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

摘要

The self-diflusion 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 ~1H, ~7Li, and ~(19)F 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 α was evaluated from the ionic conductivity, D_(Li) and D_(PF6). The α value increased from 0.17 to 0.71 as the EC ratio increased from (O to 100) %.