锂离子电池正极材料LiNi0.5Co0.2Mn0.3O2的合成及其高温容量衰减研究

采用共沉淀-高温固相烧结法合成了富镍型三元复合正极材料LiNi0.5Co0.2Mn0.3O2.恒流充放电测试表明,材料在3.0～4.4 V下0.2C放电容量达到179.2 mAh.g-1,但在55℃下经历100次充放电循环后发生急剧的容量衰减.电化学交流阻抗谱、X射线光电子能谱和原子发射光谱等实验表明,在高温高电压下,电解液与LiNi0.5Co0.2Mn0.3O2电极材料之间的副反应加剧,导致过渡金属原子溶出,该材料局域结构被破坏.同时,电极材料表面还沉积了高阻抗的LiF/MFx层,使得在电极的充放电过程中电荷转移阻抗和Li+扩散阻抗不断增加,以致电池容量急剧衰减.

Synthesis of LiNi0.5Co0.2Mn0.3O2 for Lithium Ion Batteries and the Mechanism of Capacity Fading at High Temperature

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,the LiNi0.5Co0.2Mn0.3O2 experienced the dramatic capacity fading after 100 charge-discharge cycles at 55 ℃.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/MFx layer,the charge-transfer resistance and Li+ diffusion resistance were increased,resulting in a sharp capacity degradation.