Hierarchical Multicavity Nitrogen-Doped Carbon Nanospheres as Efficient Polyselenide Reservoir for Fast and Long-Life...

Sodium-selenium (Na-Se) battery has been emerging as one of the most prospective energy storage systems owing to their high volumetric energy density and cost effectiveness. Nevertheless, the shuttle effect of sodium polyselenide (NaPSe) and sluggish electrochemical reaction kinetics present the main bottlenecks for its practical implementation. Herein, a new Se host of 3D nitrogen-doped hierarchical multicavity carbon nanospheres (3D NHMCs) is designed and synthesized via a facile self-sacrifice templating strategy. The 3D NHMCs are verified to hold a favorable structure of a hollow macropore core and numerous micro/mesopores hollow shell for hosting Se, which can not only maximize Se utilization and alleviate the volumetric expansion but also promote the electrical/ionic conductivity and electrolyte infiltration. Moreover, the abundant self-functionalized surfaces as an efficient NaPSe scavenger via robust physical-chemical dual blocking effects demonstrate high-efficiency in situ anchoring-diffusion-conversion of NaPSe, rendering rapid reaction kinetics and remarkable suppressive shuttle effect, as evidenced by systematic experimental analysis and density functional theory calculations. As a result, the high-Se-loading 3D NHMCs/Se cathode exhibits an ultrahigh volumetric capacity (863 mAh cm^-3 ) and rate capability (377 mAh g^-1 at 20 C) and unexceptionable stability over 2000 cycles at 2 C.