Mesoscale Elucidation of Surface Passivation in the Li-Sulfur Battery Cathode

The cathode surface passivation caused by Li₂S precipitation adversely affects the performance of lithium-sulfur (Li-S) batteries. Li₂S precipitation is a complicated mesoscale process involving adsorption, desorption and diffusion kinetics, which are affected profoundly by the reactant concentration and operating temperature. In this work, a mesoscale interfacial model is presented to study the growth of Li₂S film on carbon cathode surface. Li₂S film growth experiences nucleation, isolated Li₂S island growth and island coalescence. The slow adsorption rate at small S^2- concentration inhibits the formation of nucleation seeds and the lateral growth of Li₂S islands, which deters surface passivation. An appropriate operating temperature, especially in the medium-to-high temperature range, can also defer surface passivation. Fewer Li₂S nucleation seeds form in such an operating temperature range, thereby facilitating heterogeneous growth and potentially inhibiting the lateral growth of the Li₂S film, which may ultimately result in reduced surface passivation. The high specific surface area of the cathode microstructure is expected to mitigate the surface passivation.