Nitrogen-doped carbon encapsulated in mesoporous TiO₂ nanotubes for fast capacitive sodium storage

Controllable synthesis of insertion-type anode materials with beneficial micro- and nanostructures is a promising approach for the synthesis of sodium-ion storage devices with high-reactivity and excellent electrochemical performance. In this study, we developed a sacrificial-templating route to synthesize TiO₂@N-doped carbon nanotubes (TiO₂@NC-NTs) with excellent electrochemical performance. The as-prepared mesoporous TiO₂@NC-NTs with tiny nanocrystals of anatase TiO₂ wrapped in N-doped carbon layers showed a well-defined tube structure with a large specific surface area of 198 m² g⁻¹ and a large pore size of ~5 nm. The TiO₂@NC-NTs delivered high reversible capacities of 158 mA h g⁻¹ at 2 C (1 C = 335 mA g⁻¹) for 2200 cycles and 146 mA h g⁻¹ at 5 C for 4000 cycles, as well as an ultrahigh rate capability of up to 40 C with a capacity of 98 mA h g⁻¹. Even at a high current density of 10 C, a capacity of 138 mA h g⁻¹ could be delivered over 10,000 cycles. Thus, the synthesis of mesoporous TiO₂@NC-NTs was demonstrated to be an efficient approach for developing electrode materials with high sodium storage and long cycle life.