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

Abstract

The surface of LiNi_1/3Co_1/3Mn_1/3O₂ 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 LiNi_1/3Co_1/3Mn_1/3O₂ 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 LiNi_1/3Co_1/3Mn_1/3O₂ during the first-two-charge–discharge processes. NO₃⁻ from the coating process may have reacted with LiNi_1/3Co_1/3Mn_1/3O₂. The resultant decompose at the temperature of above 400 °C. Existence of NO₃⁻ in the cathode is harmful to its electrochemical properties. The LiNi_1/3Co_1/3Mn_1/3O₂ coated with 1 wt% AlPO₄ delivers a high discharge capacity and shows excellent capacity retention at 55 °C/0.5 C.