Computational dielectric relaxation spectroscopy applied to the dilute solution to solvate ionic liquid transition*

Dielectric relaxation spectroscopy (DRS) constitutes an excellent experimental tool to characterize liquid electrolytes, through the identification of solvation processes from the frequency-dependent generalized dielectric constant, and through the description of collective motion and couplings between different species. We adopt an atomic-scale computational approach to DRS, based on classical molecular dynamics simulations. With this method, we investigate structural and dynamical features of tetraglyme (G4) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) mixtures, using a newly developed interatomic potential with unprecedented accuracy. We cover a wide range of salt concentrations, which allows us to investigate the transition from a dilute solution to a solvate ionic liquid of such a mixture. Our computational approach allows to partition the frequency-dependent generalized dielectric constant according to the chemical constituents composing the electrolytes. We show how specific solvated species contribute to the total dielectric spectrum, and extract insights regarding charge transport mechanisms.