Single-crystalline Nb-doped TiO 2 particles were hydrothermally synthesized for Na-storage materials. Annealing in air changed the particle color from blue to white. The successful introduction of oxygen vacancies into Nb-doped TiO 2 without annealing was confirmed by lattice expansion, reduced electrical resistivity, a Raman peak shift, and the presence of {110} stacking faults due to streaks along the ⟨110⟩ reciprocal directions in electron diffraction. The introduction of oxygen vacancies significantly enhanced the reversible capacity of the electrode because of the improved conductivity. The electrode of Nb-doped TiO 2 with oxygen vacancies maintained high capacities over 200 mAh g −1 for 800 cycles.

We investigated the Li storage properties of spindle single-crystalline rutile TiO 2 fine particles synthesized by a large-scale sulfate process. Their anode properties were compared with those of polycrystalline rutile TiO 2 particles. An increase in the degree of single-crystal formation improved the charge−discharge capacity and initial Coulombic efficiency. In situ X-ray diffraction and transmission electron microscopic observation demonstrated the structural integrity of the spindle particles during the charge−discharge reactions. These results concluded that the degree is a critical parameter determining the anode performance of rutile TiO 2 . The anode performance was further enhanced by doping Nb into the spindle TiO 2 particles. These findings suggest that singlecrystalline rutile TiO 2 particles are very promising low-cost and high-performance Li storage materials.