Selective leaching process for efficient and rapid recycling of spent lithium iron phosphate batteries

Abstract

With the continuous development of new energy vehicles, the number of decommissioned lithium iron phosphate (LiFePO₄) batteries has been constantly increasing. Therefore, it is necessary to recover metal from spent LiFePO₄ batteries due to the high potential for environmental protection and high resource value. In this study, sodium persulfate (Na₂S₂O₈) was selected as the oxidant to regulate and control the oxidation state and proton activity of the leaching solution through its high oxidizing ability. Selective recovery of lithium from LiFePO₄ batteries was achieved by oxidizing LiFePO₄ to iron phosphate (FePO₄) during the leaching process. This paper reports an extensive investigation of the effects of various factors, including the acid concentration, initial volume fraction of the oxidant, reaction temperature, solid–liquid ratio, and reaction time, on lithium leaching. Li⁺ reached a high leaching rate of 93.3% within 5 minutes even at a low concentration of sulphuric acid (H₂SO₄), and high-purity lithium carbonate (Li₂CO₃) was obtained through impurity removal and precipitation reactions. In addition, the leaching mechanism was analysed by both X-ray diffraction and X-ray photoelectron spectroscopy characterization. The results show that the obtained high lithium-ion (Li⁺) leaching efficiency and fast Li⁺ leaching time can be ascribed to the superior oxidizing properties of Na₂S₂O₈ and the stability of the crystal structure of LiFePO₄ during the oxidative leaching process. The adopted method has significant advantages in terms of safety, efficiency and environmental protection, which are conducive to the sustainable development of lithium batteries.