Surface Segregation-Assisted Direct Regeneration of Spent Layer Cathodes.

Direct regeneration has emerged as a promising approach, owing to its economic and environmental advantages. However, the efficiency of lithium replenishment and phase reconstruction-the core steps in the regeneration process-is critically hindered by the inert rock-salt phase of spent cathode materials. Herein, we propose a segregation-assisted regeneration strategy that leverages the segregation behavior of high-valence elements to regulate reaction thermodynamics during the regeneration process, thereby preferentially inducing the in situ transformation of the NiO-type rock-salt phase. This transformation facilitates Li-ion diffusion, accelerates the reconstruction of the layered structure, and enhances the overall structural stability. As proof of concept, tungsten (W6+) is introduced into the regeneration process of spent LiNi0.5Co0.2Mn0.3O2 (NCM523) cathodes, leading to the formation of Li-W-Ni-O compounds and Li2WO4, which collectively facilitate the direct regeneration of the degraded material. The regenerated NCM523 delivers a high reversible capacity of 150 mAh g-1 at 0.5 C, outperforming commercial counterparts, and retains 83% of its capacity after 800 cycles in a 1.1 Ah pouch cell. Moreover, this strategy demonstrates broad applicability to other degraded layered cathode materials, including LiNi0.6Co0.2Mn0.2O2 and LiNi0.8Co0.1Mn0.1O2. This work provides a scalable, energy-efficient, and sustainable route for regenerating spent cathodes.