The extensive application of electric vehicles requires a new battery system with high energy density because the current lithium-ion technology can only power electric vehicles with a relatively short driving range. [1-2] With its extremely high specific capacity and exceptionally low cathode cost, lithium-sulfur (Li-S) batteries are one of the most promising next-generation battery systems. However, the low Coulombic efficiency and fast capacity fading largely hindered the mass commercialization of Li-S batteries. [3] The major reason for the rapid capacity fading is attributed to the parasitic reactions of lithium polysulfides (LiPS), which are inevitably generated during the charging process of Li-S cells. [4] Therefore, it is critical to understand the relationship between LiPS dissolution and the solvation state of electrolyte solvents in order to develop more efficient electrolytes for Li-S batteries.<br/>In this presentation, we introduce the concept of relative solvating power γ, which is defined as the ratio of the coordination ratios (α) between a solvent and the reference solvent (DOL). Although the coordination ratios of different ethereal solvents in a binary or ternary electrolyte system can hardly be measured by vibrational spectroscopy such as FTIR and Raman, the coordination ratios can be easily determined by our newly developed internally-referenced DOSY NMR method and diffusion-coordination (D-α) analysis. [5] It was discovered that the higher the relative solvating power of regular ether solvent to 1,3-dioxolane (DOL), the more severe will be the LiPS dissolution and the lower the Coulombic efficiency of the Li-S cell. A linear relationship was revealed between the relative solvating power of a solvent and the degree of LiPS dissolution, rendering relative solvating power an powerful tool in studying the quantitative structure-activity relationship of electrolyte solvents and the LiPS parasitic reactions of Li-S batteries. [6]<br/><br/>

Relative solvating power as an indicator for the selection of electrolyte solvents in lithium-sulfur batteries

2019 Spring National Meeting

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