From Delithiated Residues to High-Performance LiMn _0.4 Fe _0.6 PO ₄ through Structural Inheritance and F-Doping toward Upcycling of Spent Lithium-Ion Batteries

The sustainable upcycling of delithiated FePO 4 and MnO 2 residues from spent lithium-ion batteries (LIBs) is challenged by fluoride cross-contamination, crystalline incompatibility, and low economic value. Herein, a direct mechanochemical regeneration strategy is proposed to convert FePO 4 and MnO 2 into high-performance F-doped LiMn 0.4 Fe 0.6 PO 4, featuring the structurally inherited robust olivine framework of FePO 4, defect-enabled homogeneous Mn incorporation from MnO 2, and stabilized Mn/Fe–O bonding network through F-doping. As a result, the optimized material delivers a high capacity of 136.76 mAh g –1 at 1 C with 89.74% retention after 600 cycles and 118.74 mAh g –1 at 10 C. Mechanistic analyses reveal that defect-mediated Mn/Fe intermixing and F-doping synergistically suppress Jahn–Teller distortion, enhance structural stability, and improve Li + diffusion. Technoeconomic and environmental assessments suggest the well-round efficiency of the upcycling route with elucidated structural evolution of LiMn x Fe 1– x PO 4 (LMFP) and functional modification of the F element, thereby establishing a practical candidate toward sustainable upcycling of spent LIBs.