Molecularly Engineered Covalent Organic Framework Separator with Triple-Synergetic Mechanisms for Ultrastable Lithium Metal Batteries

Abstract

This study designed and synthesized a novel cyclic topological covalent organic framework material, TPB-DHTA-COF, through an imine condensation reaction, and in situ grew it on the surface of commercial polypropylene membranes to construct high-performance composite membranes. This material has highly ordered hexagonal annular pores and vertically arranged nanostructures. The periodic distribution of imine bonds (–C=N–) in its skeleton forms an electron delocalization system with adjacent hydroxyl groups (–OH). Through the triple synergistic mechanism of “chemical adsorption, spatial confinement, dynamic adaptation,” the performance of lithium metal batteries is significantly improved. Electrochemical tests have shown that the Li-Li symmetric battery assembled with TPB-DHTA-COF/PP composite separator can stably cycle for 1200 h (overpotential of 120 mV) at 5 mA/cm², maintain a low overpotential of 0.12 V at an ultra-high rate of 20 mA/cm², and have a cycle life of 2100 h. The average coulombic efficiency of the Li-Cu battery after 300 cycles is 98.2%. The capacity retention rate of the Li-LFP full battery exceeds 66% after 300 cycles at a 2C rate. This work achieves ion transport pathway optimization and interface stabilization through precise molecular-scale regulation, providing a new strategy for the development of high-safety and high-energy-density lithium metal batteries.