A novel ionic liquid polymer electrolyte for quasi-solid state lithium air batteries

Abstract

Novel ionic liquid polymer electrolytes based on polymer poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP), lithium bis(tri-fluoromethanesulfonyl)imide (LiTFSI) with different 1-ethyl-3-methyl-imidazolium bis(trifluoromethanesulfonyl)imide (EMITFSI) weight ratios have been synthesized and applied to quasi-solid state Li–air batteries. The morphology, electrochemical properties of prepared electrolytes, the discharge–charge capacity and cycling performance of the quasi-solid state Li–air batteries have been characterized and are discussed. Electrochemical properties of polymer electrolyte with incorporation of EMITFSI improved the electrochemical stability window (4.9 V) with higher ionic conductivity (∼4.30 × 10⁻³ S cm⁻¹), but decreased the cationic transference number. The improvements are attributed to the reducing crystallinity of polymer matrix and formation of many homogeneous, large-size across-linked pores (60% EMITFSI), which could facilitate the transmission of Li ions. While for the quasi-solid state Li–air batteries, the ionic liquid polymer electrolyte shows good compatibility and safety with an Li anode and an air breathing cathode, significantly improved galvanostatic discharge–charge capacity and cyclic stability (without capacity fading until 20 cycles) in the capacity-controlled mode, which demonstrates that the novel ionic liquid polymer electrolyte is a potential choice for the quasi-solid state Li–air batteries for future practical applications.