Tuning Ion Transport Kinetics and Interfacial Stability via a Co‐Containing Covalent Organic Framework for Stable Lithium Metal Batteries

ABSTRACT Lithium metal batteries (LMBs) are severely limited by nonuniform lithium deposition and unstable interfacial reactions, which lead to poor cycling stability and safety concerns. Regulating ion transport behavior and interfacial stability plays a decisive role in achieving stable LMBs. However, simultaneously optimizing these two aspects remains a considerable challenge. Herein, a Co‐containing covalent organic framework (Co‐COF) was developed as a multifunctional separator modifier to address these challenges. Benefiting from the ordered porous structure and lithiophilic oxygen‐containing groups, the Co‐COF@polypropylene (PP) separator homogenizes Li + flux and facilitates Li + desolvation, thereby accelerating interfacial ion transport kinetics. Meanwhile, the Co active sites moderately anchor PF 6 − anions, increasing the Li + transference number and promoting the formation of a stable LiF‐rich solid electrolyte interphase with enhanced interfacial stability. As a result, the Co‐COF@PP separator enables uniform lithium deposition, suppresses lithium dendrite growth, and improves the stability of lithium metal anodes. Consequently, Li||Li symmetric cells achieve stable lithium plating/stripping behavior for over 700 h. Furthermore, LiFePO 4 ||Li cells assembled with the Co‐COF@PP separator exhibit superior rate capability and maintain 90.1% capacity retention after 450 cycles at 1 C, significantly outperforming cells with pristine PP separators. This work provides an effective strategy for stable LMBs.