Defect-rich TiO 2-δ Nanocrystals Confined in a Mooncake-shaped Porous Carbon Matrix as an Advanced Na Ion Battery Anode

Abstract Inferior electronic conductivity and sluggish sodium ion diffusion are still two big challenges for TiO 2 anode material for Na ion batteries (SIBs). Herein, we synthesize TiO 2 /C composites by the pyrolysis of MIL-125(Ti) precursor and successfully introduce defects to TiO 2 /C composite by a simple magnesium reduction. The as-prepared defect-rich TiO 2-δ /C composite shows mooncake-shaped morphology consisting of TiO 2-δ nanocrystals with an average particle size of 5 nm well dispersed in the carbon matrix. When used as a SIBs anode, the defect-rich TiO 2-δ /C composite exhibits a high reversible capacity of 330.2 mAh g −1 at 50 mA g −1 at the voltage range of 0.001–3.0 V and long-term cycling stability with negligible decay after 5000 cycles. Compared with other four TiO 2 /C samples, the electrochemical performance of defect-rich TiO 2-δ /C is highly improved, which may benefit from the enhanced electronic/ionic conductivities owing to the defect-rich features, high surface area rendering shortened electronic and ionic diffusion path, and the suppress of the TiO 2 crystal aggregation during sodiation and desodiation process by the carbon matrix.