Selenium Encapsulated into Metal-Organic Frameworks Derived N-Doped Porous Carbon Polyhedrons as Cathode for Na-Se Batteries.

The substitution of Se for S as cathode for rechargeable batteries, which confine selenium in porous carbon, attracts much attention as a potential area of research for energy storage systems. To date, there are no reports about metal-organic frameworks (MOFs) to use for Na-Se batteries. Herein, MOFs-derived nitrogen-doped porous carbon polyhedrons (NPCPs) have been obtained via facile synthesis and annealing treatment. Se is encapsulated into the mesopores of carbon polyhedrons homogeneously by melt-diffusion process to form Se/NPCPs composite, using as cathode for advanced Na-Se batteries. Se/NPCPs cathode exhibits excellent rate capabilities of 351.6 and 307.8 at 0.5C and 2C, respectively, along with good cycling performance with high Coulombic efficiency of 99.7% and slow decay rate of 0.05% per cycle after 1000 cycles at 2C, which result from the NPCPs having a unique porous structure to accommodate volumetric expansion of Se during discharge-charge processes. Nitrogen doping could enhance the electrical conductivity of carbon matrix and facilitate rapid charge transfer.