A Novel Deep-Eutectic Solvent with Strong Coordination Ability and Low Viscosity for Efficient Extraction of Valuable Metals from Spent Lithium-Ion Batteries

A new type of deep-eutectic solvents (DESs), consisting of ethylene glycol (EG) and sulfosalicylic acid dihydrate (SAD), were designed for efficient leaching valuable metals from cathode active materials (LiCoO2 and Li14.8Ni1.7Co8.5MnO30.5) of spent lithium-ion batteries (LIBs) for the first time. The as-prepared DESs possessed strong coordination ability and low viscosity, which were suitable for metal extraction. The influences of experiment parameters on extraction of Co and Li were systematically investigated, and the leaching mechanism and kinetics were elucidated in detail. Under the optimal conditions, the leaching efficiencies of Co and Li from pure LiCoO2 reached 93.5% and 98.3%, while those of Co, Ni, Mn, and Li achieved 94.8%, 99.1%, 100%, and 100% from the spent Li14.8Ni1.7Co8.5MnO30.5, respectively. Results revealed that the Li+ ions located in the interlayer of layered LiCoO2 were replaced by H+ ions and entered into solution, while Co3+ ions in the skeleton structure were reduced and coordinated by EG and sulfosalicylic acid (SA) to form four soluble Co2+–SA complexes, realizing synergistic and efficient leaching of Li and Co from the LIB cathode active material. Moreover, Co and Li leaching kinetics conformed to the shrinking core model, in which the interfacial chemical reaction was the limiting step, and the apparent activation energies were separately about 77.38 and 79.54 kJ/mol.