Preparation And Lithium-ion Batteries Anode Properties Of Spherical Cobalt Oxide-Low-dimensional Carbon Composite

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℃. 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.