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 TiO 2 in nitrogen-doped carbon microspheres (TiO 2 -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 TiO 2 -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 Ti 4+ /Ti 3+ redox of TiO 2 are involved in the sodium storage of TiO 2 -MS.