Influence of pretreatments on the surface charge of anode and cathode materials in spent lithium-ion batteries - a key point for recycling

The flotation process for separating anode and cathode materials (blackmass) is a critical step in recycling lithium-ion batteries (LIBs), particularly before the extraction of lithium-bearing materials. Surface electric charge, measured via zeta potential, plays a pivotal role in the flotation separation of these electrode materials. The pH, roasting temperature, thermal treatment duration, and bubbles' presence can significantly influence these materials' surface properties. However, a comprehensive investigation addressing the combined effects of these factors on the zeta potential of electrode active materials is still lacking. This study aims to bridge this gap by systematically exploring the effects of pH (4.5, 7, and 10.5), roasting temperatures (0–500 °C), varied thermal treatment times (1 to 2 h), and the presence or absence of bubbles (nano and microbubbles) on the zeta potential of both anode and cathode materials. The study also examines the impact of conditioning with n-dodecane, a typical flotation collector. While zeta potential is largely pH-dependent, roasting temperature significantly influences surface charge, whereas thermal treatment duration has a minimal effect. Notably, the most considerable zeta potential difference (28.3 mV) between the anode (-18.63 mV) and cathode (9.67 mV) surfaces occurred in the absence of both collector and bubbles, at pH 7, 500 °C, and a thermal treatment time of 2 h. Under conditioning involving bubbles and collector, the highest difference observed was 2.21 mV at pH 7, 250 °C, and 1 h of thermal treatment. These findings contribute to a deeper understanding of surface charge behavior in LIB recycling processes, with implications for improving flotation separation efficiency through surface science and engineering.