Mechanisms for enhancing the properties of LiNi0.5Co0.2Mn0.3O2 by Perovskite-type oxides containing lanthanum coating

LaNi_0.5Co_0.5O₃-coated LiNi_0.5Co_0.2Mn_0.3O₂ (NCM523) was synthesized by a high temperature solid-state method with La₂O₃ serving as the lanthanum source. The findings suggest that the surface coating does not affect the crystal form and surface morphology of NCM523 particles. However, it can improve the cathode's rate performance and cycle stability. When the ratio of lanthanum source (molar fraction) is 1%, the best coating amount is obtained: the discharge specific capacities at 0.1 C and 4 C are 174.0 and 139.1mAh·g^-1 respectively, which are higher than those of the original 166.8, 117.2mAh·g^-1, and the capacity retention rate improved from 81.2% to 90.9% after 120 cycles at 1 C. Several factors contribute to enhanced properties of the coated LiNi_0.5Co_0.2Mn_0.3O₂ cathode material: Firstly, the coating treatment can elevate the content of Ni³⁺ in the cathode and minimize the Li⁺/Ni²⁺ mixing, thus stabilizing the layered structure of the cathode material. Second, synthesizing the coating layer can effectively reduce the interface resistance of the cathode, which is beneficial to lithium-ion transportation in the layered structure and decreases the polarization. Finally, the coating layer mitigates the erosion of electrolytes on the electrode surface, while maintaining the stability of the crystal structure of NCM523 during charging-discharging cycling, thus enhancing the cyclic stability of the cathode.