The chemical structure of SiO (silicon monoxide) anodes has been analyzed using X-ray photoelectron spectroscopy (XPS). Vapor deposition was used to form SiO anodes on Cu film. XPS analysis was performed on anodes at each of three stages: after deposition, after initial charge, and after discharge. The results of this analysis were then evaluated in terms of the anode's respective electrochemical characteristics. It has been found that some Si remains oxidized in the full charge state and that lithium silicates are formed. The lithium silicates serve as a buffer with respect to changes in anode volume. (c) 2005 The Electrochemical Society.