N/S co-doped biomass-based porous carbon surface-embedded small-molecule selenium as cathode for high-performance K-Se batteries

Potassium-selenium (K-Se) batteries, as an emerging energy storage system, have attracted extensive attention due to their high energy density and abundance of potassium in the earth's crust. However, similar to chalcogenide batteries, K-Se batteries also face problems such as severe pulverization of Se during the insertion/extraction of K+ ions, and the shuttle effect generated by polyselenides. In this work, small-molecule selenium was encapsulated in the natural nanoscale pores of N/S co-doped walnut shell-derived biomass carbon by a two-step carbonization method and a melt-diffusion method. The encapsulated small-molecule selenium can effectively cope with the volume change during cycling, and the abundant heteroatom doping greatly inhibits the generation of the shuttle effect. The assembled battery has a stable capacity of 581.8 mAh g−1 after 200 cycles at a current density of 0.2C and a capacity of 211.7 mAh g−1 after 3500 cycles at a current density of 10C. This study provides a rational design for K-Se battery cathode for energy storage with high energy density and long cycle life.