Priority Recovery of Lithium From Spent Lithium Iron Phosphate Batteries via H2O-Based Deep Eutectic Solvents

Abstract

The growing use of lithium iron phosphate (LFP) batteries has raised concerns about their environmental impact and recycling challenges, particularly the recovery of Li. Here, we propose a new strategy for the priority recovery of Li and precise separation of Fe and P from spent LFP cathode materials via H₂O-based deep eutectic solvents (DESs). Through adjusting the form of the metal complexes and precipitation mode, above 99.95% Li and Fe can be dissolved in choline chloride-anhydrous oxalic acid-water (ChCl-OA-H₂O) DES, and the high recovery efficiency of Li and Fe about 93.41% and 97.40% accordingly are obtained. The effects of the main parameters are comprehensively investigated during the leaching and recovery processes. The recovery mechanism of the pretreated LFP is clarified and the rate-controlling step of the heterogeneous dissolution reactions is also identified. Results show that soluble phases of Li₃Fe₂(PO₄)₃ and Fe₂O₃ are formed after roasting pretreatment, and Li(I) ions tend to form Li₂C₂O₄ precipitates with C₂O₄²⁻ during the leaching process so that Li can be recovered preferentially in purity of 99.82%. After UV-visible light irradiation, Fe(III) ions are converted into Fe(II) ions, which can react with C₂O₄²⁻ to form FeC₂O₄ precipitates by adjusting the H₂O content, and P is recovered as Na₃PO₄∙12H₂O (99.98% purity). Additionally, a plan for the recycling of used DES is proposed and the leaching and recovery performances still maintain stable after three recycling circles. The method offers an approach with a simple process, high efficiency, and waste-free recycling for priority recovery Li and precise separation of Fe and P from spent LFP batteries in DESs.