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/TiO_2–x@C nanotablets by annealing under inert atmosphere. After NaOH etching SiO₂/TiO_2–x@C which contains unbonded SiO₂ and chemically bonded SiOTi, thus the lattice Si-doped TiO_2–x@C (Si-TiO_2–x@C) nanotablets with rich Ti³⁺/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 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.