Direct upcycling of leached FePO${}_4$ from spent lithium-ion batteries toward gradient-doped LiMn${}_x$Fe${}_{1-x}$PO${}_4$ cathode material

Lithium-ion batteries (LIBs) with LiFePO${}_4$ (LFP) cathode materials have occupied a significant market share in state-of-the-art power storage systems and electric vehicles, yet the approaching "retiring wave" of these LIBs should be appropriately treated (i.e., recycling of spent LIBs). Current recycling strategies of degraded LFP materials largely direct on leaching of lithium elements, leaving the leached FePO${}_4$ residual as a waste. Inspiringly, LiMn${}_x$Fe${}_{1-x}$PO${}_4$ material is considered one of the potential candidates for next-generation cathode materials because of its high electrochemical performance, extraordinary stability, and low cost. Herein, the direct upcycling of leached FePO${}_4$ toward LiMn${}_{0.25}$Fe${}_{0.75}$PO${}_4$ (LMFP) cathode material is demonstrated via a green, simple, and scalable mechanochemical pathway. The product features a gradient-doping of Mn, as well as a uniform carbon coating for LMFP particles. As a result, the LMFP cathode material delivers superior electrochemical performance; the capacity (161.3 mA h g${}^{-1}$ at 0.1 C), rate capability (90.1 mA h g${}^{-1}$ at 5 C), cycling stability (95.6% capacity retention after 800 cycles at 1 C), and energy density (≈15% increase as compared to LFP) are almost comparable with those of fresh materials. The as-established upcycling protocol offers a favorable reuse method for leached FePO${}_4$ materials. (© 2023 Wiley‐VCH GmbH)