An XPS study of the adsorption of oxygen and water vapor on clean lithium films

Abstract

The need to develop high energy density power sources has produced a new generation of non-aqueous battery systems in which pure lithium is used as the primary anode material. In an effort to understand the complex chemical reactions which occur in these cells, it is necessary to first examine in detail the nature of the passivating films which form on lithium before it is incorporated into a cell. In this study, X-ray photoelectron spectroscopy (XPS) was used to characterize low level exposures of clean polycrystalline lithium films to molecular oxygen and water vapor. High purity lithium was vapor deposited on a sputter cleaned tantalum foil in a deposition chamber which was attached to a highly modified XPS system allowing specimens to be prepared and studied at or below 1.3×10-7 Pa pressure. Quantitative reaction rates for oxygen and water vapor were determined. A two step reaction for the interaction of water vapor with lithium was observed and appears to be a function of the total exposure. The results of these experiments differ in several respects from those previously reported in the literature. These differences are discussed.