Recovery of Valuable Metals from Spent LiNi0.8Co0.1Mn0.1O2 Cathode Materials Using Compound Leaching Agents of Sulfuric Acid and Oxalic Acid

The recovery of valuable metals from spent lithium-ion batteries is beneficial to protect the environment and avoid resource depletion. Based on the synergistic effect of the reducing ability of oxalic acid and the acidic strength of sulfuric acid, this study was conducted to recover valuable metals from spent LiNi0.8Co0.1Mn0.1O2 lithium-ion battery cathode materials with the compound leaching agents of sulfuric acid and oxalic acid. Under the optimized conditions of sulfuric acid concentration at 2.5 mol·L−1, oxalic acid concentration at 20 g·L−1, liquid-to-solid ratio at 10 mL·g−1, reaction temperature at 85 °C, and reaction time at 100 min, the leaching rate of Li, Ni, Co, and Mn measured by ICP-OES was, respectively, 99.26%, 98.41%, 96.95%, and 97.54%. It was further validated that the valuable metals were almost completely leached when combined with the XRD and SEM-EDS analysis of spent cathode materials before and after leaching. The leaching of Li, Ni, Co, and Mn was all in accordance with the Avrami model with their activation energies of 31.96 kJ·mol−1, 41.01 kJ·mol−1, 47.57 kJ·mol−1, and 42.95 kJ·mol−1, indicating that the diffusion was the control of the Li leaching process, and the surface chemical reaction was the control of the other three metals. This work provides a new idea and method for the recycling of spent lithium-ion batteries.