Theoretical Study on the Role of Solvents in Lithium Polysulfide Anchoring on Vanadium Disulfide Facets for Lithium-Sulfur Batteries

The shuttle effects by lithium polysulfides (LiPSs) and the sluggish reaction kinetics are crucial obstacles in the commercialization of Li-S batteries. Hence, effectively trapping and promoting the conversion of LiPSs is of prime importance. However, the fundamental kinetics of the electrocatalytic charging and discharging of Li-S batteries have not been sufficiently explored yet. Therefore, by taking VS2 as a model, we conducted a density functional theory-based study to investigate the ability of dominant exposed crystal planes of VS2 to trap LiPSs from leaching into electrolytes and to act as an electrocatalyst to increase the sulfur reduction reaction (SRR) kinetics. To reflect a realistic environment of a battery, the effect of solvents on the electrocatalytic activity was further investigated. Our calculations show that VS2 has moderate binding energy toward LiPSs; therefore, it can effectively inhibit LiPS shuttling and leaching. However, there was no consistent pattern for binding energies under different VS2 facets. Furthermore, VS2 (001) facets exhibit excellent electrocatalytic activity for the SRR and Li2S decomposition reaction compared to other dominant crystal planes, which significantly lowers the energy barriers of LiPS conversion during the charging and discharging process, ensuring high-rate performance and longer cycle life. Beyond the VS2 systems explored in the current study, the same approach can apply to other potential electrocatalysts as a promising pathway to improve the sluggish reaction kinetics of Li-S batteries.