Dual roles of Dy in nickel-rich layered LiNi0.6Mn0.2Co0.2O2: Synergistic mechanisms of Fermi level state regulation and enhancement of cationic ordering

Abstract

The urgent demand from society for lithium-ion batteries necessitates the research of high-performance and high-stability cathode materials. Although the high nickel material has a high theoretical capacity, its stability has hindered the commercialization progress. In this work, we propose a new strategy guided by theory. By doping NCM622 with rare earth elements that possess high-energy d-level and f-level electrons and high charge density, it is theoretically possible to contribute more electronic states near the Fermi level, thereby enhancing the internal electronic conductivity of the material. This strategy not only increases the energy density but also inhibits the Li/Ni mixing and improves the cycle stability of the battery. The 1/24 Dy-doped NCM622 exhibits metallic conductors in both R_3m and monoclinic C2/m space groups, and thus has better electrical conductivity. The results of XRD refinement show that the Li/Ni mixture is effectively inhibited. Electrochemical data confirmed that the material can reach the ultra-high capacity of 210.8 mAh g⁻¹ at 0.1 C, and can still have 87.1 % energy residual after 300 cycles. The excellent electrochemical performance also depends on the synthesis optimization of the pure phase materials that we have explored using the orthogonal method. This study provides theoretical guidance for the application of rare-earth elements in high-nickel materials.