Oxidizing Roasting Behavior and Leaching Performance for the Recovery of Spent LiFePO4 Batteries

Abstract

In this study, the effects of oxidizing roasting process on the liberation of cathode materials from Al foil under different conditions were investigated systematically. The mineralogical characteristics of the cathode materials before and after thermal treatment were extensively characterized using scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) as well as Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The results indicated that the increase in roasting temperature, oxygen concentration, and air flow rate enhanced the liberation of cathode materials. The cathode materials were gradually oxidized to Li3Fe2(PO4)3 and Fe2O3. Further, the carbon and fluorine content in the cathode materials decreased slowly during the thermal treatment, while the Al content increased. When the roasting temperature exceeded the melting point of Al, the Al foils were ablated and the cathode materials adhered to the Al foils again, resulting in difficulty in separation. The cathode materials leaching performance test results demonstrated that the oxidation of cathode materials had a negative effect on the leaching of Fe in sulfuric acid leaching system.