Pulse-gradient spin-echo H-1, Li-7, and F-19 NMR diffusion and ionic conductivity measurements of 14 organic electrolytes containing LiN(SO2CF3)(2)

The self-diffusion coefficients of the lithium ion, the anion, and the solv ent in lithium bis(trifluromethane-sulfonyl)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 orga nic solution electrolytes in lithium batteries were studied. The self-diffu sion coefficients of the corresponding pure solvents were also measured. Si nce a good correlation between the self-diffusion coefficients of the pure solvents and the inverse of the viscosity was obtained, the results are dis cussed in terms of the Stokes-Einstein equation. Comparisons of the self-di ffusion coefficients of the solvent, the lithium ion, and the anion (TFSI i on) illustrate the solvation behavior for each solvent. The relationship be tween the ionic conductivity and the sum of the diffusion coefficients of t he lithium ion and the anion gives the degree of ion-pair formation and per mits the roles of the solvents in the electrolytes to be clearly explained.