Electron-rich anion-vacancy CoSe₂ enables fast polysulfides conversion toward long-life lithium-sulfur batteries

Defect-mediated electronic-structure engineering of transition-metal compounds offers an effective route to accelerate sulfur redox kinetics in lithium-sulfur batteries (LSBs), yet the intrinsic relationship between vacancy defects and polysulfide conversion remains insufficiently clarified. Herein, selenium-vacancy-rich CoSe₂ (V-CoSe₂) is developed as an electron-rich catalytic separator modifier to regulate polysulfide adsorption and conversion. The introduced Se vacancies reconstruct the local coordination environment of CoSe₂, generating abundant low-coordinated, electron-rich Co sites with enhanced interfacial charge-transfer capability and strengthened Co-Se bond polarization. Combined experimental and theoretical results demonstrate that these vacancy-induced active sites reinforce polysulfide anchoring, facilitate Li₂S nucleation/conversion, and lower the kinetic barriers of sulfur redox reactions. Benefiting from these advantages, the V-CoSe₂-modified separator delivers outstanding electrochemical performance under a high sulfur loading of 6.0 mg cm⁻². This work highlights vacancy engineering as a powerful strategy for regulating interfacial sulfur redox chemistry and provides guidance for designing advanced catalytic separators for high-performance LSBs.