Electrochemical characterization of poly(vinylidene fluoride-co-hexafluoro propylene) based electrospun gel polymer electrolytes incorporating room temperature ionic liquids as green electrolytes for lithium batteries

A series of gel polymer electrolytes (GPEs) based on electrospun membranes of poly(vinylidene fluoride-co-hexafluoropropylene) [P(VdF-co-HFP)] incorporating room temperature ionic liquids (RTILs), 1-alkyl-3- methylimidazolium bis(trifluoromethylsulfonyl)imide complexed with lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) as electrolytes have been prepared and their fundamental electrochemical properties were investigated. The morphology of electrospun membranes was examined by a field emission scanning electron microscope (FE-SEM). The membranes show uniform morphology with an average fiber diameter of 780 nm, high porosity and high electrolyte uptake. GPEs were prepared by soaking the electrospun membranes in 1 M LiTFSI in RTILs for 1 h and exhibit a high ionic conductivity of 2.4 × 10 ^{- 3}-4.5 × 10^{- 3} S cm^{- 1} at 25 °C. A Li/GPEs/LiFePO₄ cell using these RTILs delivers high discharge capacity (~ 140 mAh g^{- 1}) when evaluated at 25 °C at 0.1 C-rate and exhibits a very stable discharge capacity under continuous cycling. Among the GPEs, EMITFSI shows the highest electrochemical properties although the solid electrolyte interface (SEI) layer was not formed.