Core-Shell Se-Doped TiO₂@Carbon Nanotubes for High-Performance Sodium-Ion Batteries

Titanium dioxide (TiO₂) has been considered as a promising anode material for sodium-ion batteries (SIBs), because of its abundance, safety and eco-friendliness. However, the inferior electronic conductivity and low sodium ion diffusion rate of TiO₂ hinder its improvement of electrochemical performance. To overcome these drawbacks, herein, core-shell Se-doped TiO₂@carbon nanotubes (denoted as Se-TiO₂@CNTs) are successfully designed and fabricated, in which the TiO₂ nanoparticle aggregated shells are conformally coated on the carbon nanotubes, while the metallic Se species are physically confined within the meso/micropores. When examined as a SIB anode, the Se-TiO₂@CNTs electrode demonstrates excellent sodium storage performance, correspondingly delivering high reversible capacities of 222.7/208.5 mA h g⁻¹ after 200/1000 cycles at current densities of 0.2/1.0 A g⁻¹, and even a capacity of 140.2 mA h g⁻¹ after 4500 cycles at a high-rate of 5.0 A g⁻¹. The high reversible capacity, long-term cycling stability, and high-rate capability of the Se-TiO₂@CNTs can be owing to the unique structure characteristics, as the hollow/porous structure with high specific surface area of 335.4 m² g⁻¹ efficiently shortens the Na⁺ diffusion length and facilitates the electrolyte penetration, while Se-doping and carbon supporting greatly enhance the electronic conductivity of the Se-TiO₂@CNTs electrode.