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 Na2Se during the discharge–charge process. The nitrogen doping in N-HRMC strongly enhances the electrical conductivity of Se and chemical adsorption on Na2Se. In particular, density functional theory (DFT) calculations demonstrate that pyridinic-N atoms provide much more chemical adsorption of Na2Se 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 20th 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.