In Situ Synthesis and Properties of Carbon-Coated LiFePO[sub 4] as Li-Ion Battery Cathodes

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Abstract
An in situ synthesis method for carbon-coated LiFePO4LiFePO4 powders has been investigated in detail using inexpensive FePO4FePO4 as an iron source and polypropylene as a reductive agent and carbon source. Thermogravimetric and differential thermal analysis of the precursor mixture indicated that the pyrolysis of polypropylene and the combination reaction of LiFePO4LiFePO4 could be processed synchronously at a synthesis temperature between 500 and 800°C. X-ray diffraction analyses and scanning electron microscopy observations showed that LiFePO4/CLiFePO4/C composites with fine particle sizes and homogeneous carbon coating could be directly synthesized by the in situ method. The electrochemical performances of the carbon-coated LiFePO4LiFePO4 powder synthesized at 700°C were evaluated using an electrochemical model cell by galvanostatic charge/discharge and cyclic voltammetry measurements. The in situ synthesized LiFePO4/CLiFePO4/C composite had a high electrochemical capacity of 164 mA h g−1 at the 0.1C rate, and possessed a favorable capacity cycling maintenance at the 0.3 and 0.5C rates. The good electrochemical properties of the LiFePO4/CLiFePO4/C composite are suggested to originate from the good crystallinity, the fine particle sizes, and the efficient electronic conductive coating layer of the material. © 2005 The Electrochemical Society. All rights reserved.