Quasi-solid-state conversion cathode materials for room-temperature sodium–sulfur batteries

Abstract

Room-temperature sodium–sulfur batteries (NaSBs) are promising candidates for next-generation large-scale energy storage solutions. However, the well-known polysulfide shuttling of soluble long-chain sulfur intermediates still remains a limitation in NaSBs, leading to rapid capacity loss arising from the dissolution of active sulfur into the electrolyte. This problem is effectively circumvented in quasi-solid-state conversion cathodes by elimination of the presence of these soluble intermediates altogether, with only insoluble intermediates formed in the process. Herein, we discuss various cathode materials that undergo quasi-solid-state conversion when cycled in a liquid electrolyte, including chemically bonded short-chain sulfur species, short-chain sulfur via physical confinement, and quasi-solid-state conversion cathodes with long-chain sulfur moieties. We conclude by highlighting the current challenges and possible strategies to improve the mechanistic understanding and cycling performance of NaSBs for practical applications.