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.