Single-Crystalline Nb-Doped Rutile TiO₂ Nanoparticles as Anode Materials for Na-Ion Batteries

Single-crystalline Nb-doped TiO2 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 TiO2 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 TiO2 with oxygen vacancies maintained high capacities over 200 mAh g–1 for 800 cycles.