High-density/efficient surface active sites on modified separators to boost Li-S batteries via atomic Co3+-Se termination

Various and critical electrocatalytic processes are involved during the redox reactions in the Li-S batteries, which extremely depend on the surface structure and chemical state. Recently, single-atom concept unlocks a route to maximize the use of surface-active atoms, however, further increasing the density of active site is still strictly limited by the inherent structure that single-atoms are only highly-dispersed on substrate. Herein, we provide a viewpoint that an elaborate facet design with single-crystalline structure engineering can harvest high-density surface active sites, which can significantly boost the electrocatalyst performance for excellent Li-S batteries. Specifically, the single-crystal CoSe2 (scCS) exhibits three-types of terminated (011) facet, efficiently obtaining the surface with a high-rich Co3+—Se bond termination, in contrast with lots of surface grain boundaries and dangling bonds in polycrystalline CoSe2. Surprisingly, the surface active sites concentration can reach more than 69%. As anticipated, it can provide high-density and high-efficient active sites, enormously suppressing the shuttle effect and improving the reaction kinetics via accelerating the conversion and deposition of polysulfides and Li2S. This surface lattice strategy with element terminated mode is a promising approach for designing electrocatalyst effect-based energy system, not merely for Li-S batteries.