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

摘要

With a high theoretical capacity of 1162 mA h g(-1), Li2S is a promising cathode that can couple with silicon, tin, or graphite anodes for next-generation energy storage devices. Unfortunately, Li2S 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 Li2S cathode remains a challenge. This work demonstrates that the low conductivity and material loss issues associated with Li2S cathodes can be overcome by forming a stable, conductive encapsulation layer at the surface of the Li2S bulk particles through in situ surface reactions between Li2S and electrolyte additives containing transition-metal salts. It is identified that the electronic band structure in the valence band region of the thusgenerated encapsulation layers, consisting largely of transition-metal sulfides, determines the initial charging resistance of Li2S. 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 Li2S directly as a cathode material and opens up new prospects to tune the surface properties of electrode materials for energy-storage applications.