Construction of triple-layered sandwich nanotubes of carbon@mesoporous TiO2 nanocrystalline@carbon as high-performance anode materials for lithium-ion batteries

Triple-layered sandwich nanotubes of carbon@mesoporous TiO2 nanocrystalline@carbon were prepared through coating hydrous titania and resorcinol-formaldehyde resin on carbon nanotubes followed by controllable crystallization and carbonization. Material characterization indicated that TiO2 nanocrystalline with the size of 5–6 nm was uniformly assembled to the mesoporous sandwich layer of carbon nanotube-in-nanotube, leading to large specific surface area of 465.4 m2 g−1 and large pore volume of 0.695 ml g−1. As anode material for lithium ion batteries, triple-layered sandwich nanotubes exhibited high lithium storage capacity (244 mAh g−1 at 0.1C), good rate capability (115 mAh g−1 at 5C), and excellent cycling stability (191 mAh g−1 with coulombic efficiency of 100.2% was retained after 200 cycles at 0.2C, presenting 79% of capacity retention ratio). The superior lithium storage properties should be attributed to synergistic superiorities of TiO2 nanocrystalline, the mesoporous sandwich layer structure and carbon nanotube-in-nanotube. These unique structural characteristics effectively reduce Li+ diffusion length; enhances intercalation storage capability and pseudocapacitive interfacial storage capability of TiO2; provides sufficient space to accommodate volume variation of TiO2 nanocrystalline; increases electron conductivity and structure stability of TiO2. It is anticipated that the present triple-layered sandwich nanotube provides a unique carbon-based hybrid structure for other energy storage materials.