New Bifunctional Deep-Eutectic Solvent for In Situ Selective Extraction of Valuable Metals from Spent Lithium Batteries

A novel bifunctional deep-eutectic solvent (DES) based on glycol (EG) and oxalic acid dihydrate (OAD) was designed for efficient and selective extraction of valuable metals from spent lithium ion batteries (LIBs) cathode active materials (LiCoO2 or Li14.8Ni1.7Co8.5MnO30.5) under mild conditions, realizing complete in situ separation of Li and Co/Ni/Mn. The effects of different experimental parameters on Li and Co extraction efficiencies (ηLi, ηCo) were explored by orthogonal and single-factor experiments in detail. Under the optimal conditions (90 °C, 5EG:1OAD, 12 h, 16 g/L), nearly 94.4 and 94.1% of Li, as well as trace amounts of Co/Ni/Mn (<1.2%), were separately leached from LiCoO2 and Li14.8Ni1.7Co8.5MnO30.5 into the filtrate, while the oxalate dihydrates (CoC2O4·2H2O or (Ni, Co, Mn)C2O4·2H2O) with nanorod structures were achieved. The specific leaching mechanism was elucidated. Moreover, the lithium oxalate (Li2C2O4) with irregular particle morphology was also obtained by evaporating the filtrate at 200 °C. The reusability of the as-prepared DES (5EG:1OAD) for the LIBs was also studied. After three cycles of DES leaching, the ηLi could still reach more than 93%, while almost all Co was remained in the solid phase. This study may shed light on developing bifunctional or even multifunctional DESs to achieve highly selective extraction of metals from LIBs.