Multi‐Field Coupling Driven in Situ Interfacial Growth of COF‐functionalized Membranes for Lithium–Sulfur Batteries

Conventional modification methods for the separator of high-performance lithium-sulfur batteries often struggle to realize the functional materials well adhering on and across the substrate. Herein, we employ a scalable top-down strategy in an oil-water-oil system to interfacially polymerize COF nanoparticles across a polyolefin substrate as a self-standing separator for Li─S batteries. By providing a suitable environment for the membrane to remain flat during polymerization, COF particles can penetrate from the surface into internal pores, forming a uniform and robust architecture. The resulting COF-functionalized membrane incorporates abundant -OH groups that effectively promote Li⁺ transport and restrict polysulfide shuttling. Benefiting from this synergy, the modified separator achieves high ionic conductivity (0.92 mS cm^-1), an elevated polysulfide diffusion barrier (0.390 versus 0.283 eV), and excellent electrochemical performance, including 678 mAh g^-1 after 500 cycles at 1.0 C. This in situ interface polymerization strategy offers a new path for more comprehensively functionalizing COF-based membrane to achieve high-performance lithium-sulfur batteries.