Degradation Analysis of LiCoO₂ Positive Electrode Material of a Li-Ion Battery Using the Li K-Edge Signal Obtained from STEM-EELS Measurements

Abstract

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. [DOI: 10.1380/ejssnt.2015.284]