Study On The Chemical Fabrications And Properties Of Energy Storage Materials

Materials with specific compositions and structures have been widely used in areas such as biological, energy and electronics. The selective fabrication of novel structures, control of its composition and structure, and the investigation of the formation mechanism have been the research focus in the field of materials chemistry. In this thesis, we focused on the crystallization of electrochemical energy storage materials such as transition-metal compound and graphene, and their synthesis methods, formation mechanism and the applications in lithium-ion batteries and supercapacitors have been systematically investigated. The main points can be summarized as follows:1. Hierarchical ordered stuctures of transition-metal compounds were fabricated by the self-assembly of nanoscale building blocks under the directing of intermediate product in the solution chemical process. In the solvothermal synthesis of copper sulfide hierarchial structure, Cu2+can be reduced by the solvent and form CuCl crystal, which can guide the assembly of subsequently formed CuS nanoplates, thus achieving the combination of "top-down" and "bottom-up" method. Hierarchical CuS architectures obtained present well defined order from nanometer to millimeter scale; TiO2with hierarchical core-shell polyhedral architecture can be prepared by a one-pot hydrothermal route. The growth of the complex crystalline geometrical structure follows a "colloidal-molecular" mediated recrystallization process. Due to the presence of F-, the core and shell show different crystallization manner, leading to a core/shell structure. When used as lithium ion battery anode materials, CuS with hierarchical ordered structure showed first discharge and reversible capacity of533and88mAhg-respectively, better than the reported value, which are480与350mAhg-1.2. Graphene paper with folding structured graphene sheets was fabricated, which overcomes the close packing problem of traditional graphene paper. Folding structured graphene paper was fabricated by mechanically pressing graphene aerogel. The as-prepared graphene paper has structure characterizatons of both graphene and multiwall carbon nanotube, which can facilite the diffusion of Li-ion and electrolyte. When used as free-standing lithium ion battery anode, this folding structured graphene paper can show a reversible capacity of864mAhg-1, and when used as supercapacitor electrode, a specific capacitance of172Fg-1was obtained, these performances are much higher than that of graphene paper fabricated by flow-directed assembly method (reversible capacity and specific capacitance of84mAhg-1and111Fg-1, respectively).3. An electrochemical oxidation route was used to modify graphene with oxygen containing groups, achieving the quantitative oxidation of graphene. The thermodynamic and kinetic of oxidation reaction can be facilely controlled by tuning the potential range and cycling time respectively. The density of functionalities (including hydroxyl, carbonyl and carboxyl group) and the change of electronic conductivity can be in-situ monitored by the change of CV curve during the electrochemical oxidation process. Pseudocapacitance can be added to graphene through such electrochemical oxidation. Without decreasing the electric conductivity, the functionalized graphene showed a specific capacitance of279Fg-1at the current density of1Ag-1,49.1%higher than that of pristine graphene, while reserving good rate performance and cycling stability. At the high current density of100Ag-1, the functionalized graphene can also deliver a specific capacitance of168Fg-1, and the capacitance retention after5000cycles was more than98%.