Introducing Hybrid Defects of Silicon Doping and Oxygen Vacancies into MOF-Derived TiO 2-X @Carbon Nanotablets Toward High-Performance Sodium-Ion Storage.

Titanium dioxide (TiO 2 ) is a promising anode material for sodium-ion batteries (SIBs), which suffer from the intrinsic sluggish ion transferability and poor conductivity. To overcome these drawbacks, a facile strategy is developed to synergistically engineer the lattice defects (i.e., heteroatom doping and oxygen vacancy generation) and the fine microstructure (i.e., carbon hybridization and porous structure) of TiO 2 -based anode, which efficiently enhances the sodium storage performance. Herein, it is successfully realized that the Si-doping into the MIL-125 metal-organic framework structure, which can be easily converted to SiO 2 /TiO 2-x @C nanotablets by annealing under inert atmosphere. After NaOH etching SiO 2 /TiO 2-x @C which contains unbonded SiO 2 and chemically bonded SiOTi, thus the lattice Si-doped TiO 2-x @C (Si-TiO 2-x @C) nanotablets with rich Ti 3+ /oxygen vacancies and abundant inner pores are developed. When examined as an anode for SIB, the Si-TiO 2-x @C exhibits a high sodium storage capacity (285 mAh g -1 at 0.2 A g -1 ), excellent long-term cycling, and high-rate performances (190 mAh g -1 at 2 A g -1 after 2500 cycles with 95.1% capacity retention). Theoretical calculations indicate that the rich Ti 3+ /oxygen vacancies and Si-doping synergistically contribute to a narrowed bandgap and lower sodiation barrier, which thus lead to fast electron/ion transfer coefficients and the predominant pseudocapacitive sodium storage behavior.