Fluorine Triggered Surface and Lattice Regulation in Anatase TiO2-xFx Nanocrystals for Ultrafast Pseudocapacitive Sodium Storage

Sodium-ion batteries (SIBs) have been considered as one of the most promising secondary battery techniques for large-scale energy storage applications. However, developing appropriate electrode materials that can satisfy the demands of long-term cycling and high energy/power capabilities remains a challenge. Herein, a fluorine modulation strategy is reported that can trigger highly active exposed crystal facets in anatase TiO2-xFx, while simultaneously inducing improved electron transfer and Na+ diffusion via lattice regulation. When tested in SIBs, the optimized fluorine doped TiO2-xFx nanocrystals exhibit a high reversible capacity of 275 mA h g(-1) at 0.05 A g(-1), outstanding rate capability (delivering 129 mA h g(-1) at 10 A g(-1)), and remarkable cycling stability with 91% capacity retained after 6000 cycles at 2 A g(-1). Importantly, the optimized TiO2-xFx nanocrystals are dominated by pseudocapacitive Na+ storage, which can be attributed to the fluorine induced surface and lattice regulation, enabling ultrafast electrode kinetics.