Designing Multifunctional Polyethylene-Polyimide Composite Separators for Rechargeable Lithium-Ion Batteries

Abstract

A novel separator of the polyethylene spin-coated electropsun polyimide (PE@PI) composite with multiple functions, including ideally thermo-dimensional stability, high electrolyte-uptake capability, good charge-discharge performance, and excellent thermal shutdown ability is designed for rechargeable lithium-ion batteries (LIBs). The uniform, sub-micrometer layer of spin-coated, low-density polyethylene provides the thermal shutdown function of this PE@PI separator without sacrificing its multi-functionality. This PE@PI film without any shrinkage at 150°C exhibits high porosity (80%), high electrolyte-uptake (1350%), and good ionic conductivity (1.2 × 10−3 S cm−1). The thermal shutdown function of PE@PI has been confirmed by both scanning electron microscopic (SEM) and electrochemical impedance spectroscopic (EIS) analyses. The full cell battery tests reveal that the cell using the PE@PI separator shows a flatter first cycle charge-discharge plateau and better capacity retention at high C rates (104 mAh g−1 at 1 C, 81% retention) in comparison with that utilizing the Celgard 2325 separator (88 mAh g−1 at 1 C, 70% retention). The high electrolyte uptake of the highly porous PE@PI film facilitates the ion conduction, which is the main reason enhancing the battery performance, revealing a promising separator for the advanced LIB application.