Covalent Organic Framework-Derived Ion-Sieving Channels Enabling Stable Lithium Metal Anodes through Interfacial Engineering and Solvation Structure Modulation.

Lithium metal anodes, despite their ultrahigh capacity, suffer from severe interfacial instability due to uncontrolled parasitic reactions and dendritic growth, limiting practical applications. Herein, a 2D covalent organic framework (NUS-9) synthesized via cryogenic interfacial growth was engineered into a NUS-9@PP composite separator to enhance lithium metal battery performance. Its unique layered architecture establishes vertically aligned Li transport channels with ion-sieving functionality, while lithiophilic polar groups regulate Li solvation structures, suppressing electrolyte-Li parasitic reactions. Modified separators demonstrated lower nucleation overpotentials of 38.2/42.8 mV at 0.3/0.5 mA cm and extended electrochemical stability to 4.7 V. Benefiting from TFSI anchoring effects and control of Li transport flux distribution, NUS-9@PP demonstrated superior Li transport properties with a high Li transference number (0.71), stable 370 h cycling at 3 mA cm, and 99.8% coulombic efficiency. XPS analysis confirmed its capability to promote the LiF-rich solid electrolyte interface (SEI) formation, effectively suppressing lithium dendrite growth. Full-cell tests further validated significantly enhanced cycling longevity and efficiency, establishing a novel strategy for stabilizing lithium metal anodes by using 2D COF materials.