Dielectric study on mixtures of ionic liquids

TL;DR

This study investigates how mixing different ionic liquids affects their physical properties, especially conductivity and fragility, providing insights into their energy landscape and offering an economical way to tune electrolyte characteristics.

Contribution

It demonstrates that the physical properties of ionic liquid mixtures can be precisely tuned by composition, revealing the relationship between mixture fractions and dynamics, and offering new insights into their fragility.

Findings

Mixtures allow precise tuning of dc conductivity.

Fragility parameter can be gradually modified through mixing.

Dynamics are well described by the fractions of parent ionic liquids.

Abstract

Ionic liquids are promising candidates for electrolytes in energy-storage systems. We demonstrate that mixing two ionic liquids allows to precisely tune their physical properties, like the dc conductivity. Moreover, these mixtures enable the gradual modification of the fragility parameter, which is believed to be a measure of the complexity of the energy landscape in supercooled liquids. The physical origin of this index is still under debate; therefore, mixing ionic liquids can provide further insights. From the chemical point of view, tuning ionic liquids via mixing is an easy and thus an economic way. For this study, we performed detailed investigations by broadband dielectric spectroscopy and differential scanning calorimetry on two mixing series of ionic liquids. One series combines an imidazole based with a pyridine based ionic liquid and the other two different anions in an imidazole based ionic liquid. The analysis of the glass-transition temperatures and the thorough evaluations of the measured dielectric permittivity and conductivity spectra reveal that the dynamics in mixtures of ionic liquids are well defined by the fractions of their parent compounds.