Pseudocapacitive Na+ Insertion in Ti-O-C Channels of TiO2-C Nanofibers with High Rate and Ultrastable Performance.

Ti-O-C channels for ultrafast sodium storage were constructed in N/S-co-doped TiO2-C nanofibers, which deliver a high rate performance of 181.9 mAh g-1 at 5 A g-1 after 3000 cycles. The existence of Ti-O-C bonds at the interface of TiO2-C phases was revealed by synchrotron radiation X-ray absorption spectra. Based on this, first-principles calculations further verified the low energy barrier for Na+ insertion/extraction in the Ti-O-C channels formed by the intimately integrated graphite layer with TiO2 near the surface. In addition, surface defects induced by heteroatoms accelerate the Na+ mass transfer through the pathway from the carbon surface to the Ti-O-C channel.