Boosting the rate capability of multichannel porous TiO2 nanofibers with well-dispersed Cu nanodots and Cu2+-doping derived oxygen vacancies for sodium-ion batteries

The use of TiO2 as an anode in rechargeable sodium-ion batteries (NIBs) is hampered by intrinsic low electronic conductivity of TiO2 and inferior electrode kinetics. Here, a high-performance TiO2 electrode for NIBs is presented by designing a multichannel porous TiO2 nanofibers with well-dispersed Cu nanodots and Cu2+-doping derived oxygen vacancies (Cu-MPTO). The in-situ grown well-dispersed copper nanodots of about 3 nm on TiO2 surface could significantly enhance electronic conductivity of the TiO2 fibers. The one-dimensional multichannel porous structure could facilitate the electrolyte to soak in, leading to short transport path of Na+ through carbon toward the TiO2 nanoparticle. The Cu2+-doping induced oxygen vacancies could decrease the bandgap of TiO2, resulting in easy electron trapping. With this strategy, the Cu-MPTO electrodes render an outstanding rate performance for NIBs (120 mAh center dot g(-1) at 20 C) and a superior cycling stability for ultralong cycle life (120 mAh center dot g(-1) at 20 C and 96.5% retention over 2,000 cycles). Density functional theory (DFT) calculations also suggest that Cu2+ doping can enhance the conductivity and electron transfer of TiO2 and lower the sodiation energy barrier. This strategy is confirmed to be a general process and could be extended to improve the performance of other materials with low electronic conductivity applied in energy storage systems.