Study On The Lithium Storage Materials Of Sulfur-metallic Oxide Composites For Vehicle Power Battery

The rapid development of electric vehicles and portable electronic devices put forward higher requirements on the capacity and life of the energy storage system. The lithium sulfur battery have attracted wide attention and research because they have very high thoeretical specific energy and sulfur has the advantages of abundant reserves and friendly environment. But the insulating of sulfur and reduction product of polysulfide dissolved in the electrolyte causing the active material loss and the large volume change of charge and discharge process hinder the commercialization application of the lithium sulfur battery.In this paper, three kinds of sulfur composite materials were prepared by using metal oxide nanomaterials and their electrochemical properties were tested.Three kinds of composite materials are S-In2O3 composite materials,S-ZnO composites and S-Co3O4 composite materials respectively. The main achievements are as follows.1. Preparation and the electrochemical properties of S-In2O3 composite materialsIn2O3 globular structure was synthesized by hydrothermal method as the metal oxide matrix for sulfur to improve electrochemical properties of sulfur electrodes. The crystal structure and morphology of samples are observed through X-ray diffraction(XRD), transmission electron microscopy(TEM) and scanning electron micrographs(SEM). The electrochemical performance of the S-In2O3 cathode is evaluated in lithium-sulfur batteries by cyclic voltammetry(CV), electrochemical impedance spectroscopy(EIS) and galvanostatic charge-discharge test. It is found that the cycle stability of sulfur-In2O3 cathode is significantly improved. It delivers a very high initial discharge capacity of 1357mAh/g at a current density of 335mA/g, and maintains 595 mAh/g after 60 cycles at a current density of 670mA/g with an average coulombic efficiency of 91.3%.. Furthermore, In2O3 globular structure materials increases the conductivity effectively, which enhances the rate performance of the prepared S-In2O3 cathode. The excellent electrochemical performance shows that the indium oxide is a promising material for the sulfur cathode in the lithium sulfur battery applications.2. Preparation and the electrochemical properties of S-ZnO compositesBlanket structure ZnO porous nanomaterials are prepared by a simple hydrothermal method followed by a calcination process, and then sulfur is infiltrated into ZnO nanomaterials via a vapour-melt method. Electrochemical tests show that the S-ZnO composites has an initial discharge specific capacity of 1414 mAh/g and an initial charge specific capacity of 1668 mAh/g, which reach to the theoretical specific capacity of 84% and 99%, respectively,and a discharge specific capacity of 663mAh/g with a coulombic efficiency of 94.7% after 100 cycles. At the same time, the effect of metal ions on the electrochemical performance of sulfur composite cathode was studied. The doping of Co and Mn improve the stability of the battery.3. Preparation and the electrochemical properties of S-Co3O4 composite materialsCo3O4 nanomaterials with high purity were prepared by the hydrothermal method, and the SEM and XRD tests show that the black Co3O4 material prepared by hydrothermal temperature of 120? for 8h, which was composed of many particles of 50-60 nanoparticles. The performance of S-Co3O4 cathode is tested in lithium-sulfur batteries by cyclic voltammetry(CV), galvanostatic charge-discharge and electrochemical impedance spectroscopy(EIS) test. It is found that the S-Co3O4 cathode has an initial discharge specific capacity of 1512 mAh/g and an initial charge specific capacity of 1543 mAh/g with the initial coulombic efficiency of 98%, which reach to the theoretical specific capacity of 84% and 99%, respectively. Co3O4 nanomaterials with different morphologies were obtained by changing the hydrothermal temperature and time. The electrochemical performance tests show that the S/Co3O4 composite cathode materials prepared by hydrothermal temperature of 95? for 8h has the excellent electrochemical properties.