Ultrasonic separation of electrode scrap in water: a sustainable method for Li-ion battery recycling

Abstract

This study investigates a water-based ultrasonic treatment as a pretreatment method for the direct recycling of electrode scrap generated in lithium-ion battery manufacturing. As production scales up to meet growing demand, such scrap is increasingly generated, and its active materials are less degraded than those in used batteries, making it well-suited for direct recycling. The focus of this work is on the separation of cathode materials, which contain valuable and scarce metals and are typically bound with organic-insoluble binders that resist water-based removal. In contrast, anode materials, which use water-soluble binders, can be easily separated using water. To enable efficient and environmentally friendly separation without the use of harsh chemicals or high temperatures, underwater ultrasonic treatment was explored. While low-frequency ultrasonication enhanced the detachment of the electrode material, it often caused damage to the aluminum (Al) foil current collector. To address this, a higher frequency with a periodic frequency sweep was employed to disperse standing waves, resulting in the successful removal of over 99% of cathode material using only water, with no damage to the Al foil. The recovered cathode powder contained less than 0.02 wt% of Al impurities, indicating high purity suitable for reuse. The study also found that water immersion prior to ultrasonication inhibited exfoliation due to the formation of petal-like compounds at the Al/electrode material interface. Thus, immersion time should be carefully optimized to ensure stable and effective processing. This nonthermal, nonmechanical, and brief water-based process offers a promising, low-impact, and energy-efficient strategy for battery material recovery.