X-RAY PHOTOELECTRON-SPECTROSCOPY STUDIES OF LITHIUM SURFACES PREPAREDIN SEVERAL IMPORTANT ELECTROLYTE-SOLUTIONS - A COMPARISON WITH PREVIOUS STUDIES BY FOURIER-TRANSFORM INFRARED-SPECTROSCOPY

Li electrodes prepared in situ in solutions and then stored in them fo r different periods were studied by X-ray photoelectron spectroscopy ( XPS) including depth profiling performed by argon sputtering followed by XPS. A set of solvents, propylene carbonate (PC), ethylene carbonat e (EC)-dimethyl carbonate (DMC) mixtures, and 1,3-dioxolane, and a set of salts, LiAsF6, LiBF4, LiPF6, LiN(SO2CF3)(2), and LiC(SO2CF3)(3), w ere investigated with respect to the effect of storage time. The resul ts of this study were compared with previous studies of Li electrodes in the same solutions by in situ and ex situ Fourier transform infrare d spectroscopy. Basically, the results thus obtained are in line with the previous studies. The Li surface chemistry is dominated by solvent reactions. However, all the above salt anions are also reduced to for m insoluble species which also contribute to the build-up of the surfa ce films (e.g., the salt anions of the type MF(y)(-) (M = As, P, B) ar e reduced to LiF and species of the Li(x)MF(z) type). The surface reac tions of these solvents and the salts on ii are discussed in detail. D epth profiling of the surface films formed on ii in solutions indicate s that they have a multilayer structure. The concentration of the orga nic salts in the surface layers decreases as the layer is closer to th e Li-film interface.