Understanding transport mechanisms in ionic liquid/carbonate solvent electrolyte blends

Oldiges, K.; Brunklaus, G.; Hooper, J. B.; Heuer, A.; Ebrahiminia, M.; Diddens, Diddo; Winter, M.; Bedrov, D.; Cekic-Laskovic, I.

doi:10.1039/C8CP01485J

Journal Article

FZJ-2018-03113

Understanding transport mechanisms in ionic liquid/carbonate solvent electrolyte blends

Oldiges, K.FZJ* ; Diddens, D.FZJ* ; Ebrahiminia, M. ; Hooper, J. B. ; Cekic-Laskovic, I.FZJ* ; Heuer, A.FZJ* ; Bedrov, D. (Corresponding author) ; Winter, M.FZJ* ; Brunklaus, G. (Corresponding author)FZJ*

2018
RSC Publ. Cambridge

Physical chemistry, chemical physics 20(24), 16579-16591 (2018) [10.1039/C8CP01485J]

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Please use a persistent id in citations: http://hdl.handle.net/2128/19121 doi:10.1039/C8CP01485J

Abstract: To unravel mechanistic details of the ion transport in liquid electrolytes, blends of the ionic liquid (IL) 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (Pyr14TFSI), ethylene carbonate (EC) and dimethyl carbonate (DMC) with the conducting salts lithium hexafluorophosphate (LiPF6) and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) were investigated as a function of the IL concentration. Electrochemical impedance, Pulsed Field Gradient Nuclear Magnetic Resonance (PFG NMR) and Raman spectroscopy supported by Molecular Dynamics (MD) simulations allowed the structural and dynamic correlations of the ion motions to be probed. Remarkably, we identified that though the individual correlations among different ion types exhibit a clear concentration dependence, their net effect is nearly constant throughout the entire concentration range, resulting in approximately equal transport and transference numbers, despite a monitored cross-over from carbonate-based lithium coordination to a TFSI-based ion coordination. In addition, though dynamical ion correlation could be found, the absolute values of the ionic conductivity are essentially determined by the overall viscosity of the electrolyte. The IL/carbonate blends with a Pyr14TFSI fraction of ∼10 wt% are found to be promising electrolyte solvents, with ionic conductivities and lithium ion transference numbers comparable to those of standard carbonate-based electrolytes while the thermal and electrochemical stabilities are considerably improved. In contrast, the choice of the conducting salt only marginally affects the transport properties.

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