The irreversible capacity loss that occurs during the first cycle in an Li ion battery was studied using Fourier transform infrared attenuated total reflectance, secondary ion mass spectrometer, x-ray photoelectron spectroscopy, and plasma spectrometer. The irreversible capacity loss was related to both the solvent decomposition and the reaction of Li with active sites in the bulb of the carbon electrode. Li remaining in the discharged electrode not only exists on the surface of the carbon but also in its bulk. The Li concentration on the surface of the carbon is higher than that in the bulk. The binding energy of Li remaining in the bulk of the discharged carbon electrode is higher by similar to 2.5 eV than that of metallic lithium (52.5.eV) and lower by similar to 0.5 eV than that of Li remaining on the surface of the discharged electrode.