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

Abstract 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 10000 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.