Vertically Aligned Binder-Free TiO 2 Nanotube Arrays Doped with Fe, S and Fe-S for Li-ion Batteries.

Vertically aligned Fe, S, and Fe-S doped anatase TiO nanotube arrays are prepared by an electrochemical anodization process using an organic electrolyte in which lactic acid is added as an additive. In the electrolyte, highly ordered TiO nanotube layers with greater thickness of 12 μm, inner diameter of approx. 90 nm and outer diameter of approx. 170 nm are successfully obtained. Doping of Fe, S, and Fe-S via simple wet impregnation method substituted Ti and O sites with Fe and S, which leads to enhance the rate performance at high discharge C-rates. Discharge capacities of TiO tubes increased from 0.13 mAh cm(bare) to 0.28 mAh cm for Fe-S doped TiO at 0.5 C after 100 cycles with exceptional capacity retention of 85 % after 100 cycles. Owing to the enhancement of thermodynamic and kinetic properties by doping of Fe-S, Li-diffusion increased resulting in remarkable discharge capacities of 0.27 mAh cm and 0.16 mAh cm at 10 C, and 30 C, respectively.