Synthesis And Electrochemical Properties Of New Type Carbon Materials And Carbon-based Composites

Lithium-ion batteries are considered as the most promising power storage device because of theirhigh potential, long cycle life, environmental friendliness. The commercialized graphite materialsexhibit good cycling performance, but their low specific capacity can’t satisfy the demand for thedensity of batteries. It is urgent to research and explore new type graphite materials. The transitionmetal oxides exhibit high specific capacity, but the cycle performance and rate performance is verypoor. The nanocomposite material of carbon materials/metal oxide have been searching to improvethe performance of the lithium battery material. In this thesis, new carbon materials have beensynthesized successfully, using different chemical methods to prepare RGO-CNTs-Co₃O₄,C-Co₃O₄-FGS and MCNTs-Fe₂O₃composite materials, and the electrochemical performances of thesamples have been tested.RGO-CNTs-Co₃O₄ternary nanocomposite was synthesized using low temperature hydrothermalreaction and low temperature treatment method. In this typical experiment, with hydrazine as reducingagent, graphene oxide was reduced to graphene. At the same time, cobalt hydroxide was obtained onthe surface of RGO and CNTs. After treating at a low temperature, RGO-CNTs-Co₃O₄ternarynanocomposite was obtained. The results of electrochemical tests show the three element compositematerial the first discharge capacity is about1650mA·h/g at a current density of100mA·h/g, itsspecific capacity was maintained at1261mA·h/g, capacity retention rate is76.4%after50charge-discharge cycles.Carbon-coated cobalt oxide and graphene composite material was prepared via a hydrothermalsynthesis method. The morphologies and crystal structures of samples were characterized by SEM、TEM and XRD. The results shows the carbide of glucose is completely coated microspheres Co₃O₄particles, and highly dispersed on the graphene sheets. N2adsorption/desorption tests show that, thecomposite material has large specific surface area. When it applied as anodes in lithium-ion cells,C-Co₃O₄-FGS electrode exhibited the best electrochemical performance, which maintained844mA·h/g after50cycles at100mA/g current density. Its performance is superior to the single FGS、Co₃O₄and Co₃O₄-FGS. C-Co₃O₄-FGS composite materials can be used as a potential electrodematerial.Preparation and study on electrochemical performance of mesoporous carbon nanotubes-ferricoxide composite materials. MCNTs composites were prepared by solvothermal method.In this process,glycol was used as carbon source. Its specific capacity was maintained at889mA·h/g, capacityretention rate is90%after50charge-discharge cycles. MCNTs-Fe₂O₃composite material were prepared by dipping and low-temperature thermal decomposition method. The first dischargecapacity of composite material is1850mA·h/g at a current density of100mA/g. Compared with thefifth capacity, the capacity retention rate is close to100%after50charge and discharge cycles.