Hydrometallurgical recycling of Li-ion batteries

Lithium-ion batteries (LIBs) have become an integral part of the increased electrification aimed at tackling environmental and power supply challenges. LIB volumes as well as their range of uses from mobile devices to electric vehicles (EVs) have steadily increased, leading to an unprecedented demand for their related critical metals. Consequently, this study focused on LIB recycling, including characterization, leaching of black mass (industrially crushed waste LIBs), solution purification through precipitation and graphite recovery. It was found that black mass concentrates often consist of several types of LIBs. Electron microscope characterization results reported in this thesis include identification of inorganic impurities – such as Fe-Cr alloys, SiO2, and AlO(OH) particles which did not dissolve during leaching. Also, CO, CO2, and SO2 were detected during pyrolysis. In the leaching studies, the reductive power of metallic impurities, such as Fe, Cu, and Al was investigated in detail using synthetic materials and black mass. The results demonstrated that scrap current collectors can be utilized as reductants to achieve leaching efficiencies of 99%. For example, Fe can catalyze NMC and LCO dissolution in the presence of Cu and/or Al, while Cu was found to cement on the Al surface and simultaneously redissolve by reducing the active material. H2O2 decomposed due to Fe, Cu, and Al oxidation, hence decreasing reductive leaching efficiency. Fe and Al were precipitated from synthetic battery leach solution at a pH value of approx. 3.5. Findings demonstrated that losses of Ni, Co, and Li were due to co-precipitation in Fe and Al hydroxide removal, dependent on the Al concentration. The addition of H3PO4, prior to neutralization, precipitated Fe and Al as phosphates at the lower pH of 3, resulting in decreased co-precipitation, faster nucleation, metal precipitation, and better cake filterability .Additional investigations of graphite recovery from leach residues showed that the quality required for battery use was maintained after leaching (2 M H2SO4, 60 °C, 3 h, 2 vol.% H2O2) and pyrolysis (800 °C, 1 h in Ar atmosphere). Organic impurity removal by pyrolysis gave a higher surface area graphite that favors Li+ intercalation. Despite some inorganic impurities, when used as a LiB cell anode, the residual graphite from EV battery black mass showed good performance (av. specific capacity = 350 mAh/g), whereas that of portable device battery black mass was lower (250 mAh/g). Capacity retention was 80% after 100 cycles, indicating good performance.