Structure Controlling Of Cobalt/Iron-based Oxides And Lithium Storage Performance Research

Lithium ion battery has attracted tremendous attentions as a clean secondary energy. Currently, graphite is selected as commercial anode materials, however, its low theoretical capacity(372 mAh g-1) limits the development of lithium ion batteries. Therefore, it is of vital importance to develop new anode materials with both good stability and high specific capacity. Among various anode materials, transition metal oxides have attracted significant attention because of their remarkably high theoretical capacities(>700 m Ah g-1). However, one of the limitations of transition metal oxide as anode materials is the large volume change during lithiation/delithiation as well as the low lithium diffusivity, which can lead to electrode pulverization, subsequently resulting poor cycling stability. Herein, we propose a strategy of designing peculiar morphologies and combining carbon materials with metal oxides to solve those problems. The main results are listed as following:1. A surfactant and template-free strategy for the synthesis of a composite of MxOy/MWCNT(M=Fe, Co, Cu, Ni) hollow spheres supported by carbon nanotubes has beed developred via an impregnation–reduction–oxidation process. All the materials exhibite desirable cycling stability when applied as anode materials for LIBs, which are closed to the hollow structure as well as the existence of MWCNTs. The addition of MWCNTs could improve the electrical conductivities of metal oxides; the hollow structure can buffer the volume expansion phenomenon.2. Hollow structured CoxFe3-xO4/MWCNT(x=2, 1.5, 1) composites are synthesized via the impregnation–reduction–oxidation method. The synergy of the composite, as well as the hollow structures in the electrode materials, both of Co2FeO4/MWCNT and Co1.5Fe1.5O4/MWCNT exhibit good rate capability, and desirable cycling stability. A reversible capacity of 1233 and 1027 mAh g-1 can be retained over 500 cycles at a current density of 1 A g-1 for Co2FeO4/MWNCT and Co1.5Fe1.5O4/MWCNT, respectively. Sufficient void spaces that mitigate volume expansion and keep good structure stability as visualized by state-of-the-art electron tomography.3. Flower-like FeS has been successfully synthesised, and then oxidized at different temperatures to obtain flower-like FeS@Fe2O3 and Fe2O3. Owing to the synergistic effect and unique structure, the FeS@Fe2O3 electrode shows excellent electrochemical performance. The synergistic effect and unique structure effective increased the electronic conductivity of electrode materials. Meanwhile, Fe2O3 shell of the composites could effectively reduce dissolution of Li2 Sx into the electrolyte during discharge-charge process.