Upcycling Degraded LiNi_0.5Co_0.2Mn_0.3O₂ to Highly Stable Single-Crystalline Cathode Materials through Molten Salt-Assisted Reconstruction

The rapid decommissioning of lithium-ion batteries (LIBs) has spurred the development of green recycling strategies that can restore degraded cathode materials. Direct regeneration is particularly challenging for spent LiNi0.5Co0.2Mn0.3O2 (NCM523) due to severe lithium deficiency and structural collapse. Here, we report an efficient molten salt-assisted reconstruction strategy to transform degraded NCM523 to highly stable single-crystalline cathode materials for LIBs. A LiOH-LiNO3 eutectic system with 0.5 mol % Al2O3 additive was used to regenerate degraded NCM523 during heat treatment. The inorganic molten salts create a liquid phase environment and speed up the reaction kinetics, which can simultaneously achieve stoichiometric lithium compensation and the formation of single-crystalline Al-doped NCM523 cathodes. The Al-doped NCM523 sample delivers a discharge capacity of 151.8 mAh g–1 at 0.2C and maintains 96.2 mAh g–1 at 5C, significantly outperforming the undoped counterpart (84.6 mAh g–1). After 200 cycles at 1C, it retains 89.4% of its initial capacity. In situ X-ray diffraction confirms that Al3+ doping suppresses lattice distortion, while density functional theory (DFT) calculations indicate that Al3+ preferentially substitutes Co sites, strengthening Al–O bonding and enhancing oxygen framework stability. This work offers an effective and scalable route for the high-value regeneration of spent LIB cathodes.