Effect of heat-treatment on the surface structure and electrochemical behavior of AlPO4-coated LiNi1/3Co1/3Mn1/3O2 cathode materials

The surface of LiNi1/3Co1/3Mn1/3O2 particles were modified by AlPO4. Influences of heat-treatment on coating were studied by X-ray diffraction (XRD) and thermal analysis. Electrochemical tests and electrochemical impedance spectroscopy (EIS) were conducted. The results show that AlPO4 can react with LiNi1/3Co1/3Mn1/3O2 and an aluminum-containing-spinel phase of M-1'M2O4 (M = Ni, Co, Mn, M' = Al) is formed at above 700 degrees C. The high surface content of aluminum is in favor of forming a stable solid electrolyte film (SEI) on the surface of LiNi1/3Co1/3Mn1/3O2 during the first-two-charge-discharge processes. NO3- from the coating process may have reacted with LiNi1/3Co1/3Mn1/3O2. The resultant decompose at the temperature of above 400 degrees C. Existence of NO3- in the cathode is harmful to its electrochemical properties. The LiNi1/3Co1/3Mn1/3O2 coated with 1 wt% AlPO4 delivers a high discharge capacity and shows excellent capacity retention at 55 degrees C/0.5 C.