IMPEDANCE SPECTROSCOPY OF NONACTIVE METAL-ELECTRODES AT LOW POTENTIALS IN PROPYLENE CARBONATE SOLUTIONS - A COMPARISON TO STUDIES OF LI ELECTRODES

Surface films formed on nonactive metals (nickel, gold, and silver) in propylene carbonate solutions were investigated using impedance spectroscopy. The salts used included LiClO4, LiAsF6, LiBF4, and LiPF6, and the impact of their concentration on the properties of the surface films was explored. In addition, the influence of the presence of additives such as O2, H2O, and CO2 in solutions and the potential of formation on the properties of these surface-films was rigorously studied. Using simple methods and simulation programs, it was possible to separate the time constants of the impedance spectra, relate them to different parts of the metal-solution interface, and to calculate the thickness of these surface films from the interfacial capacitances. Following variations of the thickness calculated for the surface films formed in the different systems as a function of applied potential and solution composition, it was possible to study the stability of the surface films, their dissolution rates and the influence of different additives on their stability. For a few systems, ex situ Fourier transform infrared spectroscopy (external reflectance mode) was also applied. The results thus obtained were correlated to previous studies of Li electrodes in the same solutions.