N, S co-doped porous carbon nanospheres with a high cycling stability for sodium ion batteries

Developing high-performance and low-cost anode materials is crucial for the practical use of sodium-ion batteries (SIBs) at room-temperature. Porous carbon nanospheres with a uniform diameter for use as SIB anode materials were synthesized by the hydrothermal treatment of glucose to obtain the spheres, and subsequent carbonization and modification with KOH activation and N, S co-doping during or after the activation using thiourea as the N and S sources. Nanospheres doped with N and S after KOH activation have a high initial specific capacity of 527 mAh g^-1 at a current density of 20 mA g^-1 and an excellent cycling stability with a 95.2% capacity retention after 1 000 cycles at a high current density of 500 mA g^-1. The capacity retention rate is higher than that of most of the state-of-the-art anode materials for SIBs. This good performance is attributed to the abundant micro-pores, the enlarged interlayer spacing produced by the co-doping, and the high conductivity of the carbon nanospheres.