Pre-oxidizing the precursors of Nickel-rich cathode materials to regulate their Li⁺/Ni²⁺ cation ordering towards cyclability improvements

Layered Nickel-rich cathode materials (LiNi_0.8Co_0.1Mn_0.1O₂) with high Ni content attract much attention of public owing to their higher specific capacity compared with LiCoO₂. However, the rapid capacity fading hinders the commercialization of LiNi_0.8Co_0.1Mn_0.1O₂. The severe Li⁺/Ni²⁺ mixing, which should become more serious with higher Ni content, is one of the main reasons for poor cycling stability. In this paper, we synthesize LiNi_0.8Co_0.1Mn_0.1O₂ under air atmosphere with an additional pre-oxidization process using nitrates. X-ray powder diffraction and Rietveld refinement reveal that the pre-oxidization treated Nickel-rich cathode material shows lower Li⁺/Ni²⁺ mixing degree, which is also supported by the incremental ratio of Ni³⁺/Ni²⁺ obtained from the X-ray photoelectron spectroscopy results. The electrochemical tests show that the pre-oxidization treated Nickel-rich cathode material exhibits superior cycle performance; after 100 cycles, the capacity retention is improved from 79.04% to 90.73% with the pre-oxidization treatment, and the corresponding Nyquist plots exhibits sharply declined impedance. The promoted electrochemical properties are owed to decreased charge transfer and more ordered cation arrangement, which is benefit from the pre-oxidization treatment that induces the increased content of Ni³⁺. Hence, it is concluded that the pre-oxidization process can regulate the Li⁺/Ni²⁺ cation ordering to improve the cycling stability of layered Ni-rich materials.