One-pot fabricating rambutan-like nitrogen-simultaneously-doped TiO2@carbon@TiO2 double shell composites with superior sodium storage for Na-ion batteries

Abstract

Herein, rambutan-like nitrogen-simultaneously-doped TiO2@carbon@TiO2 (NTO@NC@NTO) double shell composites were synthesized through one-pot simple polymerization reaction using titanium glycolate (TG) and indole as precursors. During the polymerization process, on one hand the polyindole (PIn) coats on the TG surface to form TG@PIn, and on the other hand the TG continues epitaxial growth through the PIn silt to form rambutan-like TG@PIn@TG double shell intermediate. Nitrogen can simultaneously dope into the\xa0TiO2 lattice and carbon at the subsequent annealing process. SEM and TEM images clearly exhibit the rambutan-like double shell structure. The composites deliver superior reversible capacity and long-term cycling performance at high rate when used as anode materials for sodium ion batteries. When tested at a current density of 200\xa0mA\xa0g−1, the composites can deliver a reversible capacity of 220\xa0mAh\xa0g−1 after 140 cycles, which is much higher than the pure TiO2. Even the current density increases up to 1000\xa0mA\xa0g−1, the composites can maintain a stable capacity of 91\xa0mAh\xa0g−1 after 1500 cycles.