S/N co-doped porous carbon as a stable anode for potassium-ion batteries.

Carbon materials have many advantages as anode materials commonly used in potassium-ion batteries, but due to the limited layer spacing and large radius of K+, the theoretical intercalation capacity of K+ in carbon materials is low (279 mAh g-1). Therefore, expanding the layer spacing and increasing the number of active sites in carbon materials are the key to improving their potassium storage performance. In this work, we first synthesized N-doped porous carbon materials (N-PCs). The obtained N-PCs exhibited a porous structure of channel connection, which could shorten the diffusion paths of electrons and K+, and the doping of nitrogen atoms could improve the conductivity of carbon materials and increase the number of active sites. Then, the N-PCs were doped with sulfur to produce the final product S/N co-doped porous carbon materials (S/N-PCs). The introduction of sulfur could expand the layer spacing of N-PCs and improve the intercalation ability of K+. The configuration of N could also be adjusted to induce more active sites, further enhancing the storage capacity of carbon materials for K+. As expected, S/N-PCs, as an anode material for potassium-ion batteries, exhibit better electrochemical performance than N-PCs, and their reversible capacity after 100 cycles at 100 mA g-1 is 409 mAh g-1. Even at a high current density of 1000 mA g-1, their capacity after 2000 cycles remains as high as 305 mAh g-1.