An emerging trend of ionic liquids in the separation of critical metals from spent lithium and nickel based batteries

Separation of critical metals viz. nickel, cobalt, lithium, manganese, zinc, and copper from scrap rechargeable batteries (LIB, NiMHs) is still challenging due to its heterogeneous composition. The currently prevailing multi-stage separation tools like solvent extraction, ion exchange, and ionic liquids (ILs) have the advantages of being eco-friendly and are rapidly replacing organic solvents due to their distinctive properties such as negligible vapour pressure and higher stability, structure tenability, easily recyclable, and low melting point. Creating new cations and anions and incorporating suitable functional groups can impart the exact physical properties essential for each application at the core of the ILs designing process. ILs are classified as imidazolium-based ILs, phosphonium-based ILs (PILs), non-fluorinated, and task-specific ionic liquids (TSILs). PILs and TSILs are receiving an upsurge of interest and are widely used due to their advantages, viz., minimum solute interaction, cost-effectiveness (PILs are reported to be costly), and manageability. The overview describes in vogue the recent advances to extract metals from LIBs, NiMHs, etc., using different types ILs.