The present study has been undertaken with an aim to find out the suitability of a binary solvent system, comprising an anionic liquid, 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([OHEMIM][NTf]) and ethylene glycol (EG), toward lithium ion battery applications. For this purpose, the behavior in terms of structure, intermolecular interaction, and dynamics of several solvent systems, [OHEMIM][NTf], [OHEMIM][NTf]-LiNTf(lithium bis(trifluorimethylsulfonyl)imide), [OHEMIM][NTf]-EG, and [OHEMIM][NTf]-EG-LiNTf, is investigated by carrying out steady state and time-resolved fluorescence, nuclear magnetic resonance (NMR), and electron paramagnetic resonance (EPR) measurements. Both steady-state fluorescence and EPR studies have pointed out that the micropolarities of [OHEMIM][NTf]-EG-LiNTf are close to those of neat RTIL. However, studies on rotational dynamics have revealed that the structural organization of [OHEMIM][NTf]-LiNTf is significantly influenced upon addition of EG. Interestingly, the average solvation time is observed to be relatively faster in [OHEMIM][NTf]-EG-LiNTf than those in other solvent systems. Since average solvation time and conductivity are inversely related to each other, the present observation indicates that the introduction of EG is helpful in increasing the electrical conductivity of [OHEMIM][NTf]-EG-LiNTf. Translational diffusion coefficient measurements in [OHEMIM][NTf]-EG-LiNTf and [OHEMIM][NTf]-LiNTf through NMR spectroscopy have also indicated the suitability of [OHEMIM][NTf]-EG-LiNTf as a potential electrolytic medium for battery applications.

In recent times, it has been shown that certain binary mixtures of pure ionic liquids having appropriate chemical composition can behave like a new chemical entity. However, current knowledge about the microscopic behavior of these interesting systems is rather limited. The present study is undertaken with an objective to understand the microscopic behavior in terms of intermolecular interaction, structure, and dynamics of these systems. In the present study, few (IL + IL) mixtures are chosen with a common cation and a variation of anion. The investigations are also carried out by taking individual pure ILs so that the difference in the behavior of pure IL and (IL + IL) mixtures is understood. Initially, the systems have been investigated by studying the thermophysical properties of the concerned mixtures. The synergistic effect between combining pure ILs through photochromism has also been studied. These mixtures have been investigated further through steady-state and time-resolved fluorescence spectroscopy, electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR), and fluorescence correlation spectroscopy (FCS). Interestingly, time-resolved fluorescence data also pointed out that (IL + IL) mixtures are not only spatially heterogeneous but also dynamically heterogeneous. EPR measurements have suggested that the micropolarity (E T(30)) of the (IL + IL) mixture is close to that of aliphatic polyalcohols. Measurements of translational diffusion coefficients of the diffusing species through NMR and FCS studies have provided an idea about the nanostructural organization within (IL + IL) binary mixtures. The analysis of data essentially reveals that the mixtures of ILs that are used in the current study do not behave like a nonideal solution. The behavior of the IL mixtures is observed to be more like quasi-ideal type.

No abstract