Vapor-Solid Reaction Growth of Rutile TiO2 Nanorods and Nanowires for Li-Ion-Battery Electrodes.

Abstract

A new synthetic method to grow O-deficient rutile TiO2(s) nanorods (NRs) and nanowires (NWs) by a vapor–solid reaction growth method is developed. TiCl4(g) was employed to react with commercially supplied CaTiO3(s) (size 2–4 μm) at 973 K under atmospheric pressure to generate TiO2(s) NRs (diameters 80–120 nm, lengths 1–4 μm). The reaction employing TiCl4(g) and CaO(s) at 973 K also generated CaTiO3(s) (size 4–13 μm) as the intermediate which reacted further with TiCl4(g) to produce NWs (diameters 80–120 nm, lengths 4–15 μm). This is the first report of 1D rutile TiO2(s) nanostructure with such a high aspect ratio. Both of the NRs and the NWs, with compositions TiO1.81 and TiO1.65, respectively, were single crystals grown in the [001] direction. Their morphology was affected by the reaction temperature, the concentration of TiCl4(g), and the particle size of CaTiO3(s). The NRs and the NWs were investigated as anode materials for Li+-ion batteries. At constant current rates 1, 2, and 5 C (1 C = 170 mA g–1) for 100 cycles, the cycling (1.0–3.0 V) performance data of the NRs were 146, 123, and 104 mA h g–1, respectively. On the other hand, the cycling performance data of the NWs were 120, 80, and 52 mA h g–1, respectively. This is attributed to the high Li+ ion diffusion rate (DLi+) of the NRs (29.52 × 10–15 cm2 s–1), which exceeds that of the NWs (8.61 × 10–15 cm2 s–1). Although the [001] growth direction of the NR crystals would provide the fastest channels for the diffusion of Li+ ions and enhance the battery capacity, the extremely long channels in the NWs could hamper the diffusion of the Li+ ions. The O-deficiency in the structure would increase the conductivity of the electrode material and improve the stable cycling stability of the batteries also. The long-term cycling test at 2 C for the battery constructed from the NRs retained 121 mA h g–1 after 200 cycles and 99.2 mA h g–1 after 800 cycles. The device has an excellent long-term cycling stability with a loss of only 0.04% per cycle.