3D nitrogen and sulfur equilibrium co-doping hollow carbon nanosheets as Na-ion battery anode with ultralong cycle life and superior rate capability

Abstract In sodium ion batteries, heteroatom doping is deemed to be an important way to enhance the electrochemical activity of carbon-based anode materials. In this work, we report 3D nitrogen and sulfur equilibrium co-doping hollow carbon nanosheets for sodium ion battery anode, which can deliver a maximum capacity of 497 mA h g-1 under 0.2 A g-1, good rate capability (260 mA h g-1 under 50 A g-1 and 245 mA h g-1 under 60 A g-1), and good cycling stability (339 mA h g-1 under 5 A g-1 over 5000 cycling and 249 mA h g-1 under 10 A g-1 over 5000 cycling), suggesting wonderful electrochemical performance. To the best of our knowledge, the excellent performance of the long-term cyclability at such high rates is rarely reported for carbon-based sodium ion battery anodes. Meanwhile, the storage mechanism of sodium was studied by in-situ Raman spectroscopy, cyclic/linear sweep voltammetry and electrochemical impedance spectroscopy. Its superior properties can be attributed to the special three-dimensional hollow nanosheets with high specific surface, doping regulation of N and S elements to carbon structure and synergistic effect of nitrogen doping enhancing pseudocapacitive contributions.