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

Abstract Titanium dioxide (TiO 2 ) 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 TiO 2 hinder its improvement of electrochemical performance. To overcome these drawbacks, herein, core‐shell Se‐doped TiO 2 @carbon nanotubes (denoted as Se‐TiO 2 @CNTs) are successfully designed and fabricated, in which the TiO 2 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‐TiO 2 @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‐TiO 2 @CNTs can be owing to the unique structure characteristics, as the hollow/porous structure with high specific surface area of 335.4 m 2 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‐TiO 2 @CNTs electrode.