One-Step Direct Recovery of Lithium from Spent Lithium-Ion Batteries via Water-Based Deep Eutectic Solvent

Abstract

The boom of the lithium-ion battery (LIB) industry is dialectically correlated with a scarcity of raw resources, particularly lithium (Li), so the recovery of critical metals from spent LIBs has become very essential for resource sustainability. Here, a new strategy for the one-step direct recovery of Li from spent LIB cathode active materials via water-based deep eutectic solvents (DESs) is put forward, together with the recycling and reuse of the DES. Without any reagent and pretreatment, Li₂C₂O₄ can be directly and preferentially precipitated from the H₂O-based choline chloride-oxalic acid (ChCl-OA) DES, and CoC₂O₄·2H₂O is obtained easily from the residual Co-rich leachate by adding H₂O. The leaching efficiencies are nearly 100% for Li and Co, and the recovery efficiencies reach 91.2 and 94.6%, respectively. The recovery mechanism of Li and Co is clarified based on the coordination-guided design between Li⁺ and C₂O₄^2–, which enables the precise separation of Li and Co. It is crucial to strictly control the H₂O content in the DES, which is always being ignored, serving as a diluent and complexant, avoiding the solidification of the DES, and realizing the preferential precipitation of Li. The optimization of the leaching and recovery processes is comprehensively investigated as well as the middle-sized experiments in the 2 L leaching level, and a leaching kinetic model is established. The strategy proposed here offers a promising possibility for the direct and preferential recovery of Li from spent LIBs, promoting the development of high economic efficiency and environmental protection of the battery recycling market.