Deciphering the Sulfur-Involved Bonding Interactions in Sulfurized Polyacrylonitrile: The Formation Thermodynamics and the Roles in Electrochemical Characteristics

Sulfurized polyacrylonitrile (SPAN) exhibits a very high cycle stability by overcoming the shuttle effect of conventional Li-S batteries. However, there are still controversies in SPAN about the bonding types of sulfur with the matrix, their critical synthesis temperature regions, and their roles in the electrochemical lithium storage reaction, seriously hindering the economical synthesis of SPAN, the optimization of performances, and the exploration of other SPAN-like alternatives. The key to solving the above problems lies in accurate measurements of the thermodynamic evolution of bonding interactions in the synthesis process as well as in the electrochemical process. In this study, soft and tender X-ray absorption spectroscopy (XAS) is utilized to achieve a fine resolution of specific bonding interactions through the selective excitation of C, N, and S. Sulfur-involved bonding interactions have been elucidated, including the bonding type, critical temperature region, linking site, and their interplays. Furthermore, their contributions to lithium storage and their regulations on electrochemical performances are discussed. This study demonstrates the resolving capability of XAS for organic electrode materials and provides insights for further analyzing the cyclability of SPAN and rationally designing alternatives from the perspective of bonding interactions.