Raman study of solvation in solutions of lithium salts in dimethyl sulfoxide, propylene carbonate and dimethyl carbonate

Vibrational spectroscopy of dynamic interactions and relaxation processes in ionic systems

In recent years, there has been a boom in the publication of research results on ionic (electrolyte) systems used in the creation of electrochemical energy systems (batteries, supercapacitors, etc.). One of the alternative ways to obtain dynamic information in ionic systems is spectroscopic experiments, and the most valuable information on the behavior of condensed systems at picosecond and adjacent time intervals is provided by vibrational spectroscopy. The source of this information is the analysis of the shape and width of the lines in the vibrational spectra of ion systems. This review aims to systematize the theoretical and methodological aspects of the study of the dynamics of ion systems by vibrational spectroscopy.

Why Does Dimethyl Carbonate Dissociate Li Salt Better Than Other Linear Carbonates? Critical Role of Polar Conformers

The marked difference in the ionic conductivities of linear carbonate (LC) electrolyte solutions despite their similar viscosities and permittivities is a long-standing puzzle. This study unraveled the critical impact of solvent conformational isomerism on salt dissociation in 0.1-3.0 M LiPF₆ dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) solutions using Raman and dielectric relaxation spectroscopies. The extent of salt dissociation in the LC solutions, which decreased in the order DMC > EMC > DEC, is closely related to the fraction of polar cis-trans LC conformers, as this conformer participates in Li ion solvation more readily than the nonpolar cis-cis counterpart. Our first-principles calculations corroborated that the cis-trans conformer facilitates free ion formation more than the cis-cis conformer, and the extent of this effect decreased in the order DMC > EMC > DEC. This study provides an avenue for the design of highly conductive electrolytes by exploiting the conformational isomerism of solvent molecules.

Effect of PAMAM Dendrimers on Interactions and Transport of LiTFSI and NaTFSI in Propylene Carbonate-Based Electrolytes

Poly(amidoamine) (PAMAM)-based electrolytes are prepared by dissolving the PAMAM half-generations G1.5 or G2.5 in propylene carbonate (PC), either with lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) or sodium bis(trifluoromethylsulfonyl)imide (NaTFSI) salts. The solutions, designed for ion battery applications, are studied in terms of ions transport properties. Raman Spectroscopy reveals information about the interactions between cations and PAMAM dendrimers as well as full dissociation of the salts in all solutions. Pulsed-field gradient Nuclear Magnetic Resonance (PFG NMR), measured as a function of both temperature and PAMAM concentration, are obtained for the cation, anion, solvent, and dendrimer molecules using lithium (7Li), sodium (23Na), fluorine (19F), and hydrogen (1H) NMR, respectively. It was found that lithium diffusion is slow compared to the larger TFSI anion and decreases with PAMAM concentration due to interactions between cation and dendrimer. Comparison of conductivities calculated from diffusion coefficients using the Nernst-Einstein equation, with conductivity measurements obtained from Impedance Spectroscopy (IS), shows slightly higher IS conductivities, caused among others by PAMAM conductivity.

Ultrafast intramolecular proton transfer reactions and solvation dynamics of DMSO

Ultrafast intramolecular proton transfers of 1,2-dihydroxyanthraquinone (alizarin-h2) and its deuterated product (alizarin-d2) in dimethyl sulfoxide (DMSO) have been investigated by femtosecond stimulated Raman spectroscopy. The population dynamics in the solute vibrational mode of νC=O and the coherent oscillations observed in all of the skeletal vibrational modes νC=O and νC=C clearly showed the ultrafast excited-state intramolecular proton transfer dynamics of 110 and 170 fs for alizarin-h2 and alizarin-d2, respectively. Interestingly, we have observed that the solvent vibrational modes νS=O and νCSC may also represent ultrafast structural dynamics at the frequencies for its "free" or "aggregated" species. From the kinetic analysis of the νS=O and νCSC modes of DMSO, the ultrafast changes in the solvation or intermolecular interactions between DMSO molecules initiated by the structural changes of solute molecules have been thoroughly investigated. We propose that the solvent vibrational modes νS=O and νCSC of DMSO can be used as a "sensor" for ultrafast chemical reactions accompanying the structural changes and subsequent solute-solvent interactions.