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.