Abstract:Lithium metal batteries, boasting their ultra-high theoretical capacity and elevated working voltage, are considered the top choice for the next generation of high-capacity batteries. However, the disordered ionic transport and instability at the "electrolyte/anode" interface, which leads to lithium dendrite growth, severely restrict the commercial application. In this study, the COF@PP composite separators were obtained by a vacuum self-assembly method using sulfonic acid-based covalent organic framework materials (sulfonic acid COF-1) as raw materials. It is found that the COF layer could enhance the selectivity and rapidity of lithium ion transport, the ionic conductivity and transference number of lithium ions increase from 0.21 mS cm-1 and 0.46 to 0.44 mS cm-1 and 0.66, respectively. Hence, lithium ions achieve stable depositing/stripping for over 250 h without significant lithium dendrite formation. "Li | LiFePO4" cell performance tests demonstrated that the COF@PP separator reduced active lithium loss, achieving a discharge specific capacity exceeding 150 mAh g-1 within the voltage range of 2.5-4.2V. The capacity retention rate is more than 94% after 200 cycles at 1C, significantly outperforming conventional separator batteries. The performance enhancement is attributed to the formation of uniform nanochannels after the PP are covered by COF, inhibiting the passage of large-radius anions. Moreover, the composite separator exhibits good wettability and forms internal channels with filled electrolyte, providing a rapid pathway for ion transport.