关键词: 锂离子电池正极材料, LiNi0.5Co0.2Mn0.3O2, 高温容量衰减, X射线光电子能谱, 交流阻抗谱

Abstract: The Ni-rich cathode materials, LiNi0.5Co0.2Mn0.3O2, have been synthesized by Co-precipitation and high-temperature solid-phase sintering method. Constant current charge-discharge tests showed high discharge capacity of 179.2 mAh.g-1 in the 3.0 ? 4.4 V at 0.2C. However, at 55 °C the LiNi0.5Co0.2Mn0.3O2 experienced the dramatic capacity fading after 100 charge-discharge cycles. Electrochemical Impedance Spectroscopy, X-Ray Photoelectron Spectroscopy, Atomic Emission Spectroscopy have been employed to study the capacity fading mechanism of LiNi0.5Co0.2Mn0.3O2 cycled at high temperature in range of high-voltage charge and discharge conditions. It was found that at high temperature under conditions of high-voltage range, the side reactions between the electrolyte and electrode would be accelerated, leading to dissolution of transition metal atoms and resulting in the local structure damage of cathode material. Meanwhile, the byproducts could be deposited on the electrode surface as a high impedance LiF/metal fluoride layer, the charge-transfer resistance and Li+ diffusion resistance were increased, resulting in a sharp capacity degradation.

Key words: Lithium-ion batteries, LiNi0.5Co0.2Mn0.3O2, capacity fading, X-ray photoelectron spectroscopy, AC impedance spectroscopy;