Ionic Liquid–Organic Solvent Mixture-Based Polymer Gel Electrolyte with High Lithium Concentration for Li-Ion Batteries

Abstract

In this paper, we have investigated the performance and solid electrolyte interphase formation (SEI) of a hybrid polymer gel electrolyte based on poly(vinylidene fluoride)-co-hexafluoropropylene, 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide ([Py1,4]FSI), and lithium bis(fluorosulfonyl)imide (LiFSI) for all solid-state lithium-ion batteries. The effect of the addition of acetonitrile (AN) and different concentrations of LiFSI to such a polymer gel electrolyte was also examined. Compared to 1 M LiFSI in the ionic liquid–polymer electrolyte, the addition of 4 M LiFSI along with acetonitrile led to higher lithium storage capacity. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy were performed to analyze the SEI formation on a Ge electrode. The difference in the mechanical properties and SEI composition was observed upon changing the components of the polymer electrolyte. XPS analysis revealed a difference in the composition/thickness of the SEI layer, which varies upon increasing the Li-salt concentration and upon adding AN to [Py1,4]FSI. Such differences might have led to better Li storage capacity on using the concentrated IL–organic polymer electrolyte. Our study clearly shows that the addition of an organic solvent and high concentration of Li salt to the polymer gel electrolyte improves the performance of LIBs.