We studied the surface reactions of a LiCoO<sub>2</sub>/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 Li<sub>2</sub>CO<sub>3</sub> 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 LiCoO<sub>2</sub>/Li system under high-voltage conditions. XAS measurements also confirm that the solid electrolyte interface (SEI) layer is formed on the LiCoO<sub>2</sub> electrode by decomposition of the organic solvents. The thickness of the SEI layer is less than 100 Å.
Yeonju Park, Nam Hoon Kim, Jong Myong Kim, Young Chul Kim, Yeon Uk Jeong, Sung Man Lee, Hyun Chul Choi, and Young Mee Jung, "Surface Reaction of LiCoO2/Li System under High-Voltage Conditions by X-ray Spectroscopy and Two-Dimensional Correlation Spectroscopy (2D-COS)," Appl. Spectrosc. 65, 320-325 (2011)