Introducing Hybrid Defects of Silicon Doping and Oxygen Vacancies into MOF‐Derived TiO_2–X@Carbon Nanotablets Toward High‐Performance Sodium‐Ion Storage

Abstract

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 SiOTi, 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.