Sustainable route for cobalt and lithium recovery from discarded lithium-ion batteries: A closed-loop approach using Progaline deep eutectic solvent

In this study, a more sustainable closed-loop recycling strategy was developed using Progaline deep eutectic solvent (Progaline-DES). The solvent was prepared from choline chloride (ChCl) and propylene glycol (PG) in a 1:3 M ratio (ChCl:3PG), and characterized by FT-IR. The Progaline-DES achieved maximum leaching efficiencies of 93% for cobalt (Co) and 4.67% for lithium (Li) at 160 °C, 24 h, and a solid-liquid ratio of 0.4 g/10 g. Furthermore, kinetic modeling was employed to investigate the mechanism of the leaching process. The results demonstrate that the shrinkage core model (chemical reaction controlled, diffusion control) was the best model fitted to leaching data (coefficient of determination (R²) > 0.99). The morphological analysis of the recycled Co₃O₄ was carried out using FT-IR, XRD, SEM/EDS, and XRF. The leaching mechanism analysis shows that Progaline-DES's ability to coordinate with Co primarily drives the recycling process. Electrochemical characterization (CV, GCD, EIS, cyclic stability) confirms the successful recovery of Co from battery waste and its reuse in battery electrodes. The electrochemical analyses reveal that the specific capacitance of the recovered Co₃O₄ reaches 2100 F/g and delivers an energy density of 72.8 Wh/kg, while maintaining stable electrochemical behavior even at a scan rate of 10 mVs⁻¹. The capacitance retention of ∼100% after 500 cycles ensures the excellent cyclic stability of the recovered Co₃O₄. The fabrication of battery electrodes from recycled Co₃O₄ demonstrates a promising step towards a closed-loop recycling strategy from spent LIBs.