Ultrafast flame growth of carbon nanotubes for high-rate sodium storage

Sodium-ion batteries (SIBs) are one of the most promising alternatives to lithium-ion batteries as large-scale energy storage systems (ESSs), owing to the natural abundance and low cost of sodium. Because of its capability to accommodate large-sized Na+, amorphous carbon stands out as potential anode for SIBs among the reported carbonaceous materials. However, the practical application of amorphous carbon is still limited by the poor cycling stability and unsatisfactory rate capability. Herein, we report a binder-free SIB anode by directly growing carbon nanotubes on nickel foam (CNTs-NF) via a simple and fast flame approach. Owing to highly disordered turbostratic structures and presence of abundant defects, the CNTs-NF anode delivers excellent electrochemical performance. Electrochemical impedance spectroscopy and cyclic voltammetry demonstrate low charge transfer impedance and surface-induced capacitive behavior, which favor fast transport/diffusion of electrons/ions. Particularly, such anode exhibits a high reversible capacity of 258 mA h g(-1) at 0.1 A g(-1) with an initial Coulombic efficiency of as high as 82.2% and superior rate capability of 95 mA h g(-1) at an ultrahigh current density of 20 A g(-1). The high-rate CNTs-NF anode holds great potential in application for large-scale ESSs.