Controllable Fabrication Of Micro/Nanostructured Vanadium Oxides And Their Lithiumion Battery Properties

Micro/nano structured vanadium oxides have been considered as potential electrode materials, gas sensor and switch materials due to their changeable valence, adjustable micro structure and special electrical properties. Controllable fabrication of micro/nano structured vanadium oxides and relationship between structure and performance such as lithium ion battery (LIB) are still hot topics, especially developing convenient methods which could be applied to produce micro/nano structured vanadium oxide in large scale production. This thesis attempts to improve traditional view that controllable synthesis of vanadium oxide via hydrothermal method and so on. And a novel strategy of precursor structure controlling micro/nano structured vanadium oxides via direct precipitation is brought forward. Firstly, variously morphological ammonium vanadates as precursors have been prepared by simple direct precipitation. Then the corresponding micro/nano sructured vanadium oxides were obtained by heat treating the precursors in different ways. The relationships between micro/nano structure and performance of products in the aspects of LIB have been detailedly studied. The main points of this dissertation are as follows:(1) Micro/nano structured ammonium vanadates were synthesized via direct precipitation. The reaction between V2O5 and molten urea has been studied. And based on this reaction, ammonium vanadate microspheres and flowers have been synthesized via precipitation process in ethanol-water system. The effects of ethanol/water ratio and aging time have been discussed on the morphology and structure of as-obtained ammonium vanadate products. The results show that the radius of ammonium vanadate microspheres gradually decreased with ethanol proportion increasing. And a higher percentage of ethanol could pRevent nanoplates thickening. With the increasing of aging time, close packing of flowers would form at high ethanol proportion, and thick petals would form at low ethanol proportion.(2) The corresponding micro/nano structured vanadium oxides were fabricated by calcine of ammonium vanadate precursor. And the influence of atmosphere and temperature has been detailedly discussed on the morphology and structure of as-prepared vanadium oxides. It was found that flower-like and microspheric ammonium vanadate could transform to hierarchical V2O3 flowers and V2O3 hollow microspheres via heat treatment at ammonia atmosphere. Porous VO2 microspheres and flowers have been prepared by thermal decomposition of the microspheric and flower-like ammonium vanadate at nitrogen atmosphere. The corresponding micro/nano structured V2O5 has been synthesized via calcination of the former low valent vanadium oxides at air atmosphere.(3) The influence of micro/nano structure and W doped for VO2 have been studied for their phase transition property and lithium ion battery (LIB) performance. The LIB performance for the porous microspheric and flower-like VO2 and W doped VO2 (R/M) has been studied. The results show that the porous microspheres VO2 (B) has the most stable cycle performance with high charge and discharge specific capacity (140 mAh·g-1), and the cycle capacity remain at a rate of 87% after 100 times. For the temperature susceptibility of W doped VO2, the phase transition of W doped VO2 could maintain a narrow temperature range at room temperature or even much lower by the heat treatment at 1000 ℃. And co-doping Na and W can reduce total phase change moderate resistance, and enhance the reversible storage lithium ion ability to some extent. But there is also some difference from the VO2 (B) andV2O5.(4) The LIB performance of as-obtained micro/nano structured V2O5 (including nanorods, hollow microspheres, porous microspheres, flower and hierarchical flower, etc.) have been measured. The results showed that all of as-prepared micro/nano structured V2O5 were better than above VO2 and commercial V2O5. The hierarchical V2O5 flowers showed the highest discharge specific capacity 286 mAh·g-1(close to the theoretical value 294 mAh·g-1). On the other hand, the V2O5 hollow microspheres exhibited the most stable cyclic performance.