Solvent extraction of metal ions from the leaching solutions of waste lithium-ion battery materials: A review

With the global energy transition and rapid development of electric mobility, the consumption of lithium-ion batteries has substantially increased. The recovery of valuable metal ions, such as cobalt, nickel, and lithium, from the leaching solutions of waste lithium-ion battery cathode materials can contribute to resource recycling and raw material supply. To achieve the application potential of valuable-metal-ion recovery, research has been focusing on solvent extraction as a separation technology owing to its high efficiency as well as excellent selectivity and scalability. In this review, recent research progress on the use of solvent extraction for the recovery of valuable metal ions from the leaching solutions of waste lithium-ion batteries is summarized. The extraction mechanisms for ions in various solvent extraction systems, including acidic phosphines, amines, ionic liquids, deep eutectic solvents, and multicomponent synergistic solvent extraction systems, are thoroughly analyzed. Furthermore, the separation mechanisms for target metal and impurity ions under different process conditions are examined in detail. In addition, the separation characteristics and challenges of metal-ion recovery in different extraction systems are identified. Next, traditional organic extractants and new environmentally friendly extractants are compared. Finally, sustainable development prospects of highly selective green recovery of valuable metals from waste lithium-ion batteries are proposed. These prospects include the (1) enhancement of the fundamental theory and molecular microstructure research for extraction, (2) advancement of the development of environmentally friendly, nontoxic, and cost-effective extractants, and (3) establishment of new multicomponent synergistic solvent extraction systems.