Understanding Structural and Transport Properties of Dissolved Li2 S8 in Ionic Liquid Electrolytes through Molecular Dynamics Simulations.

Abstract

Lithium-sulfur batteries with high energy density are considered as one of the most promising future energy storage devices. However, the parasitic lithium polysulfides shuttle phenomenon severely hinders the commercialization of such batteries. Ionic liquids have been found to suppress the lithium polysulfides solubility, diminishing the shuttle effect effectively. Herein, we performed classical molecular dynamics simulations to explore the microscopic mechanism and transport behaviors of typical Li2 S8 species in ionic liquids and ionic liquid-based electrolyte systems. We found that the trifluoromethanesulfonate anions ([OTf]- ) exhibit higher coordination strength with lithium ions compared with bis(trifluoromethanesulfonyl)imide anions ([TFSI]- ) in static microstructures. However, the dynamical characteristics indicate that the presence of the [OTf]- anions in ionic liquid electrolytes bring faster Li+ exchange rate and easier dissociation of Li+ solvation structures. Our simulation models offer a significant guidance to future studies on designing ionic liquid electrolytes for lithium-sulfur batteries.