Metal Compounds - Carbon Composites Preparation And Used As A Lithium-ion Battery Negative Research

A series of composites related to the modification of metal compounds by micro-or nano-carbonaceous materials has been synthesized and studied in this paper. The detailed research work is composed of two parts. Part one is focoused on the modification of metal oxides (MxOy=Fe3O4, Fe2O3and CeO2) by graphene nanosheets and carbon spheres to overcome their defects such as low coulombic efficiency at the initial cycle and poor lithium storage properties and improve their electrochemical performance when used as anode materials for lithium ion batteries. The influence of graphene nanosheets and carbon spheres as modifying elements on lithium storage performance of the MxOy is summarized after systematically investigating the phase composition, the morphology and structure, and the electrochemical perforamance of the MxOy-graphene composites. Part two is focoused on the synthesis of lanthanum carbonate hydroxides (LaOHCO3) and LaOHCO3-graphene composites with controlled morphology and the further comparation of their luminescence properties. The main contents of the paper are presented as follows:Preparation of two supported nanocomposites of Fe3O4/graphene and CeO2/graphene, and a doped micro/nanocomposite of Fe2O3-graphene is realized by utilization of graphene nanosheets as modifying elements through hydrothermal treatment. The three composites show much better electrochemical performance than the MxOy used in each system. For the Fe3O4/graphene, it shows a discharge capacity of2315mAh/g and charge capacity of1160mAh/g in the first cycle. After50cycles, the reversible capacity still remained771mAh/g. The rate of capacity increased is107%when compare with pure Fe3O4electrode. For the Fe2O3/graphene, it shows a discharge capacity of1800mAh/g and charge capacity of1420mAh/g in the first cycle. After100cycles, the reversible capacity still remained567mAh/g. The rate of capacity increased is46%when compared with pure Fe2O3electrode. For the CeO2/graphene, it shows a discharge capacity of1469mAh/g and charge capacity of991mAh/g in the first cycle. After100cycles, the reversible capacity still remained605mAh/g. The rate of capacity increased is63%when compared with pure CeO2electrode.Preparation of a doped micro/nanocomposite with carbon coated (Fe2O3@C-CSs) is realized by utilization of carbon spheres as modifying elements through hydrothermal treatment. Preparation of a supported nanocomposite with carbon coated (Fe2O3@C/graphene) is realized by utilization of carbon spheres as modifying elements through immersion method and high temperature calcination. The two composites show much better electrochemical performance than the Fe2O3or Fe2O3/graphene used in each system. For the Fe2O3@C-CSs, it shows a discharge capacity of1507mAh/g and charge capacity of978mAh/g in the first cycle. After50cycles, the reversible capacity still remained550mAh/g. The rate of capacity increased is37%when compare with pure Fe2O3electrode. For the Fe2O3@C/graphene, it shows a discharge capacity of1530mAh/g and charge capacity of1016mAh/g in the first cycle. After50cycles, the reversible capacity still remained1027mAh/g. The rate of capacity increased is34%when compare with Fe2O3/graphene.In the presence of polyvinylpyrrolidone (PVP), LaOHCO3with various morphologies are synthesized successfully via a facile hydrothermal process. The novel hierarchical nest-like architectures of LaOHCO3are obtained based on the time-controlled experiment during the process. Hierarchical LaOHCO3-graphene composites with different amounts of graphene nanosheets are synthesized subsequently. The optical properties of LaOHCO3microparticles with different morphologies and LaOHCO3-graphene composites with different amounts of graphene nanosheets are measured. For the pure LaOHCO3, it shows that all the samples exhibite emission spectrum centered at～420nm using an excitation wavelength of365nm. Their luminescence properties are very sensitive to the morphology and strongly dependent on the size. The larger the particle size, the stronger the intensity of luminescence. Comparing the particles that have the same size, the hierarchical LaOHCO3obtained at180℃in24h exhibite the highest luminescence intensity. For the LaOHCO3-graphene composites, it shows that the luminescence intensity decreased gradually and finally the fluorescence quenching occured with the amounts of graphene increased.