Electrochemical lithium intercalation into highly oriented pyrolytic graphite and natural graphite powder was investigated using in situ Raman spectroscopy. Three plateaus were observed on the charging curve for both samples. From the Raman spectral changes the first plateau was assigned to a phase transition from dilute stage 1 to stage 4, the second from a stage 2 phase to another stage 2 phase, and the third from stage 2 to stage i, which are in good agreement with Dahn's 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 from 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.
In order to elucidate surface reactions on graphite negative
electrodes of secondary lithium ion batteries,
topographical changes of the basal plane of a highly oriented pyrolytic
graphite (HOPG) in 1 M LiClO4/ethylene carbonate−diethyl carbonate (1:1 by volume) were observed
under polarization by electrochemical
scanning tunneling microscopy. A step edge on the basal plane of
HOPG was treated as a model of the
edge plane of HOPG. When the sample potential was stepped to 1.1 V
vs Li/Li+, two kinds of hill-like
structure of ca. 10 Å height appeared on the HOPG surface. The
first hill was formed far apart from a
step edge and was almost unchanged with time. The second hill was
formed in the vicinity of the step
and was spread out with time. The formation of the second hill
caused the exfoliation of graphite layers.
The observed height of the hills was comparable to the values of
the increment of the interlayer spacing
for ternary graphite intercalation compounds of alkali metal with
solvent molecules prepared by a solution
method. It was considered that the intercalation of solvated
lithium ion is responsible for the formation
of the hills and that this process corresponds to the initial stage of
the solvent decomposition and subsequent
film formation processes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.