Investigating Increasing Molar Conductivity in Low Permittivity Electrolytes for Multivalent Battery Applications

Abstract

Many of the liquid electrolyte candidates for multivalent batteries exhibit increasing molar conductivity with concentration. In other words, the concentration-normalized conductivity increases as a function of salt concentration. This is in contrast to conventional electrolytes, e.g. aqueous or cyclic carbonate-based electrolyte solutions, where the molar conductivity decreases with concentration due to increased viscosity and ion aggregation. Low permittivity electrolytes with increasing molar conductivity include Ca(BH4)2 in tetrahydrofuran, Mg(TFSI)2 in monoglyme and Mg(TFSI)2 in diglyme.In order to investigate the origin of this anomalous molar conductivity trend, we study the physicochemical properties of the electrolytes using a combined computational/experimental approach. Ab initio calculations and classical molecular dynamics simulations are undertaken to study ion speciation, ion activity and changes to solution permittivity. Furthermore, we undertake conductivity, microwave and raman spectroscopy measurements.