Ion Transport in Glyme- and Sulfolane-Based Highly Concentrated Electrolytes

Abstract

Highly concentrated electrolytes (HCEs) have a similarity to ionic liquids (ILs) in high ionic nature, and indeed some of HECs are found to behave like an IL. HCEs have attracted considerable attention as prospective candidates for electrolyte materials in future lithium secondary batteries owing to their favorable properties both in the bulk and at the electrochemical interface. In this study, we highlight the effects of the solvent, counter anion, and diluent of HCEs on the Li⁺ ion coordination structure and transport properties (e. g., ionic conductivity and apparent Li⁺ ion transference number measured under anion-blocking conditions, $t_{Li}^{abc}$ ). Our studies on dynamic ion correlations unveiled the difference in the ion conduction mechanisms in HCEs and their intimate relevance to $t_{Li}^{abc}$ values. Our systematic analysis of the transport properties of HCEs also suggests the need for a compromise to simultaneously achieve high ionic conductivity and high $t_{Li}^{abc}$ values.

Keywords: Electrolyte; Ion correlation; Ionic conductivity; Self-diffusion coefficients; Solvate ionic liquids.