Composite Polymer Electrolyte based on Liquid Crystalline Copolymer with High-temperature Stability and Bendability for All-solid-state Lithium-ion Batteries

In this study, a novel composite polymer electrolyte consist of 8-arm block liquid crystalline copolymer (8-PEG-MALC), 8-arm poly(ethylene glycol) (8-PEG), polyethylene (glycol) diacrylate (PEGDA) and bistrifluoromethanesulfonimide lithium salt (LiTFSI) was prepared successfully. The branching 8-PEG ensure high ionic conductivity of the all solid state polymer, crosslinking agent PEGDA endow good mechanical property, and 8-arm block liquid crystalline copolymer with a birefringent mesogens to tune the morphology of the composite polymer electrolytes. The polymer electrolytes can form a transparent and flexible film with nanoscale microphase separation structure, which creating well-defined ion conducting channels. The electrochemical properties of composite polymer electrolytes are analyzed and the highest ionic conductivity reaches 6.2 × 10-5 S cm-1 at room temperature after annealed from fixed temperature. It also displays high temperature stability up to 150°C, which is higher than traditional electrolytes. More intriguingly, the assembled LiFePO4/Li cells using the composite polymer electrolytes exhibit good charge/discharge cycles at 95°C. The good electrochemical properties, temperature stability and bendability of the composite polymer electrolytes indicate it potentially as a very promising material for all-solid-state flexible lithium ion batteries.