Regeneration of spent NCM622: reconstructing the rich lattice oxygen surface for enhanced stability†

Abstract

Attracted by the economic and environmental value, the direct regeneration of spent Ni–Co–Mn oxides has captured plenty of attention. However, considering the low bonding energy of metal–oxygen, F-elements from binders and LiPF₆ can be introduced into the bulk phase of regenerated samples, resulting in poor electrochemical properties. Herein, supported by CaO powders, regenerated cathodes were successfully obtained through the formation and removal of CaF₂. By tailoring thermal sintering, the as-optimized sample exhibited a smooth surface and an intact morphology/lattice structure. More importantly, benefitting from the formation of oxygen vacancies, a rich oxygen-lattice surface/near-surface was established, exhibiting high stability. As a Li-storage cathode, the as-optimized samples delivered a capacity of 149.7 mA h g⁻¹. The retention ratio remained at approximately 96.3% after 150 loops at 1.0 C. Even at 5.0 C, the capacity reached 134.1 mA h g⁻¹, maintaining ∼84.7% retention after 300 cycles. Detailed kinetic behaviors analysis indicated an improved diffusion coefficient and reduced interfacial resistance, accompanied by a reduction in the voltage gap. Moreover, in situ resistance analysis revealed that stable charge-transfer resistance further alleviated internal stress variation. Thus, this study is expected to illustrate the regeneration process of spent Ni–Co–Mn oxides after the successful removal of F-impurities.