Recycling of NMC black mass from spent lithium-ion battery using supercritical fluid extraction

The growing demand for lithium-ion battery recycling has intensified interest in selective and sustainable metal recovery techniques. In this study, we apply supercritical fluid extraction (SCFE) to real industrial black mass, containing mixed-metal oxides along with typical impurities such as conductive carbon, binder residues, and metallic fragments. Unlike previous SCFE research focused on pure cathode powders, this work demonstrates the feasibility and selectivity of the process under practical impurity conditions. Using supercritical CO₂ in combination with a tributyl phosphate–nitric acid adduct and hydrogen peroxide as a reducing agent, the process was optimized via full factorial design and response surface methodology. Under optimal conditions (65 °C, 20.7  MPa, 5  mL/g adduct-to-solid ratio in units of mL adduct per gram of black mass, 8  mL (per 8 g of feed) hydrogen peroxide), extraction efficiencies exceeded 90 % for Ni, Co, and Mn, while Li recovery reached 73 %. Characterization by XRD, SEM-EDX, Raman spectroscopy, and TC/TOC analysis confirmed metal removal and the structural persistence of carbonaceous material in the residue. Parametric tests highlighted the critical roles of the adduct and reducing agent in enabling efficient complexation and solubilization of transition metals. This work demonstrates that SCFE is a promising low-impact, chemically selective approach for lithium-ion battery recycling, capable of operating under mild conditions with reduced reagent consumption. It advances the feasibility of scalable, environmentally responsible recovery of critical materials from post-consumer batteries and sets the foundation for future integration with downstream purification or hybrid recycling technologies.