Towards High Performance Li–S Batteries via Sulfonate‐Rich COF‐Modified Separator

Abstract Lithium–sulfur (Li–S) batteries are held great promise for next‐generation high‐energy‐density devices; however, polysulfide shuttle and Li‐dendrite growth severely hinders their commercial production. Herein, a sulfonate‐rich COF (SCOF‐2) is designed, synthesized, and used to modify the separator of Li–S batteries, providing a solution for the above challenges. It is found that the SCOF‐2 features stronger electronegativity and larger interlayer spacing than that of none/monosulfonate COFs, which can facilitate the Li + migration and alleviate the formation of Li‐dendrites. Density functional theory (DFT) calculations and in situ Raman analysis demonstrate that the SCOF‐2 possesses a narrow bandgap and strong interaction on sulfur species, thereby suppressing self‐discharge behavior. As a result, the modified batteries deliver an ultralow attenuation rate of 0.047% per cycle over 800 cycles at 1 C, and excellent anti‐self‐discharge performance by a low‐capacity attenuation of 6.0% over one week. Additionally, even with the high‐sulfur‐loading cathode (3.2–8.2 mg s cm ‐2 ) and lean electrolyte (5 µ L mg s ‐1 ), the batteries still exhibit ≈ 80% capacity retention over 100 cycles, showing great potential for practical application.