Selective lithium recovery from spent LiMn₂O₄ cathodes through carbothermic reduction

Selective lithium recovery from spent lithium-ion batteries is essential for improving resource utilization and establishing sustainable recycling processes. Carbothermic reduction offers a promising pyrometallurgical route for recovering lithium from manganese-rich cathode materials, yet the reaction pathways governing lithium liberation and their influence on recovery efficiency remain poorly understood. In this study, the carbothermic reduction behavior of spent LiMn₂O₄ (LMO) cathodes was systematically investigated using integrated thermodynamic, kinetic, and experimental analyses. Simultaneous TGA-DSC and ex-situ XRD analyses performed between 800 and 1000 °C showed that LMO underwent stepwise reduction through LiMnO₂ and Mn₃O₄ intermediates, ultimately forming water-leachable lithium species and insoluble MnO. Raman spectroscopy revealed the persistence of a monoclinic LiMnO₂ local structure during the final reduction stage, indicating that the conversion of LiMnO₂ to lithium species remained sluggish. Kinetic analysis showed that the rate-controlling mechanism changed above 850 °C from an interfacial reaction to CO(g) diffusion, driven by the development of a porous reaction structure. Water leaching achieved lithium recoveries exceeding 95 % for samples reduced at 900-950 °C. Further increasing the reduction temperature did not improve lithium recovery because MnO sintering limited lithium extraction. These results establish the relationship between reaction pathway, microstructural evolution, and lithium recovery efficiency, providing practical guidance for optimizing carbothermic recycling of manganese-rich spent LiMn₂O₄ cathodes.