RESUMO
During the growth of anodic TiO2 nanotubes with a high layer thickness of greater than 20 µm, "nanograss" structures are typically formed on the outermost surface. This happens due to the fact that the engraving of the oxide tubes arises during prolonged exposure to an F- ion containing electrolyte. These TiO2 nanotubular layers have a high aspect ratio with astonishing bundles of nanograss structures on the tube top and especially a high surface area with anatase crystallites in the tubes. By two-step anodization in synergy with the hybridization of a rubber polymer binder, freestanding nanotubular layers consisting of nanograssy surfaces with nano-crystalline particles in the tubes were successfully obtained. Under the highly efficient polysulfide trapping and electrolyte perturbation, this nanotubular hybrid membrane could deliver an enriched performance with a capacity of 618 mA h g-1 after 100 cycles at 0.1C in Li-S batteries.
RESUMO
Vertically aligned Fe, S, and Fe-S doped anatase TiO2 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 TiO2 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 TiO2 tubes increased from 0.13 mAh cm-2(bare) to 0.28 mAh cm-2 for Fe-S doped TiO2 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-2 and 0.16 mAh cm-2 at 10 C, and 30 C, respectively.
