Upcycling mixed spent polycrystalline layered oxide cathodes to single‑crystal NCM622 via a ternary eutectic salt strategy

Direct regeneration of mixed cathode materials remains challenging due to the lack of feasible separation techniques and the compositional/structural heterogeneity of degraded components. This study proposes a mixed upcycling regeneration (MUR) strategy aimed at converting mixed spent layered oxide cathodes into refreshed cathode material with uniform composition and consistent structure. By constructing a LiOH-Ni(OH) 2 -Na 2 SO 4 ternary eutectic-salt system, we successfully transform a mixture of spent polycrystalline LiNi 0.8 Co 0.1 Mn 0.1 O 2 (S-NCM811), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (S-NCM523) and LiCoO 2 (S-LCO) into single-crystalline LiNi 0.6 Co 0.2 Mn 0.2 O 2 (MUR-NCM622). This strategy achieves compositional homogenization and precise transition-metal compensation of the regenerated product in the molten-salt medium, while leveraging Ostwald ripening to accomplish the structural transformation from polycrystalline to single-crystalline. Notably, the introduction of Ni(OH) 2 not only compensates for the nickel loss of the spent cathode during cycling but also significantly reduces cation disorder in the regenerated product, thereby synergistically enhancing both compositional integrity and structural ordering. The regenerated single-crystalline MUR-NCM622 demonstrates a significant advantage in electrochemical stability over commercial polycrystalline NCM622 (PC-NCM622). This work provides a viable technical route for efficient and high-value recycling of complex mixed cathodes.