The Li distribution in positive electrode material (LiCoO2) was observed after a charge-discharge cycling test by analytical transmission electron microscopy (TEM). The electron energy-loss spectroscopy (EELS) imaging method revealed an inhomogeneous Li distribution in the LiCoO2 particles after the charge-discharge cycling test. Using the alternating least-squares (ALS) method for the data matrix of the EELS spectra, we obtained LiCoO2 and Li-poor LiCoO2 spectra from the LiCoO2 particles. Around the degraded LiCoO2 particles, Co3O4 and fluoride components were detected. It is suggested that inhomogeneous electrochemical reactions are one cause of LiCoO2 and electrolyte degradation.
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