There is growing interest in electrical/electrochemical energy-storage devices with both high power and high energy densities for possible application as auxiliary-power sources for electric and/or hybrid-electric vehicles. [1,2] Although lithiumion batteries are attractive power-storage devices with high energy density, their power density is generally low because of a large polarization at high charging-discharging rates. The large polarization is thought to be due to slow lithium diffusion in the solid active material and increases in the resistance of the electrolyte and in the electric resistance of the active materials upon increasing the charging-discharging rate. Therefore, in order to obtain high performance with both high power and high energy densities, it is important to design and fabricate nanostructured electrode materials that provide interconnected nanopaths for electrolyte-ion transport and electronic conduction. Mesoporous materials are quite attractive hosts for Li intercalation because of their large surface area, which decreases the current density per unit surface area; their thin walls, which shorten the Li-diffusion length in the solid phase; and their pores, which enable electrolyte ions to be transported smoothly. Actually, it has recently been reported that control of the porous structure of the active materials is effective in increasing the capacity of Li-intercalating electrode materials, even at high charging-discharging rates. [3][4][5][6] Porous materials are often considered to have the disadvantage of having low volumetric energy density, but this is not always the case for high-rate use: because of the low diffusion coefficient in the solid phase (10 -11 -10 -13 cm 2 s -1 ), only the thin surface layer of the host material is available for Li intercalation at high charging-discharging rates for bulk materials. On the other hand, hosts for Li intercalation generally have a low electronic conductivity, and thus electronic conduction paths are also required in the host material to decrease the polarization. Although conducting additives, such as acetylene black can be mechanically mixed with the host material in conventional Libattery electrodes, it is difficult to mix such large-sized conducting additives with mesoporous host materials, because the wall of the mesoporous structure is easily destroyed by conventional mixing techniques.As a new approach, we have synthesized single-walled carbon nanotube (SWNT)-containing mesoporous TiO 2 by a bicontinuous microemulsion-aided process using a dispersed aqueous solution of cut SWNTs (c-SWNTs) as the water phase of a water/surfactant/oil ternary bicontinuous microemulsion. Although there are some reports on surface modifications of carbon nanotubes with metal oxides, [7][8][9][10] this study is the first attempt to prepare a nanocomposite material with a mesoporous structure consisting of anatase TiO 2 and c-SWNTs. We also demonstrate that the Li-intercalation capacity at high charging-discharging rates increases dramatically for c-SW...

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