Synthesis Of Fe₂O₃/Graphene Composite And Application For Lithium Ion Batteries

Today’s high-speed development largely depends on energy consumption. Sincethe environmental problem has attracted more and more people’s attention, finding adevelopment ways without sacrifice the environment has become a widely-discussedtopic. Lithium-ion batteries is the one of the most potential electrochemical powers asa green, environmental-friendly, and efficient clean energy.Nowadays, lithium-ion batteries are widely used in portable electronic devices andtools. The commonly used anode materials are carbonaceous substances such asgraphite with low specific capacity, which restricts the improvement of total capacitiesof lithium ion batteries. Therefore, it is necessary to develop novel anode materials withhigh specific capacity. Among all novel anode materials, graphene, a newly discoveredtwo-dimension material, has attracted a great deal of research interest due to itssuperior properties such as mechanical flexibility, high electrical conductivity, and largespecific surface area. A large number of researches have been focused on thegraphene-based composite as anode materials. The special microstructure of graphenewill benefit the overall electrochemical performance of the composites.In Chapter3, we first introduce the modified Hummer’s method to synthesisgraphene oxide, followed by a heat treatment to finally produce the graphene. Differenttest method has been taken to study the properties of graphene. It is has been provedthat the graphene we synthesized has large specific surface area, thin, and highreduction degree. The electrochemical performance of graphene is also studied.The transition metal oxides are considered as promising anode materials due to its high theoretical capacity. Here we study Fe₂O₃as it is environmental-friendly and easyto obtain. The surfactant-free one-step hydrothermal method to synthesized nano Fe₂O₃is included in Chapter3. The particle size of Fe₂O₃is uniform and with good crystalstructure. The specific capacity of Fe₂O₃is as high but the cycling performance is poor,which could be result from the drastic volume fluctuation upon the insertion andextraction of Li ion. Therefore, we synthesis the Fe₂O₃/graphene composites and applythe graphene as stiff framework to provide enough buffer for Fe₂O₃particles.In Chapter4, we use spray drying techniques to synthesis3D crumbled graphenesheets-wrapped nano-Fe₂O₃composites. The theoretical lithium storage mechanism andmicrostructure affect on the electrochemical properties are studied as well. Thereversible capacity of Fe₂O₃/composite is as high as900mAh·g-1. In the as-obtainedcomposites, the crumpled graphene sheet around Fe₂O₃particles could not only bufferthe volume change of Fe₂O₃, but also provide a3D conductive matrix. The nano Fe₂O₃particles will prevent irreversible aggregation and restacking of graphene sheets arisenfrom their strong inter-sheet van der Waals attraction. With the help of the simple spraydrying techniques, the synergistic effect between crumpled GS and activenano-particles is fully utilized. The Fe₂O₃/graphene composite shows dramaticimproved electrochemical performance including cyclic stability and rate capability.The spray drying techniques is simple, with good reproducible and easy to scale-up formass production. This paper can provide the necessary fundamental study for thistechnique.