Defect-engineered TiO2 nanocrystals for enhanced lithium-ion battery storage performance

EPR spectra of sintered samples. The reduced sample produces two strong EPR signals at g = 2.0010 and 1.9478, corresponding to the presence of oxygen defects and Ti 3+ , respectively. A more intense signal is generated with increasing reductive sintering time. The intensity ratio of the peak area after 3, 5 and 10 h of reductive sintering was calculated to be ∼1:6.63:13.53. This shows that the concentration of oxygen defects gradually increases with increasing reductive sintering time. • Sintering in a 5% H 2 + 95% Ar atmosphere produced oxygen defects in TiO 2 nanocrystals. • Oxygen defect concentration in the TiO 2 nanocrystals can be controlled. • Reductive sintering converted Ti 4+ to Ti 3+ due to the generation of oxygen defects in TiO 2 . • The presence of oxygen defects and Ti 3+ in TiO 2 improved the its performance of electrode material. TiO 2 nanocrystals containing oxygen defects were successfully prepared by a hydrothermal method with reductive sintering in a 5% H 2 + 95% Ar mixed atmosphere. The high-resolution transmission electron microscopy and X-ray diffraction results showed that the prepared samples were all anatase TiO 2 . X-ray photoelectron spectroscopy analysis showed that the reductive sintering converted Ti 4+ to Ti 3+ . The Ti 3+ /Ti 4+ molar ratio of the TiO 2 nanocrystals increased with increasing sintering time. The results of the electron paramagnetic resonance spectroscopy analysis showed that the reduced and sintered TiO 2 nanocrystals produced strong signals at g = 2.0010 and 1.9478, corresponding to the presence of oxygen defects and Ti 3+ , respectively. Furthermore, stronger signals were generated with increasing sintering time, indicating a progressively higher concentration of oxygen defects. The TiO 2 nanocrystalswere used as anode materials for lithium-ion batteries. One sample, H-TiO 2 -5, containing a moderate concentration of oxygen defects, presented a higher lithium ion diffusion coefficient ( D = 5.1 × 10 -13 cm 2 s −1 ) compared to the other TiO 2 samples. This sample had a Ti 3+ /Ti 4+ molar ratio of 0.179 and excellent cycling stability after 100 cycles. The discharge capacity was 124 mAh.g −1 after 500 cycles at a current density of 1C, which means that it has good cyclic stability.