Synthesis and electrochemical analyses of vapor-grown carbon fiber/pyrolytic carbon-coated LiFePO4 composite
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A vapor-grown carbon fiber/pyrolytic carbon-coated LiFePO4 (VGCF/PCLFP) composite has been prepared in one step through a solid-state reaction accompanied by a gas-phase decomposition process. This method leads to the formation of a conductive network composed of pyrolytic carbon layer and in situ vapor-grown carbon fiber in the composite. The amount of carbon in the composite has been determined by a modified formula based on thermogravimetric analysis to be around 3.0 wt%. The optimized electrode of VGCF/PCLFP composite can deliver 150 mAhg−1 at 0.5 C rate, 137 mAhg−1 at 1.0 C rate and 132 mAhg−1 at 3.0 C rate. And its discharge capacity loses only ~4% at a higher rate of 3.0 C after 100 cycles. The area-specific impedance of a cell fabricated with VGCF/PCLFP composite is lower than that made of only pyrolytic carbon-coated LiFePO4, reported here for the purpose of comparison. In comparison to the electrode made of carbon black/LiFePO4 composite (10 wt% carbon), the charge transfer resistance of the VGCF/PCLFP composite electrode decreases from 165 to 91 Ω. This technique presents an attractive way to produce high-performance LiFePO4 cathode material through a low-cost high-efficiency process.
KeywordsDischarge Capacity Cathode Material LiFePO4 Composite Electrode Conductive Network
This work was supported by the Two Hundred Plan for Talent Station of Shenzhen (Shenfu  No.182), the Science and Technology R&D Program of Shenzhen (CXB201005240010A), the Science and Technology R&D Program of Shenzhen (ZD200904290044A), the Science and Technology Project of Shenzhen (JC200903130266A), and the fund of Shenzhen Key Laboratory of Special Functional Materials (T201005). We also thank Professor Wenjun Liu for his technical guidance with electrochemical impedance spectroscopy.
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