Formation Mechanism and Molecular Structure of Sulfurized Polyacrylonitrile

Abstract Lithium‐sulfur (Li‐S) batteries have attracted considerable attention due to their high theoretical energy density and abundant sulfur resources. Sulfurized polyacrylonitrile (SPAN) effectively suppresses polysulfide dissolution and demonstrates excellent cycling stability, making it a promising candidate for cathode materials in practical Li‐SPAN batteries. This study elucidates the formation mechanism, chemical bonds, and spatial structures of SPAN. The reaction begins with the generation of ·S 2 · diradicals, followed by the dehydrogenation and cyclization of polyacrylonitrile (PAN), ultimately resulting in the formation of C─S and N─S bonds. The multilayered structure of SPAN, characterized by C‐S and N‐S layers twisted at angles of ≈30 to 40 degrees and interconnected by C─S x ─N bonds, has the potential to chemically confine sulfur up to a maximum of 63.5 wt.%, corresponding to a theoretical capacity exceeding 1000 mAh g −1 . These findings provide fundamental insights for the design of SPAN materials for advanced X‐SPAN batteries.