Mitigating mechanical degradation of single-crystal Ni-rich LiNi0.72Co0.05Mn0.23O2 via surface Ta-rich gradient doping

Abstract

Single-crystal nickel-rich layered oxides, LiNi_xCo_yMn_1-x-yO₂ (SC-NCM, x ≥ 0.7), can effectively mitigate intergranular microcracks and parasitic reactions with the electrolyte commonly observed in polycrystalline cathodes. However, the large particle size of single crystals leads to issues such as structural mechanical degradation and sluggish lithium-ion diffusion kinetics. To overcome these challenges, we propose a surface-enriched ta gradient doping strategy in single-crystal LiNi_0.72Co_0.05Mn_0.23O₂, which promotes the in-situ formation of a perovskite-type LiTaO₃ surface layer, providing a stable interface for rapid lithium-ion migration. Benefiting from the synergistic effect of the LiTaO₃ layer and bulk Ta⁵⁺ doping, electrolyte corrosion and the detrimental surface H2-H3 phase transition are significantly suppressed, thereby reducing the formation of intragranular microcracks and mitigating the structural mechanical degradation of SC-NCM during cycling. As a result, the optimized Li(Ni_0.72Co_0.05Mn_0.23)_0.98Ta_0.02O₂ delivers a high discharge capacity of 195.1 mAh g⁻¹ at 0.1C and retains 85.5 % of its capacity after 200 cycles at 1C. This work provides a promising strategy to alleviate the structural mechanical degradation of SC-NCM cathodes.