CO₂-assisted ascorbic acid leaching for metal recovery from spent NCM cathodes and battery regeneration

The recovery of critical metals from spent Ni-Co-Mn (NCM) cathodes commonly requires concentrated acids, auxiliary reductants, or energy-intensive treatment. Here, pressurized CO₂-ascorbic acid leaching was integrated with leachate-based NCM811 regeneration. Under the optimized condition, 0.30 mol/L ascorbic acid, 7 MPa CO₂, a solid-to-liquid ratio of 20 g/L, and 25 °C, Li was completely extracted within 80 min, while the extraction efficiencies of Ni, Co, and Mn reached 98.3 %, 97.1 %, and 97.2 %, respectively, without a separately added reducing agent. Control experiments confirmed that the increase in metal extraction arose from the coupled action of pressurized CO₂ and ascorbic acid rather than from physical pressurization or CO₂ alone. Equilibrium analysis further indicated that ascorbic acid provided the principal acidity and reducing capacity, while the dissolved CO₂/H₂CO₃/HCO₃^- equilibrium can maintain protons availability during lattice dissolution. Kinetic fitting showed that the leaching behavior was best described by the product-layer diffusion model. SEM-EDS, XRD, and XPS revealed particle fragmentation, progressive disruption of layered structural order, and changes in surface valence states. The Li/Ni/Co/Mn-rich leachate was further converted into regenerated NCM811, which delivered discharge capacity of 180 mAh/g initially, retained 150 mAh/g after 200 cycles, and maintained 55-60 mAh/g at 5C. This approach achieves high metal extraction at room temperature using a relatively low organic-acid concentration without separately added reducing agent, while returning the recovered metals to functional cathode production.