Stabilizing Spent LiCoO ₂ Through Interface Construction: A Sustainable Route to High‐Performance Cathode Regeneration

Abstract The large‐scale adoption of lithium‐ion batteries (LIBs) has intensified environmental burdens and resource depletion, creating urgent demands for sustainable regeneration of spent LiCoO 2 (LCO) cathodes. Structural degradation and Li + transport hindrance critically degrade their electrochemical performance. Here, a hydrothermal‐assisted surface doping strategy leveraging a NaOH‐Na 2 S 2 O 8 ‐MgCl 2 ternary system is developed to simultaneously induce controlled surface dissolution of spent LCO and construct a Li 0.96 Mg 0.04 CoO 2 surface solid‐solution layer, a targeted interface engineering approach for highly stable performance cathode regeneration. In‐ situ XRD and DFT calculations reveal that Mg 2+ preferentially occupies Li + sites via charge compensation, driving surface reconstruction from a detrimental spinel phase to a stable layered structure. This interface construction enhances structural stability and optimizes Li + diffusion kinetics by mitigating lattice strain and restoring ion transport pathways. The regenerated OR‐LCMO cathode achieves an initial discharge capacity of 170.2 mAh g −1 at 0.02 A g −1 and retains 93.13% capacity after 200 cycles in a full OR‐LCMO||graphite pouch cell (3.0–4.6 V, 1 A g −1 ). Economic analysis confirms cost and environmental benefits over conventional methods. This work presents a green, high‐value pathway for spent LCO regeneration via metal‐ion doping with interface engineering, providing universal insights for the sustainable upcycling of diverse battery cathode materials.