A Lithium‐Affinitive Covalent Organic Polymer Network Functionalized Separator for Dendrite‐Free and High‐Durability Lithium–Sulfur Batteries under Harsh Conditions

Abstract Lithium–Sulfur (Li─S) batteries are renowned for their high theoretical specific capacity and cost‐effectiveness. Nevertheless, their performance could be impeded by obstacles including lithium dendrite growth and lithium polysulfide (LiPS) shuttle, particularly under harsh conditions. Herein, an economical strategy is reported for modifying polyolefin separators (PP) with covalent organic polymer networks (TPE) to alter Li solvent structure, enhance lithium‐ion transport, and suppress shuttle effects. Combining in situ/ex situ characterization and theoretical calculations, it is demonstrated that the lithiophilic groups (‐C═N‐) in the TPE@PP separator form strong interaction with lithium, facilitating the dissociation of Li─Solvent/LiPS‐solvent to release freer lithium ion and shape a stable solid electrolyte interface rich in LiF and Li3N. The polymer network serves as a “highway” that accelerates Li transport and promotes uniform nucleation behavior. Therefore, the Li|TPE@PP|CNT/S cell enables 60% capacity retention after 2000 cycles at 1.0 C and exhibits stable cycling performance of 100 cycles from ‐40 to 80 °C. Moreover, the pouch cell maintains a capacity of more than 600 mA h g−1 after 30 cycles at 0 °C. This study provides a promising avenue for the application of high‐performance batteries in harsh environment from the perspective of separator engineering.