Green lithium extraction and recovery using a task-specific deep eutectic solvent

Abstract

The growing demand for lithium-ion batteries (LIBs) in electronic devices and electric vehicles has led to an increase in spent LIB waste, posing environmental risks and exacerbating concerns over lithium resource depletion. Traditional recycling methods often rely on toxic organic solvents, highlighting the urgent need for safer, more sustainable alternatives. In this study, a novel task-specific deep eutectic solvent (DES) composed of dibenzoylmethane (DBM) and trioctylphosphine oxide (TOPO) in a 1:1 molar ratio was developed for selective lithium extraction. Unlike conventional DESs, the DBM/TOPO-DES is hydrophobic, enabling efficient liquid–liquid extraction by minimizing miscibility with aqueous solutions. Under optimized conditions—pH 12, 30 s of vortexing, room temperature, and a 2:1 aqueous-to-DES phase ratio—the system achieved over 99% lithium extraction efficiency. It also exhibited high extraction efficiency with EDTA as a masking agent for lithium in the presence of commonly co-existing ions such as Co(II), Cu(II), and Ni(II), typically present in LIB cathode materials. Lithium was efficiently back-extracted using 0.7 M HCl, and the DES maintained excellent performance across five extraction cycles, demonstrating its reusability. Compared to other DES-based approaches, this system combines rapid kinetics, high extraction efficiency, and a greener profile without compromising performance. Thermal analysis, phase behavior, and spectroscopic characterization confirmed the stability and formation of the DES. Overall, the DBM/TOPO-DES offers a sustainable and effective alternative to traditional solvent systems, advancing green chemistry principles and contributing to the efficient recovery of critical lithium resources from spent batteries.