Separation of Li and Al from spent ternary Li-ion batteries by in-situ aluminum‑carbon reduction roasting followed by selective leaching

Abstract

During the reduction roasting of waste ternary Li-ion batteries (LIBs), a large amount of carbon reductant is introduced in the recycling process, which is not conductive to achieve the goal of carbon peaking and carbon neutrality. This research proposes to make full use of aluminum and carbon – main constituents of waste LIBs – as reductants in the roasting process. Results show that the aluminum-carbon reduction roasting method has a higher efficiency compared with the traditional carbon reduction. Lithium present in ternary materials can be almost completely transformed into soluble Li2CO3, while the associated Ni, Co and Mn are all converted into insoluble metal elements or their corresponding oxides at 650 °C (t = 90 min). The presence of Al decreases the carbothermal roasting temperature, while the presence of waste carbon allows Li to be converted into easily soluble lithium carbonate in preference to lithium aluminate. The optimal amount of carbon and Al in the spent LIBs were 14.7% and 7.0%, respectively. After roasting, > 97% of Li could be selectively leached by carbonated water leaching, while only < 0.5% of Al, Ni, Co, and Mn dissolved. The leach residues obtained were purified by alkali treatment with 3 mol/L NaOH at 90 °C to achieve > 99% Al separation. These results suggest that the in-situ aluminum-carbon reduction roasting, followed by selective leaching of Li and Al, mitigates several of the challenges related to battery recycling: (i) Li extraction is increased substantially above the state-of-the-art recovery efficiencies, (ii) Al - known to decrease battery metals extraction in hydrometallurgical processing - is selectively removed after making full use of its reducibility and (iii) battery metal-rich residues with low impurity levels is produced for further refining, therefore paving the way towards more economical, efficient and environmentally friendly spent LIBs recycling.