Lithium ion conductive polymer electrolyte by side group rotation

Abstract

Ionic conductive materials are of much interest as an electrolyte for solid-state lithium batteries. Poly(alkylene oxide) and lithium salt complex exhibits high ionic conductivity in terms of its high solubility for lithium salts. However, the temperature dependency of its ionic conductivity is quite large and non-linear, the ionic conductivity drops down at low temperature, especially below glass transition temperature of the polymer. Because its ionic conductive mechanism is derived from its segmental motion of polymer main chain. A novel ionic conductive material, poly[2,6-dimethoxy- N-(4-vinylphenyl)benzamide] is synthesized and confirm ionic conductivity even below glass transition temperature. Ionic conductivity of the polymer with lithium ditrifluoromethylsulfonate imide complex shows 10 −5 S cm −1 from 0 to 60 °C. Its temperature dependency is linear, namely Arrehnius type dependency. Evaluating from these data, activation energy of ionic conductivity for temperature region from 20 to 60 °C is calculated as 31 kJ mol −1 and that for temperature region from −20 to 20 °C is 11 kJ mol −1. Judging from these results, we conclude that the ionic conductivity of the polymer salt complex derived from 2,6-dimethoxyphenyl group rotation, instead of segmental motion of the polymer.