Hydrogenated TiO2 Nanotube Arrays as High-Rate Anodes for Lithium-Ion Microbatteries

A simple method has been developed to substantially improve the high-rate capability of electrochemically anodized TiO2 nanotube arrays targeted for use as anode material in lithium-ion microbatteries by annealing in a reducing atmosphere (5% H-2 and 95% Ar). A series of complementary techniques including X-ray diffraction (XRD) with Rietveld refining, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), Raman spectrometry (Raman), Fourier-transform infrared spectroscopy (FTIR), galvanostatic measurements, and electrochemical impedance spectroscopy (EIS) have been employed to investigate the structural and morphological changes as well as the electrochemical performance enhancement resulting from hydrogenation treatment of the TiO2 nanotube arrays. The results reveal that improvement of the rate capability is mainly attributed to the electronic conductivity increase of the bulk TiO2 nanotubes rather than conductive characteristics of the surface coating because hydrogenation treatment produces a high number of oxygen vacancies inside the crystal lattices that makes the TiO2 nanotube arrays favor a bulk n-type conductor. Furthermore, the high-rate capability of other kinds of TiO2 nanomaterials, including rutile TiO2 nanowire arrays and anatase TiO2 nanoparticles, can also be considerably improved by similar H-2 treatment. Therefore, the current H-2 treatment method is proved to be a general and facile technique to improve the power density of TiO2 anode materials for next-generation, high-power lithium-ion batteries.