Lithium-sulfur batteries are anticipated to be the next generation of energy storage devices because of their high theoretical specific capacity. However, the polysulfide shuttle effect of lithium-sulfur batteries restricts their commercial application. The fundamental reason for this is the sluggish reaction kinetics between polysulfide and lithium sulfide, which causes soluble polysulfide to dissolve into the electrolyte, leading to a shuttle effect and a difficult conversion reaction. Catalytic conversion is considered to be a promising strategy to alleviate the shuttle effect. In this paper, a CoS₂-CoSe₂ heterostructure with high conductivity and catalytic performance was prepared by in situ sulfurization of CoSe₂ nanoribbon. By optimizing the coordination environment and electronic structure of Co, a highly efficient CoS₂-CoSe₂ catalyst was obtained, to promote the conversion of lithium polysulfides to lithium sulfide. By using the modified separator with CoS₂-CoSe₂ and graphene, the battery exhibited excellent rate and cycle performance. The capacity remained at 721 mAh g⁻¹ after 350 cycles, at a current density of 0.5 C. This work provides an effective strategy to enhance the catalytic performance of two-dimensional transition-metal selenides by heterostructure engineering.