Mechanism for Hydrothermal Synthesis of LiFePO4 Platelets as Cathode Material for Lithium-Ion Batteries

The low-temperature hydrothermal synthesis method has been drawing ever-growing attention due to the fact that it has many advantages over conventional methods for preparing promising cathode material LiFePO4. However; the mechanism for hydrothermal synthesis of LiFePO4 remains unclear. Here, the hydrothermal reaction mechanism of LiFePO4 is systematically studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), trail mission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and specific surface analysis. As evidenced by apparent precursor dissolution, fast hydrothermal formation, and significant decrease in particle size with adding alcohols and/or carbon black in the reaction system, a dissolution-precipitation mechanism accounts for the hydrothermal synthesis of LiFePO4. Moreover, we identified tetraphosphate in the LiFePO4 precursor. This compound undergoes hydrolysis upon heating during the hydrothermal process, resulting in a remarkable decline of pH value.