Surface Spin-State Manipulation via a Strong Electronegative Ligand Field Enables Direct Regeneration of Spent Lithium-Ion Battery Cathodes

The rapid growth of lithium-ion batteries has intensified the need for efficient recycling of spent LiNi_0.5Co_0.2Mn_0.3O₂ (NCM) cathodes. However, direct regeneration is hindered by the high-spin state of Ni²⁺ (S = 1) in degraded surface structures, which impedes Li⁺ intercalation and limits repair efficiency. Here, we introduce a strong electronegative ligand field to modulate the surface NiO₆ coordination environment, enabling precise regulation of Ni spin state and electronic structure. This strategy alters the occupancy of Ni e_g orbitals, converting high-spin Ni²⁺ (t_2g⁶e_g², S = 1) to low-spin Ni³⁺ (t_2g⁶e_g¹, S = 1/2) while downshifting the Ni d-band center. The resulting electronic reconfiguration weakens Ni-Li interactions, enabling efficient lithiation and regeneration of the degraded NCM black mass. The regenerated cathode, when assembled into pouch cells, exhibits Ah-level capacity with electrochemical performance comparable to commercial counterparts. This work establishes a direct correlation between Li⁺ transport kinetics and the Ni spin-state regulation, offering a new chemical paradigm for the direct regeneration of degraded cathodes.