Iron-Doped Cauliflower-Like Rutile TiO2 with Superior Sodium Storage Properties

Developing advanced anodes for sodium ion batteries is still challenging. In this work, Fe-doped three-dimensional (3D) cauliflower-like rutile TiO2 was successfully synthesized by a facile hydrolysis method followed by a low-temperature annealing process. The influence of Fe content on the structure, morphology, and electrochemical performance was systematically investigated. When utilized as a sodium ion battery anode, 6.99%-Fe-doped TiO2 exhibited the best electrochemical performance. This sample delivered a very high reversible capacity (327.1 mAh g–1 at 16.8 mA g–1) and superior rate performance (160.5 mAh g–1 at 840 mA g–1), as well as long-term cycling stability (no capacity fading at 1680 mA g–1 over 3000 cycles). Density functional theory (DFT) calculations combined with experimental results indicated that the significantly improved sodium storage ability of the Fe-doped sample should be mainly due to the increased oxygen vacancies, narrowed band gap, and lowered sodiation energy barrier, which enabled much higher electronic/ionic conductivities and more favorable sodium ion intercalation into rutile TiO2.