Defect-Assisted Selective Surface Phosphorus Doping to Enhance Rate Capability of Titanium Dioxide for Sodium Ion Batteries.

Phosphorus doping is an effective strategy to simultaneously improve the electronic conductivity and regulate the ionic diffusion kinetics of TiO being considered as anode materials for sodium ion batteries. However, efficient phosphorus doping at high concentration in well-crystallized TiO nanoparticles is still a big challenge. Herein, we propose a defect-assisted phosphorus doping strategy to selectively engineer the surface structure of TiO nanoparticles. The reduced TiO shell layer that is rich in oxygen defects and Ti species precisely triggered a high concentration of phosphorus doping (∼7.8 at. %), and consequently a TiO@TiO-P core@shell architecture was produced. Comprehensive characterizations and first-principle calculations proved that the surface-functionalized TiO-P thin layer endowed the TiO@TiO-P with substantially enhanced electronic conductivity and accelerated Na ion transportation, resulting in great rate capability (167 mA h g at 10 000 mA g) and stable cycling (99% after 5000 cycles at 10 A g). Combining X-ray diffraction with electron spin resonance clearly demonstrated the high reversibility and robust mechanical behavior of TiO@TiO-P upon long-term cycling. This work provides an interesting and effective strategy for precise heteroatoms doping to improve the electrochemical performance of nanoparticles.