Stepwise recycling of valuable metals from spent lithium-ion batteries based on in situ thermal reduction and ultrasonic-assisted water leaching

Abstract

Recycling spent lithium-ion batteries (LIBs) is essential for sustainable resource utilization and environmental conservation. In this research, we have achieved simultaneous removal of organic matter, dissociation of electrode material, and reduction of high valence transition metal through the process of in situ thermal reduction, which are key points for the hierarchical selective recovery of valuable metals. The thermal reduction mechanism and phase transition behavior of mixed electrode materials were also evaluated in the meantime. It is found that the spent cathode materials were decomposed and synchronously reduced to the form of MnO, NiO, Ni, Co, LiF, Li₂O, LiAlO₂, and Li₂CO₃ through in situ thermal reduction during roasting at 650 °C for 1 h. The maximum leaching efficiency of Li under conventional water-leaching conditions was found to be 85.66%. Ultrasonic-assisted leaching has been shown to cause ultrasonic cavitation effects in the leaching process, promoting the dissolution and desorption of LiF, Li₂CO₃, and Li₂O through mechanical action and thermal impacts at the solid–liquid interface, increasing the Li leaching efficiency to 98.68% (more than a 13% increase). The recovered leaching solution was evaporated and crystallized to obtain high-purity Li₂CO₃ (≥99.5%). Subsequently, the transition metals were separated from aluminum, copper, and graphite by wet magnetic separation. The leaching of high-value metals Ni, Mn, and Co from magnetically enriched products using sulfuric acid at room temperature without a reducing agent has greatly simplified the subsequent transition metal separation process. This study presents a potential avenue for the efficient and environmentally-friendly recovery of valuable metals from mixed electrode materials of spent LIBs.