Low-dimensional Vanadium Oxide Nanomaterials And Micro/nano Devices For Electrochemical Energy Storage

In this dissertation,we mainly focus on the research of low-dimensional vanadium oxide nanomaterials.By combining the traditional strategy of energy storage material research and the novel micro-nano electrochemical devices,nanomaterials with desirable electrochemical performance are obtained.Moreover,the intrinsic relation between electron/ion transport in low dimensional nanomaterials and their electrochemical performance is also deeply investigated.Some meaningful research results are briefly summarized as follows:?1?Ultralong H₂V₃O₈ nanowires are synthesized by a simple hydrothermal method,and V₃O₇ nanowires can be obtained from H₂V₃O₈ nanowires by the calcination under a protective atmosphere.Through the electrochemical performance test and the electron transport measurement in the single nanowire devices,the close relation between the better performance of H₂V₃O₈ nanowires and its higher conductivity.LiV3O8 nanowires are further synthesized by topotactic lithium intercalation reaction,which exhibit good rate capability.When cycled at 2000 mA/g,its initial capacity is 137 mAh/g,and the capacity is able to stabilize at 120 mAh/g after 600 cycles,corresponding to a capacity fading of only 0.022%per cycle.?2?Single nanowire electrochemical devices with organic liquid electrolyte are designed and assembled.The intercalation/deintercalation reactions of Li and Na ions can be realized by using the corresponding electrolytes.With the well-designed devices,the conductance of the different parts of a single nanowire can be in situ recorded during the electrochemical process.Similar phenomena are observed when the charge carriers are Li and Na ions,indicating that they share the similar electrochemical reaction mechanisms in layered electrodes.However,the crystal structure degradation by Na ions is more severe than that of Li ions during the electrochemical processes,which mainly results from the much larger volume of Na ions and the greater energy barrier encountered by the limited interlayer space.These results indicate that the single nanowire electrochemical devices will act as a unique platform to push the fundamental and practical research of nanowire electrode materials for energy storage applications.?3?Hydrothermally synthesized NH₄V₄O₁₀ nanoflowers are used as precursor to prepare the ultrathin pre-lithiated V₆O₁₃ nanosheets by the calcination and pre-lithiation methods.The average thickness of the ultrathin pre-lithiated V₆O₁₃nanosheets is 4 nm and it exhibits the greatly improved electrochemical performance especially the cycling properties compared to pristine V₆O₁₃ nanosheets.The capacity retention can reach up to 98%after 150 cycles at the current density of 1000 mA/g.Moreover,the single nanosheet conductivity evolution during the electrochemical process is in situ recorded through the electrochemical micro-devices.Ultrathin pre-lithiated V₆O₁₃ nanosheets present the enhanced electrical conductivity,which could be the reason of its improved electrochemical performance.?4?In order to take advantage of high conductivity,high porosity and good mechanical property from the three-dimensional?3D?graphene framework,3D graphene/sulfur composites are synthesized as the electrode materials for lithium sulfur?Li-S?batteries.The sulfur content in the composites can reach up to 90%and they can be directly used as the sulfur cathode without additional binders or conductive additives.The physical encapsulation of graphene layer to sulfur particles and the chemical adsorption of the functional groups to the sulfur discharge products can efficiently inhibit the polysulfide shuttling effect.In addition,the V₂O₅·nH₂O decorated 3D graphene/sulfur composite is prepared by freeze drying the V2O5 sol.Based on the electrochemical test results,we find that V₂O₅·nH₂O is helpful to increase the coloumbic efficiency during the initial cycles,which further improves the overall stability of the batteries.