A closed-loop zero-liquid-discharge process for the precipitative separation of all valuable metals from waste lithium-ion batteries of mixed chemistries at room-temperature†

Abstract

Recycling spent lithium-ion batteries (LIBs) and recovering valuable metals is essential for resource sustainability, minimizing environmental footprint, and maximizing resource utilization. However, many existing recycling methods are costly, energy-intensive, pose fire hazards due to organic solvents, or generate extensive secondary waste. Also, most studies have focused on metal recovery from simple cathode materials, such as LCO batteries, with less attention on mixed LIBs, containing multiple metals. To address these concerns, we have developed a room-temperature leaching process for NMC-type cathode materials that shows high leaching efficiency for Li, Co, Ni, and Mn (∼98%) under optimized conditions of 4 M acetic acid, 5 vol% H₂O₂, 20 g L⁻¹ pulp density in a duration of 5 h. We have also developed a downstream process that enables the sequential and selective precipitation of all metals through judicious control of the solution pH and using specific reagents. As a result, all metal salts (Ni(DMG)₂, Co₈S₉, Mn(OH)₂, and Li₂CO₃) were recovered in pure form (≥98%) with high recovery efficiencies (85–99%). Additionally, excess acetic acid and the by-product sodium acetate (purity ≥97%) are also recovered, establishing a zero liquid discharge process. We also recycled Ni(DMG)₂ complex to recover β-Ni(OH)₂ and DMG for re-use. Furthermore, the recovered acetic acid was used to recover lithium, copper, and graphite from the anode material. This process offers several advantages over existing technologies, including low energy requirements for a room temperature process, eliminating cathode pre-treatment, the use of selective precipitation methods that preclude the necessity for organic solvents, and fire hazards. This environment-friendly zero-liquid discharge process offers a sustainable pathway for LIB recycling.