Mixed anion effect on the ionic transport behavior, complexation and various physicochemical properties of ionic liquid based polymer gel electrolyte membranes

Abstract

Li-ion conducting polymer gel electrolyte membranes (PGEMs) containing ionic liquid (IL), 1-butyl-3-methylimidazolium tetrafluroborate BMIMBF₄, polymer poly(vinylidene fluoride-co-hexafluoropropylene) PVdF-HFP and lithium bis(trifluoromethanesulfonyl)imide LiTFSI salt (having different anion i.e. BF₄⁻ and TFSI⁻) have been synthesized and characterized by various techniques. The results show that the synthesized PGEMs have good free-standing characteristics, good thermal stability (300–400 °C) and also have a wide electrochemical window (ECW) ∼4.0–4.20 V. The conductivity increases with increasing amount of IL, and attains a value of 3.2 × 10⁻³ S cm⁻¹ at room temperature for the PGEMs containing higher loadings of IL. A high total ionic transference number (∼0.99) and cationic transference number (t_Li⁺ ∼ 0.33) for the PGEMs containing higher loadings of IL have been obtained.