Hydrothermal Synthesis And Characterization Of Fe₂O₃/Graphene Composites As Anode Materials For Lithium Ion Batteries

Due to its high theoretical specific capacity, natural abundance, low cost as well as non-toxicity, Fe2O3has been regarded as one of the most promising anode materials for the next generation lithium ion batteries. However, fast capacity fading resulted from huge volume change during the cycles and poor rate performance resulted from its low electronic conductivity for Fe2O3, severely hindered its practical application in lithium ion batteries. And based on the review for research development for anode materials, this thesis proposed the surfactant-assisted and pH-controlled hydrothermal fabrication of Fe2O3/graphene composites as anode materials for lithium ion batteries in order to promote its cycle performance and electronic conductivity via building the robust structures of Fe2O3/graphene composites, and explored the effects of different experiment condition on crystal phases, morphologies and electrochemical performances of as-prepared materials.Creatively using PVP as a surfactant for dispersion of graphene oxide in solution and a reducing agent for graphene oxide, as well as a controlling agent for growth of Fe2O3, Fe2O3/graphene composites with Fe2O3particles uniformly anchoring onto graphene were successfully synthesized by this particualr hydrothermal method. After experimental optimization, the first discharge and charge specific capacity of as-prepared Fe2O3/graphene composite are1561and1206mAh·g-1, repectively, at a current density of50mA·g-1. After50cycles, it can still retain the charge specific capacity of1069mAh·g-1. Even cycled at a current density of1000mA·g-1, its discharge and charge specific capacity can be still as high as542and534mAh·g-1, respectively.Meanwhile, CTAB was tentatively applied as a substitute for PVP under hrdrothermal condition with addition of alcohol in order to ameliorate its solubility. After experimental optimization, the Fe2O3particles were effectively enwrapped by graphene and its first discharge and charge specific capacity are1962and1213mAh·g-1, respectively, at a current desity of100mA·g-1. After50cycles, it can still retain the discharge specific capacity of561mAh·g-1and charge specific capacity of552mAh·g-1. Even cycled at a current density of1200mA·g-1, its discharge and charge specific capacity can be still as high as460and456mAh·g-1, respectively.Moreover, the PEG was firstly employed to be a surfactant for dispersion of graphene oxide in solution and a controlling agent for hydrolysis of Fe3+, and after experimental optimization, the first discharge and charge specific capacity of as-prepared Fe2O3/graphene composite can be as high as1718and1114mAh·g-1, respectively, at a current density of100mA·g-1. After50cycles, it can still retain the discharge specific capacity of634mAh·g-1and charge specific capacity of621mAh·g-1.And in alcohol/water hydrothermal system, the Fe2O3/graphene composite with discharge specific capacity of936mAh·g-1and charge specific capacity of931mAh·g-1at a current density of100mA·g-1after200cycles, was prepared after optimization of different alkali source, pH value as well as addition of alcohol. Furthermore, in PEG/alcohol hydrothermal system, after optimization of different PEG type, alkali source, pH value as well as addition of PEG, the150th discharge and charge specific capacity of as-prepared Fe2O3/graphene composite can be as high as1210and1186mAh·g-1, respectively, at a current desity of100mA·g-1.82Figures,3Tables,342References.