Recent Advances in Covalent Organic Frameworks for Lithium–Sulfur Batteries: Applications in Cathodes and Separators

Lithium–sulfur batteries (LSBs) have attracted significant attention due to their high theoretical energy density and cost-effectiveness. However, their practical application is hindered by issues such as the shuttle effect of lithium polysulfides (LiPSs), sluggish redox kinetics, and the insulating nature of sulfur. Covalent organic frameworks (COFs) have emerged as a promising class of porous crystalline materials for enhancing the performance of LSBs due to their tunable structures, high surface areas, and well-defined pore environments. This review systematically summarizes the latest progress in COF-based materials for LSBs, focusing on their applications in cathodes and functional separators. For cathodes, COFs and their derived composites serve as sulfur hosts, leveraging their high surface area and functionalized pore structures to immobilize LiPSs and facilitate sulfur utilization. In separators, COFs and COF-based composites enable efficient suppression of LiPSs migration through physical confinement, chemical adsorption, and catalytic acceleration of sulfur species transformation. Despite these advancements, the practical application of COFs either as host or functional separators faces challenges such as intrinsic low conductivity, structural stability, and large-scale synthesis. Finally, the challenges and perspectives are provided regarding the future design of COF-based cathodes and functional separators for high-performance LSBs.