Polymer electrolytes based on vinyl ethers with various EO chain length and their polymer electrolytes cross-linked by electron beam irradiation

Abstract

Polymer electrolytes based on vinyl ethers with various ethyleneoxy (EO) chain length (poly-1a (m = 3), poly-1b (m = 6), poly-1c (m = 10), and poly-1d (m = 23.5)) with lithium bis(trifluoromethanesulfonimide) (LiTFSI) were prepared, and effect of pendant EO chain length in the polymers on electrochemical and thermal properties was investigated. Glass transition temperature (T g) of all polymer electrolytes increased linearly with an increase in salt concentrations. Ionic conductivities of the polymer electrolytes increased with an increase in the pendant EO chain length of the polymers at the constant [Li]/[O] ratio, but in the polymer electrolyte of the poly-1d (m = 23.5) with the longest pendant EO chain length, ionic conductivity decreased in the low temperature range of −20 to 10 °C due to the crystallization of the pendant EO chain. The highest ionic conductivity, 1.23 × 10−4 S/cm at 30 °C, was obtained in the polymer electrolyte of the poly-1c (m = 10) with pendant EO chain length of 10 at the [Li]/[O] ratio of 1/20. It was found that the cross-linking of the polymer electrolyte, composed of poly-1c (m = 10) with LiTFSI at the [Li]/[O] ratio of 1/28, by electron beam (EB) irradiation may improve the mechanical property without affecting ionic conductivity, thermal property, and oxidation stability. Polymer electrolytes based on poly-1a (m = 3), poly-1b (m = 6), poly-1c (m = 10), and poly-1d (m = 23.5) and cross-linked polymer electrolytes were electrochemically stable until 4 V and thermally stable around 300 °C.