Self-Organized, Anatase, Double-Walled Nanotubes Prepared by Anodization under Voltage Ramp as Negative Electrode for Aqueous Sodium-Ion Batteries

Abstract

In order to prepare TiO2 nanotubes of controlled morphology, anodization of titanium under fixed voltge or, alternatively, under variable voltage (voltage ramp) was used. Self-organized TiO2 nanotubes with amorphous character are obtained, and after annealing at about 500°C in air atmosphere anatase-phase nanotubes are formed. The use of aqueous electrolyte batteries may be an alternative to non-aqueous batteries. Using cyclic voltammetry, we have found that self-organized anatase nt-TiO2 electrode in aqueous solution containing lithium (or sodium) ions exhibits reversible redox processes, particularly after optimization of the electrode properties (i.e. anodization of Ti ramp of voltage) and electrolyte. It seems that the ramp of voltage drives to double-walled nanotube and this special morphology (fractal electrode) enhances the capacity to react with sodium. The electrochemical behavior of this electrode material in aqueous sodium cell may be competitive against TiO2 in non-aqueous microbatteries.