Dielectric behavior of propylene carbonate solutions with LiPF6, LiClO4, and LiBF4. I. Dielectric relaxation and Raman spectroscopic study

Abstract

Dielectric relaxation spectroscopy (DRS) is an evolving technique for extracting molecular-level information on orientational polarization and dielectric relaxation in liquids. It reveals fundamental properties, such as permittivity and dipole moments, essential for characterizing electrolyte solutions. However, the use of DRS for electrolyte analysis often faces challenges, such as low-frequency measurement limits, and difficulties in interpreting and assigning complex overlapping relaxation spectra in practical electrolytes. In this study, using propylene carbonate solutions containing three types of lithium salts as model electrolytes, we measured the salt concentration dependence of the static permittivity—a property with limited experimental reports—and discussed its relation to ionic interactions. In addition, two-dimensional correlation spectroscopy between Raman spectroscopy and DRS was employed to achieve reliable spectral assignments of the DRS spectra. CLSA, a chemometric method, was applied to Raman spectra to confirm experimentally the number of significant components and obtain their formation distribution functions. Combining these results with a modified Cavell equation allowed determination of effective dipole moments that account for environmental effects and reflect the collective behavior and dynamics of chemical species in solution. We experimentally demonstrated the capability of DRS to extract important molecular insights that are difficult to obtain using traditional analytical techniques.