Microstructures of the LiNi_1/3Co_1/3Mn_1/3O₂ cathode in a 10 Ah lithium ion battery (LIB) after 700 charging-discharging cycles at 60°C are investigated by X-ray diffraction (XRD), Rietveld refinement, X-ray photoelectron spectroscopy (XPS) and High Resolution Transmission Electron Microscopy (HR-TEM). The phase transition of H1 (initial hexagonal phase) to H2 (second hexagonal phase) is irreversible, and after that the phase of H2 is an active material during cycling. There are two consecutive layered phases H2 (H2-1 and H2-2) in charged state (4.2V) cathode while three H2 phases (H2-2’, H2-3, H2-4) in discharged state (3.0 V) one, respectively. And 2.5 wt% H2 phase is electrochemically inactive. The crystallite size decreases while strain increases, the degree of Li/Ni cation disordering also increases as well as many pulverized particles with a large number of cracks and voids appear in the cycled cathode compared to the pristine material. Besides, “active” lithium is severely irreversible consumed in the full cell system. The primary reasons for capacity fade of the positive electrode in commercial LIB are summed up as follows: i) formation of the defects in the bulk material, ii) existence of inactive H2 phase, iii) high degree of Li/Ni cation disordering and iv) the reduction of the “active” lithium in cathode.