Recent progress of composite polyethylene separators for lithium/sodium batteries

Microporous membrane separators (MMS) are at the heart of rechargeable lithium/sodium ion batteries (LIBs/NIBs) because they prevent short circuits and serve as a channel for ion transport during charge-discharge operations. Although the separator is an inactive part of the battery, its structure and properties have a significant impact on the safety, electrochemical performance, and reusability of the battery. This review article summarizes the state-of-the-art fundamental requirements and properties of ideal separators for LIBs and NIBs. Different battery membranes are briefly discussed, including microporous, non-woven, electrolyte, composite, and modified microporous membranes. This paper provides in-depth descriptions of the fabrication and development of hybrid composite separators based on porous polyethylene (PE) membranes for LIBs and NIBs. Furthermore, it discusses advanced battery separators and presents comparative deliberations on various unique preparation processes for high-performance hybrid PE separators. Finally, a brief outlook for future trends in this research area is provided. Insights from such a review article will thereby further assist researchers and developers working on hybrid polyolefin separators towards future battery expansions.