Engineering Residual Rock‐Salt Reconstruction through Near‐Surface Fluorine Regulation for Stable 4.6 V Cycling of Regenerated Spent Layered Oxide Cathodes

ABSTRACT Direct regeneration enables high‐value recovery of spent layered oxide cathodes, but their high‐voltage reuse requires stabilization of both regenerated surface and lattice oxygen beyond bulk compositional restoration. Here, we report a high‐voltage upcycling strategy for spent LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM) based on near‐surface fluorine (F) regulation of residual rock‐salt layers. Molten‐salt relithiation recovers Li content and layered bulk framework, whereas subsequent fluorine treatment converts the remaining inert surface reconstruction into a thin F‐enriched rock‐salt interphase. Rather than impeding Li + transport, this interphase stabilizes the reconstructed surface, reduces oxygen defects, and mitigates electrolyte‐induced interfacial degradation. The resulting cathode with F‐enriched rock‐salt surface (RFNCM) delivers 208.7 mAh g −1 at 0.1 C within 3.0‐4.6 V, and retains 80.28% capacity after 400 cycles at 1 C and 25°C, and 80.93% after 200 cycles at 50°C. In situ X‐ray diffraction and gas‐evolution measurements reveal more homogeneous high‐voltage structural evolution and suppressed oxygen release, respectively. According to analysis results of XPS, in situ Raman and Density functional theory calculations, these improvements can be attributed to strengthened Ni─O interactions and increased oxygen‐vacancy formation energies after fluorine incorporation. This work converts an unavoidable reconstruction product into a protective interphase for high‐voltage reuse of spent layered oxide cathodes.