Synthesis of WO3 via Hydrothermal Method with Improved Reversible Capacity and Cyclic Stability as Anode Material for Lithium Ion Batteries

• Main Author: Augus Tino Tri Widyantoro
• Other Authors: Wang, Chen-Hao
• Format: Others
• Language: en_US
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/18388965452999756232

碩士 === 國立臺灣科技大學 === 材料科學與工程系 === 102 === Tungsten trioxide (WO3) is expected to be profitable in improving of LIBs due to enhanced safety because of high melting temperature and mechanical stability, low cost, large theoretical capacity (693 mAh/g) and high volumetric capacity. The objective of the contribution is to introduce a high performance anode alternative to graphite for lithium-ion batteries. Hexagonal WO3 was synthesized via hydrothermal route using NaCl and/or Na-EDTA as structure directing templates and then these materials were evaluated as an anode material for lithium ion batteries. The Na2WO4.2H2O/Na-EDTA molar ratio and the reaction temperature are found to play important roles in determining the morphologies and electrochemical properties of the WO3 product. The morphology of WO3 product without adding either NaCl or Na-EDTA (WO_H180T20) is nanoparticle whereas that of WO3 product with adding NaCl and Na-EDTA synthesized at 210oC (WO_H210T20_CE0.8) is rod like structure. WO_H180T20 has initial discharge capacity of 814.3 mAh/g with a first coulombic efficiency of 53.7 %. On the other hand, WO_H210T20_CE0.8 has a good electrochemical performance with initial discharge capacity of 558.9 mAh/g and a high first coulombic efficiency of 86.9 %. These proved that h-WO3 is one of good candidate materials for lithium ion battery anode. The improved electrochemical performance of WO3 could be ascribed to the highly ordered self-assemble structures. Na-EDTA is not only found to be responsible for the especially good uniformity and high crystallinity of the products, but also play important role in restricting the natural growing habit of WO3 due to the possible selective interaction between EDTA and certain crystal facets, thus having a great impact over its final morphology. Tungsten trioxide/reduced graphene oxide (WO3/rGO) nanocomposites also were synthesized via hydrothermal method and evaluated as an anode material for lithium batteries. At first cycle the nanocomposite electrode (WO_H180T20_GO8%) exhibits a discharge capacity of 987.4 mAh/g with a coloumbic efficiency of 64.6%. And at a current density of 700 mA/g it can delivers as high as 219.5 mAh/g after 100 cycles. The improved electrochemical performance could be attributed to the incorporation of rGO and the unique structure of the nanocomposite.