| Lithium iron phosphate has the advantage of different sources, low price, good safty performance, and high specific capacity. So it receives extensive attention from academia and industry. The main limitation of LiFePO4performance at high rate is the low ionic and electronic conductivity, especially under low temperature environment. The LiFePO4/KB nanocomposite was modified by composite with Ketjen Black,Carbon Aerogel and Al3+doping methodes to improve the low-temperature properties.In the dissertation, we take advantage of the high dissolubility materials as precursor and Ketjen Black as the carbon skeleton which has the structure of the abundant branched chain, then use the saturated solution impregnation method to successfully prepare LiFePO4/KB nanocomposite. Investigations show that the prepared LiFePO4/KB nanocomposites retained the KB carbon skeleton and about5-10nm lithium iron phosphate relatively uniform dispersed in Ketjen Black mesoporous. The composite delivers a discharge capacity of120.3mAh/g,100.1mAh/g,85.5mAh/g and64.5mAh/g at1C,5C, IOC and20C under-20℃respectively. Moreover, the capacity maintains93.6%at5C and91.2%at10C under-20℃after200cycles.We also use both Carbon Aerogel and Ketjen Black as template to prepare the LiFePO4/C complexes. Results show that the carbon content increases so that the material high rate performance increased. By changing the percentage of carbon aerogel and Ketjen Black, the best proportion of LiFePO4/C delivers the capacity of168.9mAh/g,141.4mAh/g,128.5mAh/g and120mAh/g at0.1C,1C,5C and10C, respectively under room temperature.Using A1(NO3)3-9H2O as doping material, to synthesis LixAl(1-X)FePO4/KB composite materials. We studied the influence of different content of Al3+doping to the electrochemical properties of the composites. By Al3+doping, the material bulk conductivity improved. When the doping amount is2%Al3+, the synthesised Li0.98Alo.o2P04/KB composite material has the best electrochemical performance. |
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