Determination of Mass Transfer Parameters and Ionic Association of LiPF6: Organic Carbonates Solutions

We report herein on the determination of several mass transport properties (diffusion coefficients for cations, anions, and neutral ionic aggregates; cation transference number) and degree of salt association in electrolyte solutions of practical interest (LiPF 6 solutions in binary organic carbonate mixtures), through an analysis of pulsed field gradient NMR and specific conductivity data. Results were obtained as a function of LiPF 6 salt concentration in a binary ethylene carbonate (EC) - dimethyl carbonate (DMC) mixture at 1:1 volume ratios and 30°C, also from 5°C to 35°C for 1 M LiPF 6 dissolved in binary mixtures of EC with DMC and EMC at 3:7, 1:1 and 7:3 volume ratios. Li + transference numbers have significantly lower values than the transport numbers, ranging from 0.31 to 0.35, and display a correct (decreasing) variation with salt concentration, contrary to the trend observed for transport numbers. A remarkably high degree of ion pairing (from 36% to 67%) was observed for the solutions investigated in the present work.