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

Abstract

• Complete material recycling of spent LiFePO 4 cathode material. • Leaching efficiencies of 99 % for both iron and lithium with H 3 PO 4 . • Re -synthesis of LiFePO 4 /C from recovered FePO 4 ·2H 2 O and LiPO 4 . • Closed-loop recycling of auxiliary materials by solvent extraction. Complete material recycling is essential for a sustainable future. Herein, we report on the re-synthesis of LiFePO 4 /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.% H 3 PO 4 . Reactive oxygen microbubbles were employed to oxidize residual Fe(II) to Fe(III), before the recovery as FePO 4 ·2H 2 O via hydrothermal synthesis. The H 3 PO 4 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 H 3 PO 4 was used in subsequent cycles for treating spent LFP cathode powder. Lithium was recovered from the raffinate as Li 3 PO 4 and successfully used with the recovered FePO 4 ·2H 2 O for the solid-state re-synthesis of LiFePO 4 /C. The re-synthesized LiFePO 4 /C displayed the characteristic LFP two-phase transformation mechanism and excellent stability upon long-term cycling (94 % retention after 200 cycles at 1 C).