The Preparation Of Iron-based Graphene Composites And Their Performance On Lithium Storage

Due to the advantages of high voltage, high specific capacity, long cycle life, low pollution, etc., lithium-ion batteries(LIBs) are widely used in consumer electronics, such as smart phones and laptops. Actually, LIBs show an attractive prospect in the field of portable batteries and power batteries with high specific energy density and it has become a focus over the world. Until now, the graphite material is currently widely used as anode material for LIBs. However, it is difficult to meet the needs of power batteries due to its low theoretical capacity, poor rate performance. Therefore, the development of anode materials with high specific capacity, high stability and high cycle rate has become the key issues to promote the development of high-performance LIBs.Iron-based materials are drawing a huge concern as next generation anode materials for LIBs because of its features such as high theoretical capacity and cheapness, etc. Iron oxide(Fe2O3) and pyrite(FeS2) are chosen as the objects of study in this thesis. Combining the advantages, high specific surface area, high stability and high electrical conductivity, etc. of graphene/reduced graphene oxide(RGO) materials, iron-based composites with RGO could be prepared as new anode materials for high-performance LIBs. The following works were carried out in this thesis:(1) The preparation of Fe2O3/RGO composite and its electrochemical properties.Fusiform Fe2O3/RGO composite has been prepared with the mixture of ferric chloride solution and graphene oxide(GO) solution by a simple hydrothermal reaction. The method is simple and easy to enlarge production. The ellipsoidal fusiform Fe2O3 show as small particles with uniform size, and they uniformly load on the reduced graphene oxide(RGO), thereby Fe2O3 and RGO combining well. It shows a high reversible capacity, excellent cycling stability and good rate capability when tested as an anode material for lithium-ion battery. The reversible capacity of Fe2O3/RGO composite is 613.3mAh g-1 after 100 cycles at a current density of 100 mA g-1 and it also can deliver a high reversible capacity of 497.01 mAh g-1 after 200 cycles at a current density of 300 mA g-1, which shows better electrochemical performance than pure Fe2O3 which is prepared with ferric chloride solution without GO solution.(2) The preparation of FeS2/RGO composite and its electrochemical properties.Novel composite of RGO and FeS2 microparticles self-assembled from small size cubes has been prepared with the mixture of ferric chloride solution, graphene oxide(GO) solution and thiourea solution via a facile one-pot hydrothermal method. The prepared composite shows interconnected networks of reduced graphene oxide sheets and well-dispersed FeS2 microparticles which were composed of small-size cubic FeS2 crystals. The composite not only provides a high contact area between the electrolyte and electrode, favorable diffusion kinetics for both electrons and lithium ions, but also provides the protection against the volume changes of electroactive FeS2 materials and excellent electrical conductivity of the overall electrode during electrochemical processes as well as enhanced synergistic effect between cubic FeS2 and RGO. As an anode material for LIBs, it exhibits a very large initial reversible capacity of 1147 mAh g-1 at a current rate of 100 mAh g-1 and maintains 1001.41 mAh g-1 over 60 cycles, which is much higher than that of the theoretical capacity of graphite(372 mAh g-1) and indicates high stability.