As the byproduct of TiO2 industrial production, impure FeSO4·7H2O was used for the synthesis of LiFePO4. With the purified solution of FeSO4·7H2O, FePO4·xH2O was prepared by a normal titration method and a controlled crystallization method, respectively. Then LiFePO4 materials were synthesized by calcining the mixture of FePO4·xH2O, Li2CO3, and glucose at 700°C for 10 h in flowing Ar. The results indicate that the elimination of FeSO4·7H2O impurities reached over 95%, and using FePO4·xH2O prepared by the controlled crystallization method, the obtained LiFePO4 material has fine and sphere-like particles. The material delivers a higher initial discharge specific capacity of 149 mAh·g-1 at a current density of 0.1C rate (1C=170 mA·g-1); the discharge specific capacity also maintains above 120 mAh·g1 after 100 cycles even at 2C rate. Thus, the employed processing is promising for easy control, low cost of raw material, and high electrochemical performance of the prepared material.
In order to obtain a new precursor for LiFePO4,Fe2P2O7 with high purity was prepared through solid phase reaction at 650 ℃using starting materials of FeC2O4 and NH4H2PO4 in an argon atmosphere.Using the as-prepared Fe2P2O7,Li2CO3 and glucose as raw materials,pure LiFePO4 and LiFePO4/C composite materials were respectively synthesized by solid state reaction at 700 ℃in an argon atmosphere.X-ray diffractometry and scanning electron microscopy(SEM)were employed to characterize the as-prepared Fe2P2O7,LiFePO4 and LiFePO4/C.The as-prepared Fe2P2O7 crystallizes in the C 1space group and belongs toβ-Fe2P2O7 for crystal phase.The particle size distribution of Fe2P2O7 observed by SEM is 0.4-3.0μm.During the Li +ion chemical intercalation,radical4-2 7P Ois disrupted into two3-4 PO ions in the presence of O 2-,thus providing a feasible technique to dispose this poor dissolvable pyrophosphate.LiFePO4/C composite exhibits initial charge and discharge capacities of 154 and 132 mA.h/g,respectively.
