Coaxial Hard Carbon‐coated Carbon Nanotubes as Anodes for Sodium‐ion Batteries

Abstract Although being advantageous, the sodium‐ion storage capability of hard carbon would be better if its electrical conductivity could be improved. Herein, 3D hard carbon‐coated carbon nanotubes (CNTs@C) with interconnected conductive networks are fabricated by inducing hard carbon uniformly growth on CNTs. Compared with the isolated hard carbon spheres, the interconnected wire shape of CNTs@C reduces the ion transfer distance and increases the conductivity of hard carbon. By optimizing the thickness of the hard carbon layer and annealing temperature, the optimized CNTs@C displays a reversible specific capacity of 275.9 mAh g⁻¹ at 0.1 A g⁻¹ as anode material for SIBs. Furthermore, the material shows remarkable rate capability (102.8 mAh g⁻¹ at 5 A g⁻¹) and long‐life cycling performance (∼100% capacity retention after 1000 cycles at 5 A g⁻¹). The results of this study provide an effective route for designing novel carbon‐based composite materials as anodes for SIBs.