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

The sustainable recycling of spent lithium-ion batteries (LIBs) is essential for the global transition toward a circular, low-carbon economy. Nevertheless, owing to an insufficient systematic understanding of leaching mechanisms, existing deep eutectic solvents (DESs) commonly suffer from critical limitations, including low solid-liquid ratios and high leaching temperatures. 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 1g:15g 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, valencestate 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.