Construction of Safety and Non-flammable Polyimide Separator Containing Carboxyl Groups for Advanced Fast Charing Lithium-ion Batteries

With the wide applications of lithium-ion batteries (LIBs) in electronic devices and electric vehicles, it is of great importance to improve their safety and electrochemical performance. Herein, soluble polyimides (PI) containing carboxyl groups (?COOH) were synthesized by a simple one-step method and PI separators with sponge-like, interpenetrating porous structures were prepared via non-solvent induced phase separation (NIPS). The obtained PI separators exhibited excellent thermal stability and fire-resistance properties, with the electrolyte uptake of 344% and good dimensional integrity in air at 200 °C. The results showed that the lithium-ion transference number of the obtained PI separator could reach 0.48, which was much higher than that of the Celgard-2400 separator (0.38). The Li/LiFePO₄ half-cell with the PI separator showed excellent cycle capability and high-rate performance with a high capacity of 121.80 mA·h·g^?1 at 5 C, which was better than that of the cell with the Celgard-2400 separator (54.3 mA·h·g^?1), demonstrating the promising applications of this PI separators in LIBs.