Anatase Titania Nanorods as an Intercalation Anode Material for Rechargeable Sodium Batteries

Abstract

For the first time, we report the electrochemical activity of anatase TiO2 nanorods in a Na cell. The anatase TiO2 nanorods were synthesized by a hydrothermal method, and their surfaces were coated by carbon to improve the electric conductivity through carbonization of pitch at 700 °C for 2 h in Ar flow. The resulting structure does not change before and after the carbon coating, as confirmed by X-ray diffraction (XRD). Transmission electron microscopic images confirm the presence of a carbon coating on the anatase TiO2 nanorods. In cell tests, anodes of bare and carbon-coated anatase TiO2 nanorods exhibit stable cycling performance and attain a capacity of about 172 and 193 mAh g–1 on the first charge, respectively, in the voltage range of 3–0 V. With the help of the conductive carbon layers, the carbon-coated anatase TiO2 delivers more capacity at high rates, 104 mAh g–1 at the 10 C-rate (3.3 A g–1), 82 mAh g–1 at the 30 C-rate (10 A g–1), and 53 mAh g–1 at the 100 C-rate (33 A g–1). By contrast, the anode of bare anatase TiO2 nanorods delivers only about 38 mAh g–1 at the 10 C-rate (3.3 A g–1). The excellent cyclability and high-rate capability are the result of a Na+ insertion and extraction reaction into the host structure coupled with Ti4+/3+ redox reaction, as revealed by X-ray absorption spectroscopy.