Chemical and Morphological Characteristics of Lithium Electrode Surfaces

Abstract

In order to elucidate the physical and chemical characteristics of the anode passivating film in secondary lithium batteries, we have conducted ESCA (electron spectroscopy for chemical analysis) and SEM (scanning electron microscopy) studies of lithium electrode surfaces. The samples include lithium metal as‐received from the vendor, and lithium electrodes which were cycled in a 1.5M lithium arsenic hexafluoride/two‐methyl tetrahydrofuran electrolyte. The results of studies of the as‐received lithium indicate that the surface is covered by a film containing only carbon, oxygen, and lithium. Binding energy analysis and model compound studies indicate that this “native” film has a probable two‐layer structure consisting of covered by an outer adduct, at a total thickness of 100–200Å. No evidence of was found. ESCA/SEM studies of cycled lithium electrodes reveals the presence of a second film formed in the electrochemical environment. This film appears to consist, in some part, of degradation products and impurities associated with the electrolyte, possibly in the form of lithium arsenic oxyfluorides.