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

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 (similar to 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.