Synthesis And Modification Study Of Lithium Ion Battery Cathode Material LiNi_0.5Co_0.2Mn_0.3O₂

As a conventional cathode material for battery applications, LiFePO₄ has reached its performance ceiling nowadays. A new generation of lithium-ion batteries material with higher energy density, longer cycling life, higher charge-discharge rate and more safety is in urgent need. LiNi_0.5Co_0.2Mn_0.3O₂ cathode material affracted much attention by virtue of its low cost, high capacity and low toxicity, but its cycling stability and rate performance are relatively poor limiting its application and development. In the article, we concentrate our interest on the cycling stability and rate performance improvements of LiNi_0.5Co_0.2Mn_0.3O₂ materials. The various methods such as XRD, TEM, SEM and TG have been utilized to inspect the compositions and microstructures of these materials. What’s more, cycling test, CV and EIS were also used to examine the electrochemical performance of those mentioned materials.Firstly, we explored the synthetical conditions of LiNi_0.5Co_0.2Mn_0.3O₂ material, studied the influence of stirring speed, reaction pH and calcination temperature on the structure and electrochemical properties of the material. Under such conditions, which are at mediun-high stirring speed, pH of 7.8⁸.0 and calcining at 800 ℃, the material delievers the best electrochemical performance.Secondly, we synthesised LiNi_0.5Co_0.2Mn_0.3O₂ material under the above optimum conditions and discussed the impact of doping of Zn with different transition metal sites on its properties. XRD pattern shows that the material doped with 2 % of Zn has more orderly layered structure with weakened the degree of cation mixing to some extent, of which the Mn-doped has the most stable structure. Under charge-discharge rate of 0.5 C, initial Coulombic efficiency of Zn2+ doped samples can reach 84%, the initial discharge capacity can reach 156 mAh·g^-1, and the capacity retention is 91% after 50 cycles, Ni-doped material enhances the least and Mn-doped material enhances the best in electrochemical performance.Finally, we studied the effects of Arabic gum on the structure and properties of LiNi_0.5Co_0.2Mn_0.3O₂ materials. We firstly synthesized the LiNi_0.5Co_0.2Mn_0.3O₂ materials via coprecipitation method with Acacia gum. By analyzing its XRD and SEM, we find that samples with Arabic gum added have lower mixed cationic degree, higher degree of crystallization and more ordered hexagonal layered structure. The adding of Arabic gum makes the materials a narrower particle size range, smaller particle size and larger specific surface area, which are conducive to the diffusion of lithium-ion. Under charge-discharge rate of 0.5C, the initial Coulombic efficiency can reach more than 84%, the initial discharge capacity can reach 164 mAh·g^-1 or more, and further the capacity retention is 87.5 % after 100 cycles, the capacity can reach 131.7 mAh·g^-1even at current densities of 5 C. The characterization of cyclic voltammetry and AC impedance also fully demonstrates its characteristics.