Translational and Reorientational Mobility of Ions in the “BMPyrrTFSI–LithiumTFSI” System According to NMR Data

Abstract

A detailed NMR study of translational and reorientation mobility in mixtures of [BMPyrrTFSI] with [LiTFSI] (0; 0.1 and 1.5 mol/kg) was carried out in the temperature range of 278 K ≤ T ≤ 333 K. To realize the NMR advantage, the resonances of the ¹H, ¹³C, ⁷Li, and ¹⁹F nuclei were registered. The diffusion data clearly indicate a strong correlation of the translational motion of all ions in the studied objects at all used temperatures. On the basis of the data obtained, the activation energies, \({E}_{a}\), for translational motion have also been calculated. The energy barriers for the translational diffusion of the IL cations and anions are close, but for the movement of the Li⁺ cations, the activation energy \({E}_{a}\) is significantly greater. It follows that the lithium cation moves together with the solvate shell of a certain number of anions. To investigate the local mobility, the temperature dependences of the spin–lattice relaxation rates in the studied systems were measured. A comparison of the activation energy values calculated from diffusion and NMR-relaxation data indicates that the energy barriers for the translational motion of ions in the system under study are much higher than for local reorientation processes. The data obtained confirm the conclusion that there is a strong solvate shell (big \({\tau}_{c}\)) around lithium cations.