The Preparation And Application Study Of LiNi_0.5Co_0.2Mn_0.3O₂ Cathode Material

Li(Ni, Co, Mn)02 (NCM) materials have gain more and more attention of vehicle battery manufacturers for its higher specific capacity, good cycle performance and thermal stability. In addition, the reduction of cost and improvement of safety have strengthened the advantage of NCM materials.As an important member of NCM materials, LiNi0.sCo0.2Mn0.3O2 becomes an appropriate candidate of vehicle lithium-ion battery application for its advantages in energy density, power density and cycle stability.However, LiNi0.5Co0.2Mn0.3O2 also has some problems during application. As we know, preparation process has great influence on the properties of material. Parameters of electrode fabrication, such as component ratio, compact density and choice of conductive additives, also affect the performance of batteries significantly. In addition, test condition also has effect on the electrochemistry performance of battery. In this article, several factors affecting the performance of LiNi0.5Co0.2Mn0.3O2 material and electrode are studied.In the first, LiNi0.5Co0.2Mn0.3O2 material was prepared under different temperature (800-980℃). With different physical property, material prepared under different temperature has shown variant electrochemical performance. It was found out that the sample fired under 850℃ possesses the highest initial specific capacity (176.7mAh·g-1) and columbic efficiency (90.3%).In the experiment of electrode preparation, the porosity of electrode, the ratio of conductive additives to binder and the application of different kinds of conductive additives were studied. (1) At 91:2:3:4(LiNi0.5Co0.2Mn0.3O2/KS-6/Super P/PVDF) ratio, the cell with porosity of 30% shows the best power density;(2) Containing about 90% active material in the electrode, the cell with 1:1.2 conductive additive to PVDF ratio represents the lowest DC conductivity and the best discharge rate capability; (3) While used as conductive additive, carbon nanotubes need to be treated by ultrasonic dispersion in the solvent containing appropriate surfactant. The cell with 94:1:2:3 (LiNi0.5Co0.2Mn0.3O2/CNTs/VGCF/PVDF) ratio shows the best discharge rate capability.Charging rate was also found to have significant effect on cathode performance. Under high charging rate(1C,0.8C), cathode and active material have suffered irreversible damage and the capacity retention (0.1C) is lower than that at charging rate of 0.5C.The electrochemical impedance spectroscopy demonstrated that the higher the charging rate is, the higher surface diffusion impedance Li-ion shows.