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

Abstract

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′1M2O4 (M = Ni, Co, Mn, M′ = Al) is formed at above 700 °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 °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 °C/0.5 C.