High‐Voltage Upcycling of Spent Ni‐Rich Cathodes Enabled by Spatially Decoupled Bulk–Interphase Stabilization

ABSTRACT

The capacity of spent polycrystalline LiNi _0.8 Co _0.1 Mn _0.1 O ₂ cathodes (SNCM) can be restored through direct regeneration. However, high‐voltage durability is frequently curtailed by the coupled evolution of bulk lattice‐oxygen destabilization, and interfacial parasitic reactions. Here, molten‐salt‐mediated upcycling strategy is developed to reconstruct SNCM into a Mg/Nb‐modulated single‐crystal cathode (RNCM‐NM), achieving spatially decoupled bulk–interphase stabilization through the in situ incorporation of functional cations and reconfiguration of the interphase within a single molten‐salt medium. The interslab framework is stabilized by Mg‐induced Li‐layer pillaring. As revealed by in situ X‐ray diffraction, H2→H3 phase transition and its associated lattice distortion are alleviated during deep delithiation. Concurrently, a Nb‐derived LiNbO ₃ interphase is formed via surface Nb enrichment, providing Li ⁺ ‐conductive yet electronically insulating interfacial passivation that mitigates interfacial parasitic reactions at high voltage. At a 4.5 V cutoff, lattice‐oxygen stability, and the transition‐metal–oxygen coordination environment are reinforced through synergistic bulk pillaring and interphase passivation, as supported by X‐ray absorption spectroscopy and density functional theory. A discharge capacity of 191.7 mAh g ^{− 1} is delivered at 1 C with 82.5% retention after 300 cycles, while a capacity of 166.3 mAh g ^{− 1} is maintained at 10 C. Overall, durable high‐voltage cycling is enabled by spatially decoupled bulk–interphase stabilization, advancing regenerated Ni‐rich cathodes toward practical reuse.