Studies On Synthesis, Electrochemical Energy Storage Properties And Mechanism Of Several Nanomaterials

Since electric motors and generators were invented in the1870s, electrical energy has become the most important secondary energy source and the primary form of consumed energy. Electricity can be generated from fuel-burning power, solar power, hydropower, wind power, nuclear power, tide power, and biopower systems, and is indispensable in almost every part of our lives from lighting, warming and cooling, from cooking to entertainment, transportation, and communication. With the rapid development of modern industries and the durative increase of global population, the rate of electrical energy consumption has dramatically increased and its consumption manner is diversified. Energy storage becomes even more complex and important, and desirable and high-performance energy storage techniques are needed to enable efficient, versatile, and environmentally friendly uses of energy including electricity. Among the various alternative energy storage technologies, electrochemical energy storage shows advantages of high efficiency, versatility, and flexibility. Lithum ion batteries (LIBs) are the most important and widely used rechargeable battery with advantages of high voltage, low self-discharge, long cycling life, low toxicity, and high reliability. Supercapacitors have attracted increasing interest because of their high power storage capability, which is highly desirable for applications in electric vehicles and hybrid electric vehicles. The performance of LIBs and supercapacitors is intimately related to the electrode materials used. With the development of materials design strategies, synthesis techniques, and characterization methodologies, electrode materials and consequently the performance of batteries and supercapacitors have been progressing rapidly.Electrode materials are key parts of the electrochemical energy storage devices, and the morphology, structure, specific surface area and electrical conductivity are important for the performance of the electrode materials. In this thesis, several electrode materials with special morphology and novel structures were successfully prepared and the electrochemical performance was investigated. The main contents include the following:1. Carbon bundle arrays are successfully synthesized. A ZnO/C core/shell structure was firstly fabricated by a in situ CVD method, using ZnO nanowire array on a Ti substrate as both the template and catalyst. SEM, XRD, TEM and HRTEM were introduced to investigate the morphology and the structure of the sample. The results show that the carbon shells exhibit a scaly structure. After removing the ZnO cores, the scaly carbon array remains on the Ti substrate and has an extremely high specific surface area and electrical conductivity, which are two vital factors for the use of this material in supercapacitors. Electrochemical tests were examined with a dual channel electrochemical workstation using a conventional three-electrode system, and the results show a high specific capacitance (140F/g) and excellent cycling performance of-81%capacitance retention over10000cycles. Experiments using the rough carbon shells coated intimately on the ZnO exhibited a much lower specific capacitance.2. Hybrid Ni(OH)2/graphene structure on nickel foam were succefully obtained by a new two-step approach. Firstly, the graphene was synthesized on nickel foam, which was used both as catalyst and template, by a CVD method. Then the three-dimensional network structured Ni(OH)2nanosheets were deposited on the graphene-coated nickel foam by a hydrothermal method. Electrochemical tests of this kind of electrode show a high specific capacitance (1440F/g) and excellent cycling performance of-100%capacitance retention over2000cycles. The presence of the graphene is critical to the high-performance of the electrode, and the experiment using the Ni(OH)2on bare nickel foam exhibited a much worse cycling performance.3. A facile solvothermal method to synthesize self-assembled three-dimensional Ni2+-Fe3+layered double hydroxides (LDHs), using ethylene glycol (EG) as a chelating reagent and urea as a hydrolysis agent. The effects of solvent constituents (volume ratio of ethylene glycol to water), and iron source on the morphologies were investigated. The reaction mechanism and self-assembly process were discussed. and the electrochemical performance were investigated. After calcinating the as-prepared LDHs at450℃in nitrogen gas, porous NiO/NiFe2O4nanosheets were obtained.4. Uniform crystalline MgSn(OH)6nanocubes were synthesized by a hydrothermal method. The influences of reaction conditions were investigated and the results showed that the solvent constituents significantly affected the shape and size of MgSn(OH)6. SnO2/Mg2SnO4has been obtained by thermal treatment at850℃for8h under a nitrogen atmosphere using MgSn(OH)6as the precursor. The electrochemical tests of SnO2/Mg2SnO4revealed that SnO2/Mg2SnO4has a higher capacity and better cyclability compared to pure SnO2or Mg2SnO4. The electrochemical performance of SnO2/Mg2SnO4was sensitive to the size of the nanoparticles. The lithium-driven structural and morphological changes of the electrode after cycling were also studied by the ex-situ XRD pattern and TEM tests. This work indicates that SnO2/Mg2SnO4is a promising anode material candidate for application in Li-ion batteries.