Abstract
Developing highly efficient anchoring materials to suppress sodium polysulfides (NaPSs) shuttling is vital for the practical applications of sodium sulfur (Na-S) batteries. Herein, we systematically investigated pristine graphene and metal-N4@graphene (metal = Fe, Co, and Mn) as host materials for sulfur cathode to adsorb NaPSs via first-principles theory calculations. The computing results reveal that Fe-N4@graphene is a fairly promising anchoring material, in which the formed chemical bonds of Fe-S and N-Na ensure the stable adsorption of NaPSs. Furthermore, the doped transition metal iron could not only dramatically enhance the electronic conductivity and the adsorption strength of soluble NaPSs, but also significantly lower the decomposition energies of Na2S and Na2S2 on the surface of Fe-N4@graphene, which could effectively promote the full discharge of Na-S batteries. Our research provides a deep insight into the mechanism of anchoring and electrocatalytic effect of Fe-N4@graphene in sulfur cathode, which would be beneficial for the development of high-performance Na-S batteries.
Highlights
Our results demonstrate that Fe-N4 @graphene can tightly combine with NaPSs through chemical bonds, and its electric conductivity is well retained
As the structural data shows, the Na-S bond lengths (~2.50 Å) of low-order Na2 Sn (n = 1, 2) species are significantly shorter than those (~2.75 Å) of high-order Na2 Sn (n = 4, 6, 8) species clusters, while the S-S bonds slightly decrease with the increase in the number of S atoms, similar to the scenario of Li2 Sn species [28,36]
8 compristine graphene, which is mainly contributed by the strong chemical bonds of metal-S
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Owing to the extremely high theoretical specific capacity of the elements sulfur (1672 mAh/g) and sodium (1165 mAh/g), and to the batteries’ high theoretical energy density of 1274 Wh/kg of cell weight [10,11,12,13], the rapidly developing room temperature (RT) sodium-sulfur (Na-S) batteries are widely considered as one of the most promising alternative candidates for the next-generation rechargeable batteries to replace the conventional insertion-type LIB [14,15,16,17] Both sodium and sulfur element materials are earth-crust abundant, sufficiently low-cost, and environmentally friendly [18,19]. Zhang and co-workers reported that Fe-N4 and Cr-N4 co-doped graphene shows a strong adsorption and full discharge of LiPSs, resulting in a greatly improved performance of Li-S batteries [41].
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