The stability of charged Li1.2Ni0.13Mn0.54Co0.13O2 at elevated temperature was investigated by using thermal desorption spectrometry-mass spectrometry (TDS-MS), X-ray diffraction (XRD), and X-ray absorption fine structure (XAFS) measurements. The TDS-MS and XRD spectra indicated that the crystal structure of the delithiated Li1.2Ni0.13Mn0.54Co0.13O2 changed from layer to spinel, and oxygen was released at high temperature. However, the amount of oxygen released from Li1.2Ni0.13Mn0.54Co0.13O2 in a full-charge state was much less than that released from LiNi0.8Mn0.1Co0.1O2 in a full-charge state. The XAFS spectra indicated that the high oxidation state of manganese was more stable than that of nickel and cobalt. The high stability of charged Li1.2Ni0.13Mn0.54Co0.13O2 at high temperature was, therefore, attributed to the high manganese content of the transition metal.