Multichannel Porous TiO2 Hollow Nanofibers with Rich Oxygen Vacancies and High Grain Boundary Density Enabling Superior Sodium Storage Performance.

TiO2 as an anode for sodium-ion batteries (NIBs) has attracted much recent attention, but poor cyclability and rate performance remain problematic owing to the intrinsic electronic conductivity and the sluggish diffusivity of Na ions in the TiO2 matrix. Herein, a simple process is demonstrated to improve the sodium storage performance of TiO2 by fabricating a 1D, multichannel, porous binary-phase anatase-TiO2 -rutile-TiO2 composite with oxygen-deficient and high grain-boundary density (denoted as a-TiO2-x /r-TiO2-x ) via electrospinning and subsequent vacuum treatment. The introduction of oxygen vacancies in the TiO2 matrix enables enhanced intrinsic electronic conductivity and fast sodium-ion diffusion kinetics. The porous structure offers easy access of the liquid electrolyte and a short transport path of Na+ through the pores toward the TiO2 nanoparticle. Furthermore, the high density of grain boundaries between the anatase TiO2 and rutile TiO2 offer more interfaces for a novel interfacial storage. The a-TiO2-x /r-TiO2-x shows excellent long cycling stability (134 mAh g-1 at 10 C after 4500 cycles) and superior rate performance (93 mAh g-1 after 4500 cycles at 20 C) for sodium-ion batteries. This simple and effective process could serve as a model for the modification of other materials applied in energy storage systems and other fields.