Recycling of Spent LiFePO₄ Batteries Using Ultrasonic-Assisted Reducing Leaching

The application of a huge number of lithium-ion batteries (LIBs) to electric vehicles has produced much solid waste. If not disposed properly, the solid waste may cause environmental pollution and is, per se, a waste of resources. Therefore, recycling valuable metals from LIBs is considered an ideal option for preventing environmental pollution and alleviating waste. Taking sulfuric acid (H₂SO₄) as the leaching agent and glucose (C₆H₁₂O₆) as the reducing agent, the ultrasonic-assisted reducing leaching was used to recycle lithium (Li) and iron (Fe) from spent lithium iron phosphate (LFP) batteries. Based on experimental results of conventional leaching, the research aimed to examine the influence of ultrasonic treatment on leaching rates of Li and Fe. Results show that the leaching rates of Li and Fe are separately 96.53% and 96.8% when the concentration of H₂SO₄ is 2 mol/L, the concentration of C₆H₁₂O₆ is 2 mol/L, the liquid-solid ratio is 15 mL/g, leaching temperature is 70 °C, leaching time is 60 min, and ultrasonic power is 100 W. Compared with conventional leaching, the leaching rates of Li and Fe separately increase by 10.84% and 12.33% through ultrasonic-assisted leaching under the same experimental conditions. Kinetics analysis of ultrasonic-assisted reducing leaching indicates that the activation energies of Li and Fe are 10.84 kJ/mol and 16.24 kJ/mol, respectively. The ultrasonic-assisted reducing leaching process of Li and Fe from LFP batteries is controlled by diffusion.