Zwitterion-containing electrolytes with semi–crystalline PVDF-Co-HFP as a matrix for safer lithium-ion batteries

Abstract

A promising method of synthesizing lithium-containing room temperature ionic liquids (RTILs) and poly(ionic liquid)s (PILs) based on zwitterionic effect was used to prepare electrolytes for safer lithium-ion batteries. In this work, to explore the different performance between ionic liquids and poly(ionic liquid)s in electrolytes, we have prepared two zwitterion analogues 3-(1-methyl-3-imidazolio)-propane sulfonate (MIPS) and 3-(1-vinyl-3-imidazolic) propanesulfonate (VIPS). Polymer electrolytes membranes based on semi-crystalline poly(vinylidene fluoride–co–hexafluoropropylene) (PVDF-Co-HFP) as the matrix, containing zwitterion and lithium salts, were prepared through solution casting method. By comparing two different types of electrolytes, PIL retained the properties of IL while endowed the electrolytes with new features such as prevented leakage, enhanced mechanical properties and improved processability. PIL-based solid polymer electrolyte displayed comparable ionic conductivities comparable to IL-based ionogel electrolyte due to the Li+ ions transport channels formed by zwitterionic ion-dipole interaction and the dissociation effect of zwitterions. PIL electrolyte had a higher lithium ion migration number deriving from the simultaneous physical and chemical cross-linking having more limited effect on the movement of anions. This method supplies an intriguing class of ILs to the electrolyte materials that may combine the outstanding properties of ionic liquids into safer lithium ion batteries and other energy storages.