High solid-to-liquid ratio leaching of strategic metals from spent lithium-ion batteries: design of a green and sustainable deep eutectic solvent system

Abstract

Sustainably recycling spent lithium-ion batteries (LIBs) supports the global transition to a circular, low-carbon economy. However, because the leaching mechanisms are not yet well understood, current deep eutectic solvents (DESs) often face key drawbacks such as low solid–liquid ratios and high temperature requirements. In this study, a three-in-one driven leaching strategy is proposed, through which a scalable DES is rationally designed to enable efficient metal recovery at a high solid–liquid ratio of 1 g : 15 g and at a temperature of 80 °C, without the addition of external reducing agents. The leaching efficiencies of Li, Ni, Co, and Mn reach 98.64%, 98.12%, 98.05%, and 98.13%, respectively. Within the DES leaching system, the integration of active proton attack, redox reactions, and coordination-driven interactions effectively induces crystal lattice collapse, valence-state reduction, and coordination stabilization. Furthermore, both theoretical calculations and experimental results demonstrate that the cooperative ligand choline chloride (ChCl) enhances metal–ligand coordination interactions, thereby promoting the transfer of metals into the liquid phase. Environmental and techno-economic assessments further indicate that, compared with conventional metallurgical routes, this strategy achieves a more favorable balance between technical efficiency and energy, environmental, and economic sustainability.