X-RAY PHOTOELECTRON-SPECTROSCOPY ANALYSES OF LITHIUM INTERCALATION AND ALLOYING REACTIONS ON GRAPHITE-ELECTRODES

Electrochemical lithium intercalation reactions occurring in silver-su pported graphite anodes were investigated by X-ray photoelectron spect roscopy (XPS), The binding energy of Li(1s) of intercalating lithium w as higher than that of lithium metal, which suggests that lithium exis ts in the form of a positive ion in the graphite layers, The core leve l of the C(1s) signal of lithium intercalated graphite was higher than that of graphite, which implies that the carbon in lithium-intercalat ed graphite has a negative charge, This finding agrees with previous X PS studies indicating that carbon has a negative charge in a graphite- intercalation compound produced by a molten lithium intercalation reac tion to graphite, Lithium carbonate, lithium fluoride and organic comp ounds were produced on the graphite surfaces in charge/discharge react ions in 1 M LiPF6/EC-DMC electrolytic solution, It was also confirmed that the initial charge current supplied to the graphite electrode wit h a potential between 2.8 and 0.6 V did not cause a lithium-intercalat ion reaction. It caused, however, other reactions such as decompositio n of the electrolytic solution and production of passivating films. (C ) 1997 Published by Elsevier Science S.A.