Core–Shell Structured Polyimide@γ-Al₂O₃ Nanofiber Separators for Lithium-Ion Batteries

Owing to its excellent thermal stability, polyimide (PI) is regarded as one of the most promising alternatives among separators for high-safety lithium-ion batteries (LIBs). Unfortunately, the wettability of the PI separator to electrolytes is still undesirable. The complexation–hydrolyzation method was used to develop a composite membrane with a core–shell structure that anchors γ-Al2O3 nanoparticles on PI nanofiber (PI@γ-Al2O3) as an LIB separator. The effects of surface treatment on the physicochemical and electrochemical properties of PI composite membranes are studied in detail, using the pristine PI nanofiber membrane as a reference. The results show that the PI@γ-Al2O3 nanofiber membrane exhibits better physicochemical properties and electrochemical performances. Specifically, the wettability property of the PI@γ-Al2O3 nanofiber membrane is improved with an almost zero contact angle, which significantly meets the requirements of high-performance LIBs. Furthermore, the electrochemical performance of the PI@γ-Al2O3 nanofiber membrane also shows excellent comprehensive properties with the ionic conductivity improving from 0.81 to 1.74 mS cm–1. Besides, the PI@γ-Al2O3 nanofiber membrane maintains a long charge–discharge process with a capacity retention rate of 98% at 0.5 C after 100 cycles. Consequently, the aforementioned excellent performances illustrate that core–shell PI@γ-Al2O3 nanofiber membranes have a promising future for the safety and stability of LIBs.