In situ nitrogen-doped, defect-induced carbon nanotubes as an efficient anode for sodium-ion batteries

The incorporation of heteroatoms and defects in carbonaceous material is a well-known approach to improve the electrochemical performance of the anode in a sodium-ion battery (NIB). However, previous works aimed to use either heteroatom-doped or defect-enriched carbon material. The present work focuses on nitrogen-doped, defect-induced surface-modified carbon nanotubes (MN-BCNT) having the synergy of both the effects to improve the electrochemical performance of the NIB. Initially, in situ nitrogen-doped CNTs were grown using a scalable, cost-effective and green synthesis technique. In situ nitrogen doping introduces lattice defects resulting in bamboo-shaped CNTs. The defects were further enriched by opening the ends of the tubes and also by shortening them. This structure demonstrates the high capacity of 278 mA h g^-1 at a current density of 50 mA g^-1, which is more than double compared to conventional CNTs. The improved performance of MN-BCNT is attributed to the improved electrical conductivity due to nitrogen doping and the availability of significant active sites as a result of tube shortening. Moreover, the designed structure shows good cyclic stability at 200 mA g^-1 accompanied with excellent rate capability.