AlF3-coated Li[Li0.2Mn0.54Ni0.13Co0.13]O-2 materials have been synthesized as positive electrode materials for lithium-ion batteries. The pristine and AlF3-coated Li[Li0.2Mn0.54Ni0.13Co0.13]O-2 materials were characterized by X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, and charge-discharge techniques. The electrochemical studies indicated that the AlF3-coated Li[Li0.2Mn0.54Ni0.13Co0.13]O-2 showed initial irreversible capacity loss of only 47 mA h/g compared to 75.5 mA h/g for pristine material. Meanwhile, the coated material also exhibited better rate capability and cyclic performance, which has higher capacity retention of 87.9% after 80 cycles at 0.5 C rate at room temperature in comparison with only 67.8% for the pristine one. The functional mechanism of AlF3 coating on the performance of Li[Li0.2Ni0.13Mn0.54Co0.13]O-2 was also investigated by electrochemical impedance spectroscopy (EIS) and in situ differential electrochemical mass spectrometry (DEMS). EIS analysis indicated that AlF3-coated Li[Li0.2Mn0.54Ni0.13Co0.13]O-2 had stable charge transfer resistance (R-ct). In situ DEMS results revealed that the activity of extracted oxygen species from layered positive electrode material was greatly reduced and the decomposition of the electrolyte was significantly suppressed for AlF3-coated Li[Li0.2Mn0.54Ni0.13Co0.13]O-2. Therefore, more oxygen molecules rather than carbon dioxide were observed in the coated material system. It is demonstrated again that the AlF3 coating layer played an important role in the stabilization of the electrode/electrolyte interface for the coated material. (C) 2008 The Electrochemical Society.