Liquid-like Poly(ionic liquid) as Electrolyte for Thermally Stable Lithium-Ion Battery

A liquid-like poly­(ionic liquid) (PIL) with a very low glass transition temperature of −51 °C and a thermal decomposition temperature of 202.7 °C was synthesized. A PIL-based electrolyte by mixing this poly­(ionic liquid) with additives of 10 wt % propylene carbonate and 0.1 M LiClO4 is proved to be an excellent electrolyte for lithium-ion battery. The obtained PIL-based electrolyte exhibits a high ionic conductivity of 8.3 × 10–5 S cm–1 at 25 °C and 2.0 × 10–4 S cm–1 at 60 °C and a wide electrochemical potential window up to 5.61 V at 25 °C and 4.14 V at 60 °C. The Li/LiFePO4 batteries equipped with this PIL-based electrolyte achieve high capacity, outstanding cycling stability and rate capability at 25 °C, and even improved performance at high temperature like 60 °C. Such excellent performances of batteries are attributed to the formation of stable solid-electrolyte interface film at the lithium-electrolyte interface and the stability of electrolyte during cycling.