From 2D To 3D Graphene: Preparation And Application In Energy Storage

With the fast development of the economy, the shortage of energy sources and environmental pollution become the two threats to the human society. Many countries put their efforts to develop the new energy storages. Among them, clean energy technologies, supercapacitors and batteries are the most representative electrochemical energy storage and conversion, which playing the important role in national defense, medical treatment and the new industry because of their extremely high-energy and power densities, superior cycle lifetime and conversion efficiency. As a heart of the energy storage device, the key to expanding its application is to improve the electrode’s performance and structures. At present, the commercial energy storage devices in general are used graphite powder based electrodes containing such as Cr, Li. However, these devices are not only heavy, high toxicity, and poor cycle efficiency, but also quite low energy and power densities. Therefore, high-energy and power densities, long cycle lifetime and light new energy storage device have high research value and application prospect.In this thesis, the novel 3D porous graphene electrode materials and devices are brought forward to solve the mainly problems of energy storage devices, such as the loss of the capacity, aging, the restriction of energy and power densities. By developing the new electrode materials, devices and energy storage module,3D graphene based integrated electrode construction and functional architectures is reported. This work reveals the mechanism of energy storage, and the influence mechanism of its structure to performance to energy storage properties, providing an essential theoretical and experimental basis for the application of new 3D graphene based integrated energy storage device. The main research results and contributions of this thesis are listed as follows:1. Systematic research on graphene on Cu by CVD for the nucleation mechanism, defect formation and control mechanism, and reveal the impact of the key factors such as the Cu pretreatment, the growth temperature, the ratio and flow of the gas on qualities and performance of graphene. On the basis of the model of growth crystal high quality graphene, a novel low pressure CVD method was used to prepare squite large crystal single domain size of 2D graphene over 1 mm, carrier mobility of 6000 cm2/Vs (transferred on r-sapphire), which has achieved the international advanced level.2. A study of the influence mechanism of the nondestructive transferred and modified large size graphene, analyses the various amorphous, polycrystalline and crystal of the substrates, such as crystal type, surface planeness, hydrophobicity and polarity. Moreover, in order to solve the annealing problem of the preparation of the graphene based device, a comprehensive study on the combined effects of hydrogen thermal annealing process on the morphological, structural and electrical properties of transferring graphene is proposed. Finally, a novel self-supporting transfer method was brought to investigate on the electrical and optical properties of the layer-stacked graphene transparent electrodes, achieving smoother surface morphologies than the traditional transfer method, which provides a new approach of graphene in the application of transparent conductive films.3. Based on the nucleation and controlled preparation mechanism of the 2D graphene, an innovative mechanism for the synthesis of 3D multilevel porous graphene superstructures using strategically engineered Cu-Ni catalysts are reported. The as-grown graphene is 3D, multilevel porous, freestanding, and flexible after selective etching of the catalysts and CVD. Then systematically discuss the mechanism of equilibrium potential, liquid phase transmission, Flarch potential to porous alloy substrate construction, reveal the nucleation of 3D porous graphene (3DMG). Overall, the reported mechanism for the synthesis of 3D porous graphene is the first of its kind, which may potentially spur a new paradigm for manufacturing 3D porous graphene materials for an array of energy storage applications.4.3DMG coated with thin nickel hydroxide nanoplates (Ni (OH) 2) was applied as integrated electrodes, and discuss the energy storage properties of its high performance. Then, the influence mechanism of quality and mophynologe of the crystal Ni (OH) 2 was discussed. When these electrodes as supercapacitors, the integrated electrodes offer the capacitance of ～1149 F/g based on total weight of the electrodes. Moreover, when the electrodes as alkaline batteries, a remarkable discharge capacity of 480 mAh/g at a rate of 1.5 A/g. Compared with previous reports, they also exhibit excellent cycling performance with 97.5% capacitance retention after 4000 cycles. The performance above has achieved the international advanced level.5. Based on the energy storage properties of high performance of 3DMG above, 3DMG/Mn3O4 were made as integrated electrodes, and deeply investigated the influence mechanism of 3DMG/Mn3O4 interface characteristics and crystal size to electrode performance. Moreover, the influence mechanism for 3DMG/Mn3O4 mophynologe to capacitive performance was also discussed. The proton diffusion and electron transfer kinetics within the microspores and mesopores reveals the micro mesoporous is a key factor in the redox rapid diffusion. Finally, high performance asymmetric supercapacitor of 3DSG/Mn3O4/3DMG was made in order to improve the work voltage and energy densities. This supercapacitor has a remarkable energy density of 71.4 Wh/Kg, and power density of 300 KW/Kg. It also exhibits cyclability with 90% capacitance retention after 3000 cycles, which providing the basis of theoretical and experimental of the applications asymmetric supercapacitor.