Surface Reactivity of Lithium (Poly)sulfides in a Polarizable Environment from First Principles

Abstract

The present work deals with a first principles comparative study of the decomposition of Li2S and different polysulfides on graphitic surfaces in different dielectric media. This work aims at contributing to the understanding of the reactions that take place during the charging of a lithium-sulfur (Li-S) battery in different solvents. The barrier for the Li-S bond breakage is determined using the nudged elastic band method, and a detailed analysis of the atomic charges along this pathway is performed. The role of the solvent is found to be twofold: on one side, increasing the environment dielectric constant lowers the energy barrier for the decomposition of the polysulfides. On the other hand, it weakens the interaction energy of the adsorbates on the surface. These two effects are opposite. While the first effect is expected to increase the reaction rate, the second one will contribute to decreasing the concentration of poly(sulfide) species on the surface. The present results also suggest that the rate determining step for the overall oxidation process of Li2S to S8 is changed by the nature of the solvent.