Upcycling of Air-Degraded Ni-Rich Cathodes via In Situ Surface Reconstruction

Ni-rich cathodes are well-known for their high specific capacity but require extremely dry conditions for prolonged storage due to their inherent sensitivity to tiny amounts of moisture in the atmosphere. Once LiOH/Li₂CO₃ is formed from exposure to moisture on the cathode surface, these impurities unavoidably obstruct Li insertion into/extraction out of bulk electrodes and simultaneously cause a further loss of the active Li source. In this work, we propose to convert the LiOH/Li₂CO₃ layer on spent NCM82 particles (S-NCM82) into a high-kinetic Li₃PO₄/LiF interphase via a simple phosphide reaction in aqueous LiPO₂F₂ solution. Meanwhile, such a conformal interphase prevents side reactions with electrolytes and alleviates structural strain during the service. The regenerated NCM82 electrode (R-NCM82) demonstrates a high specific capacity of 102 mAh/g at 5C, surpassing the 79 mAh/g observed in the pristine NCM82 (P-NCM82). Additionally, the R-NCM82//Gr full-cell exhibits 76% of its initial capacity after 300 cycles at 1C. This conversion process is easily scalable and could inspire the development of upcycling techniques for regenerating various spent electrodes.