The Volcano Relationship between d_<i>z</i>² Electronic States and Sulfur Redox Reaction Kinetics in Lithium–Sulfur Batteries

The d orbital physics are closely related to the catalytic activity of transition-metal-based catalysts in Li-S batteries. However, challenges remain in understanding the optimal electronic configuration, causing a lack of guidance in the precise design of catalysts. Herein, by virtue of LaCoO₃-based catalysts with different combinations of low-spin states and high-spin states of Co³⁺, a volcano relationship between d_<i>z</i>² filling number (from 0.95 to 1.29) and S/Li₂S redox reaction kinetics is revealed. The best kinetics are provided at the d_<i>z</i>² filling number of 1.12. As a result, the assembled Li-S battery shows a low decay rate of 0.026% per cycle in a 1500-cycle test and a high energy density of 460.7 Wh kg^-1 in a practical pouch cell. This work reveals the critical influences of d_<i>z</i>² electronic states on catalyzing the S/Li₂S redox reaction and provides insights into finely regulating the electronic structures of high-performance catalysts for practical Li-S batteries.