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Phase behaviour, transport properties, and interactions in Li-salt doped ionic liquids

Jagath Pitawala (Institutionen för teknisk fysik, Kondenserade materiens fysik) ; Jae-Kwang Kim (Institutionen för teknisk fysik, Kondenserade materiens fysik) ; Per Jacobsson (Institutionen för teknisk fysik, Kondenserade materiens fysik) ; V. Koch ; F. Croce ; Aleksandar Matic (Institutionen för teknisk fysik, Kondenserade materiens fysik)
Faraday Discussions (1364-5498). Vol. 154 (2011), p. 71-80.
[Artikel, refereegranskad vetenskaplig]

We report on the influence of lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) doping on the glass transition temperature (T(g)), the ionic conductivity, and Li-ion coordination of two dicationic ionic liquids (DILs) based on the TFSI anion. The results are compared to the behaviour of traditional mono-cationic ionic liquids. The cations of the DILs contain two imidazolium rings, connected by a decane hydrocarbon chain. Homogeneous mixtures of these ILs and LiTFSI can be obtained in a large concentration range. With increasing Li-salt concentration the ionic conductivity decreases whereas the glass transition temperature increases in both systems. However, the influence of the salt doping on the ionic conductivity and the glass transition temperature is low compared to typical mono-cationic ionic liquids, based on for example the pyrrolidinium cation and the TFSI anion. This behaviour is mirrored in the average coordination number of TFSI anions around Li-ions, determined by Raman spectroscopy. The coordination number is systematically lower in the DILs, suggesting a connection between the difference in the Li-ion environment and the behaviour of the glass transition and the ionic conductivity. A T(g)-scaled Arrhenius plot of the ionic conductivity shows that the ionic conductivity for all LiTFSI concentrations has the same temperature dependence, i.e. the fragility of the liquid is the same. This implies that the conduction process is dominated by the viscous properties of the liquids over the entire concentration range. This provides further support for linking the local environment of the Li-ions to the glass transition and conduction process in the ionic liquid/salt mixtures.

Nyckelord: physicochemical properties, raman-spectroscopy, lithium, electrolytes, conduction, cation, anion, tfsi, solvation, batteries

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Denna post skapades 2012-01-05. Senast ändrad 2015-12-17.
CPL Pubid: 151771


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Institutionen för teknisk fysik, Kondenserade materiens fysik (1900-2015)



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Physical Properties and Interactions of Ionic Liquids and Ionic Liquid Li-salt mixtures