Rational Design of WO3 Nanostructures as the Anode Materials for Lithium-Ion Batteries with Enhanced Electrochemical Performance
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A facile, one-step hydrothermal method was employed to synthesize two kinds of WO3 nanostructures. By using different kinds of sylvine, tungsten trioxide (WO3) with different morphologies of microflowers and nanowires was obtained, respectively. The discharge capacities for microflowers and nanowires are 107 and 146 mAh g−1 after 180 cycles, and their corresponding capacity retentions after the first cycle are 72 and 85 %, respectively. Even at a high current density of 1,600 mAh g−1, the discharge capacities of WO3 microflowers and nanowires are as high as 433 and 557 mAh g−1 after 40 cycles, in which the current densities were increased stepwise. It is worth mentioned that the rate capability of the nanowires is superior to that of the microflowers. However, the cycle performance of the microflowers is better than nanowires, revealing that the morphology and structure of the as-synthesized WO3 products can exert great influence on the electrochemical performances.
KeywordsWO3 nanostructures Anode materials Li-ion batteries
In the past few years, owing to the development of new type energy materials, more and more researchers devote their efforts to investigate high-performance power sources with higher power and energy densities for long time operation, i.e., lithium-ion batteries (LIBs) and supercapacitors (SCs) [1, 2, 3, 4, 5, 6, 7, 8, 9]. Especially, the LIBs are obviously superior to the supercapacitors in aspect of energy storage due to the higher energy density [10, 11, 12]. Moreover, as one of the most important low-cost, light-weight, highly efficient, and environmentally friendly rechargeable power sources for consumer electronic products, LIBs have attracted worldwide attentions because of the increasing concerns about energy and environmental problems. Therefore, more and more efforts are devoted to develop high performance and miniaturization LIBs [13, 14, 15].
It is well known that the electrode materials correlate to the performance of lithium-ion batteries, which is strongly influenced by the sort and the structure of a material [16, 17, 18]. Hence, to rational design and synthesize semiconductor nanostructures with desired structures and shapes are a very important task. As an important n-type semiconductor, tungsten trioxide (WO3) has received a lot of attentions in recent years due to its attractive physiochemical properties and extensive potential applications [19, 20, 21, 22, 23, 24].
In this paper, we developed a simple hydrothermal strategy to design and fabricate WO3 nanostructures with two different morphologies and investigated their electrochemical performance as anode materials for LIBs. The rate capability of the WO3 nanowires was found to be superior to that of the microflowers. However, the cycle performance of the microflowers is better than that of the nanoribbons, revealing the morphology and structure of the as-obtained product might exert great influence on their electrochemical performances.
All chemicals used are analytical grade without further purification. In a typical procedure to prepare WO3 microflowers, 12.5 mmol Na2WO4·2H2O was added to 100 mL deionized water. After being stirred for 20 min at room temperature, 3 M HCl was added dropwise to the solution until the pH reached 12, and a yellow transparent solution was formed. Subsequently, 35 mL H2C2O4 was added in the above solution with continuous stirring, and then the solution was diluted to 250 mL.
After that 1.0 g of KCl was added into above 20 mL solution with stirring, followed by transferred into a 40 mL Teflon-lined stainless steel autoclave, and the autoclave was sealed and maintained at 180 °C for 16 h. After the solution was cooled down to room temperature naturally, the as-prepared yellow precipitation was rinsed extensively with deionized water and ethanol, and finally dried in air at room temperature for further characterization. WO3 nanowires were synthesized through the same method except 1.0 g of K2SO4 was added instead of KCl.
3 Results and Discussion
When using K2SO4 to replace KCl with other parameters constant, some nanowires were formed. From Fig. 1c, it can be observed that these nanowires possess a certain orientation, and their average lengths are more than 10 μm. Further observation (Fig. 1d) found that each nanowire has a smooth and uniform surface.
A comparison of cycle performances of WO3 microflowers, nanowires with SnO2 microflowers
Initial discharge capacities
718.8 mAh g−1
664.3 mAh g−1
664.3 mAh g−1
Final discharge capacities
549.8 mAh g−1
503.9 mAh g−1
664.3 mAh g−1
Such good rate capability and reversibility of WO3 microflowers and nanowires can be attributed to the superior uniform structures and small size of the products that reduce lithium ion diffusion distance and facilitate rapid lithium ion diffusion. Nanoscale particles are able to diffuse much more easily and have better accommodation of structural strain for the electrochemical reaction of lithium, resulting in improving the electrochemical performance. Similar case has also been encountered in the SnO2/α-MoO3 core–shell nanobelts and hierarchical WO3 flowers [29, 30]. Moreover, it has been demonstrated that small size effect of WO3 nanostructures, arising from an increased total number of surface atoms, can greatly increase the electrochemical reactivity and make the conversion between Li+ and Li2O reversible [31, 32].
In conclusion, WO3 microflowers and nanowires have been successfully synthesized through a facile hydrothermal process. Potassium salt plays an important role in adjusting the morphology of the products. The as-prepared two WO3 structures show significantly improved cycle lives and rate performance due to their unique structures.
This work was supported by the Scientific Research Fund of Heilongjiang Provincial Education Department (12531179) and Program for Scientific and Technological Innovation Team Construction in Universities of Heilongjiang (No. 2011TD010).
- 1.Y. Liu, Y. Jiao, Z.L. Zhang, F.Y. Qu, A. Umar, X. Wu, Hierarchical SnO2 nanostructures made of intermingled ultrathin nanosheets for environmental remediation, smart gas sensor and supercapacitor applications. ACS Appl. Mater. Interfaces 6(3), 2174–2184 (2014). doi: 10.1021/am405301vCrossRefGoogle Scholar
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