Lithium solvation and diffusion in the 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ionic liquid

The Raman spectra of (1 − x)(BMITFSI), xLiTFSI ionic liquids, where 1‐butyl‐3‐methylimidazolium cation (BMI+) and bis(trifluoromethane‐sulfonyl)imide anion (TFSI−) are analyzed for LiTFSI mole fractions x < 0.4. As expected from previous studies on similar TFSI‐based systems, most lithium ions are shown to be coordinated within [Li(TFSI)2]− anionic clusters. The variation of the self‐diffusion coefficients of the 1H, 19F, and 7Li nuclei, measured by pulsed‐gradient spin‐echo NMR (PGSE‐NMR) as a function of x, can be rationalized in terms of the weighted contribution of BMI+ cations, TFSI− ‘free’ anions, and [Li(TFSI)2]− anionic clusters. This implies a negative transference number for lithium. Copyright © 2008 John Wiley & Sons, Ltd.