Encapsulating Nanocrystalline TiO2 in Nitrogen-Rich Carbon Microspheres for Enhanced Sodium Storage

Sodium-ion batteries (SIBs) are attractive candidates for stationary energy storage. However, most SIB anodes suffer from slow ion diffusion, low capacity, and large volume change. Herein, we encapsulate nanocrystalline TiO2 in nitrogen-doped carbon microspheres (TiO2-MS) with an ultrahigh N content (16.6 wt %) for sodium storage. Ultrahigh N-doping not only introduces rich active sites for sodium storage but also facilitates electron transfer. The anatase nanocrystals dispersed in the N-rich carbon matrix also contribute a certain capacity. The resultant TiO2-MS hybrid delivers a high capacity (390 mAh g–1 at 0.2C) with good durability. In situ and ex situ characterizations reveal that both the adsorption/intercalation of Na+ ions in carbon and the Ti4+/Ti3+ redox of TiO2 are involved in the sodium storage of TiO2-MS.