Encapsulation of sulfur in MoS₂-modified metal-organic framework-derived N, O-codoped carbon host for sodium-sulfur...

Room-temperature sodium-sulfur batteries (RT Na-S) are promising energy storage systems with high energy densities and low costs. Nevertheless, drawbacks, including the limited cycle life and sluggish redox kinetics of sodium polysulfides, hinder their implementation. Herein, a heterostructure of MoS₂ nanosheets coated on a metal-organic framework (MOF)-derived N, O-codoped flower-like carbon matrix (NOC) was designed as a sulfur host for advanced RT Na-S batteries. The NOC@MoS₂ hierarchical host provided a sufficient space to guarantee a high sulfur loading and confinement for the volume expansion of sulfur during the charge/discharge process. According to first-principle calculations, the NOC@MoS₂ composite exhibited metallic conductivity because electronic states crossed the Fermi level, which indicates that the introduction of NOC significantly improved the electronic conductivity of MoS₂. Furthermore, electron transfer from MoS₂ to the O-doped carbon sites was observed owing to the strong electronegativity of O, which can effectively increase the Lewis acidity of MoS₂ and weaken the sodium-sulfur bonds in sodium polysulfides after adsorption on the cathode, leading to reductions in the Na₂S dissociation energy barrier and Gibbs free energy for the rate-limiting step of the sulfur reduction process. Therefore, with the synthetic effects of MoS₂ and N, O-codoped carbon, the obtained cathode exhibited a superior electrochemical performance.