Boosting polysulfide redox via cobalt spin-state manipulation in lithium-sulfur batteries

The commercialization of lithium-sulfur batteries (LSBs) has been significantly hindered by rapid performance degradation during long-term cycling, which originates from lithium polysulfides (LiPSs) shuttling and uncontrolled lithium dendrite growth. In this work, guided by ligand field theory and molecular orbital principles, we modulate the spin state of spinel-type oxides via boron doping, leading to the formation of nanoflower-structured catalysts with an intermediate spin (IS, t_2g⁵e_g¹) configuration. Boron doping effectively regulates the spin state of Co³⁺, resulting in the generation of numerous unpaired electrons distributed across different 3d orbitals. This electronic reconstruction causes an upshift in energy levels and creates more active electronic states, which collectively enhance LiPSs adsorption, facilitate charge transfer, and improve redox kinetics. Employing the modified separator enables outstanding rate performance, with the cell delivering 1255.2 and 960 mAh g⁻¹ at 0.2 and 2 C, respectively. The electrode maintains exceptional capacity retention with suppressed polysulfide loss under high sulfur loading, confirming the functional separator's efficacy. This work proposes a doping-based strategy for electronic spin-state modulation in LSBs catalysts, offering a promising direction for next-generation energy storage systems.