H₃PO₄-Impregnated Covalent Organic Framework Membrane on Separators to Prevent Lithium Metal Anode Dendrite Growth

Inhibiting the growth of lithium dendrites is crucial for battery safety. For separators, their favorable electrolyte wettability, uniform current density, and high ionic conductivity are beneficial for avoiding Li dendrite growth. In this work, we propose a separator (PA@COF/PP) by modifying a polypropylene separator with H₃PO₄-functionalized covalent organic frameworks. The uniform channels of the covalent organic frameworks and H₃PO₄ can homogenize the current and act as ionic conductors for efficient Li⁺ migration. The synthesized separator effectively suppresses the growth of lithium dendrites and improves the stability of the batteries. A symmetric cell with the PA@COF/PP separator exhibits a stable life span over 4000 hours at a high current density of 5 mA cm^-2, compared to the commercial PP separator, which lasts only 159 hours. This work provides an efficient method and novel inspiration for the construction of dendrite-free lithium metal batteries.