possible structural and morphological variations in polymer matrix owing to the addition of TEGDME and EMIMBF₄ solution have been explored by X-ray diffraction (XRD) and scanning electron microscopic (SEM) study. The UV–visible spectroscopy depicts the rise in absorption and decline in the optical band gap on incorporation of salt and molecular solvent.