Hydrothermal co-upcycling of mixed LiFePO4 and LiMn2O4 waste: From mechanistic insights to high-energy LiMnxFe1-xPO4 cathodes

The escalating accumulation of spent lithium ion batteries has rendered efficient and profitable recycling imperative, yet current technologies are challenged by complex metal separation and poor economic returns for low value cathodes such as LiFePO 4 and LiMn 2 O 4 . To address this, a synergistic direct upcycling strategy is proposed to convert these two waste streams into high value LiMn x Fe 1-x PO 4 cathodes via a hydrothermal route. The resulting regenerated LMFP delivers an initial capacity of 140.0 mAh·g −1 (1C) and gradually increases to 149 mAh·g −1 over the first 100 cycles. After 500 cycles, the capacity maintains at 140.6 mAh·g −1 , with comprehensive kinetic evaluations further demonstrating outstanding reaction reversibility and substantially reduced phase transition impedance compared to commercial counterparts. Density functional theory calculations were performed to understand the thermodynamic mechanism of the observed performance. The results indicate that oxalic acid selectively stabilizes Mn/Fe trioxalate complexes, while transition metals are effectively separated from lithium and impurities. XRD refinement and SEM show that the material possesses a highly ordered olivine lattice structure and exhibits a microspherical morphology, which together endow it with excellent rate performance and long-term cycling stability. This work establishes a compelling, closed loop paradigm for upcycling multicomponent battery waste into next generation, high energy density cathodes.