Synthesis And Electrochemical Properties Of MoO₂ Nanomaterials

Notable for their extremely small feature size and a broad variety of specific properties, nanomaterials have the potential for wide-ranging applications such as industrial, biomedical, environment protection, and electronic, all of which have conspired to fascinate scientists and made nanotechnology an attractive field in recent years. As a member of nanomaterial family, MoO2 nanomaterial, the researches about which have developed a lot in recent years, especially in the field of Li-ion battery.In this dissertation, molybdenum dioxide nanomaterials were synthesized via hydrothermal method, the morphology and structure of the samples were characterized by XRD and SEM. The electrochemical property of the products were also studied.1. The hydrothermal products are monoclinic rod-like MoO2 reducted by ethyl alcohol with the length of 150 nm, the diameter of 50 nm and sphere-like MoO2 material reduced by acetone, whose size is about 2μm in diameter and composed of nanoparticls about several tenth of nanometers in diameter.2. Different testing conditions and sample preparation methods for the electrodes were investigated by galvanostatic charge and discharge, cyclic voltammetry and electrochemical impedance spectrometry tests, the results indicate that the electrochemical capacity shows an decreased state with the increasing of current density and an earlier raised and later decreased state while the the concentration of MoO2 increases.The galvanostatic charge and discharge test shows the best result in electrochemical performance at the current density of 0.1 mA/cm2 with the mass ratio of MoO2 to acetylene black of 6:4; owning to the small size and high specific area, the rod-like MoO2 material shows high specific capacity as much as 600 mAh/g in the first discharge process and keeps highly reversible in the following cycles, which behaves much better than that of sphere-like MoO2(244 mAh/g).3. The growth mechanism of MoO2 nanorods were studied via the investigation about the influence of hydrothermal temperature, time duration, alcohol content and precursor concentrations on the structure and morpholoy. The hydrothermal preparation experiences a process of crystallization, dissolving, recrystallization and splitting. The peroxomolybdic acid sols transformed into MoO3 nanobelts first, then MoO3 nanobelts dissolved and recrystallized into Mo8O23 sector-shaped nanoflakes and finally split into nanorods under the effect of ethanol.4. PANI/MoO2 nanocomposites were prepared by hydrothermal method, the structure was still monoclinic phase, but the crystallinity of the product decreased with the introduce of PANI, the size of the particle were reduced and aggregated together. Appropriate introduce of PANI could remarkably enhance the electrochemical properties of MoO2. First, the polymers can serve as conducting matrix that will improve the conductivity of inorganic materials to raise the utilization rate of active material, second, its viscoelasticity could reduce the influence of volume change in active materials and keep the structure stable, thus improve the cycling performance.