Solvation-Property Relationship of Lithium-Sulfur Battery Electrolytes Probed via Potentiometric Measurements

Abstract

The Li-S battery is a promising next-generation battery chemistry that offers high energy density and low cost. Li-S battery has a unique chemistry with intermediate sulfur species readily solvated in electrolytes, and understanding their implications is important from both practical and fundamental perspectives. However, the nature of the solvated sulfur species, their interactions and their impact on the battery remains elusive, in part due to the paucity of techniques. Recently, our group developed a potentiometric technique to probe the solvation free energy of electrolytes. In this study, we utilize the technique to formulate solvation-property relationships in various electrolytes and investigate its impact on the solvated lithium polysulides (LiPS). We find that solvation free energy impacts Li-S battery voltage profile, LiPS solubility, Li-S battery cyclability and the Li metal anode, which are all critical to the battery's performance. Weaker solvation leads to a lower 1st plateau voltage, higher 2nd plateau voltage, lower LiPS solubility, and superior cyclability of Li-S full cell and Li metal anode. We explore the mechanisms behind these observed phenomena and discuss the implications for the design of high-performance electrolytes for Li-S batteries.