Tin-filled carbon nanotubes as insertion anode materials for lithium-ion batteries

The electrochemical lithium insertion properties of tin-filled multi-walled carbon nanotubes are described. Carbon nanotubes synthesized by the catalytic decomposition method were purified, oxidatively opened, and filled with a tin salt by capillary action. Two methods, an NaBH4-reduction process and a hydrothermal process, were employed to reduce the salt to the metal. Structural characterization of the products was done by X-ray diffraction and transmission electron microscopy. At a 0.1 C rate, the hydrothermally-filled nanotubes gave first-cycle insertion and deinsertion capacities of 1916 and 834 mAh/g, respectively, while the NaBH4-reduced sample gave 2474 and 889 mAh/g. This was much higher than those for the opened carbon nanotubes, which were 1281 and 340 mAh/g, respectively. The reversible capacities of the tin-filled nanotubes were remarkably high, stabilizing in the 720800 mAh/g region over the first 20 cycles. The electrochemical performance of the materials is correlated with their structural characteristics. (C) 2004 Elsevier B.V. All rights reserved.