N-doped carbon tubes with sodiophilic sites for dendrite free sodium metal anode

Sodium metal is one of the most promising anodes for sodium ion batteries (SIBs) owing to its high theoretical capacity, low redox potential, abundant content and low price. However, due to the high reactivity and infinite volume change of sodium metal, unstable SEI film and dendrite are formed during the repeated plating and stripping process, leading to low Coulombic efficiency (CE) and inferior cycle stability, even serious safety issue. Herein, linear shaped sodiophilic N-doped hollow carbon tubes (NCTs) were designed and constructed as stable sodium metal hosts. The plating and stripping behavior of sodium metal in NCT is investigated by in-situ transmission electron microscopy (TEM). The results show that sodium metal is preferentially nucleated and deposited in the tube, and then could be completely stripped off from the tube. Moreover, Na@NCTs anode can be stably cycled for more than 800 h with a high CE of 98.53% at a current density of 1 mA cm(-2) and a capacity of 1 mAh cm(-2). The analysis result indicates that the improved electrochemical performance can be attributed to the special designed nitrogen functional groups tuned sodiophilic surface with enhanced fast surface kinetics and the hollow carbon tube structure. Finally, a full cell with NVP@C and Na@NCTs as the cathode and anode, respectively, was assembled and delivered a capacity of 81.46 mAh g(-1) after 100 cycles at 100 mA g(-1). Our results demonstrate that NCT is a promising candidate as a sodium metal host for future generation of sodium metal batteries.

Automated summary

In this study, linear shaped sodiophilic N-doped hollow carbon tubes (NCTs) were designed as stable sodium metal hosts, showing excellent performance in stable cycling with improved Coulombic efficiency and cycle stability. In-situ transmission electron microscopy was used to investigate the plating and stripping behavior of sodium metal in NCT, revealing that sodium metal preferentially nucleates and deposits in the tube.