Salt and Solvent Control of Elemental Sulfur (Cyclo-S8) and Lithium-Ion Diffusion in Liquid Li-S Battery Electrolytes Revealed by DFTB Molecular Dynamics.

In recent years, lithium-sulfur (Li-S) batteries have become attractive owing to their high energy density and higher charge-storage capacity than Li-ion batteries. Despite this, practical applications of Li-S batteries remain limited by several challenges that still need to be resolved, including Li-dendrite formation, which leads to short-circuiting. In the present study, divide-and-conquer density-functional tight-binding molecular dynamics (DC-DFTB-MD) simulations examine neutral cyclo-S8, while lithium polysulfides and polysulfide anions are not included. Increasing LiOTf concentration generally reduces the self-diffusion coefficients because denser, more highly coordinated ionic environments restrict translational motion. The Li+ ion preferentially coordinates with electronegative oxygen atoms of the solvent and triflate anion, whereas nonpolar, neutral S8 interacts mainly through induced-polarization and dispersion forces. These competing coordination environments explain the weak direct Li+-S8 association and the coupled decline of ionic and molecular mobility with salt loading.