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 (LiCoO2 and Li3.2Ni2.4Co1.0Mn1.4O8.3) 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 (ηLi and ηCo) from LiCoO2 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 (MEG:TA) of 5:1, and solid to liquid ratio (RS/L) of 20 g/L), the ηLi from LiCoO2 reached 98.34%, and Co was formed as a purple precipitate of cobalt tartrate (CoC4H4O6), which was transformed into a black powder of Co3O4 after calcination. Notably, the ηLi 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 Li3.2Ni2.4Co1.0Mn1.4O8.3, the in-situ selective separation of Li (ηLi = 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.