Long-Length Titania Nanotubes Obtained by High-Voltage Anodization and High-Intensity Ultrasonication for Superior Capacity Electrode

Abstract

To modify the morphology and electrochemical properties of the resulting titanium oxide layer, we have applied high-intensity ultrasonication during the potentiostatic anodization of metallic titanium, and the applied voltage and anodizing time has been changed. The influence of the imposed voltage, anodizing time, and ultrasonication on the nanotubes growth has been studied. Additional dissolution process takes place under ultrasonication, as is observed in the anodizing curves (current density vs time) that show values on the order of ca. 200 A/m2. After only 30 min of ultrasound-assisted anodization at 42 V, the resulting nanotubes length is ca. 4 μm and, in contrast, in the case of non ultrasound-assisted anodization, the length is only ca. 1 μm. Further prolonged anodization under ultrasound induced the complete dissolution of the titanium. After anodization at 60 V during 20 h (no ultrasounds), the observed length of the nanotubes is as long as ca. 45 μm. The nanotube TiO2 aspect ratio has been tailored between 40 and 320. The obtained nanotubes of TiO2 exhibit high areal capacity (up to ca. 2 mAh/cm2 and stabilized around 0.3 to 0.5 mAh/cm2) and good cycling behavior in lithium batteries. A nonlinear relationship between the nanotubes length and the resulting capacity has been revealed.