Ultrafast sodium storage in anatase TiO2 nanoparticles embedded on carbon nanotubes

The main disadvantage of using transition metal oxides for Na+-ion batteries is the sluggish kinetics of insertion of Na+ ions into the structure. Here, we introduce nanosized anatase TiO2 that is partially doped with fluorine (TiO2-delta F delta) to form electro-conducting trivalent Ti3+ as an ultrafast Na+ insertion material for use as an anode for sodium-ion batteries. In addition, the F-doped TiO2-delta F delta is modified by electro-conducting carbon nanotubes (CNTs) to further enhance the electric conductivity. The composite F-doped TiO2 embedded in CNTs is produced in a one-pot hydrothermal reaction. X-ray diffraction and microscopic studies revealed that nanocrystalline anatase-type TiO2-delta F delta particles, in which fluorine is present with TiO2 particles, are loaded on the CNTs. This yields a high electric conductivity of approximately 5.8 S cm(-1). The first discharge capacity of the F-doped TiO2 embedded in CNTs is approximately 250 mA h (g-oxide)(-1), and is retained at 97% after 100 cycles. As expected, a high-rate performance was achieved even at the 100 C discharging rate (25 A g(-1)) where the composite material demonstrated a capacity of 118 mA h g(-1) under the 0.1 C-rate charge condition. The present work also highlights a significant improvement in the insertion and extraction of Na+ ions when the material was charged and discharged under the same rate of 35 C (8.75 A g(-1)), delivering approximately 90 mA h (g-oxide)(-1). (C) 2015 Elsevier Ltd. All rights reserved.