| Olivine structured lithium iron phosphate, LiFePO4, as a new generation cathode material for lithium ion batteries, has received extensive concern from research and engineering field. In order to improve its low ion diffusion rate and low electronic conductivity, people have finished a lot of modified work to guide industrialization. In this paper, LiFePO4/C composites were synthesized by one-step solid-state reaction using Fe2O3 as raw materials, and polypropylene as reductive agent and carbon source. The effect of synthesis temperature on the electrochemical performance of the LiFePO4/C composites was studied.LiFePO4/CNFs composites were synthesized by chemical vapor deposition (CVD) of acetylene (C2H2). LiFePO4/CNFs with good electrochemical performance were obtained by improving calcination temperature and CVD conditions. At the same time, the industrialization of LiFePO4 were carried out byNH4H2PO4andFe2O3.First of all, a one-step solid-state reaction for synthesis of LiFePo4/C were carried out by using Fe2O3, and polypropylene as raw materials under different temperature, the effect of synthesis temperature on the electrochemical performance of the LiFePO4/C composites was studied.It is found that all obtained materials show the single olivine structure by XRD patterns. The as-prepared materials also have a regular distribution at SEM. The particle grew up gradually with the rise of temperature, and a certain degree of aggregation was investigated. The electrochemical properties of the materials showed that the materail synthesized at 700℃exhibits a first discharge capacity of 160,143,108 mAh/g at 0.1,1 C and 5 C respectively. The materials also exhibit a good rate capability. After 100 cycles at 1 C and 5 C, the specific capacities of 138 and 100 mAh/g are still maintained.LiFePO4/CNFs cathode materials were also in-situ synthesized by chenical vapor deposition in base of acetylene and Fe2O3, with strong reductibility and catalysis respectively. By improving calcination temperature and CVD conditions, it is found that the growth of LiFePO4 particles and CNFs occurs simultaneously and competitively; the formation of LiFePO4 by Fe2O3 will decrease due to the rapid growth of CNFs under unreasonable CVD conditions, and the properties of the materials will decline at the same time. Among the products synthesized at the experiment, the material after 80 min CVD reaction at 700℃exhibits the best electrochemical performance, which yields the highest discharge capacity of 153 mAh/g at 0.1 C rate and a retention rate of 97%after 50 cycles at 1C.LiFePO4 with high purity was synthesized by pilot plant test, in the base of NH4H2PO4. Fe2O3. Li2CO3, and stearic acid. The products with fine homogeneous distribution were investigated by SEM and no aggregation phenomenon was occurred. According to the galvanostatic tests, the as-prepared materials showed a first discharge capacity of 143 mAh/g and 117 mAh/g at 0.1C and 1C rate, respectively. Based on the preliminary work of our research group, industrialization trial production was carried out by using NH4H2PO4. Fe2O3. LiOH/Li2CO3 and starch as raw materials. The two prepared materials showed the single olivine structure of LiFePO4. First discharge capacity of these cathode materials are 116 mAh/g and 117 mAh/g at the charge and diacharge rate of 0.1 C,... |
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