Correlating Local Structure and Dynamics in Li-salt Liquid Electrolytes using Dielectric Relaxation Spectroscopy

Understanding the interplay between local structure and dynamics is critical for developing design rules for the next generation of safer, high-performing liquid electrolytes. We present an overview of a set of Li-salt liquid electrolytes at a variety of concentration, studied using dielectric relaxation spectroscopy (DRS). The electrolytes investigated include lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in varying solvents, as well as varying Li-salts with tetraethylene glycol dimethyl ether (tetraglyme) as a solvent. While the conductivity and other physical properties of many of these electrolytes have been previously reported, in this study, DRS is used, in combination with other experimental techniques, to identify relaxation processes associated with the solvent and different ion-solvent coordinating structures. This is accomplished by examining correlations between several electrolyte properties, including conductivity, relaxation time and strength, ionicity, and viscosity. The systematic analysis of the wide range of Li-salts and solvents in this single study provides valuable insight into the different local structures and dynamic processes that contribute to bulk conductivity, laying a foundation for the development of new liquid electrolyte systems.