The surface films formed on deposited lithium in electrolyte solutions based on ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) were analyzed by pyrolysis-gas chromatography-mass spectroscopy (Py-GC-MS). In I M LiClO4/EC, the main component of the surface film was easily hydrolyzed to give ethylene glycol after exposure to air, and hence was considered to have a chemical structure of ROCH2CH2OR', of which -OR and -OR' are -OLi or -OCO2Li. Ethylene oxide, acetaldehyde, and 1,4-dioxane were detected in decomposition products, and they were considered to have been formed by pyrolysis of ROCH2CH2OR' in the pyrolyzer. The presence of ethanol in decomposition products confirmed that ring cleavage at the CH2-O bonds of EC occurs by one electron reduction. In addition, the presence of methanol implied the cleavage of the C-C bond of EC upon reduction. From the surface films formed in I M LiClO4/DEC and /DMC, ethanol and methanol, respectively, were detected, which suggested that corresponding lithium alkoxides and/or lithium alkyl carbonates were the main components. In I M LiClO4/EC + DEC (1:1), EC dominantly decomposed to form the surface film. The surface film formed in I M LiPF6/EC + DEC (1: 1) contained a much smaller amount of organic compounds. (C) 2003 Elsevier Science B.V. All rights reserved.