Carbon-Coated Anatase TiO₂Nanotubes for Li- and Na-Ion Anodes

Carbon-coated, anatase titanium dioxide nanotubes were prepared by carbonizing a polyacrylonitrile-based block copolymer grafted on the as-synthesized titanate nanotubes. As revealed by high resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS), this approach results in a very homogeneous and thin carbon coating, which is advantageous for those active materials storing lithium without undergoing significant volume changes upon ion (de-)insertion. As a matter of fact, thus prepared carbon-coated TiO 2 nanotubes presented an excellent long-term cycling stability for more than 500 cycles (0.02% capacity fading per cycle) and a very promising high rate performance (about 130 and 110 mAh g −1 at 10 C and 15 C, respectively). The influence of the tubular morphology on the rate performance is briefly discussed by comparing carbon-coated nanotubes and nanorods. Finally, the carbon-coated nanotubes were also investigated as sodium-ion anode material, showing very promising reversible capacities of around 170, 120, and 100 mAh g −1 at C/10, 1 C, and 2 C, respectively, rendering them as versatile anode material for lithium- and sodium-ion applications