Investigation of surface engineering on single-crystal NCM613 cathode through Eu2O3 coating to enhance performances

Abstract

The medium- and high-nickel layered cathode material LiNi_xCo_yMn_zO₂ (x+y+z = 1, x ≥ 0.5) has garnered significant research attention due to its high capacity and low cost. However, high-nickel ternary materials inevitably suffer from issues such as Li⁺/Ni²⁺ cation mixing, poor cycling stability, and inferior thermal stability. Even for medium-nickel ternary materials, enhancing specific capacity by increasing the charging cutoff voltage, they also undergo irreversible phase transformation when subjected to high-voltage conditions, leading to capacity degradation. In this study, single-crystal LiNi_0.6Co_0.1Mn_0.3O₂ (NCM613) cathode material is synthesized via the molten salt method, and Eu₂O₃ coating layers with varying amounts are introduced to investigate their effects on electrochemical performance. Electrochemical tests conducted at 25 °C within an operating voltage spanning from 2.75 to 4.5 V demonstrated that the 1 wt% coated material exhibits optimal discharge specific capacity of 181.39 mAh/g at 0.1 C current density, as well as improves the cyclic performance by about 5% and shows excellent rate performance. The influence of the structure, morphology, and surface characteristics of the coating layers on the electrochemical and kinetic properties of the material are studied by XRD, SEM, TEM, XPS, and EIS. Furthermore, SEM characterization after 500 cycles reveals that the coated material can effectively inhibit material breakage. In conclusion, the incorporation of Eu₂O₃ as a surface coating demonstrates significant enhancement in the electrochemical behavior of single-crystal NCM613 cathode material.