Mechanism of selective lithium extraction from spent LiFePO₄ cathodes in oxidizing alkaline leaching system

Lithium-ion batteries (LIBs) usher in an explosive growth, but followed by many spent LIBs processing problems. Recycling the spent LIBs with both economic attributes and environmental benefits is imperative. However, the existing recycling processes have the problem of high cost, low efficiency and environmental pollution. In this study, NaOH is innovatively adopted as leaching agent for the hydrometallurgical recovery of spent LiFePO₄ cathodes, realizing the efficiently selective lithium extraction without additional oxidizing agent addition. Meanwhile, Li₃PO₄ product is obtained by in-situ concentration of the leaching solution without adding precipitant, and Fe₂O₃ by-product can be obtained by leaching residue. Under the conditions of 2 mol/L NaOH, L/S ratio of 50:1 mL/g, 50 °C and 2 h, the leaching efficiencies of Li and P can reach 98.2 % and 99.9 %, and all of Fe is converted into Fe₃O₄. The kinetic study reveals that the leaching process is controlled by chemical reaction. Moreover, it is innovatively found that NaOH play the dual role of leaching agent and oxidant, and the Na⁺ may have intercalation effect on the structure of LiFePO₄. Compared with traditional process, this method has the advantages of low cost, high efficiency and environmental friendliness.