| Summary: | TiO<sub>2</sub> represents one of the promising anode materials for lithium ion batteries due to its high thermal and chemical stability, relatively high theoretical specific capacity and low cost. However, the electrochemical performance, particularly for mesoporous TiO<sub>2</sub>, is limited and must be further developed. Elemental doping is a viable route to enhance rate capability and discharge capacity of TiO<sub>2</sub> anodes in Li-ion batteries. Usually, elemental doping requires elevated temperatures, which represents a challenge, particularly for sulfur as a dopant. In this work, S-doped TiO<sub>2</sub>nanotubes were successfully synthesized in situ during the electrochemical anodization of a titanium substrate at room temperature. The electrochemical anodization bath represented an ethylene glycol-based solution containing NH<sub>4</sub>F along with Na<sub>2</sub>S<sub>2</sub>O<sub>5</sub> as the sulfur source. The S-doped TiO<sub>2 </sub>anodes demonstrated a higher areal discharge capacity of 95 µAh·cm<sup>−2</sup> at a current rate of 100 µA·cm<sup>−2</sup> after 100 cycles, as compared to the pure TiO<sub>2 </sub>nanotubes (60 µAh·cm<sup>−2</sup>). S-TiO<sub>2</sub> also exhibited a significantly improved rate capability up to 2500 µA. cm<sup>−2</sup> as compared to undoped TiO<sub>2</sub>. The improved electrochemical performance, as compared to pure TiO<sub>2</sub> nanotubes, is attributed to a lower impedance in S-doped TiO<sub>2</sub> nanotubes (STNTs). Thus, the direct S-doping during the anodization process is a promising and cost-effective route towards improved TiO<sub>2</sub> anodes for Li-ion batteries.
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