Supercritical CO2 technology for the treatment of end-of-life lithium-ion batteries

The penetration of Li-ion batteries (LIBs) in the automotive market makes a zero-waste vision for battery recycling urgent. This can play a crucial role in developing a circular economy through the recovery of critical raw materials (CRMs) as well as bringing non-metallic components back to use. In recent years, recycling technologies for LIBs entered a new stage focused on the development of advanced pre-treatment processes to separate all the valuable battery components and more sustainable metallurgical approaches. Compared to common recycling processes, supercritical fluid (SCF) technology has great advantages related to its environmental benignity; chiefly, if CO2 is used as the SCF (scCO2), it is an outstanding solvent for green chemistry approaches. This review aims at providing an overview on the current progresses and open challenges of SCF technology for the treatment of end-of-life LIBs. The fundamentals of SCF technology process are discussed, providing the reader a brief overview of principles, operation procedures and instrumentation. Thereafter, the main applications in the field of battery recycling are reviewed. Successful methods for battery electrolyte recovery via scCO2 are discussed together with pioneering studies on the extraction of critical metals from the cathode that demonstrate promising recovery rates (>60%) for Li, Co, Mn, and Ni. Finally, a specific focus is given on the huge innovation potential of scCO2 to separate and reuse the fluorinated binder from the electrode. At present, the binder is burnt in common recycling processes, leading to hazardous fluorinated gas emissions. This review aims to emphasize the opportunities of the SCF technology in battery waste treatment as a promising approach for resource recovery with significant economy and environmental perspectives.