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).