Phase behaviour, transport properties, and interactions in Li-salt doped ionic liquids
Journal article, 2011

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.

electrolytes

physicochemical properties

raman-spectroscopy

solvation

lithium

conduction

tfsi

cation

batteries

anion

Author

Jagath Pitawala

Chalmers, Applied Physics, Condensed Matter Physics

Jae-Kwang Kim

Chalmers, Applied Physics, Condensed Matter Physics

Per Jacobsson

Chalmers, Applied Physics, Condensed Matter Physics

V. Koch

Covalent Associates, Inc.

F. Croce

University of G. d'Annunzio Chieti and Pescara

Aleksandar Matic

Chalmers, Applied Physics, Condensed Matter Physics

Faraday Discussions

1359-6640 (ISSN) 1364-5498 (eISSN)

Vol. 154 71-80

Subject Categories

Materials Engineering

Areas of Advance

Energy

Materials Science

Roots

Basic sciences

DOI

10.1039/c1fd00056j

More information

Created

10/7/2017