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 H-1, F-19, and Li-7 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 (C) 2008 John Wiley & Sons, Ltd.