Green Leaching of Lithium-Ion Battery Cathodes by Ascorbic Acid Modified Guanidine-Based Deep Eutectic Solvents

The replacement of traditional solvents in lithium-ion battery recovery process by deep eutectic solvents (DESs) has been widely reported. This work proposed a DES modified by reducing agents for the efficient leaching of LiCoO₂ (LCO) and lithium nickel cobalt manganese oxides (NCMs) to overcome the intractable difficulty of previous research (high viscosity, poor reuse performance, and operation conditions). The DES of guanidine hydrochloride (GUC) and lactic acid (LAC) with 1 wt % ascorbic acid could dissolve almost 100% of LCO and NCMs under a very mild condition at a solid–liquid ratio of 1:50. The maximum contents in GUC-LAC were 3188 ppm for Li and 19,045 ppm for Co. After stripping Co by oxalic acid and supplementing VC, GUC-LAC-VC could maintain the dissolution properties with at least three cycles. In addition, the acidity and reducibility were measured through Hammet acidity and cyclic voltammetry methods, as key factors for the dissolution of Li and Co.