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

Abstract

Widespread commercialization of high-energy-density lithium–sulfur (Li–S) batteries is difficult due to the lithium polysulfide, Li2Sn (n = 4, 6, 8), shuttle effect. Efficient adsorption/conversion of Li2Sn species on an electrocatalytic surface can suppress the shuttle effect. Modeling of the adsorption of Li2Sn 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 Li2Sn 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 Li2Sn species. A geometry parameter, Gscore, is defined as a function of bond length and number of lithium-atom interactions between the Li2Sn species and the binding surface. The design principle is extended to sulfur-deficient (TMSs-x) and edge-exposed (TMS(100)) surfaces. The Gscore predicts the most effective binding energy zone distinctive to these materials—TMS (1.7–2.1 eV/Gscore ≥ 2.0), TMSs-x (2.0–2.8 eV/Gscore ≥ 2.1), and TMS(100) (2.5–3.2 eV/Gscore ≥ 1.09).