Colloidal Synthesis Of Pure Phase Iron Sulfide Nano-materials And Lithium Ion Batteries Study

Environmental issues caused by the excessive consumption of the non-renewable resources make people race towards the development and use the renewable resources, such as solar, wind, hydropower and geothermal energy. However, these intermittent energy resources heavily rely on natural conditions. Thus, to strike a balance between the needs of widespread energy demands and ecological issues, lithium ion batteries（LIBs） have attracted increasing interests as the advanced energy storage devices. Low-cost and environment-friendly iron sulfide nanomaterials are promising anode materials owing to the unique physical and chemical properties, as well as the high theoretical capacity. However, the complex component and solid-phase structure make the synthesis of pure-phase iron sulfide nanomaterials with controllable morphology a big challenging. Among the chemical methods, the colloidal synthetic system is rationally able to select the employed the solution and surfactants based on the target products. Additionally, the morphology, size, composition and structure of products can be easily controlled by adjusting the thermodynamic and kinetic parameters of the reaction. In this thesis, we develop the colloidal synthesis of the iron sulfide nanomaterials with the different morphology and composition through controlling the reaction parameters and then introduce several kinds of the growth mechanism. It is reasonable to expect that they will promote the practical application of iron sulfide nanomaterials in LIBs field.In chapter 2, we demonstrate the facile and controlled synthesis of the small-sized and high-quality marcasite nanoparticles with orthorhombic crystalline structure for the first time in colloidal solution via hot-injection protocol. Based on the Ostwald ripening growth mechanism, the reactivity of the Fe monomers increases with high reaction temperature and generate the size increment of the marcasite Fe S₂ nanoparticels. The marcasite Fe S₂ nanoparticles possess good dispersibility, optical and magnetic properties. The as-prepared marcaiste Fe S₂ nanoparticels treated by annealing are fabricated in a coin cell as the anode materials. The electrode exhibits low electrochemical resistance and high activity in lithiation/delithiation cycling process. Whereas, the coulombic efficiency of this electrode is only 17 % at a current density of 1000 m A/g. Lower discharge capacity is attributed to the larger concentration polarization. And on this basis we treat the marcasite Fe S₂ nanoparticles by modifying the reduced graphene oxide sheets through the self-assembly in liquid phase. The obtained hybrid materials show an obviously improved electrochemical performance and good rate performance as a LIBs anode.In chapter 3, an easy and controlled method for hot injection synthesis of Fe₃S₄ NPs with a lateral dimension in the region of 100 nm was demonstrated. In this method, we develop an effective method to perform the phase and composition transformation from Fe S₂ to Fe₃S₄ that is parallel to doping method by introducing a Fe（III） source, which is attributed to the weak reductant of octadecylamine（ODA）. The single crystalline Fe₃S₄ nanoplates are ferromagnetic with the saturation magnetization as high as 25.6 emu/g. We study the nucleation and growth stage, respectively. At the nucleation process, by regulating the experimental variables, such as the reaction temperature, the Fe/S molar ratio, the diphenyl ether（DE）/ODA ratio, control the quantity of Fe S₂ nuclei based on the reduction from high stability constant of Fe（acac）3 to Fe（II）. At the subsequent growth stage, the lateral size and the thickness of the nanoplate also relate to growth duration, reaction temperature, DE/ODA ratio, and Fe/S molar ratio. Therefore, the doping mechanism is proposed in the composition transformation from Fe S₂ to Fe₃S₄, which facilitates the two-dimensional orientated growth of Fe₃S₄ nanoplates. At last, the as-synthesized Fe₃S₄ NPs exhibit good Li+ storage properties and stable charge–discharge performance in LIBs applications.In chapter 4, we demonstrate a Fe₃O₄ nanoparticles-seeded approach for producing ultrathin pyrite Fe S₂ nanosheets on the basis of Oriented Attachment growth firstly. The seeds with good lattice matching and monodispersity can further grow into ultrathin nanosheets, because OA growth is essentially guided by the crystal facets with high surface energy. The injection of S solution leads to the replacement of O in Fe₃O₄ through anion-exchange, which generates（110） facets-riched Fe S₂ nuclei. The subsequent（110） facets-mediated oriented attachment and fusion of Fe S₂ nuclei produce ultrathin Fe S₂ nanosheets with the thickness of 2.1 nm. The reaction parameters include reaction temperature, solvent ratio are achieve the controllable thickness of pyrite Fe S₂ nanomaterials. The as-prepared Fe S₂ nanosheets exhibit good electrocatalytic activity and stability as the catalysts for hydrogen evolution reaction. Secondly, we propose a double S resource method to synthesize the ultrathin greigite Fe₃S₄ nanosheets with the thickness of 1 nm, in terms of the oriented attachment self-assembly. Dodecanethiol（DT）, which has dual characters including S resource and surface ligand, plays a crucial role in the hot-injection procotol. Before injection S powder dissolved in DE, the uniform Fe₃S₄ nucleus generate by DT and Fe precursor. In the subsequent the process of the oriented attachment self-assembly, the morphogy and sizes of greigite Fe₃S₄ nanomaterials are controlled by the solvent ratio. The ultrathin Fe₃S₄ nanosheets assembling in the LIBs as anode materials present an excellent cycling and rate performance.