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

Solid-state lithium batteries are uniquely suited foroperationat elevated to even high temperatures (>100 degrees C). Under theseconditions, however, oxide cathode materials are unstable with high-conductivitysulfide-based electrolytes while elemental sulfur suffers from poorutilization due to its insulating nature. Here, we developed an ionicliquid 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 % sulfurloading, exhibits good thermal stability of over 200 degrees C. A specificcapacity of over 800 mAh g(-1) at 100 degrees C is realizedwhen poly-SCN is used as a cathode in an all-solid-state battery (ASSB).Mechanistic studies show that during discharge, both C-S andS-S bonds in poly-SCN are cleaved along with the formationof Li2S. During charge, the re-formation of poly-SCN structureis observed. The scalable synthesis procedure, high thermal stability,high sulfur loading, and high capacity make poly-SCN a promising candidatefor high temperature solid state batteries.