Preperation And Performance Of Graphene Based Anode Materials For High Power Lithium Ion Batteries

The capacity and power performance of electrode material are requested to befurther improved when the application of lithium ion battery (LIB) is extended tosuperlarge capacitance energy storage devices and electric vehicles. As the buildingblock of sp~2carbon materials, graphene provides an opportunity to design andconstruct LIB anode materials with unique nanostructure and excellent performance.In this thesis, a series of graphene-based anode materials have been prepared by anassembly process of graphene oxide nanosheets (GON) followed by a heat-treatmentand in the assembly process, small organic molecules or macromolecules areintroduced as the support to avoid the tight stacking of GON and to leave an expandedchannel for fast ion transport after heat-treatment. Compared with powdered graphene,the obtained nanostructured materials show great improvement in capacity, cyclingand rate performance.During the fabrication process, organic components with different structure andmolecular weight were integrated with graphene oxide by the chemical forcesbetween the hydroxyl groups. After the reduction of graphene oxide and thecarbonization of organic components by the thermal treatment, the graphene-basedanode materials with different nanostructures were obtained. The material, in whichpolyvinyl alcohol (PVA)(10%of graphene oxide in mass) is employed as the supportand was carbonized at900℃, abbreviated as PGN, shows the best performanceamong the materials with different supports. Its reversible charge capacity is475mAh/g at a current density of500mA/g and230mAh/g at5000mA/g. In addition,PGN shows extraordinary cycling performance.PGN is characterized by a curly and loosely beehive-like structure whichprovides fast transport channels for the lithium ions during the charge/dischargeprocess, while the materials obtained by introducing small organic molecules, such asglucose, sucrose and oxalic acid show tighter layered structure. Due to the stronginteraction between PVA and graphene oxide nanosheets and the superior supportfunction of the long polymer chains, expanded channel structure was formed andsustained even after carbonization, leading to higher ion conductivity and improved rate performance of PGN. Furthermore, the above two factors also induce thestabilization of the final microstructure, ensuring the good cycling performance.To summarize, by introducing the long chain polymers with abundant hydroxylgroups in the reassembly process of graphene oxide nanosheets, a graphene basednanostructure with expanded ion transport channels is obtained after the heattreatmentprocess. This nanostructure shows improved ion conductivity and has excellent rateperformance. The fabrication process is facile and easy to be scaled up, providing anew route for the design and assemble of high performance anode materials.