Ion Transport Properties of Six Lithium Salts Dissolved in γ-Butyrolactone Studied by Self-Diffusion and Ionic Conductivity Measurements

Abstract

The self-diffusion coefficients of the lithium ion, anion, and solvent in electrolytes prepared by dissolving six lithium salts (LiBF4,(LiBF4, LiPF6,LiPF6, LiSO3CF3,LiSO3CF3, LiN(SO2CF3)2,LiN(SO2CF3)2, LiN(SO2C2F5)2,LiN(SO2C2F5)2, and lithium bis(oxalateborate)) in γ-butyrolactone (GBL) were measured using pulsed gradient spin-echo nuclear magnetic resonance. The ionic conductivity calculated from the ion self-diffusion coefficients was compared with the electrochemically measured ionic conductivity. In each sample, GBL diffused the fastest, followed by the anion and then the lithium ion. The diffusion of the solvent and cation were insensitive to the anions. On average each lithium ion was solvated by about two GBL molecules. The hydrodynamic size of the anions normalized by their respective van der Waals radius was determined and almost independent of the salt concentration for PF6−,PF6−, N(SO2CF3)2−,N(SO2CF3)2−, N(SO2C2F5)2−,N(SO2C2F5)2−, and B(C4O8)−,B(C4O8)−, but increased with salt concentration for BF4−BF4− and CF3SO3−CF3SO3− due to ion association. © 2003 The Electrochemical Society. All rights reserved.