Atomically dispersed Co-N4C2 catalytic sites for wide-temperature Na-Se batteries

Sodium-selenium (Na-Se) batteries have been widely regarded as promising large-scale energy storage systems owing to the high volumetric energy density of 2530 W h L-1 and natural abundance of the element sodium. However, critical drawbacks including sluggish redox kinetics, severe volume variation and shuttle effect seri-ously deteriorate the electrochemical performance. Herein, we propose a precompetitive coordination strategy for over-coordinated single-atom catalyst, and subsequently synthesize the six-coordinated Co electrocatalyst supported carbon nanofibers (Co-N4C2) for solid-state conversion in wide-temperature Na-Se batteries. The Co-N4C2 catalyst can not only boost the redox kinetics of solid-phase Na2Se2/Na2Se, but also accelerate the elec-troreduction of ethylene carbonate to construct robust cathode electrolyte interphase, thereby inhibiting the irreversible phase transformation of active Se species. Furthermore, for the first time, the components of the cathode electrolyte interphase as sodium ethylene mono-carbonate are identified. Consequently, the as -synthesized free-standing Se@Co-N4C2 cathode with high Se-loading realizes high capacity, cycling stability and rate capability at both room temperature (20.0/40.0 degrees C) and low temperature (-11.7 degrees C).

Automated summary

Sodium-selenium (Na-Se) batteries have been considered as potential large-scale energy storage systems due to their high volumetric energy density and natural abundance of sodium. However, issues such as slow redox kinetics, significant volume changes, and shuttle effect have negatively affected their electrochemical performance. In this study, a precompetitive coordination strategy was proposed to synthesize a Co-N4C2 catalyst for solid-state conversion in Na-Se batteries. The Co-N4C2 catalyst enhanced the redox kinetics and electroreduction of ethylene carbonate, leading to the formation of a robust cathode electrolyte interphase and preventing irreversible phase transformation. The study also identified the components of the cathode electrolyte interphase as sodium ethylene monocarbonate. The resulting Se@Co-N4C2 cathode exhibited high capacity, cycling stability, and rate capability at both room temperature and low temperature.