XPS Analysis of the Surface of a Carbon Electrode Intercalated by Lithium Ions

Abstract

Surface states of carbon electrodes reduced in nonaqueous electrolytes containing 1.0 mol dm-3 LiClO4 were analyzed by an X-ray photoelectron spectroscopy (XPS) in order to decide chemical compositions of surface films formed on two different carbon materials. One is a low crystalline carbon, and the other is a highly crystalline carbon. The XPS spectra measured in this study suggest that the chemical compositions of the surface film formed on the highly crystalline carbon depends on the type of solvent. The carbon surface was almost bare when using propylene carbonate. On the other hand, a well-defined surface film mainly consisting of LiOH was formed in a mixed solvent of ethylene carbonate and diethyl carbonate. When the low crystalline carbon was used, the surface films formed in both electrolytes were a well-developed layer mainly consisting of LiOH. The electrochemical characteristics of these carbon materials in the two electrolytes showed that irreversible reactions were suppressed by the formation of a well-developed LiOH layer. These results suggested that such a well-developed LiOH layer formed on carbon materials has a function to suppress the irreversible reactions occurring on carbon materials during the first cathodic reduction process.