Pulse-Gradient Spin-Echo 1H, 7Li, and 19F NMR Diffusion and Ionic Conductivity Measurements of 14 Organic Electrolytes Containing LiN(SO2CF3)2

Abstract

The self-diffusion coefficients of the lithium ion, the anion, and the solvent in lithium bis(trifluromethanesulfonyl)imide (LiTFSI, LiN(SO₂CF₃)₂) solvent systems were measured using the pulse-gradient spin-echo (PGSE) NMR method. Fourteen different organic solvents that are commonly used as organic solution electrolytes in lithium batteries were studied. The self-diffusion coefficients of the corresponding pure solvents were also measured. Since a good correlation between the self-diffusion coefficients of the pure solvents and the inverse of the viscosity was obtained, the results are discussed in terms of the Stokes−Einstein equation. Comparisons of the self-diffusion coefficients of the solvent, the lithium ion, and the anion (TFSI ion) illustrate the solvation behavior for each solvent. The relationship between the ionic conductivity and the sum of the diffusion coefficients of the lithium ion and the anion gives the degree of ion-pair formation and permits the roles of the solvents in the electrolytes to be clearly explained.