A high-temperature oxidation strategy for the safe and efficient recovery of lithium and iron from spent LiFePO4 cathode

Abstract

The growing demand for sustainable recycling of spent lithium-ion batteries necessitates environmentally friendly processes for the efficient recovery of valuable metals. Herein, we present a green and facile strategy that integrates high-temperature oxidation with phosphoric acid leaching to recover α-Fe₂O₃ and Li₃PO₄ from spent lithium iron phosphate (LiFePO₄) batteries. The process involves dismantling, followed by oxidation of the cathode material at 600 °C under O₂ to remove impurities and oxidize Fe²⁺ to Fe³⁺, and subsequent leaching with 2 mol per L H₃PO₄ (liquid-to-solid ratio of 10 : 1, 60 °C, 4 h). Subsequent pH adjustment to 6 precipitates Fe³⁺, and the residue is mixed with NH₄H₂PO₄ and calcined at 700 °C to yield α-Fe₂O₃. The filtrate is concentrated and adjusted to pH 12 to precipitate Li₃PO₄. Comprehensive characterization confirms the morphology, phase purity, and magnetic properties of the obtained products. The α-Fe₂O₃ consists of uniform quasi-spherical particles (∼90 nm) with a purity of 96.27% and a recovery yield of 91.38%, while Li₃PO₄ forms hexagonal prismatic crystals (1–2 µm) with 94.58% purity and 92.53% yield. Magnetic measurements show a remnant magnetization of 0.001 emu g⁻¹ and coercivity of 10.39 Oe at low temperature, and 0.10 emu g⁻¹ and 1072.8 Oe at room temperature for α-Fe₂O₃. This pH-gradient separation approach provides a robust, low-cost pathway for valorizing spent LiFePO₄ batteries, advancing circular economy principles and mitigating environmental impacts of electronic waste.