A structural study of LiTFSI–tetraglyme mixtures: From diluted solutions to solvated ionic liquids

Abstract

We report on the nano-structure of solvated ionic liquids (SILs) formed by dissolving a Li-salt (LiTFSI) in the solvent tetraglyme. Using small angle X-ray scattering (SAXS), supported by Raman spectroscopy and computational modeling we follow how the nano-structure develops as Li-salt is added to the solvent. We find that, as the Li-salt concentration is increased a peak at Q≈0.95Å−1 grows in intensity, signaling the presence of structural correlations typical of those found in traditional ionic liquids. The intensity of the peak reaches its maximum at the equimolar concentration, where each Li-ion can be solvated by one solvent molecule forming an effective cation complex. Combining the SAXS data with computer modeling we show that this peak can be assigned to charge alternation, also found in traditional ionic liquids. However, we also show that even at the equimolar concentration not all Li-ions are solvated by the solvent molecules, but a small fraction interacts directly with the anion (TFSI).