A novel green deep eutectic solvent for one-step selective separation of valuable metals from spent lithium batteries: Bifunctional effect and mechanism

Abstract

This study used a novel green bifunctional deep eutectic solvent (DES) containing ethylene glycol (EG) and tartaric acid (TA) for the efficient and selective recovery of cathode active materials (LiCoO₂ and Li_3.2Ni_2.4Co_1.0Mn_1.4O_8.3) used in lithium-ion batteries through one-step in-situ separation of Li and Co/Ni/Mn. The effects of leaching parameters on the recovery of Li and Co (η_Li and η_Co) from LiCoO₂ are discussed, and the optimal reaction conditions are verified, for the first time, using a response surface method. The results demonstrate that under optimal conditions (120 °C, 12 h, EG to TA mole ratio (M_EG:TA) of 5:1, and solid to liquid ratio (R_S/L) of 20 g/L), the η_Li from LiCoO₂ reached 98.34%, and Co was formed as a purple precipitate of cobalt tartrate (CoC₄H₄O₆), which was transformed into a black powder of Co₃O₄ after calcination. Notably, the η_Li for DES 5 EG:1 TA was maintained at 80% after five cycles, indicating good cyclic stability. When the as-prepared DES was used to leach the spent active material Li_3.2Ni_2.4Co_1.0Mn_1.4O_8.3, the in-situ selective separation of Li (η_Li = 98.86%) from other valuable elements such as Ni, Mn, and Co, was achieved, indicating the good selective leaching capacity and practical application potential of the DES.

Keywords: Bifunctional green DES; Cyclic stability; In-situ selective leaching; Response surface methodology; Spent LIB cathode Active material.