Transition metal extraction from spent Li‐ion batteries using deep eutectic solvents: Mechanistic and molecular insights

Abstract

This study systematically elucidates the microscopic mechanism underlying the selective extraction of transition metal ions from spent lithium‐ion batteries (LIBs) leachates using a decanoic acid‐lidocaine (DecA:Lid) deep eutectic solvent (DES) with ligand tributyl phosphate (TBP). Given the close similarity in physicochemical properties among transition metal ions including Co ²⁺ , Ni ²⁺ , and Mn ²⁺ , Co ²⁺ was selected as a representative for detailed investigation. Theoretical calculations indicated that the dominant electrostatic interaction between Co ²⁺ and deprotonated DecA is mainly enhanced by orbital interaction with the PO group of TBP, a mode inaccessible to closed‐shell Li ⁺ . During Co ²⁺ extraction, Lid migration is directed to the aqueous‐rich region, while a hydrophobic domain is formed around Co ²⁺ in the aqueous‐deficient region via assembly of DecA and TBP. Through synergistic coordination, Co ²⁺ is encapsulated, enhancing its organic‐phase retention. This work provides theoretical foundations for novel DES design to enable efficient LIBs recovery.