Toward efficient recovery of lithium via synergistic extraction using novel salicylate‐based deep eutectic solvents

Abstract An effective strategy based on hydrophobic deep eutectic solvent (HDES) synergistic extraction was developed for extracting lithium ions from spent lithium battery recycling effluent. Solid phenethyl salicylate (PES) forms a liquid HDES with trialkyl phosphine oxide (TRPO), overcoming the solid‐phase limitation of PES and enhancing lithium extraction via synergistic coordination. Under optimal conditions, the PES‐TRPO HDES achieves an 87.8% lithium extraction efficiency and a Li + /Na + separation selectivity of 168. After three‐stage counter‐current extraction, lithium recovery exceeds 99%. The cyclic extraction capability of HDES is confirmed through multiple cycling experiments. The synergistic extraction mechanism reveals that hydrogen bonding between PES and TRPO drives the formation of HDES, while their synergistic coordination with lithium ions enhances the hydrophobic character of the complex, enabling efficient lithium extraction. This HDES‐based synergistic extraction strategy is applicable to other extractants limited by solid‐phase behavior, providing more opportunities for the development of novel high‐performance separation systems.