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

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 degrees C) and also have a wide electrochemical window (ECW) similar to 4.0-4.20 V. The conductivity increases with increasing amount of IL, and attains a value of 3.2 x 10(-3) S cm(-1) at room temperature for the PGEMs containing higher loadings of IL. A high total ionic transference number (similar to 0.99) and cationic transference number (t(Li)(+) similar to 0.33) for the PGEMs containing higher loadings of IL have been obtained.