Syntheses, Structures And Properties Of Iron Oxides/C Composites As Anode Materials For Lithium-ion Batteries

Iron oxides have attracted wide attention due to its high specific capacity, high abundance and low cost applied to lithium ion batteries. In this thesis, nano-sized hematite and multiply structured Fe3O4/C composites were prepared by a spray drying process and a solvothermal method.The effect on structures and electrochemical properties of the preparation technology with its parameters has been intensively studied by using some modern material analyzing and testing methods such as XRD, SEM, EA and constant current charge-discharge testing.Key factors which impacted cycle performance of Fe3O4/C composites as well as its charge-discharge mechanism were also discussed.The results showed that the hematite synthesized by a spray drying process had a specific capacity of1181mAh/g. Fe3O4/C composites were prepared after a calcination process by adding carbon sources, which enhanced cycle performances. Porous structured Fe3O4/C composites were succesfully synthesisd with sucrose as the carbon source and with sodium stearate as the surfactant. With increased addition of sucrose the cycle stabilities of Fe3O4/C composites turned better and the specific capacities firstly rised and then descended. The cycle performance of Fe3O4/C was obviously improved by adding graphite.Core-shell structured Fe3O4was prepared by a solvothermal method. The solvothermal conditions such as reaction temperature, solvent, reaction time and addion of sodium acetate were researched. As a result, spherical structured Fe3O4with excellent monodispersity was obtained on condition of using anhydrous ferric chloride as iron source, mixed solvent with volume ratio of NMP and EG3:1, sodium acetate as reaction promoter at200℃reacting for24h,which had a particle size about300run. Fe3O4/C composites were prepared by adding different carbon sources with a solvothermal process. Fe3O4/C with ketjen black or ketjen black/VGCF composites as carbon sources expressed specific capacities of1170mAh/g and1402mAh/g, and after40cycles corresponding specific capacities were845mAh/g and829mAh/g.