The Preparation Of Vanadium Oxide Nanomaterials And The Research On Their Electrochemical Performance

The destruction of the environment and the depletion of natural resource promote the second energy revolution.Lithium ion battery with high energy density,long life and no pollution to the environment arises at the historic moment,but the specific capacity of cathode material which can decide the working voltage of the battery is too low to achieve large-scale applications.Vanadium oxide is a kind of ideal energy storage material with variable valence state and layer structure because it is cheap,abundant and it has high theoretical specific capacity.Among them,V₂O₅ and V₂O?B?are two relatively mature systems with good electrochemical properties.However,the structure of V₂O₅ will be irreversibly changed in the process of embedding,and the layered compound after embedding is flawed,which lead to a lower actual specific capacity and bad cyclic stability.Therefore,developing vanadium oxide with high specific capacity and good cyclic stability is of great significance.In this paper,we prepared V₂O?D?hollow nanosphere and V₃O₇·H₂O nanobelt using hydrothermal method,explored the influence of reaction time,temperature and other factors on microstructure and phase composition of our products,and achieved the best parameters.Then,the electrochemical properties of the nanomaterials were measured.To improve the electrochemical performance,we prepared composites with carbon materials such as reduced graphene oxide and C₃N₄.Principal results are as follows:?1?We prepared a kind of V₂O hollow nanosphere with new phase structure?named as V₂O?D??using V₂O₅ as vanadium source and oxalic acid as reductant.The average particle size is about 500 nm with uniform size,good monodispersity and shape rules.According to the experiment,we achieved the best preparation process parameters: reaction temperature was 230?,reaction time was 10 h,the ratio of alcohol to water was 6:1,the container volume was 50 ml.The obtained V₂O?D?hollow nanosphere has a good performance of phase change and catalytic decomposition of ammonium perchlorate.The lithium battery using V₂O?D?hollow nanosphere as anode material exhibited a initial discharge specific capacity of 128.6m Ah/g under the current density of 50 m A/g,which decreased to 70.6m Ah/g after 50 cycles and showed good electrochemical performance;?2?Using V₂O₅ as vanadium source and H2O2 as reductant,We prepared V₃O₇·H₂O nanobelt.It is more than 200?m in length,and forms layer structure through interwining with each other.According to the experiment,we achieved the best preparation process parameters: reaction temperature was 210?,reaction time was 10 h,H2O2 volume was 90 ml.Due to the good film-forming property,larger specific surface area and less adverse events happened in the process,it has higher specific capacity and better cycle stability than V₂O?D?hollow nanosphere.The initial discharge specific capacity was 168.2m Ah/g under the current density of 50 m A/g,and decreased to 126.5m Ah/g after 50 cycles,which showed great electrochemical performance;?3?V₂O?D?/GO?V₂O?D?/C₃N₄?V₃O₇·H₂O/GO and V₃O₇·H₂O/C₃N₄ composites were prepared according to the freeze-drying method and the mechanical stirring method.It turned out that the composite of reduced GO increased the specific capacity substantially and improved the cycle stability and rate capability because of the better electrical conductivity,large specific surface area,layer structure and high mobility ratio.Among them,the composite materials prepared by freeze-drying method have better performance because the composite of reduced GO using this method is more uniform and doesn't generate agglomeration.The initial discharge specific capacities of these two compounds with reduced GO?mass ratio 20:1?were 214.3m Ah/g and 274.6m Ah/g respectively under the current density of 50 m A/g,and decreased to 110.4m Ah/g and 176.2m Ah/g respectively after 50 cycles.On the other side,the specific capacity of materials composited with C₃N₄ have not been improved on account of its unstable structure which leaded to rapid decline after the first cycle,but the rate capability has been improved due to the good conductivity of C₃N₄.