Polythiocyanogen as Cathode Materials for High Temperature All-Solid-State Lithium–Sulfur Batteries

Solid-state lithium batteries are uniquely suited for operation at elevated to even high temperatures (>100 °C). Under these conditions, however, oxide cathode materials are unstable with high-conductivity sulfide-based electrolytes while elemental sulfur suffers from poor utilization due to its insulating nature. Here, we developed an ionic liquid mediated synthesis procedure for polythiocynogen (poly-SCN) and applied it as a sulfur-rich cathode. The material, with uniform, submicrometer particle size and a > 55 wt % sulfur loading, exhibits good thermal stability of over 200 °C. A specific capacity of over 800 mAh g–1 at 100 °C is realized when poly-SCN is used as a cathode in an all-solid-state battery (ASSB). Mechanistic studies show that during discharge, both C–S and S–S bonds in poly-SCN are cleaved along with the formation of Li2S. During charge, the re-formation of poly-SCN structure is observed. The scalable synthesis procedure, high thermal stability, high sulfur loading, and high capacity make poly-SCN a promising candidate for high temperature solid state batteries.