Ternary Deep Eutectic Solvent (DES) with a Regulated Rate-Determining Step for Efficient Recycling of Lithium Cobalt Oxide

Deep eutectic solvents (DESs) have attracted extensive research for their potential applications as leaching solvent to recycle valuable metal elements from spent lithium ion batteries (LIBs). Despite various advantages like being economical and green, the full potential of conventional binary DES has not yet been harnessed because of the kinetics during leaching. Herein, we consider the fundamental rate-determining-step (RDS) in conventional binary DES and attempt to design ternary DES, within which the chemical reaction kinetics and diffusion kinetics can be regulated to maximize the overall leaching rate. As a proof of concept, we show that the ternary choline chloride/succinic acid/ethylene glycol (ChCl/SA/EG) type ternary DES can completely dissolve LCO powder at 140 °C in 16 h. By systematically studying the leaching process at various conditions, the energy barrier during leaching can be calculated to be 11.77 kJ/mol. Furthermore, we demonstrate that the extraction of the cobalt ions from the leaching solution can be directly achieved by adding oxalic ions without neutralizing the solution. The precipitate can be used to regenerate LCO with high purity. The recycled materials show comparable electrochemical performance with commercial LCO. Our design strategy of ternary DES with regulated RDS is expected to have both scientific and technological significance in the field of hydrometallurgical recycling of LIBs.