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.

Neutron diffraction measurements have been carried out for Li/Li isotopically substituted aqueous 1.0 mol % (0.5 mol/kg) LiCl and 1.1 mol % (0.56 mol/kg) LiClO solutions in DO to obtain structural insight concerning hydration structure of Li in more dilute electrolyte solutions. The first-order difference function, Δ(Q), was analyzed by means of the least squares fitting procedure to obtain short-range structural parameters around the Li. It was revealed that the nearest neighbor Li···O(DO) distance, r, and the coordination number, n, for the aqueous 1.0 mol % LiCl solution are 2.01 ± 0.02 Å and 5.9 ± 0.1, respectively. The values, r = 1.97 ± 0.02 Å and n = 6.1 ± 0.1, are obtained for aqueous 1.1 mol % LiClO solution. These results indicate that the hydration number of Li in a dilute solution is close to 6, which is much larger than 4, which has long been believed. A possible explanation is that the hydration number of Li varies with the solute concentration.