Nano-sized precursor FePO4·xH2O particles were obtained by oxidation co-precipitation using FeSO4⋅7H2O, H2O2 and ammonia. The powder was characterized by differential thermal analysis (DTA) and thermogravimetry (TG), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The TG-DTA results determined the content of crystal water of FePO4·xH2O, i.e. x = 1.5. The SEM observation suggested that FePO4·xH2O particles were spherical in shape and its grain size was about 150 nanometers. The dispersion of the synthesized powder was improved through the addition of surfactant. The XRD analysis indicated that the synthesized FePO4·xH2O was amorphous. After being calcined at 720 °C for 10 hrs, the synthesized FePO4·xH2O at pH of ~3.5 was crystallized and FePO4 in a single phase was obtained. According to the test results, the optimized preparation process parameters were determined.
LiFePO 4 /C composite powders were prepared by a simple reaction of as-synthesized FePO 4 •2H 2 O, LiOH•H 2 O, oxalic acid and citric acid. The influence of oxalic acid and citric acid in different ratios was investigated on morphology and electrochemical performance of LiFePO 4 /C composite powders. The characterization of the composites included X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD analysis indicates that the material is well crystallized without impurities. The obtained LiFePO 4 /C composite powders with well dispersion at CA/OA ratio of 1:1.50 and the initial charge capacity reached 159.3 mAhg -1 at 0.1C rate, meanwhile, the particles prepared at 1:0.75 were close to spherical in shape and the specific capacity value was 149.8 mAhg -1 at 0.1C rate, with a slight decrease on greater C-rates reaching 141.3 mAhg -1 at 1C.
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