Corn-straw derived nitrogen and oxygen codoped carbon host for advanced sodium sulfur batteries by regulating the formation of CS bonds

Room-temperature sodium–sulfur (RT Na-S) batteries are promising candidates for large-scale grid energy storage applications due to the abundant availability of sodium resources and their low acquisition cost. However, the shuttling effect of long-chain sodium polysulfides severely degrades the cycle stability of RT Na-S batteries. In this study, a biomass-derived (corn-straw) porous carbon material with self-doped nitrogen and oxygen atoms was fabricated as a sulfur host (denoted as NOC). Sulfur was subsequently loaded covalently via the vapor-infiltration method to form the cathode material for RT Na-S batteries. Owing to the high cellulose content in corn-straw, the derived NOC composite exhibits excellent electrical conductivity and large pores, which facilitate Na + transport and accommodate the volume expansion of active sulfur during cycling. More importantly, theoretical calculation reveals that compared to pure carbon matrices, the N and O dopants make carbon become unsaturated, increasing the electron density distribution and enhancing bonding ability to form C S bonds. When used as a cathode, in-situ Raman and ex-situ XRD measurements confirm that covalently bonded sulfur inhibits the shuttle effect by directly forming Na 2 S during the reduction reaction. Consequently, the NOC/S cathode delivers superior electrochemical performances with excellent cycle stability. This study introduces an innovative approach to developing advanced RT Na-S batteries by utilizing cost-effective carbon materials derived from biomass.