Surface-driven fast sodium storage enabled by Se-doped honeycomb-like macroporous carbon

Selenium (Se) is an ideal doping agent to modulate the structure of carbon materials to improve their sodium storage performance but has been rarely investigated. In the present study, a novel Se-doped honeycomb-like macroporous carbon (Se-HMC) is prepared by a surface crosslinking method using diphenyl diselenide as the carbon source and SiO₂ nanospheres as the template. Se-HMC has a high Se weight percentage above 10%, with a large surface area of 557 m² g^-1. Owing to the well-developed porous structure in combination with Se-assisted capacitive redox reactions, Se-HMC exhibits surface-dominated Na storage behaviors, thus presenting large capacity and fast Na storage capability. To be specific, Se-HMC delivers a high reversible capacity of 335 mA h g^-1 at 0.1 A g^-1, and after an 800-cycle repeated charge/discharge test at 1 A g^-1, the capacity is stable with no dramatic loss. Remarkably, the capacity remains 251 mA h g^-1 under a very large current density of 5 A g^-1 (≈20 C), demonstrating an ultrafast Na storage process. As far as we know, such a good rate performance has been rarely achieved for carbon anodes before.