An optimum route to prepare FePO_4 ·2H_2O and its use as an iron source to synthesize LiFePO_4

LiFePO4 cathode material is synthesized by a simple solid-state reaction method with FePO42H20 as iron source and citric acid as reductive agent and carbon source. This study examines the effects of different oxidation routes to prepare FePO4＂2H20 on the electrochemical performance of as-synthesized LiFePO4. Iron phosphate was prepared by two routes from FeSO4＇7H20. One is the formation of Fe3（PO4）2 precipitate in the first step and subsequent oxidation to FePO4 precipitate. The other is the oxidation of ferrous to ferric ion firstly, and then to form FePO4 precipitate directly. The results indicate that substantial differences in the structure and electrochemical properties of LiFePO4 depend on the behavior of FePO4. Iron phosphate obtained through one step precipitation has a smaller particle size and more uniform particle distribution, which is demonstrated to be more applicable as the iron source to synthesize LiFePO4/C. As-prepared LiFePO4/C shows an excellent rate capability and cycle performance. The initial discharge capacities of 160.6 mAh/g and 107 mAh/g are achieved at 0.1 C and 10 C, respectively. The good capacity retention of 97% after 300 cycles is maintained at the rate of 5 C.

LiFePO4 cathode material is synthesized by a simple solid-state reaction method with FePO4 ·2H2O as iron source and citric acid as reductive agent and carbon source. This study examines the effects of different oxidation routes to prepare FePO4 ·2H2O on the electrochemical performance of as-synthesized LiFePO4 . Iron phosphate was prepared by two routes from FeSO4 ·7H2O. One is the formation of Fe3(PO4)2 precipitate in the first step and subsequent oxidation to FePO4 precipitate. The other is the oxidation of ferrous to ferric ion firstly, and then to form FePO4 precipitate directly. The results indicate that substantial differences in the structure and electrochemical properties of LiFePO4 depend on the behavior of FePO4 . Iron phosphate obtained through one step precipitation has a smaller particle size and more uniform particle distribution, which is demonstrated to be more applicable as the iron source to synthesize LiFePO4 /C. As-prepared LiFePO4 /C shows an excellent rate capability and cycle performance. The initial discharge capacities of 160.6 mAh/g and 107 mAh/g are achieved at 0.1 C and 10 C, respectively. The good capacity retention of 97% after 300 cycles is maintained at the rate of 5 C.