| Lithium ion batteries are a new kind of green energy storage devices with high energy density, high operating voltage and good cycling performance, etc. and it is widely used in many areas of society. C urrently, the low energy density and poor cycle stability constraint the rapid development and extensive application of lithium- ion batteries. Thus, to design and synthesize electrode material of controllable morphology and size as well as optimization is an important breakthrough to solve the above problems. Transition metal manganese-based oxide(such as MnO2, Mn3O4, Mn2O3 and MnO, etc.) has a high theoretical specific capacity, low cost, wide potential window, and environmental friendliness, so it is considered to be a lithium ion battery electrode materials having important application prospects. However, manganese-based oxide has their own shortcomings of transition metal oxides, such as poor electronic conductivity, unstable structure, and large volume changes of material during charging and discharging. These drawbacks result in low real capacity and poor cycle performance, and limit its practical application greatly. In this paper, developing high-performance lithium- ion battery is seen as research background, and the applications of manganese-based oxide as a starting point, finally manganese-based oxide/carbon and manganese-based oxide/tin dioxide composite are synthesized by hydrothermal method. This method improves the rate capacity and cyclic stability of manganese-based oxide effectively. Specific studies are as follows:(1) Firstly, Graphene oxide is prepared by modified Hummer’s method. Then, manganese tetroxide/RGO composite having three-dimensional network structure is prepared by hydrothermal method using manganese sulfate monohydrate and graphene oxide as precursors. The morphology and composition of the sample is characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM), transmission electron microscopy(TEM), Raman spectroscopy. The electrochemical test results show that as the lithium ion battery anode material, such material has a high reversible specific capacity, high rate capability and excellent cycle stability. The discharge capacity can still maintain 546.9 mAh/g after 100 cycles at current density of 0.1A/g, equivalent to 37.1% of the initial discharge capacity. In addition, the study also finds that the quality ratio of manganese precursor and graphene oxide(mMn/mGO) has a great impact on the morphology and electrochemical properties of the composites. These results suggest that Loading graphene not only can effectively improve the conductivity of the manganese-based oxide, and a unique three-dimensional network structure provides an effective three-dimensional way for electronic and lithium ion transmission. Finally rate capability and cycle stability of the manganese-based oxide can be effectively improved.(2) Three kinds of manganese dioxide nanostructures are synthesized by hydrothermal method. Then, tin tetrachloride pentahydrate is added to manganese dioxide dispersion, and then MnO2/SnO2 composites of different morphologies are synthesized after hydrothermal treatment. The morphology and composition of the three samples is characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM), transmission electron microscopy(TEM) and other tests. The results show that the three materials exhibit good cycling performance, and MnO2/SnO2-3 is the best. The discharge capacity of MnO2/SnO2-3 can still maintain 81.2 mAh/g after 100 cycles at current density of 0.1A/g, equivalent to 67.8% of the initial discharge capacity. Experimental results show that tin dioxide coating not only improves the conductivity of manganese dioxide electrode, but also mitigates coalescence of manganese dioxide nanoparticles. Meanwhile, composite materials create a loose internal space, and provides access to transmission of ions and diffusion of electrolyte. This effectively reduces performance degradation caused by volume expansion. |
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