In a previous work, we have found that the pseudo-protic ionic liquid N-methylimidazolium acetate, [C1HIm]­[OAc] or [Hmim]­[OAc], mainly consists of the electrically neutral molecular species N-methylimidazole, C1Im, and acetic acid, AcOH, even though the mixture has significant ionic conductivity. This system was revisited by employing isotopic substitution Raman spectroscopy (ISRS) and pulsed field gradient (PFG) NMR self-diffusion measurements. The ISRS and PFG-NMR results obtained fully confirm our earlier findings. In particular, the self-diffusion coefficient of the hydroxyl hydrogen atom in AcOH is identical to that of the methyl hydrogen atoms within the experimental uncertainty, consistent with very little ionization. Therefore, a proton conduction mechanism similar to the Grotthuss mechanism for aqueous acid solutions is postulated to be responsible for the observed electrical conductivity. Laity resistance coefficients (rij ) are calculated from the transport properties, and the negative values obtained for the like-ion interactions are consistent with the pseudo-ionic liquid description, that is, the mixture is indeed a very weak electrolyte. The structure and rotational dynamics of the mixture were also investigated using high-energy X-ray total scattering experiments, molecular dynamics simulations, and dielectric relaxation spectroscopy. Based on a comparison of activation energies and the well-known linear free energy relationship between the kinetics and thermodynamics of autoprotolysis, we propose for [C1HIm]­[OAc] a Grotthus-type proton conduction mechanism involving fast AcOH/AcO− rotation as a decisive step.

Isotropic Raman scattering and time-of-flight neutron diffraction measurements were carried out for concentrated LiTFSA-EC solutions to obtain structural insight on solvated Li as well as the structure of contact ion pair, Li···TFSA, formed in highly concentrated EC solutions. Symmetrical stretching vibrational mode of solvated Li and solvated Li···TFSA ion pair were observed at ν = 168-177 and 202-224 cm, respectively. Detailed structural properties of solvated Li and Li···TFSA contact ion pair were derived from the least-squares fitting analysis of first-order difference function, Δ(Q), between neutron scattering cross sections observed for Li/Li isotopically substituted 10 and 25 mol % *LiTFSA-ECd solutions. It has been revealed that Li in the 10 mol % LiTFSA solution is fully solvated by ca. 4 EC molecules. The nearest neighbor Li···O(EC) distance and Li···O(EC)═C(EC) bond angle are determined to be 1.90 ± 0.01 Å and 141 ± 1°, respectively. In highly concentrated 25 mol % LiTFSA-EC solution, the average solvation number of Li decreases to ca. 3 and ca. 1.5. TFSA are directly contacted to Li. These results agree well with the results of band decomposition analyses of isotropic Raman spectra for intramolecular vibrational modes of both EC and TFSA.

Lithium–glyme solvate ionic liquids (Li–G SILs), which typically consist of a lithium-ion (Li+) solvated by glymes of oligoethers and its counter anion, are expected as promising electrolytes for lithium secondary batteries. Additionally, a specific ligand-exchange Li+ conduction mechanism was proposed at the electrode/electrolyte interface of the cell using Li–G SILs. To reveal Li+ conduction in SILs, Li–G SILs with varying ethylene oxide chain lengths were investigated using various techniques that are sensitive to solution structure and dynamics. We found good correlations between the relaxation time of the slowest dielectric mode and the ionic conductivity as well as viscosity. We propose that a dynamic chelate effect, which is closely related to solvent exchange and/or contact ion-pair formation/dissociation, is important for Li+ conduction in these Li–G SILs.

Lithium−glyme solvated ionic liquids (Li−G SILs) and superconcentrated electrolyte solutions (SCESs) are expected to be promising electrolytes for next-generation lithium secondary batteries. The former consists of only the oligoether glyme solvated lithium ion and its counteranion, and the latter contains no full solvated Li + ion by the solvents due to the extremely high Li salt concentration. Although both of them are similar to each other, it is still unclear that both should be room-temperature ionic liquids. To distinctly define them, speciation analyses were performed with the Li−G SIL and the aqueous SCES to evaluate the free solvent concentration in these solutions with a new Raman/infrared spectral analysis technique called complementary least-squares analysis. Furthermore, from a thermodynamic point of view, we investigated the solvent activity and activity coefficient in the gas phase equilibrated with sample solutions and found they can be good criteria for SILs.

Neutron diffraction measurements on 6 Li/ 7 Li isotopically substituted 10 and 33 mol % *LiTFSA (lithium bis-(trifluoromethylsulfonyl)amide)-AN-d 3 (acetonitrile-d 3 ) and 10 and 33 mol % *LiTFSA−DMF-d 7 (N,N-dimethylformamide-d 7 ) solutions have been carried out in order to obtain structural insights on the first solvation shell of Li + in highly concentrated organic solutions. Structural parameters concerning the local structure around Li + have been determined from the least squares fitting analysis of the first-order difference function derived from the difference between carefully normalized scattering cross sections observed for 6 Li-enriched and natural abundance solutions. In 10 mol % LiTFSA-AN-d 3 solution, 3.25 ± 0.04 AN molecules are coordinated to Li + with a intermolecular Li + ••• N(AN) distance of 2.051 ± 0.007 Å. It has been revealed that 1.67 ± 0.07 AN molecules and 2.00 ± 0.01 TFSA − are involved in the first solvation shell of Li + in the 33 mol % LiTFSA-AN solution. The nearest neighbor Li + •••N AN and Li + •••O TFSA − distances are obtained to be r(Li + •••N) = 2.09 ± 0.01 Å and r(Li + •••O) = 1.88 ± 0.01 Å, respectively. The first solvation shell of Li + in the 10 mol % LiTFSA-DMF-d 7 solutions contains 3.4 ± 0.1 DMF molecules with an intermolecular Li + •••O DMF distance of 1.95 ± 0.02 Å. In highly concentrated 33 mol % LiTFSA-DMF-d 7 solutions, there are 1.3 ± 0.2 DMF molecules and 3.2 ± 0.2 TFSA − in the first solvation shell of Li + with intermolecular distances of r(Li + •••O DMF ) = 1.90 ± 0.02 Å and r(Li + •••O TFSA − ) = 2.01 ± 0.01 Å, respectively. The Li + •••TFSA − contact ion pair stably exists in highly concentrated 33 mol % LiTFSA-AN and -DMF solutions.