Preparation And Properties Of Metal Oxides-graphene Composites As Lithium-ion Battery Anodes

Because of their large specific surface area, mechanical properties，specialelectronic structure and good electrical conductivity, graphene has been studied aselectrode materials and carbon matrix for lithium-ion battery. In recent years, metaloxides have been extensively studied for lithium-ion battery anode material for theirhigh specific capacity. However, during the charge-discharge process, dramaticvolume change damage the electrode structure; the active material particlesagglomerate and capacity decay; all these factors limit the application of metal oxidesin the actual production. To solve this problem，one way is to fabricate composites ofmetal oxides and graphene which can take full advantages of electrical conductivity ofcarbon materials and high capacity of metal oxides. In this paper, the compositematerials of metal oxides (SnO2, Fe3O4, Co3O4) and graphene were synthesized. Bythe recombination of metal oxides and graphene, the cyclic performance and itselectrochemical properties of metal oxide have a significant improvement. The maincontents of this paper are summarized as follows:1. The SnO2nanoparticles were synthesized by hydrothermal synthesis, potassiumtin as the tin source, ethanol as solvent, the urea as the additives. The surface of SnO2nanoparticles was modified by APS to achieve positively charged SnO2nanoparticles,after self-assembly with graphite oxide and reduction by hydrazine hydrate, GE-SnO2nanocomposites were prepared. Both the SnO2and GE-SnO2were characterized byscanning electron microscope(SEM), X-ray diffraction(XRD) and N2adsorption-desorption, etc. The electrochemical properties were characterized bycyclic voltammetry and galvanic charge and discharge. The results show thatcompared with pure SnO2, GE-SnO2composite materials show better performance.The initial discharge capacity was2399mAh/g at the current density of156mA/g,after30cycles, the composite materials remain stable capacity of852mAh/g; at thecurrent density of395mA/g and780mA/g, after30cycles, the discharge specificcapacity is603mAh/g and521mAh/g indicating that the GE-SnO2has a better cycleperformance and high reversibility.2. The Fe3O4hollow nanospheres were prepared by hydrothermal synthesis,ferric chloride hexahydrate as an iron source, glycol solution as solvent. The Fe3O4hollow nanospheres were modified by APS to achieve positively charged Fe3O4 hollow nanospheres, after self-assembly with graphite oxide and reduction byhydrazine hydrate, GE-Fe3O4composite material was prepared. The SEM show theiron oxide hollow nanospheres were in the range of300-400nm, the Fe3O4hollownanospheres were composed by many nanoparticles about30nm. Theelectrochemical tests show that the discharge capacity was1301.5mAh/g at thecurrent density of277.8mA/g，after50cycles, the composite materials remain stablecapacity of440.9mAh/g；at the current density of463mA/g, after30cycles, thedischarge specific capacity was306.6mAh/g.3. The Co3O4spheres were prepared by hydrothermal-thermal decompositionmethod, acetic acid cobalt for cobalt. After self-assembly with graphite oxide andreduction by hydrazine hydrate, GE-Co3O4composite material was prepared. Thesynthesized Co3O4was spherical structure and the particle size was in the range of20-30um, the Co3O4spheres were composed by many layer，the thickness of the layerstructure is about20nm. The electrochemical properties were characterized bygalvanic charge and discharge and cyclic voltammetry. At the rate of2C, after30cycles, GE-Co3O4still has a capacity of386.8mAh/g,indicating good cycleperformance.