Determination of Mass Transfer Properties and Ionic Association in LiPF6 - Organic Carbonates Solutions from PFG-NMR and Specific Conductivity Data

We derive herein several mass transport properties (diffusion coefficients for cations, anions, and neutral ionic aggregates; cation transference number; salt association constant) of LiPF6 solutions in binary mixtures of ethylene carbonate (EC) and dimethyl carbonate (DMC) or ethyl methyl carbonate (EMC) through an analysis of PFG-NMR and specific conductivity data. Results were obtained as a function of salt concentration for EC:DMC 1:1 v/v, also from 5 ºC to 35 ºC for 1M LiPF6 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 decrease with concentration. Under the assumptions that the higher order neutral aggregates beyond ion pairs can be neglected and that the intrinsic diffusion coefficients of cations and ion pairs are the same (valid only for solutions containing LiPF6, LiBF4 or LiClO4salt and significant amounts of EC), one can determine the degree of ion pairing as well as the intrinsic diffusion coefficients for cations, anions and ion pairs. A high degree of ion pairing (from 36% to 67%) was observed for the solutions investigated in the present work. Acknowledgements The authors acknowledge funding through the NSERC APC program and GM of Canada. Figure 1