t₂ occupancy as a descriptor for polysulfide conversion on spinel oxides

Transition metal oxides with partially filled d orbitals serve as effective polysulfide conversion catalysts in lithium-sulfur batteries. Nonetheless, a predictive descriptor to elucidate their structure-activity relationship is still lacking. To fill this gap, here we investigate the occupancy of t₂ orbitals as a possible descriptor for the polysulfide conversion activity of spinel oxides. The electrochemical characterizations reveal a volcano relationship between t₂ occupancy and the polysulfide conversion activity of spinel oxides. The theoretical calculations indicate that the t₂ occupancy effect is associated with the ability of tetrahedral cations to cleave S-S bonds and form Li-S bonds. As such, Mn_0.5Co_0.5Cr₂O₄, with an optimized average t₂ occupancy of 2.88, is designed and demonstrates promising polysulfide conversion activity among representative oxides. This work elucidates that t₂ occupancy serves as an effective descriptor for evaluating the polysulfide conversion activity of spinel oxides. With the catalytic mechanism proposed, the current study prompts further exploration of the application of t₂ occupancy as a descriptor for predicting the polysulfide conversion efficiency of other catalytic systems beyond the spinel structure.