Enhancing potassium ions adsorption on mesoporous carbon spheres with abundant internal surface via engineering sulfur doping sites towards superior rate capability.

Mesoporous carbon spheres (MCSs) show great potential for using as high-performance anodes in potassium-ion batteries (PIBs). Design and synthesis of MCSs with suitable multiscale structures and heteroatom doping or co-doping in MCSs are successfully employed to optimize the ion and electron transportation, however, it is still a challenge to explore MCS-based anodes with satisfactory potassium storage performance. In this work, we report novel S-doped MCS samples with abundant internal surfaces for potassium storage. The S doping sites are controlled during the synthesis, and the effect of different doping sites on the potassium storage is systematically studied. It is found that S doping between the carbon layers enlarges interlayer spacing and facilitates potassium ion adsorption. Consequently, the optimized sample shows an excellent rate capability of 144 mAh/g at 5.0 A/g, and a high reversible specific capacity of 325 mAh/g after 100 cycles at 0.1 A/g with a capacity retention of 91.2%. The important role of element doping sites on ion adsorption and ion storage performance is confirmed by theoretical investigations. Controlling the doping sites in MCSs provides a new approach to designing high-performance electrodes for energy storage and conversion applications.