Dielectric relaxation spectroscopy for evaluation of the influence of solvent dynamics on ion transport in succinonitrile-salt plastic crystalline electrolytes

Abstract

Influence of succinonitrile (SN) dynamics on ion transport in SN−lithium perchlorate (LiClO₄) electrolytes is discussed here via dielectric relaxation spectroscopy. Dielectric relaxation spectroscopy (∼2 × 10^-3 Hz to 3 MHz) of SN and SN−LiClO₄ was studied as a function of salt content (up to 7 mol % or 1 M) and temperature (−20 to +60 °C). Analyses of real and imaginary parts of permittivity convincingly reveal the influence of trans−gauche isomerism and solvent−salt association (solvation) effects on ion transport. The relaxation processes are highly dependent on the salt concentration and temperature. While pristine SN display only intrinsic dynamics (i.e., trans−gauche isomerism) which enhances with an increase in temperature, SN−LiClO₄ electrolytes especially at high salt concentrations (∼0.04−1 M) show salt-induced relaxation processes. In the concentrated electrolytes, the intrinsic dynamics was observed to be a function of salt content, becoming faster with an increase in salt concentration. Deconvolution of the imaginary part of the permittivity spectra using Havriliak−Negami (HN) function show a relaxation process corresponding to the above phenomena. The permittivity data analyzed using HN and Kohlrausch−Williams−Watta (KWW) functions show non-Debye relaxation processes and enhancement in the trans phase (enhanced solvent dynamics) as a function of salt concentration and temperature.