The Alchemy of Two Degraded Cathodes: Synergistic Surface‐Bulk Upcycling for Degraded NCM Materials by Leached LiFePO ₄

Abstract The enormous growth in the number of spent lithium‐ion batteries (LIBs) poses significant challenges for both environmental conservation and resource management. The efficient and sustainable recycling of diverse degraded cathode materials is a central focus because of their high cost and technical complexity, yet present approaches are energy‐intensive or produce hazardous by‐products. Herein, we propose a simple and green upcycling strategy for degraded NCM 622 (LiNi _0.6 Co _0.2 Mn _0.2 O ₂ ) cathode by using leached LiFePO ₄ material as a functional dopant. This dual anion/cation doping practice effectively achieves elemental compensation, particle size refinement, and surface‐bulk structure optimization for NCM 622 material. Therefore, the upcycled material exhibits high specific capacity (176.18 mAh g ⁻¹ at 0.1 C), excellent rate performance (125.48 mAh g ⁻¹ at 10 C), and superior cycling stability (85.92% capacity retention after 200 cycles at 1 C and 81.20% capacity retention after 300 cycles at 5 C). This strategy not only enables high‐value utilizations of both degraded LiFePO ₄ and NCM 622 materials but also facilitates a paradigm shift for recycling of spent LIBs from structural restoration to performance improvement, which may offer a promising pathway toward a low‐energy, high‐value closed‐loop recycling system.