A global design principle for polysulfide electrocatalysis in lithium–sulfur batteries—a computational perspective

Widespread commercialization of high-energy-density lithium–sulfur (Li–S) batteries is difficult due to the lithium polysulfide, Li₂S_n (n = 4, 6, 8), shuttle effect. Efficient adsorption/conversion of Li₂S_n species on an electrocatalytic surface can suppress the shuttle effect. Modeling of the adsorption of Li₂S_n species using density functional theory (DFT) calculations has contributed significantly toward an understanding of their anchoring mechanism at a surface. Different surfaces show a unique range of binding energies for faster Li₂S_n adsorption/reaction kinetics. To predict the optimum binding energy zone, a systematic DFT study is performed on transition-metal sulfide (TMS) surfaces including TiS₂, VS₂, NbS₂, MoS₂, WS₂, and SnS₂. The investigation revealed that the geometric properties at the anchoring site possibly regulate the adsorption energy of Li₂S_n species. A geometry parameter, G_score, is defined as a function of bond length and number of lithium-atom interactions between the Li₂S_n species and the binding surface. The design principle is extended to sulfur-deficient (TMSs-x) and edge-exposed (TMS(100)) surfaces. The G_score predicts the most effective binding energy zone distinctive to these materials—TMS (1.7–2.1 eV/G_score ≥ 2.0), TMSs-x (2.0–2.8 eV/G_score ≥ 2.1), and TMS(100) (2.5–3.2 eV/G_score ≥ 1.09).