Deep Eutectic\nSolvent-Aqueous Two-Phase Leaching System\nfor Direct Separation of Lithium and Critical Metals

Developing an effective recycling process for reclaiming\nvaluable\nmetals from lithium-ion batteries is an urgent issue owing to increasing\nbattery waste from electric vehicles. In this study, we developed\na leaching method that enables the direct separation of lithium from\nother critical metals, namely, nickel and cobalt, using a two-phase\nsystem that consists of a deep eutectic solvent (DES) and water. The\nDES consisting of 4,4,4-trifluoro-1-phenyl-1,3-butadione and tri-n-octylphosphine\noxide showed the highest leaching performance when combined with water.\nSeveral operational parameters, such as the aqueous fraction, solid-liquid\nratio, reaction time, and operation temperature, were evaluated.\nThe optimum results in the two-phase direct leaching system were obtained\nusing a 1:1 DES-water ratio and 10 g/L solid-liquid ratio, reacted\nat 80 °C for 24 h. An <i>in-situ</i> stripping phenomenon\nwas observed, revealing that lithium transferred from the DES phase\nto the aqueous phase. In the application of black mass leaching, the\naqueous phase significantly enhanced Co, Ni, and Mn extraction into\nthe DES phase and thus plays an important role in separating lithium\nfrom other metals. The efficiency of direct lithium leaching from\nthe black mass reached 99% within 24 h.