Hydrogenated TiO2 Nanotubes as High-Power Anode Materials for Lithium-Ion Batteries

Wednesday, 8 October 2014
Expo Center, 1st Floor, Center and Right Foyers (Moon Palace Resort)
J. Y. Eom, J. H. Yun, S. E. Yoo (Korea Automotive Technology Institute), W. H. Ryu, S. J. Lim, and H. Kwon (Korea Advanced Institute of Science and Technology)
Titanium oxide (TiO2) has received much attention as the most promising alternative to the conventional graphite anode of Li-ion batteries for high energy and power. The performance of TiO2 anode for Li-ion batteries depends strongly on the crystalline phase, the morphology, and the porosity of the structure. The nanostructured TiO2 materials, such as nanoparticles, nanorods, nanowires, and nanotubes have been studied to improve the performance of TiO2 anode. Recently, it was reported that the hydrogenated TiO2, called a ‘black TiO2’ nanostructures are more attractive for photovoltaics, photocatalysis, and supercapacitors owing to their narrower bandgap (less than typical 3 eV value) and relatively high electrical conductivity.

The smooth and well-ordered TiO2 nanotubes were synthesized on a Ti disk successfully by anodization in a non-aqueous solution containing fluoride ions. The as-prepared TiO2 nanotubes were annealed to obtain crystalline anatase (A-TiO2 NTs) and hydrogenated TiO2 nanotubes (H-TiO2 NTs) at 450 °C for 2 h in air and hydrogen atmosphere, and then their electrochemical performances were investigated as alternative anode materials for Li-ion batteries.

The initial discharge capacity of the H-TiO2 NTs (0.117 mAh cm-2) was superior to that of the A-TiO2 NTs (0.110 mAh cm-2) and the discharge capacities of the H-TiO2 NTs and A-TiO2 NTs maintained nearly 72 and 44 % at a current density of 10 mA cm-2. In addition, the H-TiO2 NTs (89 %) exhibited much higher the capacity retention than the A-TiO2 NTs (70 %) at the current density of 1 mA cm-2 (~10 C-rate) after 300 cycles, as shown in Figure 1. The H-TiO2 NTs presented smaller the crystallite size and charge transfer resistance (Rc) compared with the A-TiO2 NTs and the oxygen vacancies were formed in the H-TiO2 NTs during hydrogenation, which was proved by the presence of Ti3+ from the XPS analysis.

These results indicate that the insertion and extraction of Li+ through the H-TiO2 NTs were preferable to those through the A-TiO2 NTs, which were probably attributed to the short diffusion length for Li+, innumerable reaction sites, and relatively high electrical conductivity. Therefore, the H-TiO2 NTs exhibited vastly superior the rate capability and capacity retention property during cycling to the A-TiO2 NTs at high current density as anode materials for Li-ion batteries.