Synthesis Of Nano-sized Hematite Via Precipitation-Spray Drying Method And Its Electrochemical Properties As Anode Material For Li-ion Batteries

Nano-sized hematite is widely applied in industrial fields due to high abundance and excellent chemical stability. However, the low yield limits the extensive application of hematite nanoparticles. Based on reviews of various methods for fabricating nanomaterial, a facile method in this thesis is proposed to produce hematite nanoparticles in large scale, which includes solution precipitation, spray-drying and calcination processes. Moreover, the electrochemical performance of hematite with various morphologies is also investigated when tested as anode materials for lithium ion batteries.A series of modern material analyzing and testing methods such as X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), thermo gravimetry (TG) as well as constant current charge-discharge testing, cyclic voltammetry (CV) are employed to systematically investigate the influence of preparation conditions including different volume ratios of saturated FeCl3solution, ammonia, ethanol and water, precipitation temperature, calcination temperature, the amount of surfactant, on the size distribution, morphology and uniformity of the hematite nanoparticles. Furthermore, the effect of morphology, size and FeO/C composite on the electrochemical performance is also studied when used as anode material.The precursor was obtained after spray drying process from the solution with saturated FeCl3, ammonia, ethanol and deionized water in a volume ratio of1:0.5:0.3:8. And then hematite nanoparticles with particle size between50nm and80nm were obtained after calcined at550℃for1h. In addition, when added sodium dodecyl benzene sulfonate or sodium stearate into saturated FeCl3solution as surfactant, the particle size of the well dispersed hematite nanoparticle reduced to30-50nm.Hematite materials with different morphologies and structures, such as micro-nano hierarchical hollow spheres, dispersed nanoparticles, microspheres assembled by nanorods, were prepared by spray drying and calcination treatment when adjusting the molar ratios of FeCl3and urea during homogenous precipitation.Among those three types of hematite with different structures, the material with micro-nano hierarchal hollow spheres exhibited the highest reversible specific capacity. After100cycles, capacity of the hollow spheres still stabilized at980mAh/g and the reversible capacity retention reached about89.9%. The exceptional electrochemical performance of micro-nano hierarchal hematite was because the nanoparticle size (less than100nm) could shorten Li+diffusion route, decrease the volume changes in cycling, and the hollow structure accommodated the volume changes during lithiation/delithiation, improving the utilization of hematite active material.FeO/C composites were successfully prepared by a quite facile carbothermal reduction of the mixtures of nano-sized Fe2O3and acetylene black. The maximum discharge capacities of511mAh/g after50cycles for the FeO/C composites is obtained at AB addition of50wt%. The superior electrochemical property of the FeO/C composites is attributed to the higher electronic conductivity of FeO and possibly strengthened connecting of the FeO and AB particles after the carbothermal reduction.