Polyimide separators for rechargeable batteries

Separators are indispensable components of modern electrochemical energy storage devices such as lithium-ion batteries (LIBs). They perform the critical function of physically separating the electrodes to prevent short-circuits while permitting the ions to pass through. While conventional separators using polypropylene (PP) and polyethylene (PE) are prone to shrinkage and melting at relatively high temperatures (150 °C or above) causing short circuits and thermal runaway, separators made of thermally stable polyimides (PIs) are electrochemically stable and resistant to high temperatures, and possess good mechanical strength—making them a promising solution to the safety concerns of LIBs. In this review, the research progress on PI separators for use in LIBs is summarized with a special focus on molecular design and microstructural control. In view of the significant progress in advanced chemistries beyond LIBs, recent advances in PI-based membranes for applications in lithium-sulfur, lithium-metal, and solid-state batteries are also reviewed. Finally, practical issues are also discussed along with their prospects.