An Evaluation Method of Liquid Electrolytes for Lithium Batteries by the Multinuclear Pulsed-gradient Spin-echo NMR - The Diffusing Radii of Lithium Ion and Anions in Organic Solvents

The individual self-diffusion coefficients of the lithium ion, anion and solvent in the electrolytes for lithium batteries have been measured by the pulsed-gradient spin-echo (PGSE) ⁷Li, ¹⁹F, and ¹H NMR, respectively. Based on the classical Stokes-Einstein equation for self-diffusion coefficient, bulk viscosity and Stokes radius of the diffusing species, the solvation effects around the lithium ion in 17 different solvents are discussed from the hydrodynamic diffusing radius of the lithium ion. The normalized anion hydrodynamic sizes of N(SO₂CF ₃)₂ (TFSI) and BF₄ in GBL and PC are also calculated by using the diffusion coefficients and the van del Waals radius. The self-association of BF₄ at concentrated region is discussed.