Selective lithium recovery from black powder of spent lithium-ion batteries via sulfation reaction: phase conversion and impurities influence

The aim of this study is to present a new understanding for the selective lithium recovery from spent lithium-ion batteries (LIBs) via sulfation roasting. The composition of roasting products and reaction behavior of impurity elements were analyzed through thermodynamic calculations. Then, the effects of sulfuric acid dosage, roasting temperature, roasting time, and impurity elements were assessed on the leaching efficiency of valuable metals. Characterization methods such as X-ray diffraction (XRD), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), and X-ray photoelectron spectroscopy (XPS) were employed to analyze the phase transformation mechanism during roasting process. The results indicate that after sulfation roasting (n(H2SO4):n(Li) = 0.5, 550 degrees C, 2 h), 94% lithium can be selectively recovered by water leaching and more than 95% Ni, Co, and Mn can be leached through acid leaching without the addition of reduction agent. During the sulfation roasting process, the lithium in LiNixMnyCozO(2) is mainly converted to Li2SO4, while the Ni, Co and Mn are first transformed to sulfate and then converted into oxide form. In addition, impurity elements such as Al and F will combine with lithium to form LiF and LiAlO2, which will reduce the leaching rate of lithium. These results provide a new understanding on the mechanisms of phase conversion during sulfation roasting and reveal the influence of impurity elements for the lithium recovery from spent LIBs.