Green recycling of spent Li-ion batteries by deep eutectic solvents (DESs): Leaching mechanism and effect of ternary DES

Spent Li-ion batteries (LIBs) contain large amounts of hazardous metals (Co, Ni, Li, and Mn) that cause environmental pollution and health risks. In this study, one ternary (choline chloride (ChCl):Urea: ethylene glycol (EG)) and two binary (ChCl: Urea and ChCl: EG) nontoxic deep eutectic solvents (DESs) were developed as environmentally friendly, cost-effective, and safe approaches for recycling of spent LIBs. FT-IR Analysis of DESs solvents showed that the ternary DES spectrum overlaps the spectra of ChCl:Urea and ChCl: EG. Therefore, the EG structure is stable in ChCl:Urea: EG. The leaching results indicated that temperature directly affects the extraction of valuable metals in the presence of all DESs. Among the three DES types, the ternary DES exhibits optimal extraction performance (Li:97%, Co:41%, Ni:40%, and Mn:34%). In addition, kinetic modeling was used to study the reaction mechanisms. The results showed that the mixed control model by shrinking core model (diffusion control and chemical reaction control) was the best model fitted to all data (coefficient of determination (R2) > 0.90). According to the Arrhenius equation, the activation energies for all valuable metals in the presence of all DESs are between 13 and 42 KJ/mol, reflecting a mixed control reaction.