Selenium embedded in MOF-derived N-doped microporous carbon polyhedrons as a high performance cathode for sodium–selenium batteries

Selenium cathodes have attracted much more attention due to their much higher electronic conductivity and comparable volumetric capacity when compared with sulfur cathodes. However, selenium cathodes still suffer from low utilization of active materials, high volume changes and the shuttle effect of polyselenides, resulting in rapid capacity fading. Herein, we prepared selenium–carbon composites as cathodes for sodium–selenium batteries to improve the utilization of selenium by embedding selenium in ZIF-8 derived N-doped microporous carbon polyhedrons (denoted as Se@N-MCPs). The N-MCPs could effectively accommodate the volume change of Se@N-MCPs, and alleviate the shuttle effect of polyselenides. The Se@N-MCP cathodes deliver an excellent discharge capacity of 612 mA h g−1 after 100 cycles at a current density of 0.1 A g−1 and a superior rate capability of 496 mA h g−1 at 5 A g−1 for Na–Se batteries. In addition, they also show a superior cycling life of ∼460 mA h g−1 at the current density of 1 A g−1 after 500 cycles with only 0.049% capacity decline per cycle.