Pressure-Induced Defects and Reduced Size Endow TiO₂ with High Capacity over 20 000 Cycles and Excellent Fast-Charging Performance in Sodium Ion Batteries

Anatase TiO₂ as sodium-ion-battery anode has attracted increased attention because of its low volume change and good safety. However, low capacity and poor rate performance caused by low electrical conductivity and slow ion diffusion greatly impede its practical applications. Here, a bi-solvent enhanced pressure strategy that induces defects (oxygen vacancies) into TiO₂ via N doping and reduces its size by using mutual-solvent ethanol and dopant dimethylformamide as pressure-increased reagent of tetrabutyl orthotitanate tetramer is proposed to fabricate N-doped TiO₂/C nanocomposites. The induced defects can increase ion storage sites, improve electrical conductivity, and decrease bandgap and ion diffuse energy barrier of TiO₂. The size reduction increases contact interfaces between TiO₂ and C and shortens ion diffuse distance, thus increasing extra ion storage sites and boosting ion diffusion rate of TiO₂. The N-doped TiO₂ possesses highly stable crystal structure with a slightly increase of 0.86% in crystal lattice spacing and 3.2% in particle size after fully sodiation. Consequently, as a sodium-ion battery anode, the nanocomposite delivers high capacity and superior rate capability along with ultralong cycling life. This work proposes a novel pressure-induced synthesis strategy that provides unique guidance for designing TiO₂-based anode materials with high capacity and excellent fast-charging capability.