Nitrogen and sulfur co-doped mesoporous carbon derived from ionic liquid as high-performance anode material for sodium ion batteries

Sodium ion batteries (SIBs) are widely considered as one of the most potential alternatives to traditional lithium ion batteries (LIBs) thanks to abundance of sodium on earth. Although these batteries have very similar electrochemistry, the graphite-based LIB anode cannot be directly applied for SIBs due to the much larger ionic radius of Na+. Herein, we report nitrogen and sulfur co-doped mesoporous carbon (NSPC) as high-performance anode material for SIBs, which is synthesized via a salt template strategy with an ionic liquid as the carbon and doping source. After carbonization, the mesoporous NSPC contains a high nitrogen content of 10.45 wt% and 1.52 wt% of sulfur with an enlarged graphite interlayer spacing to facilitate Na+ intercalation. When used as an anode in SIBs, the NSPC shows a good electrochemical performance with a specific capacity of 243 mAh g−1 after 240 charge-discharge cycles at 0.14 A g−1. The reversible capacity remains at 102 mAh g−1 after 5,000 cycles at 1.40 A g−1. The high-performance of the NSPC for Na+ storage is attributed to the double doped heteroatoms and mesoporous structure, which synergistically enhance the storage capacity and rate capability, and maintain the electrode stability during cycling.