Insight into the Impact of Electrolyte on Passivation of Lithium–Sulfur Cathodes

One of the remaining challenges for lithium–sulfur batteries toward practical application is early cathode passivation by the insulating discharge product: Li$_2$S. To understand how to best mitigate passivation and minimize related performance loss, a kinetic Monte–Carlo model for Li$_2$S crystal growth from solution is developed. The key mechanisms behind the strongly different natures of Li$_2$S layer growth, structure, and morphology for salts with different (DN) are revealed. LiTFSI electrolyte in dimethyl ether leads to lateral Li$_2$S growth on carbon and fast passivation because it increases the Li$_2$S precipitation-to-dissolution probability on carbon relative to Li$_2$S. In contrast, LiBr electrolyte has a higher DN and yields a particle-like structure due to a significantly higher precipitation-to-dissolution probability on Li$_2$S compared to carbon. The resulting large number of Li$_2$S sites further favors particle growth, leading to low passivation. This study is able to identify the key parameters of the electrolyte and substrate material to tune Li$_2$S morphology and growth to pave the way for optimized performance.