Effects of reaction conditions on preparation of FePO4·2H2O and properties of LiFePO4 by solution precipitation route

FePO₄·2H₂O precursor was synthesized from FePO₄·7H₂O, NH₄H₂PO₄, NH₃·H₂O and H₂O₂ as the oxidizing agent by solution precipitation route. Effects of reaction conditions, such as solution concentration, reaction temperature, stirring speed, adding amount of H₂O₂, pH and drying time on synthesis of FePO₄·2H₂O precursor were studied. Afterwards, Li₂CO₃, FePO₄·2H₂O and glucose were ground by wet process and dried fully. And then, LiFePO₄ was prepared by carbothermal reduction. The phases, structure and morphology of FePO₄·2H₂O and LiFePO₄ were characterized by ICP, TG-DSC, XRD and SEM. Effects of reaction conditions on electrochemical performance of LiFePO₄ were explored. The results show that no impurities exist in the FePO₄·2H₂O when reaction temperature is 80°C, stirring speed is 800r/min, adding amount of H₂O₂ is 3mL, pH is 2, drying time is 12h and reactant concentration is from 0.1mol/L to 1.5mol/L. However, production rate of FePO₄·2H₂O is no more than 100% when pH is below 2 with either reactant concentration. LiFePO₄ made from FePO₄·2H₂O precursor synthesized under the condition that pH is 2 and reactant concentration is 1mol/L shows excellent electrochemical performance. It has an initial discharge capacity of 154.4mAh/g at 0.1C.