Untying thioether bond structures enabled by “voltage-scissors” for stable room temperature sodium–sulfur batteries

Abstract

A steady sulfur cathode is central to realizing stable room temperature sodium–sulfur (RT Na–S) batteries. Here, sulfur atoms are incorporated into carbon to form thioether bond functionalized carbon (SC) as a cathode material for sodium storage, which is capable of the complete elimination or great suppression of the shuttle effect of soluble poly-sulfides by the generation of insoluble sulfides in RT Na–S batteries using an ordinary carbonate electrolyte. This thioether bond structure (C–S–C) in sulfur-doped carbon can be disassembled by the assistance of “voltage-scissors” in the low voltage range of 0.01–0.50 V vs. Na/Na⁺. The small sulfur species derived from the thioether bond structure react with the sodium anode to form insoluble sulfides. Moreover, the insoluble sulfides Na₂S₂ and Na₂S are confined in the carbon defects induced by the cleaved sulfur to prevent them from degrading the long-chain poly-sulfides. The distinctive electrochemical performance of SC enriches our understanding of the sulfur cathode, and could provide novel insights for constructing stable sulfur cathode materials for specific energy storage devices.