Mitigating kinetic hindrance of single-crystal Ni-rich cathodes through morphology modulation, nickel reduction, and lithium vacancy generation achieved by terbium doping

Single crystallization has proven to be effective in enhancing the capacity and stability of Ni-rich LiNi_1−x−yCo_xMn_yO₂ (SNCM) cathode materials, particularly at high cut-off voltages. Nevertheless, the synthesis of high-quality single-crystal particles remains challenging because of severe particle agglomeration and irregular morphologies. Moreover, the limited kinetics of solid-phase Li⁺ diffusion pose a significant concern because of the extended diffusion path in large single-crystal particles. To address these challenges, we developed a Tb-doped single-crystal LiNi_0.83Co_0.11Mn_0.06O₂ (SNCM-Tb) cathode material using a straightforward mixed molten salt sintering process. The Tb-doped Ni-rich single crystals presented a quasi-spherical morphology, which is markedly different from those reported in previous studies. Tb⁴⁺ doping significantly enhanced the dynamic transport of Li⁺ ions in the layered oxide phase by reducing the Ni valence state and creating Li vacancies. A SNCM-Tb material with 1 at% Tb doping shows a Li⁺ diffusion coefficient up to more than 9 times higher than pristine SNCM in the non-diluted state. In situ X-ray diffraction analysis demonstrated a significantly facilitated H1-H2-H3 phase transition in the SNCM-Tb materials, thereby enhancing their rate capacity and structural stability. SNCM-Tb exhibited a reversible capacity of 186.9 mA h g⁻¹ at 5 C, retaining 94.6% capacity after 100 cycles at 0.5 C under a 4.5 V cut-off. Our study elucidates the Tb⁴⁺ doping mechanisms and proposes a scalable method for enhancing the performance of single-crystal Ni-rich NCM materials.