Facile Preparation of Higher Conductivity Porous Polyimide‐based Separators by Phase Inversion and its Overcharge‐sensitive Modification for Lithium‐ion Batteries

Abstract Separator plays multiple roles in the performance and safety of lithium‐ion batteries owing to the lower conductivity of the organic electrolyte and the hyperactive electrode materials. However, the commercial polyolefin separator suffers from the poor thermal stability, weak electrolyte‐wettability, low porosity as well as the demanding and costly manufacturing. Herein, we demonstrate the facial synthesis of a sponge‐like, isotropic, polyimide‐based separator by phase inversion, which possessed the higher electrolyte‐saturating conductivity (1.74 mS cm⁻¹) and ion transference number (0.81) besides its excellent wettability and thermal stability. Meanwhile, the bearable stress was further promoted by 60 % with the 30 wt % epoxy‐strengthening tactic and the high porosity (67 %) and conductivity (1.47 mS cm⁻¹) still preserved. Additionally, an overcharge‐sensitive PI separator was further developed by combining the conductive copolymer of coumarin‐triphenylamine by virtue of the eminent processability of PI, which demonstrated the outstanding voltage‐restraining capability for LiFePO₄‐based cell during overcharge. Therefore, polyimide‐based separator could be a quite promising candidate due to its facile manufacturing, preferable performance and versatile functionalizing.