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Issue 48, 2011
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Physicochemical properties of imidazolium-derived ionic liquids with different C-2 substitutions

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Abstract

Five room temperature ionic liquids based on C-2 substituted imidazolium cations and bis(trifluoromethanesulfonyl)imide (TFSI) anions were synthesized and their physicochemical properties: thermal property, density, viscosity, ionic conductivity, self-diffusion coefficients, and electrochemical stability, were systematically investigated. The temperature dependence of both viscosity and ionic conductivities of these ionic liquids can be described by the Vogel–Fulcher–Tamman (VFT) equation. Compared with the reference, 1-propyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, the introduction of functional groups at the C-2 position generally increased the viscosity and lowered the ionic conductivity. The introduction of an ether group (–CH2OCH2CH2CH2CH3) at the C-2 position not only enhanced the reduction stability of the ionic liquids but also exhibited the lowest solid electrolyte interfacial resistance (RSEI). In contrast, the introduction of a cyano group (–CN) at the C-2 position not only decreased the reduction stability but also adversely increased the SEI resistance. The effect of the C-2 substitution on the reduction stability was explained by the change in the energy level of the lowest unoccupied molecular orbital. The self-diffusion coefficients (D) of each ion were measured by pulsed field gradient nuclear magnetic resonance (PFG-NMR). The lithium transference number (tLi) of 0.5 M LiTFSI/IL solutions calculated from the self-diffusion coefficients was in the range of 0.04 to 0.09.

Graphical abstract: Physicochemical properties of imidazolium-derived ionic liquids with different C-2 substitutions

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Publication details

The article was received on 21 Jul 2011, accepted on 13 Oct 2011 and first published on 08 Nov 2011


Article type: Paper
DOI: 10.1039/C1CP22375E
Citation: Phys. Chem. Chem. Phys., 2011,13, 21503-21510
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    Physicochemical properties of imidazolium-derived ionic liquids with different C-2 substitutions

    C. Liao, N. Shao, K. S. Han, X. Sun, D. Jiang, E. W. Hagaman and S. Dai, Phys. Chem. Chem. Phys., 2011, 13, 21503
    DOI: 10.1039/C1CP22375E

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