Unified Upcycling of Degraded LiFePO4 Materials toward a High-Performance LiMn0.25Fe0.75PO4 Cathode for High-Voltage Lithium-Ion Batteries

The approaching “decommissioning wave” of lithium-ion batteries (LIBs) has posed the efficient recycling of degraded electrode materials as a major challenge, among which the green and low-cost treatment of spent LiFePO4 (LFP) cathodes with mixed degrees of degradation is of particular complexity. Presently, the prevailing hydrometallurgical method is designed to extract lithium from degraded LFP (D-LFP) materials, while the FePO4 (FP) residues are largely neglected. Herein, we demonstrate a unified upcycling strategy to manage those D-LFP materials by directly transforming the leached FP materials after complete lithium extraction of D-LFP into high-voltage LiMn0.25Fe0.75PO4 (LMFP) materials through a sequential hydrothermal and solid-state sintering treatment. The LMFP product features with a uniform particle size (220 nm) together with a homogeneous Fe/Mn distribution, which is remarkably beneficial for the electrochemical performance. As a result, the as-upcycled LMFP delivers a high discharge capacity (162.7 mAh g–1 at 0.1 C), a high capacity retention rate (97.5% after 800 cycles at 1 C), and a notable improvement in energy density (14.34%) compared with LFP materials. This simple and scalable workflow provides a refined route for the regeneration of D-LFP and is promising for dealing with large-scale spent LIBs.