A closed process for recycling and re-synthesis of spent LiFePO4 cathode material

Complete material recycling is essential for a sustainable future. Herein, we report on the re-synthesis of LiFePO₄/C from spent lithium-iron-phosphate (LFP) cathode powder. After oxidative treatment of the spent LFP powder at 550 °C, the resulting material was dissolved quantitatively (99 %) in 60 wt.% H₃PO₄. Reactive oxygen microbubbles were employed to oxidize residual Fe(II) to Fe(III), before the recovery as FePO₄·2H₂O via hydrothermal synthesis. The H₃PO₄ was recovered from the mother liquor through solvent extraction using cyclohexanol, tributyl phosphate, and Escaid 110 as the organic phase. After water stripping and up-concentration, the recovered H₃PO₄ was used in subsequent cycles for treating spent LFP cathode powder. Lithium was recovered from the raffinate as Li₃PO₄ and successfully used with the recovered FePO₄·2H₂O for the solid-state re-synthesis of LiFePO₄/C. The re-synthesized LiFePO₄/C displayed the characteristic LFP two-phase transformation mechanism and excellent stability upon long-term cycling (94 % retention after 200 cycles at 1 C).