Streamlined regeneration of cathode materials from spent lithium–ion batteries with deep eutectic solvents

Abstract

With the increasing generation of spent lithium-ion batteries (LIBs), there is an urgent need for efficient and environmentally friendly recycling methods. Compared to traditional pyrometallurgical and hydrometallurgical processes, deep eutectic solvents (DESs) offer advantages for recycling valuable metals from spent LIBs, including better biocompatibility and high recovery efficiency. However, complex procedures, long processing times, and solvent regeneration remain challenges. To address these limitations, we propose a streamlined recycling approach using a DES synthesised from guanidine hydrochloride (GUC) and tartaric acid (TA). This method promotes Li enrichment in the leachate while Co, Ni, and Mn mainly precipitate. Adding ethanol as an antisolvent enhances crystallisation and precipitation, producing Li-rich solutions and precursors containing only trace amounts of Li for Co-Ni-Mn (NCM) cathodes. Subsequent carbonisation converts Li into Li₂CO₃, which is then mixed with precursors in controlled ratios and subjected to high-temperature solid-state sintering to regenerate NCM cathode materials. Notably, ethanol and the DES are recovered by distillation with recovery efficiencies of 91.6% and 80%, respectively. This optimised process achieves leaching of NCM cathode materials under mild conditions and significantly improves the separation efficiency between Li and Co/Ni/Mn through a simplified workflow. Overall recovery efficiencies reach 97.51% for Li, 98.57% for Ni, 100% for Co, and 97.24% for Mn in regenerated NCM materials. This study presents a green, efficient, and simplified method for recovering valuable metals from spent LIB cathode materials.