DISPROPORTIONATION OF POLYSULFIDES FACILITATED BY A BI-FUNCTIONAL CARBON HOST IN LI-S BATTERIES

Abstract

Lithium-sulfur (Li-S) batteries are regarded as one of the promising alternatives to conventional lithium-ion batteries (LIBs) due to their high theoretical energy density (2600 Wh kg-1), abundant resources on Earth, and low cost of sulfur. Nevertheless, several significant challenges persist in the practical application of Li-S batteries, including the insulating nature of sulfur, volume changes of cathodes, and, most critically, the shuttle effect of dissolved long-chain lithium polysulfide (PS) species during cycling. In this thesis, a novel carbon host for sulfur cathode, derived from natural silk and denoted as NC, was developed. This carbon host possesses excellent cycling performance because of its hierarchical porous structure and nitrogen-contained functional groups. In addition, it demonstrated the ability to facilitate the disproportionation reactions of PS, converting PS ions into solid products of elemental sulfur (S8) and probably lithium disulfide (Li2S2). This reduces the residence time of PS ions in the electrolyte. Consequently, Li-S cells with S/NC cathodes display enhanced electrochemical performance in both coin cells and pouch cells, even with high sulfur loading and lean electrolytes.