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Local Structural Characterization for Electrochemical Insertion-Extraction of Lithium into CoO with |
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Cobalt oxide is known to exhibit a large capacity as a negative electrode in lithium-ion batteries. Here, Co
K-edge X-ray absorption spectroscopy (XAS) was used to investigate variations in the local structure during
the first electrochemical cycle of the insertion-extraction of lithium into CoO. The XANES and EXAFS
spectra in LiyCoO (y: lithium content) varied markedly with the lithium content. The initial insertion of
lithium leads to the reduction of Co2+ in the pristine CoO to the reduced metallic Co0 state. The systematic
variations observed in intensities of the peaks corresponding to the 1s f 3d and 1s f 4p transitions indicate
that the mole ratio of Co to CoO increases gradually with the electrochemical insertion of lithium ions. Insertion
of lithium causes the local structure around the Co atoms to become asymmetric. The systematic decrease in
the magnitude of the Fourier transform (FT) with increasing amount of inserted lithium is closely related to
an increase in static disorder due to the presence of two phases: Co0 clusters and CoO. The small-sized Co
particles evolve gradually with a well-separated distribution in the Li2O matrix. In the successive extraction
of lithium, the reduced Co particles return reversibly to the high-temperature cubic phase of CoO.
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