Carbothermal Reduction for High-Efficiency Lithium Recovery from Spent Ternary Cathode Materials

Carbothermal reduction roasting has been widely studied for the recycling of lithium resources from ternary (NCM523) lithium-ion cathode materials. However, the recovery mechanism is controversial; thus, we performed a thermodynamic study of the carbothermal reduction process. The software was used to study the reaction predominance and phase diagrams, and the Gibbs free energy of possible reactions was calculated. The results show that nickel (Ni) and cobalt (Co) can be reduced to low-valent oxides and monomers at around 600 °C, while manganese (Mn) requires a higher temperature. These findings were verified by thermogravimetric analysis-differential scanning calorimetry (TG-DSC) analysis of different reactants. Subsequent analysis of the reaction products revealed that nickel and cobalt are reduced first, while manganese is initially reduced to LiMnO 2 and further reduced to MnO as the temperature increases. Increasing the carbon content or prolonging the roasting time can further promote reduction of LiMnO 2 . Additionally, the effects of roasting time, temperature, and carbon content on lithium leaching efficiency were investigated. Under conditions of 20% carbon content, a roasting temperature of 700 °C, and a roasting time of 4 h, the lithium leaching rate reached 98.28%, and the recovered Li 2 CO 3 can serve as a precursor for producing cathode materials. This study provides new theoretical support for the mechanism of carbothermal reduction in cathode materials.