Emulsion drying synthesis of olivine LiFePO4/C composite and its electrochemical properties as lithium intercalation material

The electroactive LiFePO4/C nano-composite has been synthesized by an emulsion drying method. During burning-out the oily emulsion precipitates in an air-limited atmosphere at 300 degreesC, amorphous or low crystalline carbon was generated along with releasing carbon oxide gases, and trivalent iron as a cheap starting material was immediately reduced to the divalent one at this stage as confirmed by X-ray photoelectron spectroscopy, leading to a low crystalline LiFePO4/C composite. Heat-treatment of the low crystalline LiFePO4/C in an Ar atmosphere resulted in a well-ordered olivine structure, as refined by Rietveld refinement of the X-ray diffraction pattern. From secondary electron microscopic and scanning transmission electron microscopic observations with the corresponding elemental mapping images of iron and phosphorous, it was found that the LiFePO4 powders are modified by fine carbon. The in situ formation of the nano-sized carbon during crystallization of LiFePO4 brought about two advantages: (i) an optimized particle size of LiFePO4, and (ii) a uniform distribution of fine carbon in the product. These effects of the fine carbon on LiFePO4/C Composite led to high capacity retention upon cycling at 25 and 50degreesC and high rate capability, resulting from a great enhancement of electric conductivity as high as 10(-4) S cm(-1). That is, the obtained capacity was higher than 90 mAh (g-phosphate)(-1) by applying a higher current density of about 1000 mA g(-1) (11C) at 50degreesC. (C) 2004 Elsevier Ltd. All rights reserved.