| The purposes of the thesis are to systemically research the inexpensive manganese dioxide as the electrode material which is prepared by hydrothermal method and thermal decomposition method. A manganese dioxide-graphene composite material and graphene/Ni-doping MnO2 composite material were prepared at a optimal condition. The physical and electrochemical testing methods such as XRD, TEM, CV, EIS, constant current charge-discharge were employed to investigate the structure and electrochemical performance of the materials. The main results are as follows:1.We demonstrated a simple hydrothermal synthesis to prepare a mesoporous MnO2 materials use four hydrated manganese chloride and urea as raw material.The influence to MnO2 physical and chemical properties was studied on factors of reaction temperature, heat treatment temperature and synthesis routes. The sample synthesized at 100 ℃ showed a better crystalline phase, uniform particle size, high specific capacitance and better electrochemical stability. With the increase of hydrothermal temperature the crystallinity of material get poor and the agglomeration get more seriously, specific volume also decreased. MnO2 precursor calcination at 300 ℃has better morphology and electrochemical properties than treated at 400 ℃. We used liquid phase mixing method to synthesis MnO2 in the same material ratio conditions and find that the prepared MnO2 showed a loose hollow microsphere structure which is unstable and a large hole. The electrochemical performance was worse than the MnO2 prepared by hydrothermal method.2.Based on hydrothermal method,we showed a graphene coated MnO2 composites material.In this experiment, by adding graphene with different mass fraction, the conductivity of MnO2 could be improved and the graphene coated structure could also prevent MnO2 from reunite and shedding from collector in the process of charge and discharge. It has provides a effective method to improve the cycle stability for practical usage.The results indicates that the composite materials contained a 15% mass percentage of graphene showed a larger specific surface area, excellent capacitance characteristics, good energy density and the cycling stability.3.We synthesis a Ni doped manganese oxide and its graphene composite by hydrothermal synthesis.XRD and SEM showed the Ni doped into the MnO2 lattice, with the increase of Ni content, the size of the particle will decrease and the spherical become more obvious.Electrochemical testing results showed that the doped Ni is helpful to improve the performance of this supercapacitor material, when molar ratio of Mn:Ni was 10:1, the specific capacity of composite could reach to 356F/g in 2M KOH solution.The capacitance have been improved significantly. When the material was incorporated with graphene at the same Ni:Mn ratio, the maximum capacity was increased to 563F/g. The graphene-Ni dotted MnO2 composits exhibited a good impedance properties, the electrochemical performance has been improved obviously.4.We prepared Mn-Co and Mn-Ru complexes through liquid phase coprecipitation, XRD found that the crystallinity of manganese dioxide and cobalt oxide in complexes is poor, ruthenium oxide has a decent crystallinity. SEM showed the morphology of complexes has a significant change to the pure MnO2, Mn-Co complex is composed of flowerlike structure, Mn-Ru composite is nano-scale square column structure. Electrochemical testing showed that the electrochemical reversibility and high current charge discharge characteristics are improved to a certain extent, the specific capacity of Mn-Co and Mn-Ru composite can reach 250F/g and 402F/g in 0.2A/g respectively. |
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