A novel green deep eutectic solvent for one-step selective separation of valuable metals from spent lithium batteries: Bifunctional effect and mechanism

This study used a novel green bifunctional deep eutectic solvent (DES) containing ethylene glycol (EG) and tartaric acid (TA) for the efficient and selective recovery of cathode active materials (LiCoO 2 and Li 3.2 Ni 2.4 Co 1.0 Mn 1.4 O 8.3 ) used in lithium-ion batteries through one-step in-situ separation of Li and Co/Ni/Mn. The effects of leaching parameters on the recovery of Li and Co ( η Li and η Co ) from LiCoO 2 are discussed, and the optimal reaction conditions are verified, for the first time, using a response surface method. The results demonstrate that under optimal conditions (120 °C, 12 h, EG to TA mole ratio (M EG:TA ) of 5:1, and solid to liquid ratio (R S/L ) of 20 g/L), the η Li from LiCoO 2 reached 98.34%, and Co was formed as a purple precipitate of cobalt tartrate (CoC 4 H 4 O 6 ), which was transformed into a black powder of Co 3 O 4 after calcination. Notably, the η Li for DES 5 EG:1 TA was maintained at 80% after five cycles, indicating good cyclic stability. When the as-prepared DES was used to leach the spent active material Li 3.2 Ni 2.4 Co 1.0 Mn 1.4 O 8.3 , the in-situ selective separation of Li ( η Li  = 98.86%) from other valuable elements such as Ni, Mn, and Co, was achieved, indicating the good selective leaching capacity and practical application potential of the DES.