Efficient and Selective Recovery of Spent NCM Cathode Materials: A Green Deep Eutectic Solvent Process via Synergistic Acidity-Viscosity Regulation

Abstract

Facing the large-scale recycling demand for retired ternary lithium-ion batteries (NCM) from electric vehicles, conventional pyrometallurgical and hydrometallurgical processes are challenged by high energy consumption, significant secondary pollution, or complex flowsheets. This study constructed a novel green deep eutectic solvent (TL-DES) using lactic acid (LA) as the hydrogen bond donor and tetramethylammonium chloride (TMAC) as the hydrogen bond acceptor for the efficient leaching of valuable metals (Li, Ni, Co, Mn) from severely degraded NCM cathode materials. The synergistic effect between acidity and viscosity in this system and its leaching behavior were systematically investigated, revealing a cooperative leaching mechanism of "proton attack -coordination dissociation -reduction stabilization". Experiments demonstrated that under conditions of 100 ℃ and 2 h, the leaching efficiencies of Li, Co, Ni, and Mn all exceeded 95%, meeting the requirements of the EU's new Battery Regulation. By introducing anhydrous ethanol as an antisolvent, highly selective separation characterized by "complete precipitation of Ni/Co, partial precipitation of Mn, and no precipitation of Li" was achieved. The precipitated product was a structurally ordered lactate-intercalated layered double hydroxide (LDH), which can be directly used as a cathode precursor. Life cycle assessment indicated that this process significantly outperforms traditional pyrometallurgy and direct regeneration in terms of greenhouse gas emissions (0.52 kg/kg) and energy consumption (7.22 MJ/kg), while maintaining good economic feasibility. Based on the degree of material degradation, this study further proposes a "graded regeneration" strategy, offering a viable technical pathway for the short-process, closed-loop recycling of spent ternary batteries.