Solvent-Mediated Li2S Electrodeposition: A Critical Manipulator in Lithium-Sulfur Batteries

Controlling electrochemical deposition of lithium sulfide (Li2S) is a major challenge in lithium-sulfur batteries as premature Li2S passivation leads to low sulfur utilization and low rate capability. In this work, the solvent's roles in controlling solid Li2S deposition are revealed, and quantitative solvent-mediated Li2S growth models as guides to solvent selection are developed. It is shown that Li2S electrodeposition is controlled by electrode kinetics, Li2S solubility, and the diffusion of polysulfide/Li2S, which is dictated by solvent's donicity, polarity, and viscosity, respectively. These solvent-controlled properties are essential factors pertaining to the sulfur utilization, energy efficiency and reversibility of lithium-sulfur batteries. It is further demonstrated that the solvent selection criteria developed in this study are effective in guiding the search for new and more effective electrolytes, providing effective screening and design criteria for computational and experimental electrolyte development for lithium-sulfur batteries.