Synthesis and Characterization of LiFePO 4 /C Composite Obtained by One-Step Solid-State Reaction Using Solid PVA as Car
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Synthesis and Characterization of LiFePO4/C Composite Obtained by One-Step Solid-State Reaction Using Solid PVA as Carbon Source Limei Yang1, Guangchuan Liang2, Li Wang3, Xiaoke Zhi4, Xiuqin Ou5 1 Institute of Power Source and Ecomaterials Science, Box1055, Hebei University of Technology, 300130, Tianjin, China. E-mail: [email protected] 2 Institute of Power Source and Ecomaterials Science, Box1055, Hebei University of Technology, 300130, Tianjin, China. Corresponding author, E-mail: [email protected] 3 Institute of Power Source and Ecomaterials Science, Box1055, Hebei University of Technology, 300130, Tianjin, China. E-mail: [email protected] 4 Institute of Power Source and Ecomaterials Science, Box1055, Hebei University of Technology, 300130, Tianjin, China. E-mail: [email protected] 5 Institute of Power Source and Ecomaterials Science, Box1055, Hebei University of Technology, 300130, Tianjin, China. E-mail: [email protected] ABSTRACT LiFePO4/C composite cathode materials were synthesized by one-step solid-state reaction using FePO4 as main raw materials and solid PVA (Polyvinyl Alcohol) as a reductive agent and carbon source. The sample was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), particle size analysis and charge-discharge test. The results indicated that the carbon generated from the pyrogenation of PVA did not affect the olivine structure of the cathode materials but considerably improved its high-rate discharge ability and cycle performance. The initial discharge capacity of the sample was 149.7, 133.1, 120.6, 93.0 mAh/g at 0.2C, 1C, 2C, 5C respectively, and the discharge capacity could reach 90 mAh/g at 5C rates after 80 cycles. It is believed that the carbon coating could lead to small particle size and high electronic conductivity of active materials, thus leading to excellent electrochemical performance of LiFePO4/C cathode materials. INTRODUCTION Olivine structured LiFePO4 is one of the most promising cathode materials for power lithium ion batteries used in power tools due to its long cycling life, high safety, low-cost as well as environmental benignity[1-3]. However, the low electronic conductivity and low ion diffusion kinetics limit the electrochemical properties and applications in pure LiFePO4, and result in the poor reversible capacity of this material [4-6]. Carbon-coated technology is the most widely used method of modification for reasons of low-cost, effectiveness, and ease of use in industrial production. It is reported that the roles of carbon-coated technology were refining the particles, densifying the material, enhancing conductivity and supplying a reductive atmosphere in the reaction process[6-9]. But the carbon
source and its form have a direct impact on the electrochemical properties of LiFePO4/C composite materials. Finding a more suitable carbon source was an important goal. PVA has been studied as a carbon source recently. It has been previously reported that pyrolysis of PVA in a nitrogen gas flow occured
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