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

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 mgs cm‐2) and lean electrolyte (5 µL mgs‐1), the batteries still exhibit ≈80% capacity retention over 100 cycles, showing great potential for practical application. An all‐in‐one strategy of a sulfonate‐rich covalent organic framework (COF)‐modified separator is proposed for Li–S batteries, which provides a solution for tackling the issues of polysulfide shuttling and dendrite growth simultaneously. Benefiting from the chemical merits of strong electronegativity and large interlayer spacing for SCOF‐2, the capacity and stability of rechargeable Li–S batteries are greatly improved.