An X-ray photoelectron spectroscopy study on the surface film on carbon black anode in lithium secondary cells

The property of the surface film formed on the carbon black anode of a lithium cell at the initial reduction stage was investigated. About 90% of the carbon black surface was covered with a smooth film about 10–15 Å in thickness after five cyclic voltammetry cycles. The X-ray photoelectron spectroscopy analysis revealed that this film contained oxygen atom bonding directly to the carbon atoms and was formed by decomposition of the solvent. The inhibiting effect of the surface film against further solvent decomposition reaction disappeared after washing with ethanol or heat treatment above 200 °C. The surface film was confirmed to form also by chemical reduction using lithium naphthalide, where lithium insertion in the carbon black took place. The inhibiting effect of a chemically formed surface film against the solvent decomposition was less marked than that of an electrochemically formed film.