Synthesis and characterization of non-plasticized solid-state polyvinylidene fluoride-co-hexafluoroprolene-lithium bis(oxalato)borate electrolytes

Abstract

High-performance solid-state polymer electrolytes are considered as a promising alternative for liquid electrolytes widely used in electrochemical-based energy storage devices such as rechargeable batteries, fuel cells and supercapacitors, etc. Because of their solid nature, polymer electrolytes offer many advantages compared with conventional liquid ones such as no leakage, high reliability, light weight, high breakdown voltage, and ease of processing. However, most solid polymer electrolytes have low room temperature ion conductivity which is insufficient for practical applications. Although polymer gel electrolytes show good ion conductivity, they show poor mechanical stability. To overcome these issues, novel solid-state polymer electrolytes possessing both high ion conductivity and good mechanical strength are needed. In the present research, composite polymer electrolyte membranes based on polyvinylidene fluoride-co-hexafluoropropylene-lithium bis (oxalate) borate (LiBOB) via the solution casting methods have been prepared and characterized. The effect of salt concentration and inorganic filler concentration on electrochemical and physical properties are studied. An optimized ionic conductivity of 6×10^-5 Scm^-1 for solid PVDF-HFP/LiBOB (1:1 wt. %) has been achieved and an ionic conductivity up to 1.1 × 10^-4 Scm^-1 has been attained in PVDF-HFP/LiBOB/SiO₂ (6 wt.%) at room temperature, which is almost one order of magnitude higher than those of conventional solid polymer electrolyte. The improvement is mainly attributed to a much improved ion mobility. It is found the large anion BOB- having a weak interaction with Li⁺ can help the Li salt dissolution in PVDF-HFP while SiO₂ can suppress crystallinity and increase amorphous phase, leading to a significantly enhanced ion conductivity. A variety of techniques such as Differential Scanning Calorimetry (DSC), Fourier Transform Infrared (FTIR) spectroscopy, Electrochemical Impedance Spectroscopy (EIS), and Scanning Electron Micrographs (SEM) are performed to elucidate the relationship between the structural and dynamic properties of the hybrid electrolyte and the ion mobility.

Date of Award	2014
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology