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

Sodium-ion batteries (SIBs) are attractive candidatesfor stationaryenergy storage. However, most SIB anodes suffer from slow ion diffusion,low capacity, and large volume change. Herein, we encapsulate nanocrystallineTiO(2) 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 sodiumstorage but also facilitates electron transfer. The anatase nanocrystalsdispersed in the N-rich carbon matrix also contribute a certain capacity.The resultant TiO2-MS hybrid delivers a high capacity (390mAh g(-1) at 0.2C) with good durability. Insitu and ex situ characterizations revealthat both the adsorption/intercalation of Na+ ions in carbonand the Ti4+/Ti3+ redox of TiO2 areinvolved in the sodium storage of TiO2-MS.