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Electrochemical l ithium intercalation into highly oriented pyrolytic graphite and natural graphite powder was inves-tigated using in situ Raman spectroscopy. Three plateaus were observed on the charging curve for both samples. F rom the Raman spectral changes the first plateau was assigned to a phase transition f rom dilute stage 1 to stage 4, the second f rom a stage 2 phase to another stage 2 phase, and the third f rom stage 2 to stage i, wh ich are in good agreement with Dahns results by in situ x-ray diffraction. The spectral changes associated with the phase transitions occurred reversibly during a charge and discharge cycle. It was shown f rom the Raman spectral changes of the HOPG electrode that the electrode potential during the electrochemical intercalation is determined by the surface stage of graphite intercalation compounds. Electrochemical l ithium intercalation into graphite ma-terials has been extensively studied for use in negative electrodes of secondary lithium batteries. ~ ~ At the graphite electrode lithium is intercalated into graphite upon charging and is deintercalated f rom graphite upon discharging. The phase transition mechan ism upon electro-chemical Li intercalation has been investigated so far using
Inaba et al. (Sun,) studied this question.