Sustainable Upcycling of Spent LiCoO₂ Toward High-Stability NCM Cathode via Eutectic Molten Salt Synthesis

Spent LiCoO₂ (S-LCO) cathode materials from retired lithium-ion batteries (LIBs) pose severe environmental threats and represent a noteworthy waste of strategic resources. The emerging regeneration/upcycling approach for S-LCO mainly adopts solid-state treatment, showing significant potential of short-range, high-efficient reactivation of S-LCO materials. Yet it suffers from the complex pre-determination of lithium content as well as the varying degradation degrees of S-LCO materials from different batches of retired LIBs. Meanwhile, the cost-effective ternary layered oxides have become the mainstream cathode materials for LIBs due to the rapid popularization of electric vehicles. Herein, we use a LiOH-LiNO₃ eutectic molten salt as the reaction medium to upcycle S-LCO for single-crystalline LiNi_1/3Co_1/3Mn_1/3O₂ (NCM111) cathode materials. The molten salt treatment not only achieves self-saturating relithiation and direct transformation of S-LCO toward stoichiometric NCM111 materials but also rejuvenates the product with structural and compositional integrity for outstanding electrochemical performance. The product delivers a specific capacity of 161.6 mAh g^-1 at 0.1 C and a 92.4% capacity retention after 200 cycles at 1 C, outperforming those of commercial NCM111 materials. This study provides a simple, green, and scalable approach for handling those S-LCO materials, suggesting a sustainable and transformative solution for recycling retired LIBs.