Direct regeneration method of spent LiNi1/3Co1/3Mn1/3O2 cathode materials via surface lithium residues

Abstract

With the increasing quantity of spent lithium-ion batteries, their recycling problem has become an urgent issue for the economics of such batteries and for the protection of environment. In this study, we proposed a novel green method for the recycling of spent single-crystal LiNi_xCo_yMn_1−x−yO₂ (NCM) materials. No additional compounds were induced during the direct calcination process to acquire regenerated cathode materials. The surface lithium compounds residues could be fully reutilized combined with an over-discharging pre-treatment, which allowed them to serve as a lithium supplement for the reconstruction of the NCM crystal structure and for the promotion of its electrochemical performance. Via this method, the electrochemical performance of spent cathode materials could be enhanced distinctly and the lithium contents could be reused with high efficiency to alleviate resource shortages. Lithium vacancies were replenished with the decomposition of surficial lithium impurities, and the regenerated NCM exhibited improved cycling stability (129.1 mA h g⁻¹ at 0.5C after 200 cycles) with a well-ordered layered structure compared with spent NCM. Further, the composition and structure evolution of the spent NCM during the regeneration process was also investigated comprehensively combined with in situ XRD characterization. The layered structure of spent NCM remained unchanged, and the regenerated NCM showed bigger lattice parameters, confirming the lithium transmission to reconstruct the lattice structure occurred without phase transformation during the calcination process. This research both provides a new insight into the regeneration mechanism of spent cathode materials and the possibility to recycle spent cathode materials greenly with lower energy consumption than from manufacturing virgin NCM materials.