Preparation Of Graphene/Metal Compounds Composite Nanomaterials And Their Application In Sodium-ion Batteries

With the continuous economic development, conflicts between limited natural resources and human’s growing demands push the scientific community to seek and develop clean energy and advanced energy storage devices. As the most important and most widely used rechargeable power sources, lithium-ion batteries have a high energy, low toxicity and a relatively long-term cyclic life. However, lithium-ion batteries still have many unavoidable problems, such as security and price. With a large number of existing global demands for lithium-ion batteries, the price of lithium sources has doubled in recent years, but raw lithium materials are still in short supply. Even the establishment of a wide range of battery recycling program may not be able to prevent future lithium resource depletion. In addition, the applications of lithium materials in the mid-size electric vehicles as lithium ion batteries continue to raise the price of lithium compounds, resulting in the increase in the price of energy-storage devices. The foreseeable shortage of lithium source prompt researchers to look for new replaceable batteries. The most promising and preliminary research should be Sodium-ion batteries. Sodium’s reserves are very rich on earth, and thus their prices are far cheaper than that of lithium. As the first main group of alkali metals, the chemical properties of lithium and Sodium are very similar. Because of the abundant storage of Sodium mineral in the earth’s crust and low mining costs, the Sodium-ion batteries have a very promising future. In addition, the Sodium-ion battery itself has a low potential plateau and non-aqueous electrolyte solution, guaranteeing its good stability. Electrode materials play an important role in Sodium-ion batteries. Developing electrode materials with high-capacity and high stability is critical for the preparation of Sodium-ion batteries with good performance. Graphene, with strong electronic conductivity, biocompatibility, high mechanical strength and high specific surface area, has been widely used in many aspects of chemistry, biology and materials in recent years. Graphene prepared by chemical methods normally possesses active groups on its surface, easily interacting with metal oxides, sulfides, and organic conductive polymers, forming stable interfaces. Hence, these materials exhibit better electrochemical performance. Hence, this material exhibits better electrochemical performance.In this work, we selected vanadium oxide and indium sulfide with graphene to fabricate composite electrode materials,respectively. The obtained products were used and tested as the electrode materials for Sodium-ion batteries. The phase composition, structure, and chemical surface analysis of the resulted samples were systemically characterized by X-ray diffraction（XRD）, field emission electron microscopy（FESEM）, transmission electron microscopy（TEM） and X-ray photoelectron spectroscopy（XPS）. Meanwhile, electrochemical workstation and battery charge/discharge tester were used to test the materials’ electrochemical performance. The main contents of this thesis include: firstly, synthesized graphene oxide by chemical methods as the original materials. Vanadium oxide and indium sulfide were used to get the composite nanomaterials by spin-coating and hydrothermal, respectively. These nanomaterials were applied as electrode materials for Sodium-ion batteries, and their battery performances were tested. The detail contents include:1. Using a simple spin-coating method, the pre-made graphene oxide and vanadium oxide colloidal aqueous solution were spin-coated on the current collector layer by layer to fabricate the multilayer construction. After annealed under nitrogen at 500°C, we obtained the resulted graphene-vanadium oxide multilayer composite nanomaterials（GNS/VOx-500）. XRD and XPS were used to analyze the chemical composition, phase and structure of the materials. Microstructure characterizations of the materials were conducted by TEM and SEM. The GNS/VOx hybrid cathode exhibited high capacities and good stability during the whole battery testing. These GNS/VOx composite nanomaterials showed a high initial capacity of 224 mA h g-1 at a current density of 0.2 A g-1 and kept for 200 cycles. After 500 cycles, the specific capacity was 145.1 mA h g-1 and still retained 85% of the initial specific capacity（171.2 mA h g-1）, which may show great potential to push forward SIBs into practical applications. This preparation method is quite easy to realize multi-layer hybrid configurations, and can be readily extended to other significant applications.2. Based on the study of high-performance GNS/VOx multilayer materials, we envisage adopting graphene to enhance the performance of sulfide electrode materials for Sodium-ion batteries. The indium sulfide with graphene oxide were mixed and reacted through hydrothermal method at 240°C for 24 h, obtained 3D nanoparticles structured In₂S₃-RGO composite nanomaterials. The In₂S₃-RGO composite nanomaterials were used as anode materials for Sodium-ion batteries, showing good cycle stability and high battery capacities. At up to 4 A g-1 of the current density, the battery still has a high specific capacity of 186.8 mA h g-1 during the rate test. After 50 cycles discharge/charge cycling test at a current density of 1 A g-1, the specific capacity has a retention rate of 77.2%. CNT and 3D structured graphene were composed with In₂S₃ to fabricate composite nanomaterials,respectively. The products were tested as anode electrode materials for Sodium-ion batteries as well. The In₂S₃-RGO composite nanomaterials exhibited the best performance in the battery performance tests.