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 (TiO2) 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 TiO2-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 SiO2/TiO2-x@C nanotablets by annealing under inert atmosphere. After NaOH etching SiO2/TiO2-x@C which contains unbonded SiO2 and chemically bonded Si-O-Ti, thus the lattice Si-doped TiO2-x@C (Si-TiO2-x@C) nanotablets with rich Ti3+/oxygen vacancies and abundant inner pores are developed. When examined as an anode for SIB, the Si-TiO2-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 Ti3+/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.