Temperature Dependence of Self-Diffusion Coefficients of Ions and Solvents in Ethylene Carbonate, Propylene Carbonate, and Diethyl Carbonate Single Solutions and Ethylene Carbonate plus Diethyl Carbonate Binary Solutions of LiPF6 Studied by NMR

The self-diffusion coefficients, D, of lithium, anions, and solvents in four binary-solution electrolytes of ethylene carbonate (EC)-diethyl carbonate (DEC) and three single-solution electrolytes of EC, DEC, and propylene carbonate (PC) including 1 M LiPF6 were measured by H-1, Li-7, and F-19 NMR spectroscopy from (353 to 243) K or above freezing for seven solution electrolytes. In the single DEC electrolyte, D-Li and D-PF6 had almost the same values at every temperature, whereas D-Li was smaller than D-PF6 in the EC and PC solutions. In the binary EC-DEC electrolytes, as the ratio of EC increased, D-Li gradually became smaller, while D-PF6 remained almost unchanged in the temperature range studied. At 303 K, the degree of ion dissociation alpha was evaluated from the ionic conductivity, D-Li and D-PF6. The alpha value increased from 0.17 to 0.71 as the EC ratio increased from (0 to 100) %.