A lithium phosphorus oxynitride (LiPON) thin film, which is a solid ionic conductor, was deposited on a Li(Ni0.53Co0.2Mn0.27)O-2 electrode to improve the thermal stability of the delithiated cathode. The LiPON thin films were deposited by radio-frequency magnetron sputtering. The thermal stability of electrochemically delithiated Li1-x(Ni0.53Co0.2Mn0.27)O-2 cathodes with electrolyte was investigated by differential scanning calorimetry (DSC), in which the cathode was charged to different upper cutoff voltages of 4.3, 4.5, and 4.7 V (vs Li/Li+). The LiPON-coated Li(Ni0.53Co0.2Mn0.27)O-2 cathodes exhibited an enhanced cycle performance for a high upper cutoff voltage, i.e., 4.7 V. However, the LiPON film appears to be thermally unstable as compared to the delithiated Li1-x(Ni0.53Co0.2Mn0.27)O-2 pristine electrodes, especially when charged to a higher upper cutoff voltage. As a result, the LiPON-coated electrodes exhibited a lower onset temperature and peak position of the exothermic peak in DSC scans than the pristine electrodes. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3430090] All rights reserved.