Selective recovery of critical metals from spent lithium-ion batteries using maleic acid-based deep eutectic solvent

• One of the first studies to report the direct crystallisation of Co, Ni, and Mn from BM using maleic acid and choline chloride DES. • Over 99 % of leaching efficiencies for Li, Co, Ni, and Mn in NMC cathodes are achieved. • This DES, demonstrating superior room temperature fluidity compared to other DESs, operates at 60 °C to minimise the risk of thermal degradation of sensitive materials and DES loss ratio. • Co, Ni, and Mn are selectively recovered from spent lithium-ion batteries as M(C 4 H 3 O 4 ) 2 ·4H 2 O crystals (M = Ni, Co, or Mn). • The use of extra reagents is minimised, and the need for additional purification steps is reduced through the cooling crystallisation process. The sustainable recovery of critical metals from spent lithium-ion batteries (LIBs) is essential for environmental preservation and meeting the growing demand for critical minerals. This study presents an eco-friendly approach using a deep eutectic solvent (DES) composed of maleic acid and choline chloride (1:1) for the selective recovery of Co, Ni, and Mn through a cooling crystallisation process. By precisely regulating the leaching system with DES, we were able to control the supersaturation of the leachate solution, allowing maleic acid to selectively form metal maleate complexes and crystallise them directly from the leachate solution. Under optimal conditions, leaching experiments achieved over 99 % recovery of all elements from lithium nickel manganese cobalt oxide (NMC) cathodes. Detailed characterisations reveal that this method reduces the need for additional purification steps and minimises the use of extra reagents, demonstrating significant potential for the selective recovery of critical metals.