Synthesis And Electrochemical Properties Of Nanostructured Materials Based On Niobium Oxide,Vanadium Oxide, And Their Composites

Transition metal oxides---NbaO5and V2O5---and their nano/micro composites were synthesized; their electrochemical (EC) properties and the correlation between the properties and materials structures were studied in the field of energy storage. Recently, due to the depletion of fossil fuels and increasing concern on sustainability of human society, researches on energy storage devices such as lithium ion battery (LIB) and supercapacitor have been attracting intensively interest. Generally, lithium ion battery provides high energy density, which has been widely used in industries and daily life. On the other hand, supercapacitor with high power density and long cycle life bridges lithium ion battery and conventional capacitors, and holds a great potential in the applications of renewable energy storage and next-generation transportations such as electric vehicles or hybrid electric vehicles. In this context, seeking new nanostructured materials with excellent properties and designing new electrode structures with high EC performance represent an essential task. The main research work of this thesis is as detailed below:1. Nb2O5nanocrystals were synthesized throught a one-pot hydrothermal method. Electrodes based on nanocomposites of carbon nanotubes (CNTs)/Nb2O5nanocrystals were fabricated with different compositions. Such nanocomposites showed very good electrochemcial properties, and improved performance was achieved of assymetric supercapacitors comprised of nanocomposite and activated carbon, such as high specific capacitance, excellent rate capability and long cycle life. This work provides an effective structure design by integrating metal-oxide nanocrystals and conductive CNTs networks into robust nanocomposite structure, which may be generalized to synthesize other nanocomposites for better-performance energy storage devices.2. A simple sol-gel technique was applied to synthesize the Nb2O5/V2O5nanocomposites.Nb2O5/V2O5composites have been applied to anode materials of lithium-ion batteries with outstanding rate capability and enhanced cycling performance. The improved conductivity and stability mainly arise from the introduction of V atoms into Nb2O5system and the synergistic effect between the two oxides. Such composites of transition metal oxides possesses a high packing density, thus ensures a high volumetric energy density of an device based on the composite electrode. This work provides a new concept to design electrode materials for lithium ion batteries.3.(Nb,V)2O5nanorods were synthesized through an aerosol-assisted method.(Nb, V)2O5nanocrystals with a unique rodlike morphology and investigated the electrochemical properties. Electrode based on such a novel material delivered an initial capacity of203mA h g-1and a superior cyclablity,even after500cycles, the capacity still remained as the80%of the initial, as well as a good rate performance. The improvement makes this material a promising anode candidate in the application of high performance lithium ion batteries.4. Li1+xV1-xO2have been studied theoretically with less actual synthesis. It has a layered structure,which will help the lithium in and out. Fisrt,solid-state method was used to synthesis Li1.07V0.93O2material. The working potential of Li1+xV1-xO2is very low,in our work,the capacity could reach200mA h g-1even after50cycles which is a substantial increase then the existing literature. Subsequently, aerosol-assisted method was used to synthesis Li1.07V0.93O2mateirals. The size of the materials decreased which means a shorter distance for lithium ion diffusion. The experimental demonstrates that Li1.07V0.93O2nano-materials with high energy density and long cycle life have the great advantages in the application of lithium-ion batterials.