Direct Regeneration of Degraded High‐Nickel Layered Cathode with a Grain‐Growth Inhibitor by Epitaxial Boundaries

Abstract The direct regeneration of degraded cathode materials for lithium‐ion batteries holds significant promise for closed‐loop recycling. However, fully recovering the structure and performance of degraded LiNi _x Co _y Mn _z O ₂ (NCM) cathodes remains a significant challenge, limiting its practical applications. Here, this study uncovers that the regrowth of primary grains is a critical factor leading to microstructural rearrangement and grain boundary reformation, which compromises the performance of regenerated polycrystalline NCM materials. Therefore, to inhibit excessive grain growth, an epitaxial Li ₃ Ni ₂ NbO ₆ grain boundary is successfully incorporated into the regenerated NCM (Nb‐R‐NCM) through a niobium (Nb)‐assisted eutectic method, which preserves structural integrity and minimizes cationic disorder. Additionally, the Li ₃ Ni ₂ NbO ₆ epitaxial layer relieves internal strains of NCM, thereby mitigating the lattice expansion and contraction during charging and discharging processes. All these are conducive to the high‐voltage stability of Nb‐R‐NCM. As expected, it demonstrates a high capacity of 183.13 mAh g⁻¹ at 0.1 C comparable to commercial NCM materials, and even maintains stable cycling with 83.4% retention over 300 cycles at 1C in the voltage range of 3.0–4.5 V. This work presents a constructive approach for the direct regeneration of ternary cathode materials, paving the way for enhanced practicality and performance in sustainable energy applications.