Design, Characterization And Electrochemical Properties Of One-dimensional Hollow Manganese Oxide/carbon Nanostructure

With the growing demand for energy sources, solar, wind and other renewable energy have gained wide attention. Therefore it has been a research topic today to explore new type of energy storage materials with excellent properties. Lithium batteries, with high specific capacity, long life and fast charge and discharge rate, have delivered great potential in the field of electronic devices and electric vehicles. Electrode material is one of the key factors for the development of advanced lithium batteries. So, it is particularly important to design and construct new electrode materials.Manganese oxide, as a new type of lithium battery electrode material, has been widely developed because of its high theoretical capacity, low price and environmental friendliness. However, manganese oxide still suffers some disadvantages as electrode materials:(1) the low electronic conductivity and ionic conductivity make manganese oxide difficult to achieve high charge and discharge rate;(2) manganese oxide suffers larger volume variation during the lithium insertion and extraction precess, which can destroy the integrity of electrode material and result in poor cycling performance;(3) the volume changes of material may lead to the repeated formation and rupture of the SEI film, which consumes a amount of lithium source in the electrolyte and leads to low coulombic efficiency.As to these issues, we have carried out some relative research and acquired the following results:(1) With the solution-phase synthesis approach such as hydrothermal method, sol-gel method and hard template et al, we prepared one-dimensional manganese oxide nanorods, one-dimensional manganese oxide/carbon co-axial nanorods, one-dimensional manganese oxide/carbon co-axial hollow nanorods, trying to enhance the rate property of electrode materials through carbon coating, to improve the cycling stability and reversibility of electrode materiasl by hollow structure construction. Then, advanced characterization techniques such as XRD, SEM, TEM, XPS, Raman and TGA are utilized to characterize the morphology, structure and chemical state of the materials systematically.(2) The three kinds of materials are tested for electrochemical properties as anode materials for lithium batteries by the following three methods such as cyclic voltammetry, galvanostic charge/discharge and electrochemical impedance spectrum. The results demonstrate that the one dimensional manganese oxide/carbon co-axial hollow nanorods have delivered high specific capacity and enhanced cycling performance when compared with the other two materials. Especially, at the current density of 100 mA/g, the electrode shows an initial reversible capacity of 660 mAh/g. At a larger current density of 500 mA/g, the reversible discharge capacity is 634 mAh/g even after 900 cycles. The above results can substantially prove the reasonability of the morphology construction.(3) Based on the above results, we make a research focusing on the corrleration between the morphology and electrochemical properties and we consider the excellent electrochemical performance may be ascribled to the following factors: the larger specific surface area can increase the interface between the active material and the electrolyte, providing more reaction sites; the carbon coating method can improve the electronic conductivity and accelerate the electrochemical reaction rate; the hollow structure can effectively alleviate the volume change in the cycling process, which can maintain the integrity of the overall structure and further keep the stability of the SEI film.