Homogenizing phase–component regeneration of spent NCM811 into single-crystal NCM622 with enhanced structural and electrochemical stability

Capturing the great economic and environmental value, the recycling of spent batteries has been devoted to numerous attentions. As a cost-effective and energy-efficient approach, direct regeneration has attracted considerable attention in recent years in the field of sustainable lithium-ion battery recycling. However, the practical application of direct regeneration to spent high-nickel cathodes is still limited due to multiphase complexity and severe structural degradation. Herein, the homogenizing phase-components regeneration (HPCR) was proposed, achieving the transformation from spent polycrystalline NCM811 to single-crystal NCM622 with enhanced structural and electrochemical stability, which simultaneously solved the issues above. Through controlled high-temperature sintering and element rebalancing, uniform particle morphology, reduced Li/Ni disorder, and suppressed oxygen vacancies are achieved. The regenerated cathode delivers a capacity of 163.0 mAh g⁻¹ with 93.9 % retention after 100 cycles at 1.0 C, meeting the demand of commercial systems. Density functional theory and electrochemical analysis reveal that minimized defect concentrations promote Li⁺ diffusion and structural integrity. Significantly, the growth mechanism from NCM811 towards NCM622 was disclosed, showing the clear phase transformation and vital elements diffusion process. Overall, this work provides an effective and scalable strategy for the homogeneous regeneration of spent NCM811, supported by a clearly revealed regeneration mechanism.