Selective Lithium Recovery via Stepwise Transition Metal Crystallization in a Natural Deep Eutectic Solvent

The global shift toward electric vehicles is driving unprecedented demand for lithium-ion batteries, underscoring the urgent need for sustainable lithium (Li) recycling technologies. Deep eutectic solvents (DESs) have emerged as promising green alternatives to conventional leaching agents, yet challenges persist in preferential Li selectivity and process scalability. Here, a natural DES composed of choline chloride, lactic acid, and ascorbic acid (1ChCl-10LA-VC) is designed to overcome these limitations. In this system, LA provides high acidity, VC serves as a mild reductant, and ChCl promotes selective complexation and controlled precipitation of transition metals (TMs: Co, Ni, Mn, Fe). This synergistic formulation enables a stepwise separation mechanism: Li⁺ remains solubilized, while TMs undergo rapid reduction, complexation, hydrolysis, and eventual crystallization within one hour. The method is broadly effective across various cathode chemistries - including LiCoO₂, LiNiO₂, LiMn₂O₄, LiFePO₄, and NCMs (NCM 111, NCM 523, NCM811) - and demonstrates exceptional selectivity, particularly for high-Ni cathodes. Co-dissolved Mn impurities are effectively removed via antisolvent crystallization, enabling high-purity Li₂CO₃ recovery. When applied to black mass, the method achieves >96% Li leaching, >94% overall recovery, and excellent DES recyclability over four cycles. Furthermore, scale-up to gram-scale in a 2-liter glass reactor confirmed process robustness and industrial feasibility.