Preparation and performance of polyimide lithium‐ion battery separator based on benzonorbornene main chain structure

Abstract Separators are of significance in the thermal safety and energy‐storage performance of lithium‐ion batteries. Polyimide (PI) separators have great prospects as membrane candidate materials due to their high thermal and chemical stability. Here, a series of PI lithium‐ion battery membranes containing benzonorbornene and pyridine were prepared by using polyethylene glycol (PEG) or polyvinylpyrrolidone (PVP) as pore‐forming agents. The obtained porous polymer membrane PI‐PEG600 had excellent thermal stability (initial weight‐loss temperature up to 300°C and T g of 278°C), satisfying liquid electrolyte uptakes (up to 132.65%), and admirable ionic conductivity (1.62 × 10 −4 S cm −1 ). The battery with PI porous membranes showed greatly enhanced electrochemical performance with high C‐rate discharge capability (167.3–108.8 mAh g −1 , 0.1–2 C) and excellent capacity of 155.6 mAh g −1 at 0.2 C after 55 cycles, meanwhile, it could work steadily at 180°C. This work offers a feasible and effective route to develop membranes of heat‐resistant PI separators for safe lithium‐ion batteries.