Selenium clusters in Zn-glutamate MOF derived nitrogen-doped hierarchically radial-structured microporous carbon for advanced rechargeable Na-Se batteries

Sodium-selenium (Na-Se) batteries are a promising substitute for traditional Li-ion batteries due to their high theoretical volumetric capacity (∼3260 mA h cm ^-3 ). However, shuttle effects and large volume changes still limit their practical applications. Herein, we embed Se clusters in nitrogen-doped hierarchically radial-structured microporous carbon (N-HRMC) derived from a zinc-glutamate metal-organic framework (MOF) for advanced sodium storage. In this carbon-based composite, the micropores and the C-Se and C-O-Se bonds in N-HRMC effectively confine the Se clusters and Na ₂ Se during the discharge-charge process. The nitrogen doping in N-HRMC strongly enhances the electrical conductivity of Se and chemical adsorption on Na ₂ Se. In particular, density functional theory (DFT) calculations demonstrate that pyridinic-N atoms provide much more chemical adsorption of Na ₂ Se than graphitic-N and pyrrolic-N atoms. Consequently, the cathode with Se clusters embedded in N-HRMC deliver a capacity of 612 mA h g ^-1 after 200 cycles at 0.2C, with cycling stability for >500 cycles and a capacity retention of ∼100% from the 20 ^th cycle at 0.5C, representing one of the best reported results for Na-Se batteries. Our work here suggests that embedding Se clusters in nitrogen-doped hierarchically structured microporous carbon systems presents an attractive strategy to enhance the capacity and rate capability of Na-Se batteries.