Recycling of Li and transition metals from spent lithium-ion batteries cathodes by sequential formic acid and deep eutectic solvent leaching

The complexity and similar characteristics for multiple valuable metals presented in LIBs cathode materials result in difficulties in their extraction and separation. This study introduces a novel two-stage approach to recovery valuable metals from spent lithium-ion batteries (LIBs) by formic acid (FA) selective leaching and other transition metals by a deep eutectic solvent (DES) leaching. Li is first selectively leached by FA with leaching efficiency of 98.87 % and further recovered in Li 2 CO 3 by distillation and calcination, whereas transition metals (Ni, Co, Mn) exhibited minimal co-leaching just with 1.41 %, 0.68 %, and 8.66 %. FA can be regenerated through atmospheric pressure distillation and reused in Li leaching process. Furthermore, the use of betaine hydrochloride (BeCl) in the synthesis of novel DES with FA to leach Mn, Co and Ni from FA leaching residue. Under optimal conditions, the leaching efficiencies for Mn, Co and Ni reached 96.87 %, 99.61 % and 98.88 % respectively. BeCl released Cl − and formed soluble complexes [MeCl 4 ] 2− with Ni 2+ , Co 2+ , and Mn 2+ . The leaching process conformed to the contraction-nucleation model and controlled by interfacial chemical reactions. The activation energies of 44.01, 43.08, and 34.40 kJ/mol for Co, Mn and Ni leaching process. Finally, Mn, Co and Ni were precipitated and recovered from the leachate by introducing oxalic acid. Mn, Co and Ni were recovered in the forms of MnC 2 O 4 ·2H 2 O、CoC 2 O 4 ·2H 2 O、NiC 2 O 4 ·2H 2 O with recovery efficiencies of 98.45 %, 96.13 %, and 97.42 %, respectively. This method achieved separation and recycling valuable metals through a two-stage leaching strategy, with the characteristic of high efficiency and simple recycling process.