One-pot synthesis of core-shell structured Sn/carbon nanotube by chemical vapor deposition and its Li-storage properties
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Core–shell structured Sn/carbon nanotube (CNT) was prepared by one-pot chemical vapor deposition (CVD) method in N2/C2H2 (10% C2H2) using nanosized SnO2 as the starting material. The obtained onedimensional material is composed of a disordered carbon shell and a single-crystalline Sn nanorod core. The diameter of the Sn nanorod and the thickness of the carbon shell are around 40–50 and 4–5 nm, respectively, when the CVD reaction was carried out at 650 °C for 2 h. The core–shell structured Sn/CNT exhibits improved electrochemical performance compared with bare Sn with a diameter of around 100 nm. A reversible capacity of around 350 mAh/g can be retained after 20 cycles at 50 mA/g for Sn/CNT, while for bare Sn, the capacity drops rapidly to 100 mAh/g after the same cycles.
I. INTRODUCTION
Although carbon-based materials are still the dominant anodes in commercial Li-ion batteries, great interest has been focused on the noncarbonaceous materials with high specific capacity since Fujiphoto Film Celltec first reported that amorphous Sn-based oxides exhibited a high specific capacity and a long cycle life.1 It seems that metallic Sn is more suitable to be used as anode since the introduction of oxygen will decrease the specific capacity and bring the irreversible capacity. However, Sn anode undergoes large volume changes during Li-insertion/extraction processes, causing a rapid capacity fading. In recent years, great effort has been made to alleviate the large volume changes. One of the effective methods is to use Sn-based intermetallic compounds, MxSny, instead of metallic Sn, where M is a Li-inert element.2–11 The introduction of the Li-inert element, however, decreases the overall capacity. The long-term cycling stability of the intermetallic compounds is not satisfactory yet due to the limited buffering effect of the Li-inert element. An alternative strategy is to mix metallic Sn with a matrix. Among various potential matrices, carbon-based materials are considered to be best choices because they not only buffer the volume changes owing to their ductibility but also contribute to the overall capacity. Besides, the high electronic conductivity offers the conducting channels. An improvement in electrochemical performance was realized in some Sn-based anodes by using carbon-based materials, such as amorphous carbon,12–14 carbon fibers,15,16 graphite,17,18 and carbon nanotube (CNT).19,20 Nevertheless, it is difficult to realize a uniform dispersion of Sn particles in the carbon matrix. Furthermore, the buffering capability of the a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.308 J. Mater. Res., Vol. 26, No. 21, Nov 14, 2011
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carbon matrix becomes progressively weakened because both the carbon matrix and the Sn particles will aggregate after repeated cycling. A useful method to overcome this problem is to incorporate Sn particles into one-dimensional (1D) carbon material because the particles aggregation can be effectiv
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