Defect‐Driven Upcycling of Spent NCM With Tailored Oxygen Vacancies Toward Great Energy‐Storage Properties

ABSTRACT Captured by economic and environmental values, direct regeneration of spent NCM (SNCM) has been regarded as a next‐generation recycling strategy. To meet the demand of commercial applications, solid‐state Li‐replenishing methods have been explored, but the as‐regenerated samples still suffer from uneven Li distribution and inferior crystalline phase. Herein, through controlling oxygen vacancies (OVs) concentrations, SNCM is successfully upcycled into high‐performance NCM, displaying uniform Li distribution and significant phase traits. And, the structural strain is obviously reduced; meanwhile, the conductivity is increased by ∼20%. Moreover, its Li‐ion diffusion energy barrier is reduced from 0.43 to 0.29 eV, and the lowered formation energy brings about improvements in lattice structure stability. The as‐optimized samples exhibited high‐capacity retention of 91.3% at 1.0C and 76.0% at 5.0C, 94.1% capacity retention at 1.0C for full‐cells. Supported by kinetics analysis and ex situ measurements, the charge transfer is accelerated, and the structural stability is guaranteed with low internal strain distribution and local element balance during cycling. More inspiringly, this upcycling method could be extended to spent NCM613, Ni65, and NCM811. Given this, this work is expected to shed light on the controlling mechanism of OVs in solid‐state reaction, whilst providing upcycling strategies for SNCM.