Solution Synthesis Of Hierarchical Fe₃O₄ Structures And Their Electrochemical Performance

Fe3O4 has a series outstanding characteristic of high theoretical specific capacities(~926 m Ah g-1), low cost, environmental friendly, relative safety and so on, which makes it a promising anode material of Li-ion battery. However, Fe3O4 based anode electrodes often exhibit fast mechanical degradation and pulverization, mainly caused by severe volume variation during repeated cycling. Moreover, the electrical conductivity of Fe3O4 is much lower than graphite, resulting in unsatisfied rate performance. Herein we firstly gets Fe-glycolate precursor through solution synthesis followed by calcination in Ar gas flow, to prepare two typical Fe3O4 nanostructures: hierarchical self-assembly hollow Fe3O4 microspheres and Ti-doped Fe3O4 nanoflowers.This article has studied the different technological parameter for the preparation of Fe-glycolate precursor and calcination process and then the XRD, SEM, TEM, BET of reaction products was tested. At last a series of electrochemistry properties including cyclic stability, rate capability and CV, as well as the impedance measurement were performed, the main results are as following:We successfully prepared hierarchical self-assembly hollow Fe3O4 anode with the size of 1 μm, which are assembled by nanosheets. The amount of Na HCO3 has a great influence on the morphology of Fe-glycolate precursor. The Fe3O4 hollow spheres possess a high specific surface area of 117.55 m2 g-1. Electrochemical testes show that the Fe3O4 hollow spheres exhibit good cycling stability. After 50 cycles, the specific capacity could maintain about 800 m A h g-1 at a current density of 500 m A g-1. The Fe3O4 hollow spheres also manifest a good rate capability and low impedance of 90 Ω. It is supposed that this excellent performance attributes to merits of the hierarchical hollow structure which could largely relieve the volume change and promote the diffusion of Li+ and electrons.We got Ti-doped Fe3O4 anode through solution synthesis. It is found that TBT plays an important role on the morphology of Fe-glycolate precursor. When the amount of TBT is 0.1 m L, very uniform nanoflowers assembled by nanosheets are obtained. The electrochemical results showed that, when measured at a current density of 500 m A g-1 after 100 cycles, its specific capacity could reached a stable level of 800 m A h g-1, which was much better than that of non-doped material prepared at the same condition. Impedance measurement demonstrates that Ti-doped Fe3O4 nanoflowers could effectively improve the electrical conductivity, which results in a higher cyclic stability and a better rate capability.