New Insights into the N-S Bond Formation of a Sulfurized-Polyacrylonitrile Cathode Material for Lithium-Sulfur Batteries.

Sulfurized polyacrylonitrile (S-cPAN) has been recognized as a particularly promising cathode material for lithium-sulfur (Li-S) batteries due to its ultra-stable cycling performance and high degree of sulfur utilization. Though the synthetic conditions and routes for modification of S-cPAN have been extensively studied, details of the molecular structure of S-cPAN remain yet unclear. Herein, a more reasonable molecular structure consisting of pyridinic/pyrrolic nitrogen (N/N) is proposed, based on the analysis of combined X-ray photoelectron spectroscopy, C/N solid-state nuclear magnetic resonance, and density functional theory data. The coexistence of vicinal N/N entities plays a vital role in attracting S molecules and facilitating N-S bond formation apart from the generally accepted C-S bond in S-cPAN, which could explain the extraordinary electrochemical features of S-cPAN among various nitrogen-containing sulfurized polymers. This study provides new insights and a better understanding of structural details and relevant bond formation mechanisms in S-cPAN, providing a foundation for the design of new types of sulfurized cathode materials suitable for application in next-generation high-performance Li-S batteries.