Low-Coordinated Zn–N<sub>2</sub> Sites as Bidirectional Atomic Catalysis for Room-Temperature Na–S Batteries
Daliang Fang, Shaozhuan Huang, Tingting Xu, Pan Sun, Xue Liang Li, Yew Von Lim, Dong Yan, Yang Shang, Bing‐Jian Su, Jenh‐Yih Juang, Qi Ge, Hui Ying Yang
Abstract
The rational design of advanced catalysts for sodium–sulfur (Na–S) batteries is important but remains challenging due to the limited understanding of sulfur catalytic mechanisms. Here, we propose an efficient sulfur host consisting of atomic low-coordinated Zn–N 2 sites dispersed on N-rich microporous graphene (Zn–N 2 @NG), which realizes state-of-the-art sodium-storage performance with a high sulfur content of 66 wt %, high-rate capability (467 mA h g –1 at 5 A g –1 ), and long cycling stability for 6500 cycles with an ultralow capacity decay rate of 0.0062% per cycle. Ex situ methods combined with theoretical calculations demonstrate the superior bidirectional catalysis of Zn–N 2 sites on sulfur conversion (S 8 ↔ Na 2 S). Furthermore, in situ transmission electron microscopy was applied to visualize the microscopic S redox evolution under the catalysis of Zn–N 2 sites without liquid electrolytes. During the sodiation process, both surface S nanoparticles and S molecules in the mircopores of Zn–N 2 @NG quickly convert into Na 2 S nanograins. During the following desodiation process, only a small part of the above Na 2 S can be oxidized into Na 2 S x . These results reveal that, without liquid electrolytes, Na 2 S is difficult to be decomposed even with the assistance of Zn–N 2 sites. This conclusion emphasizes the critical role of liquid electrolytes in the catalytic oxidation of Na 2 S, which was usually ignored by previous works.