Pyrrolidinium-Based Ionic Liquids Doped with Lithium Salts: How Does Li+ Coordination Affect Its Diffusivity?

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• 作者：Franca Castiglione ; Antonino Famulari ; Guido Raos ; Stefano V. Meille ; Andrea Mele ; Giovanni Battista Appetecchi ; Stefano Passerini
• 刊名：Journal of Physical Chemistry B
• 出版年：2014
• 出版时间：November 26, 2014
• 年：2014
• 卷：118
• 期：47
• 页码：13679-13688
• 全文大小：455K
• ISSN：1520-5207

文摘

We present the characterization of LiX-doped room-temperature ionic liquids (ILs) based on the N-butyl-N-methyl pyrrolidinium (PYR₁₄) cation with two fluorinated anions: (trifluoromethanesulfonyl)-(nonafluorobutanesulfonyl)imide (X鈺怚M₁₄) and bis(pentafluoroethanesulfonyl)imide (X鈺怋ETI). The new data are also compared with previous results on PYR₁₄TFSI (bis(trifluoromethanesulfonyl)imide). Their local organization has been investigated via NMR nuclear Overhauser effect (NOE) experiments for {¹H鈥?sup>19F} and {¹H鈥?sup>7Li} that give us details on PYR₁₄⁺/X^{鈥?/sup> and PYR₁₄+/Li+ contacts. We confirm the presence of [Li(X)₂]鈭?/sup> coordinated species in all systems. The long-range, intermolecular NOEs have been detected and provide information on the ions鈥?organization beyond the first solvation sphere. The ionic conductivity, viscosity and self-diffusion coefficients of the ionic mixtures have also been measured. The activation energies for the diffusion of the individual ions and for the fluidity are compared with those for the pure ILs. Finally, density functional calculations on [Li(BETI)₂]鈭?/sup>, [Li(IM₁₄)₂]鈭?/sup>, and [Li(TFSI)₂]鈭?/sup> complexes demonstrate that the minimum energy structures for all systems correspond to a tetrahedral coordination of the Li-ion by four oxygen atoms of the anions. Assuming very simple key steps for the Li+ diffusion process (i.e., the concerted breaking and formation of Li鈥揙 bonds or the rearrangement around a tetrahedrally coordinated Li+), we calculate activation barriers that agree well with the experimental results (approximately 46 kJ/mol, in all systems).}