Long-Term Cycling Performance of Nitrogen-Doped Hollow Carbon Nanospheres as Anode Materials for Sodium-Ion Batteries

Nitrogen-doped hollow carbon nanospheres (N-HCSs) were prepared by a facile template method with dopamine as the precursor and subsequently used as the anode material for sodium-ion batteries. The N-HCSs demonstrated high reversible capacities with a retained capacity of 162.2 mAhg(-1) over 100 cycles at 0.1 Ag-1 and an excellent rate capability with an attainable capacity of 90 mAhg(-1) at a high current density of 5 Ag-1. Detailed characterization revealed that nitrogen doping introduces defects into the carbon wall structure and enables the storage of additional Na ions in the walls of the carbon spheres. We then show that the addition of an electrolyte additive [fluorinated ethylene carbonate (FEC)] also effectively enhances the cyclability of the N-HCSs anode; a capacity of 136.4 mAhg(-1) was obtained after 2500 charge-discharge cycles at a current rate of 0.2 Ag-1.