Ethanol-driven bifunctional deep eutectic solvents for efficient in situ selective recovery of valuable metals from spent lithium batteries

A new type of bifunctional Deep Eutectic Solvent (DES), crafted from a blend of ethylene glycol (EG), ethanol (EtOH) and citric acid (CA), has been developed for the efficient and selective extraction of valuable metals from spent lithium-ion batteries (LIBs) cathode materials. This innovative solvent leverages the inclusion of EtOH to fine-tune the solubility of metal complexes, notably enhancing the separation of Co by reducing its concentration in the leachate from 3.099 g/L to 0.7508 g/L. This adjustment facilitates the in situ separation of Li and Co/Ni/Mn. Through meticulous single-factor leaching experiments, the influence of various parameters on the extraction efficiency of Li and Co was explored. It is revealed that EtOH’s presence not only improves separation efficiency but also promotes the precipitation of a novel cobalt citrate complex, Co 3 (C 6 H 6.8 O 7 ) 5 , formed between Co 2+ and CA. A comprehensive analysis of the Co leaching and separation mechanism was conducted, characterizing the properties of the formed complex. Optimal extraction conditions (150 °C, 16 h, 8 g/L, 6 EG: 6 EtOH: 1 CA) resulted in the leaching of 97.4 % of Li from LiCoO 2 and 94.4 % from Li 3.2 Ni 2.3 Co 0.9 Mn 1.4 O 6.3 , along with a partial Mn (52.6 %) and small amounts of Co/Ni (<15 %). The leaching mechanism and reaction kinetics were investigated, confirming that diffusion is the rate-limiting step of the reaction. After 5 cycles of DES leaching, the η Li exceeded 90 %, demonstrating the reusability of DES. Through precipitation, evaporation, and calcination processes, high-purity CoC 2 O 4 ·H 2 O, EG, EtOH, and Li 2 CO 3 can be recovered. This research introduces EtOH as a key component in DES formulation, offering a strategy to enhance the selectivity of dual-functional DESs.