Experimental and molecular insights into ionic liquid-based recovery of valuable metals from spent lithium-ion batteries

A new type of collaborative extractants consisting of the ionic liquid (IL) 1-aminoprooyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)imide, ([APMIM][Tf₂N]) and Cyanex 923 (C923) is first applied for selective extraction of valuable metals from spent lithium-ion batteries (LIBs). The one-stage extraction efficiencies of Co²⁺, Ni²⁺ and Mn²⁺ are up to 99.87 %, 97.74 %, 99.98 %, respectively, at the optimal conditions, and the high-purity Li⁺ was enriched at the raffinate. It is found that the extraction process follows the so-called “cation exchange mechanism”, and the molecular-level mechanism is revealed via quantum chemical (QC) calculations. The findings show that C923 plays the role of coordinating with metal ions, the cation of IL exchanges metal ions from the aqueous to organic phases, and the anion [Tf₂N]^- of IL can stabilize the complex species of metal ion-[Tf₂N]^--C923 in organic phase. This work provides new insights for the design of novel IL-based extractants for the recycling of spent LIBs.