Phase preconversion enables mild deep eutectic solvent leaching for efficient recycling of spent LiNixCoyMn1−x−yO2 cathodes

ABSTRACT Deep eutectic solvents (DESs) offer a greener leaching route for the efficient recycling of spent lithium-ion batteries (LIBs), especially high-energy-density LiNi x Co y Mn 1 − x − y O 2 (NCM) cathodes. However, their direct application still requires overcoming harsh conditions such as high temperature and the constraint of high liquid-solid ratios (L/S). Here we show that a tailored phase-preconversion step fundamentally overcomes this barrier. Guided by thermodynamic analysis, spent NCM cathodes are precisely reduced at 650 °C using waste anode graphite to form readily leachable low-valence oxides (NiO, CoO, MnO) and Li 2 CO 3 , and metallic phase formation is minimized to avoid hazardous H 2 generation during subsequent acid leaching. This preconversion dismantles the stable NCM structure, enabling subsequent DES leaching under remarkably mild conditions: 50 °C (vs. >90 °C reported) and L/S ratio of 8 g·g −1 (vs. > 20 g·g −1 reported). Lithium is first extracted by water leaching, achieving up to 96.5% efficiency at 5 °C (compared with ∼93.0% reported), and subsequently recovered as Li 2 CO 3 with a recovery yield of 88.2%. The remaining transition-metal-enriched residue is then treated with choline-chloride-based DES, yielding extraction efficiencies of 96.6%, 98.3%, 99.9% for Ni, Co, and Mn, respectively. Techno-economic analysis shows a net profit of 9.32 USD·kg −1 with low GHG emissions (844 g·kg −1 ). The profit surpasses those of hydrometallurgy (8.60 USD·kg −1 ), pyrometallurgy (4.87 USD·kg −1 ), and direct recycling (7.15 USD·kg −1 ). This work provides a scalable, environmentally sound route for metal recovery from spent LIBs and underscores the enabling role of tailored phase preconversion for industrial DES applications.