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Preparation and Lithium-ion Batteries Anode Properties of Spherical Cobalt Oxide-Low-dimensional Car

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Tutor: KuangYaFei
School: Hunan University
Course: Chemical Engineering and Technology
Keywords: cobalt oxide,graphene,carbon nanotubes,composite materials,lithium ion battery a
CLC: TM912
Type: Master's thesis
Year:  2013
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Abstract:
Lithium-ion batteries are considered as the most promising new energy storagedevice£¬the commercialized graphite-based anode materials exhibit excellent cyclingperformance, but their low specific capacity can¡¯t satisfy the demand for the highenergy density of batteries. Therefore, it is urgent to develop new anode materialswith larger capacity. Owing to their high capacity, transition metal cobalt oxide are anew class of promising anode materials for rechargeable Li-ion batteries. But thelarge irreversible capacity loss in the first cycle and relatively fast capacity fadingrate during electrochemical cycling of cobalt oxides limit their practical applications.composite of the transition metal oxide and conductive carbon material £¨such asgraphene, carbon nanotubes, etc.£© is one of the methods to solve the above problems.Graphene has become a rapidly rising star on the horizon of new energy, because ofits larger surface area,good electrical conductivity properties and potentialapplications in energy storage materials. carbon nanotubes £¨CNTs£© have attractedconsiderable attention as promising anode materials for Li-ion batteries due to theirexceptional structure allowing rapid insertion extraction of lithium into/from thenanotubes.In this thesis, transition metal cobalt oxide, graphene/cobalt oxide and carbonnanotube/cobalt oxide were prepared, The physical and electrochemical properties ofthe materials were systematicly examined using a variety of characterization methods.The three main aspects of the listed as follows:£¨1£© We preparation and study of cobalt oxide £¨Co3O4£© spheres byHydrothermal-Thermal decomposition processes. The as-obtained Co3O4werecharacterized by X-ray diffraction £¨XRD£©, scanning electron microscope £¨SEM£© andThermogravimetric Analysis £¨TGA£©, etc. We study of the influence of experimentalconditions on the morphology of the Co3O4precursor, and determine the optimumconditions of preparing Co3O4spheres precursor: the ratio of ethylene glycol andwater=80:40mL, the hydrothermal reaction time=24h, the temperature of thehydrothermal=200-230¡æ. The electrochemical performances of the as-obtainedCo3O4toward Lithium-ion batteries were investigated by cyclic voltammetry andgalvanic charge and discharge.The results suggest that Co3O4sheets and loose Co3O4spheres possess higher initial charge capacity, but compact Co3O4spheres exhibit relatively excellent cycling performance.£¨2£© graphene-encapsulated Co3O4spheres composite £¨GE/Co3O4£© was preparedby electrostatic interactions. The morphologies and compositions of the as-preparedGE/Co3O4composites were characterized by scanning electron microscope £¨SEM£©,energy-dispersive X-ray spectroscopy £¨EDS£©, X-ray diffraction spectroscopy £¨XRD£©and Thermogravimetric Analysis spectroscopy £¨TGA£©. The results show that graphenesheets intimately and Uniformly encapsulate the The surface of the Co3O4spheres, thecontent of graphene was approximately20wt%. The electrochemical performances ofthe as-obtained composites toward Lithium-ion batteries were investigated by cyclicvoltammetry and galvanic charge and discharge. Compared to Co3O4and GE-Co3O4which was fabricated by mechanically mixing, GE/Co3O4exhibits much higherreversible capacity, and it remains850mAh/g after30cycles, showing good cyclingperformance and rate capability.£¨3£© Carbon nanotubes-wrapped Co3O4spheres composite £¨CNTs/Co3O4£© wassynthesized by the self-assembly of Carbon nanotubes and Co3O4spheres. Themorphologies and compositions of the as-prepared CNTs/Co3O4composites werecharacterized by scanning electron microscope £¨SEM£©, energy-dispersive X-rayspectroscopy £¨EDS£©, X-ray diffraction spectroscopy £¨XRD£© and ThermogravimetricAnalysis spectroscopy £¨TGA£©. The results show that Carbon nanotubes presents amesh-like morphology and wrapped around the surface of Co3O4spheresuniformly,The electrochemical performances of the as-obtained composites towardLithium-ion batteries were investigated by cyclic voltammetry and galvanic chargeand discharge. The results demonstrate that compared to Co3O4and CNTs-Co3O4which was fabricated by mechanically mixing, CNTs/Co3O4exhibits much higherreversible capacity and much better cycling performance, but its rate capability is notsatisfactory.
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