Dissertation > Industrial Technology > General industrial technology > Materials science and engineering > Special structural materials

Preparation, Structure and Properties Study on VO_x/CNT Nanocomposites

Author HuSiPing
Tutor ZhuQuan
School Wuhan University of Technology
Course Building materials and engineering
Keywords Vanadium oxide CNT Doping Nanocomposites Electrochemical properties
CLC TB383.1
Type Master's thesis
Year 2010
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Energy is the lifeblood of modern society. Global warming, city pollution and finite fossil-fuel supplies conspire to make the use of renewable energy, a worldwide imperative. There is great demand to design electrical-energy-storage systems to balance supply with demands. Vanadium lithium oxides as a kind of ion implantation, which has the potential applications for energy conversion and storage. Vanadium oxide and carbon nanotubes composites are synthesized via hydrothermal method. We investigate the morphology and structure of the nanocomposite by adjusting the ratio of the reactant, the reaction time and temperature in the hydrothermal procedure, and discuss the mechanism for the formation of the composite. In addition, the electrochemical performance has been analysed by doping in the host material. The concrete research contents and results are summarized as follow:The VOx/CNT nanocomposites have been synthesized by hydrothermal assitanted sol-gel method. The XRD analysis indicates that the stable V2O5/CNT composite structrue can be obtained while the reaction temperature arrives at 170℃. The crystallinity decreases with the increase of the ratio of the CNT, and the phase transformation from V2O5 to V3O7 by prolonging reaction time. The SEM and TEM image shows the structure of composites are interpenetrating networks, the length of VOx nanowire is several micrometers with a diameter of 100 nm, the lengthe of CNT is several micrometers with a diamter of 20~40 nm. The proper formation machanism can be discribed as follow:the hydroxy and carboxyl of modified CNT induced the self-assembled growth, nanowires growing up and detachment happened when the scale of oxide vanadium nanowires arrived at a certain level. In the doping system, MoO3, TiO2 doping in VOx/CNT can not change the morphogy and structrue of composites.The electrochemical property of VOx/CNT composites are investigated. When the VOx/CNT is assembled in lithium cell battery, the 1st discharge capacity is 331.3 mAh/g, and the capacity is 187.1 mAh/g after the 50 times cyclying. The charge-discharge efficiency is above 97.2%. The cycling stablity of MoO3 doped VOX/CNT composite have been enhanced, the 1st discharge capacity is 277.4 mAh/g, and the capacity remains 207.9 mAh/g after the 50 times cyclying. The 1st discharge capacity have been increased after TiO2 doped VOx/CNT composite. The obvious charge-discharge voltage plateaus can be observed. The 1st discharge capacity is 382 mAh/g, and the capacity is 127 mAh/g after 50 time cycles which is increased by 15.3 %comparing to the undoping nanocomposite.Moreover, the application in supercapacitor electrodes of the nanocomposite are researched. The results show that the VOx/CNT composite electrodes can exhibit a combination of double-layer and pseudocapacitance in LiNO3 and NaNO3 electrolyte. In contrast, in the KNO3 solution, the voltage rage 0.2~0.8 V could be arrived at the absence of CNT which only exhibit the form of the pseudocapacitance.

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