A Green and Efficient Solvent for Simultaneously Leaching Co and Li from Spent Li-Ion Batteries: Dicarboxylated Polyethylene Glycol

Recovery of high-valued metals such as Li and Co from spent Li-ion batteries is quite important for sustainability reasons. The novelty of this work was based on the view of molecular design, proposing a strategy that inserts another group between two −COOH groups on an organic acid to activate them. On this basis, a novel solvent dicarboxylated polyethylene glycol (dcPEG), i.e., HOOC–CH2(CH2CH2O)nCH2–COOH, was chosen to leach Li and Co from LiCoO2. Expectedly, HOOC–CH2(CH2CH2O)nCH2–COOH (n = 250), which was denoted as dcPEG250, showed appealing leaching performance without the help of H2O2 and quaternary ammonium salt. It can simultaneously extract Co and Li, and the leaching efficiency reached as high as almost 100% under the proper conditions. The excellent performance was ascribed to structural feature of dcPEG. The presence of main chain (CH2CH2O)n extended the distance between two −COOH groups at the ends, limited their intramolecular interaction, and activated the −COOH groups. Accordingly, the active H atom on the −COOH group can react with LiCoO2, and the active O atoms on ether (C–O–C) and carbonyl (C═O) groups can coordinate with metals. In a word, this work could not only provide a promising solvent but also inspire researchers to engineer more novel solvents from the view of molecular design.