Separator Engineering with Molten-Salt-Derived Carbon for Suppressing Polysulfide Shuttle in Li–S Batteries

Lithium–sulfur (Li–S) batteries are widely regarded as one of the most promising candidates for next-generation battery systems because of their exceptionally high 1675 mAh g –1 theoretical capacity. However, the polysulfide shuttling severely hinders their real-world application. To address this challenge, we introduce a separator engineering strategy using novel molten-salt-derived carbon (MSDC) spheres coated onto polypropylene (PP) separators to effectively suppress polysulfide migration and enhance overall electrochemical performance. The synthesized MSDC spheres display a uniform morphology with a defect-rich framework and oxygen-containing groups that synergistically provide strong chemisorption and catalytic conversion sites for polysulfides. Structural and spectroscopic analyses confirm the hierarchical porous architecture, predominantly microporous (<2 nm), providing abundant active sites for efficient polysulfide immobilization. Electrochemically, a Li–S battery employing an MSDC-coated separators delivered an initial discharge capacity of 1366 mAh g –1 at 0.1C and retained a high capacity of 950 mAh g –1 after 100 cycles. Furthermore, it demonstrated exceptional long-term stability over 400 cycles at 0.5C, maintaining a reversible capacity above 800 mAh g –1 with nearly 100% Coulombic efficiency. Additionally, symmetric Li∥Li batteries showed that lithium–metal stability was improved. Collectively, these results demonstrate that the rapid, solvent-free molten-salt synthesis is a prominent route for developing functional carbon materials and that MSDC-coated separators represent a highly promising strategy for advancing Li–S batteries toward practical implementation.