TiO ₂ nanotubes with different spacing, Fe ₂ O ₃ decoration and their evaluation for Li-ion battery application

In the present work, we report on the use of organized TiO 2 nanotube (NT) layers with a regular intertube spacing for the growth of highly defined α -Fe 2 O 3 nano-needles in the interspace. These α -Fe 2 O 3 decorated TiO 2 NTs are then explored for Li-ion battery applications and compared to classic close-packed (CP) NTs that are decorated with various amounts of nanoscale α -Fe 2 O 3 . We show that NTs with tube-to-tube spacing allow uniform decoration of individual NTs with regular arrangements of hematite nano-needles. The tube spacing also facilitates the electrolyte penetration as well as yielding better ion diffusion. While bare CP NTs show a higher capacitance of 71 μ Ah cm −2 compared to bare spaced NTs with a capacitance of 54 μ Ah cm −2 , the hierarchical decoration with secondary metal oxide, α -Fe 2 O 3 , remarkably enhances the Li-ion battery performance. Namely, spaced NTs with α -Fe 2 O 3 decoration have an areal capacitance of 477 μ Ah cm −2 , i.e. they have nearly ∼8 times higher capacitance. However, the areal capacitance of CP NTs with α -Fe 2 O 3 decoration saturates at 208 μ Ah cm −2 , i.e. is limited to ∼3 times increase.