Tuning Li-excess to optimize Ni/Li exchange and improve stability of structure in LiNi_0.8Co_0.1Mn_0.1O₂ cathode material for lithium-ion batteries

Ni/Li exchange is a detrimental effect on electrochemical performances for high-Ni cathode materials (LiNi_xCo_yMn_zO₂, x ≥ 0.6). Adjusting Li-excess degree has been proved to be an effective way to optimize Ni/Li exchange in the materials. However, until now, how the Ni/Li exchange and thus the structural properties is affected by the Li-excess has not been understood and clearly elucidated in the literature. Herein, a feasible strategy is utilized to optimize Ni/Li exchange and the amount of anti-Li⁺ in LiNi_0.8Co_0.1Mn_0.1O₂ by mixing Ni_0.8Co_0.1Mn_0.1(OH)₂ precursor with different amounts of lithium sources during lithiation. It was found that morphology and phase stability of the material can be tuned with moderate excessive lithium. With 10% Li-excess, LiNi_0.8Co_0.1Mn_0.1O₂ exhibits an initial discharge capacity of 211.5 mAh·g^–1 at 0.1 C and maintains 93.3% of its initial capacity after 100 cycles at 1 C. Different technologies were used to characterize the materials and it shows that the formation of broader Li slab space, decreased anti-Ni²⁺ in Li layer, and gradient distribution of Ni³⁺ in the surface is contributed to moderate Li-excess in the materials. Broader Li slab space facilitates diffusion of Li⁺, decreased antisite-Ni²⁺ and gradient distribution of Ni³⁺ in materials surfaces optimizes the Ni/Li exchange. Based on these results, we thus believe that it is the moderate Li-excess in material that optimized the electrochemical performance of high-Ni cathode materials.