Selective Separation of critical metals from lithium-ion batteries in two-phase leaching system based on hydrophobic deep eutectic solvent and H2O2 solution

Abstract

An efficient two-phase leaching system using a hydrophobic deep eutectic solvent (DES) composed of 2 mol of 4,4,4trifluoro-1-(2-thienyl)-1,3-butanedione and 1 mol of tri-n-octylphosphine oxide, with H 2 O 2 as the aqueous phase, was developed for the selective recovery of Li, Co, Ni, and Mn from spent lithium-ion batteries. Under optimized conditions (1:1 DES/aqueous phase, 80 °C, 30 min), the two-phase leaching system achieved leaching efficiencies of 98% Li, 94% Co, 94%Ni, 98% Mn, with 73% Cu, 54% Al, and 76% Fe in the DES phase and minor Cu and Al in the aqueous phase, demonstrating pronounced phase-selective partitioning in a single-step process. The equilibrium pH of the aqueous solution determined the ability of this system to strip either Li only or Li, Co, Ni, and Mn. DES exhibited stable performance over three successive cycles without regeneration or stripping, confirming its recyclability and operational robustness. This facile, rapid, and selective leaching strategy provides a promising route for the valorization of critical metals in spent lithium-ion batteries.