Design,Synthesis And Lithium Storage Properties Of Iron-based Micro/Nano Materials

Li-ion batteries have been widely used in many energy storage fields owing to its high energy density,light weight,environmental benignity and excellent electrochemical performance.The successful commercialization of Li-ion batteries is largely due to the wide application of graphite,but graphite with the low theoretical capacity can't meet the growing needs of Li-ion batteries,so,it has attracted great attention to find a new anode material.Iron-based oxides and iron-based sulfide materials stand out from the others anode material owing to abundant resources,environmental benignity,inexpensive and excellent electrochemical properties.However,iron-based oxides and iron-based sulfide materials also suffer from some problems,such as pulverization and agglomeration due to volume expansion.The design of hollow,core shell,particle assembled and other unique structures can alleviate the volume expansion problem,which will effectively improve the cycle stability of the material and increase the reversible specific capacity.In this thesis,we design and synthesize unique structures of several binary transition metal oxides and iron-based sulfide materials by hydrothermal method and one-pot method.Morphological structure and electrochemical properties of sample are characterized by X-ray diffraction?XRD?patterns,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,N2 adsorption-desorption and X-ray photoelectron spectroscopy?XPS?etc.1)FeS₂ nanosheets assembled FeS₂ microspheres are synthesized by using ferric chloride?II?and sodium thiosulfate as raw materials by one-pot hydrothermal method.We regulate the concentration ratio of iron source to sulfur source and hydrothermal time,meanwhile,we combine with XRD and SEM characterization results and filter optimal conditions to improve the electrochemical performance.At the current density of 500 mA g^-1,first discharge/charge capacity can reach 905 mA h g^-1 and 800 mA h g^-1,respectively,and the coulombic efficiency is 88.4%.Even at high current density of 2000 mA g^-1,the FeS₂ exhibit excellent cycling behavior with a stable capacity of 350 mA h g^-1 after 500 cycles.2)Zinc oxide,ammonia water,ferric chloride?II?,cobalt chloride and manganese chloride as key materials,small ZnFe2O4 subunits assembled hollow ZnFe2O4 nanospheres are synthesized and the electrochemical performance of ZnFe2O4 is tested at the current density of 500 mA g^-1.Large discharge/charge capacities of 1305 mA h g^-1 and 960 mA h g^-1are achieved in the first cycle,and even at current density of 1000 mA g^-1,ZnFe₂O₄ still deliver high reversible capacity of 900 mA h g^-1 after 400 cycles.Furthermore,ZnCo₂O₄,ZnMn2O4 and CoFe2O4 can be further fabricated by our strategy,which maybe provide a new way to synthesize multiple oxides.3)ZnFe₂O₄ nanoparticles are used as precursors,after vulcanization,the high ZnS/FeS₂nanospheres assembled by small ZnS/FeS2 particles are successfully obtained and test electrochemical performance.At the current density of 500 mA g^-1,the initial discharge capacity can reach 950 mA h g^-1,and the ZnS/FeS₂ exhibit excellent cycling behavior with a stable capacity of 439 mA h g^-1 after 200 cycles.Excellent electrochemical performance of ZnS/FeS2 material is attributed to the uniquely accumulated structure with small particles and synergistic interaction between the two materials.