Electrochemical Properties of LiAsF6 Solutions in Propylene Carbonate—Acetonitrile Binary Mixtures

Resumo

Conductivity of LiAsF₆ solutions in propylene carbonate—acetonitrile binary mixtures containing 0.2 to 1.4 mol/kg of ionophore is measured at temperatures of 283.15, 293.15, 303.15, and 313.15 K throughout the mixed solvent entire composition range. Concentration dependences of the system’s conductivity can be described by the Casteel—Amis equation, except the lithium hexafluoroarsenate solution in acetonitrile. The activation energy of the charge transfer process in the studied solutions is determined; the LiAsF₆ solution in acetonitrile has the lowest activation energy. From conductometry measurements in dilute solutions, the electrolyte limiting molar conductivity is calculated using the Lee—Wheaton equation. The LiAsF₆ ionic association in the propylene carbonate—acetonitrile mixtures with the acetonitrile mole fraction from 0.2093 to 0.9006 is not observed; the salt is fully dissociated over this concentration range. The electrochemical stability range for 0.5 mol/kg LiAsF₆ in the propylene carbonate—acetonitrile mixture was determined by means of voltammetry at 298.15 K. The decomposition potentials in the cathodic region are due to lithium electro-deposition; they depend on ion—molecule and intermolecular interactions in the system; the anodic decomposition potentials are associated with the solvent oxidation.