Cationic Covalent Organic Framework Nanosheets as the Coating Layer of Commercial Separator for High-Efficiency Lithium-Sulfur Batteries

Ion-selective separators, are crucial and in high demand for maximizing the performance of lithium-sulfur (Li–S) batteries, which can conduct lithium ions while efficiently blocking polysulfides. However, commercial separators cannot effectively block the shuttle of polysulfides after multiple cycles due to their large porosity and easy dissolution, resulting in a reduced battery life. Herein, a covalent organic framework nanosheets (CON) ion-coated separator is prepared on the commercial separator. Due to the smaller pore size of CON-TFSI compared to polysulfides, the CON-TFSI modified separator can effectively block the polysulfide from migrating across the separator. By incorporating this innovative functional layer, Li–S batteries demonstrate outstanding performance. In a Li–S battery featuring a sulfur loading of 0.6 mg/cm2, it attains an initial discharge specific capacity of up to 891.9 mA h g−1, and exhibits the capacity retention of 54.6 % after 500 cycles at a current density of 0.2 C. This work offers a fresh perspective on the advancement of high-performance membranes for Li–S batteries.