Sulfur-Doped Anatase TiO₂ as an Anode for High-Performance Sodium-Ion Batteries

Sulfur-doped anatase TiO2 was prepared through a calcination conversion route for the first time. The grain size of TiO2 with S-doping obviously decreased after S-doping, manifesting that the introduction of S species could inhibit the crystal growth. Applied as an anode material for sodium-ion batteries, this material exhibited an impressive specific capacity of 174.4 mA h g–1 at a high current density of 10 C after 10 000 cycles. The remarkable performance results from the unique crystal structure of anatase TiO2 with bidirectional pore channels for sodium-ion intercalation, and S-doped TiO2 could increase the electronic conductivity, as well as enlarge the channel structure. Furthermore, density functional theory calculations manifested that the S-doping increases the volume of the lattice slightly, leading to the ease of insertion for sodium ions into anatase TiO2 and a reduced band gap with higher electronic conductivity. Therefore, S-doped TiO2 showed high reversible capacities and excellent long-term cycling performance.