Surface reaction of LiCoO₂/Li system under high-voltage conditions by X-ray spectroscopy and two-dimensional correlation spectroscopy (2D-COS)

We studied the surface reactions of a LiCoO₂/Li cell under high-voltage conditions using X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and two-dimensional correlation spectroscopy (2D-COS). 2D XPS correlation spectra show that Li₂CO₃ is formed first by decomposition of the organic solvents, and then polycarbonate, which is formed by polymerization of the electrolytes, is produced on the cathode surface of the LiCoO₂/LÍ system under high-voltage conditions. XAS measurements also confirm that the solid electrolyte interface (SEI) layer is formed on the LiCoO₂ electrode by decomposition of the organic solvents. The thickness of the SEI layer is less than 100 Å.