Surface states of carbon electrodes reduced in nonaqueous electrolytes
containing 1.0 mol dm(-3) LiClO4 were analyzed by an X-ray photoelect
ron spectroscopy (XPS) in order to decide chemical compositions of sur
face films formed on two different carbon materials. One is a low crys
talline 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 pr
opylene carbonate. On the other hand, a well-defined surface film main
ly consisting of LiOH was formed in a mixed solvent of ethylene carbon
ate and diethyl carbonate. When the low crystalline carbon was used, t
he surface films formed in both electrolytes were a well-developed lay
er mainly consisting of LiOH. The electrochemical characteristics of t
hese carbon materials in the two electrolytes showed that irreversible
reactions were suppressed by the formation of a well-developed LiOH l
ayer. These results suggested that such a well-developed LiOH layer fo
rmed on carbon materials has a function to suppress the irreversible r
eactions occurring on carbon materials during the first cathodic reduc
tion process.