S@FeS Core-Shell Cathode Nanomaterial for Preventing Polysulfides Shuttling and Forming Solid Electrolyte Interphase in High-Rate Li-S Batteries.

Lithium-sulfur (Li-S) battery is a potential next-generation energy storage technology over lithium-ion batteries for high capacity, cost-effective, and environmentally friendly solutions. However, several issues including polysulfides shuttle, low conductivity and limited rate-capability have hampered its practical application. Herein, a new class of cathode active material with perfect core-shell structure is reported, in which sulfur is fully encapsulated by conductivity-enhancing FeS (named as S@FeS), for high-rate application. Surface-stabilized S@FeS cathode exhibits a stable cycling performance under 2 - 20 times higher rates (1-2 C, charged in 30-60 min) than standard rates (e.g., 0.1-0.5 C, charged in 2-10 h), without polysulfides shuttle event. Surface analysis results reveal the unprecedented formation of a stable solid electrolyte interphase (SEI) layer on S@FeS cathode, which is distinguished from other sulfur-based cathodes that are not able to form the SEI layer. The data suggest that the prevention of polysulfides shuttling is owing to the surface protection effect of FeS shell and the SEI layer formation overlying core-shell S@FeS. This unique and potential material concept proposed in the present study will give insight into designing a prospective fast charging Li-S battery.