An integrated closed-loop process for high-value recovery of spent LiFePO₄ batteries via coupled acid leaching,...

To address the challenges of fragmented processes and low-value recovery of spent LiFePO₄ (SLFP) batteries, this study developed an integrated closed-loop process for the high-value recovery of mixed cathode and anode powders through acid leaching, oxidation, and extraction coupling. Under optimal conditions (4 mol L^-1 HCl, 60 °C), the simultaneous leaching efficiencies of Li, Fe, and P reached 99.96%, 99.93%, and 98.64%, respectively, while graphite was efficiently separated from the mixed powder. After oxidizing Fe(II) to Fe(III) in the leachate using H₂O₂, a trioctylamine (TOA)/n-Octanol/kerosene system (30 vol% TOA/20 vol% n-Octanol) was employed for selective extraction of Fe(III), achieving an extraction efficiency of 98.90% and a separation factor β_Fe/Cu of 531.44. Notably, n-Octanol acts as both a phase modifier and an anti-synergistic agent, suppressing impurity co-extraction and enhancing Fe selectivity. By constructing an innovative H₃PO₄/(NH₄)₂HPO₄ stripping system, coordination competition drove in-situ formation of battery-grade FePO₄·2H₂O (purity 99.67%). High-purity Li₃PO₄ (99.91%) was subsequently recovered from the raffinate after cyclic enrichment. Mechanistic analysis demonstrated an ion-pair association mechanism, in which Fe(III) forms [FeCl₄]^- and is subsequently bound by two protonated TOA molecules. The regenerated LiFePO₄ delivered an initial discharge capacity of 141.32 mAh g^-1 at 1 C, approaching that of commercial-grade materials. Meanwhile, the leaching residue retained an intact hexagonal graphite structure, providing a foundation for anode material regeneration. This integrated strategy offers a compact, high-value, and environmentally sustainable industrial pathway for holistic recycling SLFP batteries.