Unified Interplay of Chemical Bond and Solid-State Kinetics in Lithium-Sulfur Batteries

It is proposed that the unified interplay between the chemical hardness of the Li-X (X = S, Se, and Te) bond and solid-state conversion kinetics enables intrinsic reshaping of materials for fabricating high-energy density lithium-sulfur batteries. This concept is evaluated using three cathode models: (i) Li2S, (ii) Se-doped Li2S (Se-Li2S), and (iii) Te-doped Li2S (Te-Li2S). Theoretical calculations reveal that the Li-X bond in the Se-Li2S cathode shows low chemical hardness, and the chemical hardness decreases at a higher rate for the Te-Li2S cathode. The local structural effect induces a decrease in the phase transition barrier during the solid-state conversion reaction in the Se- and Te-doped crystal phases, as revealed by electrochemical measurements and ex-situ X-ray photoelectron spectroscopy analysis. Investigation of the three sulfide-based cathodes sheds light on the mechanism behind the kinetics of phase transition in the solid-state conversion region, illuminating the intriguing concept of a local structure for harnessing the full potential of sulfur cathodes to achieve high-energy-density lithium-sulfur batteries.