Sulfur@microporous Carbon Cathode with a High Sulfur Content for Magnesium–Sulfur Batteries with Nucleophilic Electrolytes

To enhance the long-term cycling stability of sulfur cathode for high-energy-density magnesium–sulfur (Mg–S) batteries with easily prepared (PhMgCl)2–AlCl3/tetrahydrofuran-based nucleophilic electrolytes, a sulfur@microporous carbon (S@MC) composite with a high sulfur content (64.7 wt %) was prepared by impregnating sulfur into microporous carbon. S@MC cathode combines the merits of both small chainlike S2–4 molecules and large ringlike S8 molecules with S2–4 existing as a highly dispersed state inside the micropores of carbon and S8 on the outside surface of carbon. MC as a host improves the electrode reaction kinetics and physically adsorbs sulfur and polysulfides. Copper sulfides formed when sulfur is coated on a Cu current collector at 50 °C provide a strong chemical interaction between Cu and sulfur, which protects sulfur from the electrolyte and relieves the dissolution of polysulfides. Based on the advantages of the microporous carbon and Cu current collector, S@MC exhibits an initial discharge capacity of approximately 979.0 mAh g–1 and maintains a capacity of 368.8 mAh g–1 after 200 cycles at a rate of 0.1C, demonstrating improved sulfur utilization and cycle stability. When the rate increases to 0.2C, the composite can still deliver a capacity of about 200 mAh g–1 with 100% Coulombic efficiency. This strategy of stabilization of S2–4 small molecules in MC and chemical bond of Cu to S8 large molecules provides an effective approach to improve the cycling stability, rate performance, and sulfur content for Mg–S batteries with nucleophilic electrolytes.