Carbon nanotubes (CNTs) have been suggested as a substitute for the graphite anode in lithium-ion batteries. Their unique one-dimensional tubular structure, high electrical conductivity, and large surface area [1][2][3][4][5][6][7][8] are promising features for highly efficient Li storage. However, two disadvantages are inherent in a CNT anode: low volumetric capacity owing to the presence of a large internal void, which is of no use for Li storage, [2] and a specific capacity that is limited by the theoretical maximum capacity of the graphite structure (372 mAh g -1 ). The capacity of a CNT anode can, in principle, be increased by filling the CNT interior with high-capacity Li-storage compounds, such as those derived from Sn, Sb, and Si (e.g., Sn has about twice the gravimetric and three times the volumetric capacity of carbon). [9][10][11][12][13][14] These elements, while impressive for their capacity for Li storage through alloy formation, are significantly less cyclable than graphite in battery applications. It is believed that a carefully crafted combination of CNTs and high-capacity Li-storage compounds may work synergistically to deliver both high capacity and good cyclability. The SnO 2 nanotubes with uniform CNT skins synthesized here are a good example.
Lately, considerable effort has been devoted to encapsulating foreign matter within the hollow cavity of CNTs, [1,2,[15][16][17][18] which could significantly alter the properties of CNTs and the filler material. [3,19,20] The commonly used filling techniques include electrochemical deposition, [15] solution-chemistry methods, [17] and physical deposition by capillary forces. [3] The size, shape, and uniformity control of the filler material is made difficult by the small bore and considerable length of the CNTs, resulting in a very low filling rate. [3,17] In addition, the external surface of the CNTs would be randomly decorated by the filler material, a rather undesirable side effect.
Herein, we report a method for synthesizing SnO 2 -tube-in-CNT nanostructures. As opposed to current techniques based COMMUNICATIONS