Surface atomic arrangement of primary particles through pre-oxidation to enhance the performance of LiNi0.8Co0.1Mn0.1O2 cathode materials

Abstract

The primary drawback of Ni-rich LiNixCoyMn1-x-yO2 (NCM, x ≥ 0.8) cathodes lies in their capacity and voltage fading, a phenomenon principally attributed to interfacial instability and intergranular cracks. This study introduces a simple pre-oxidation treatment to modify the grain boundary of LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode material as an efficient solution to these issues. Spectroscopic analysis and atomic-level imaging affirm that this pre-oxidation treatment facilitates both the conversion of Ni2+ to Ni3+ and the formation of an ordered NiOOH structure on the surface of precursor primary particles. Consequently, the final NCM811 product displays a distinct layered structure with a reduced degree of Li/Ni disorder. Furthermore, a rock-salt phase surface reconstruction layer is in-situ induced on the surface of NCM811 primary particles during the solid-state lithiation process, providing a protective coating against further degradation of the R3¯m-layered phase beneath it. Therefore, this enhanced NCM811 demonstrates superior structural stability regarding phase transition, cathode-electrolyte interface structure, and morphological integrity. When compared to bare NCM811 and modified NCM811 based on secondary particles, this enhanced NCM811 exhibits greater reversible capacity, superior initial coulombic efficiency, and excellent capacity retention. This study thus offers a promising approach to induce the ordered surface reconstruction of primary cathode particles, forming a conformal protective layer that improves electrochemical stability.