Study on the mechanism of liquid-phase regulated preparation of battery-grade iron phosphate

Abstract

LiFePO₄ batteries play a crucial role in energy storage and electric vehicles, with their precursor, FePO₄, directly determining the electrochemical performance of LiFePO₄. The key to preparing high-quality FePO₄ is the precise regulation of crystal morphology. This study investigates the inter-ionic interaction of Fe³⁺ in a complex phosphate system to form monoclinic FePO₄ with high crystallinity by precisely controlling process parameters such as pH and reaction temperature. The optimized process parameters are as follows: during the leaching stage, a P/Fe feeding ratio of 3:1 and a reaction temperature of 90 °C; during the oxidation stage, a 140 % excess of H₂O₂ and a reaction temperature of 50 °C; and during the crystallization stage, a pH of 1.5 and a reaction temperature of 90 °C, with an aging time of 1 h. The resulting FePO₄ has a round cake morphology with a diameter of approximately 1.5 μm and a thickness of about 0.5 μm. The particle size distribution is narrow, with a D₅₀ of 2.64 μm. The products exhibit consistent crystalline morphology, high crystallinity, an Fe content of 36.595 %, a P content of 20.676 %, and an Fe/P ratio of 0.981. The synthesized LiFePO₄/C derived from this FePO₄ shows a discharge capacity of 154 mAh/g at 0.2C. The proposed preparation mechanism has significant theoretical implications for the efficient and environmentally friendly production of FePO₄ in the industry.