Covalent organic frameworks-based functional separators for rechargeable batteries: Design, mechanism, and applications

Covalent organic frameworks (COFs) have been intensively investigated and used to develop advanced separators for rechargeable batteries due to their high specific surface area, well-defined structure, and ordered nano-channels. The tunable structure of COFs promises demand-oriented design at the molecular/atomic level to obtain the desirable separator. Currently, the design principle and mechanism of COF-based separators are still ambiguous, while a guide is requisite for further in-depth research and exploration. In this review, we comprehensively summarize and analyze the recent progress, core challenges and perspectives of COF-based functional separator engineering in rechargeable batteries. Among them, the regulation of separator properties such as pore size, wettability, surface charge, thickness, and stability through the COF structural design and fabrication optimization are specifically emphasized. In particular, the working mechanism of COF separators in various rechargeable batteries is highlighted to provide insightful guidance for designing better separators. This review presents a comprehensive and in-depth analysis of COF-based separator designs and mechanisms aiming to provide new perspective on improving the electrochemical performances of rechargeable batteries.