Confined Sulfur in Microporous Carbon Renders Superior Cycling Stability in Li/S Batteries

The use of sulfur in the next generation Li‐ion batteries is currently precluded by its poor cycling stability caused by irreversible Li 2 S formation and the dissolution of soluble polysulfides in organic electrolytes that leads to parasitic cell reactions. Here, a new C/S cathode material comprising short‐chain sulfur species (predominately S 2 ) confined in carbonaceous subnanometer and the unique charge mechanism for the subnano‐entrapped S 2 cathodes are reported. The first charge–discharge cycle of the C/S cathode in the carbonate electrolyte forms a new type of thiocarbonate‐like solid electrolyte interphase (SEI). The SEI coated C/S cathode stably delivers ≈600 mAh g −1 capacity over 4020 cycles (0.0014% loss cycle −1 ) at ≈100% Coulombic efficiency. Extensive X‐ray photoelectron spectroscopy analysis of the discharged cathodes shows a new type of S 2 species and a new carbide‐like species simultaneously, and both peaks disappear upon charging. These data suggest a new sulfur redox mechanism involving a separated Li + /S 2− ion couple that precludes Li 2 S compound formation and prevents the dissolution of soluble sulfur anions. This new charge/discharge process leads to remarkable cycling stability and reversibility.