An Effective Lithium Sulfide Encapsulation Strategy for Stable Lithium–Sulfur Batteries

With a high theoretical capacity of 1162 mA h g −1 , Li 2 S is a promising cathode that can couple with silicon, tin, or graphite anodes for next‐generation energy storage devices. Unfortunately, Li 2 S is highly insulating, exhibits large charge overpotential, and suffers from active‐material loss as soluble polysulfides during battery cycling. To date, low‐cost, scalable synthesis of an electrochemically active Li 2 S cathode remains a challenge. This work demonstrates that the low conductivity and material loss issues associated with Li 2 S cathodes can be overcome by forming a stable, conductive encapsulation layer at the surface of the Li 2 S bulk particles through in situ surface reactions between Li 2 S and electrolyte additives containing transition‐metal salts. It is identified that the electronic band structure in the valence band region of the thus‐generated encapsulation layers, consisting largely of transition‐metal sulfides, determines the initial charging resistance of Li 2 S. Furthermore, among the transition metals tested, the encapsulation layer formed with an addition of 10 wt% manganese (II) acetylacetonate salt proved to be robust within the cycling window, which is attributed to the chemically generated MnS surface species. This work provides an effective strategy to use micrometer‐sized Li 2 S directly as a cathode material and opens up new prospects to tune the surface properties of electrode materials for energy‐storage applications.