Synthesis of Highly Cyclized Polyacrylonitrile via Liquid-Phase Cyclization for Advanced Cathode Materials

Sulfurized polyacrylonitrile (SPAN) based on a solid–solid reaction has attracted wide attention due to its advantages of no shuttle effect. However, the solid-state polyacrylonitrile raw material is used during the preparation of SPAN and results in a low vulcanization efficiency. Meanwhile, a series of side reactions such as the formation of cyclic polyamines and conjugated polyenes, cross-linking side reactions, and polymer degradation prevent an ideal trapezoidal conjugated main-chain structure. In this work, a liquid-phase cyclization method is proposed to prepare SPAN materials (SPAN-L). The reaction temperature is significantly lowered by leveraging the high reactivity characteristics under liquid-phase conditions, thereby inhibiting a series of side reactions caused by high temperature and improving the structural regularity of SPAN. The SPAN-L cathode has good structural regularity and a uniform sulfur distribution, which contribute to its enhanced electrical conductivity and high sulfur utilization ratio. Additionally, ex situ Raman and XPS analyses reveal stable C–S bonds in SPAN-L during cycling, indicating enhanced electrode stability. This study synthesizes SPAN cathode materials with enhanced performance by adjusting the reaction environment, showing better electronic conductivity, sulfur utilization, and cycle stability than the solid-phase methods.