Mo₂ N-W₂ N Heterostructures Embedded in Spherical Carbon Superstructure as Highly Efficient Polysulfide Electrocatalysts for Stable Room-Temperature Na-S Batteries

Room-temperature sodium-sulfur (RT Na-S) batteries are highly desirable for a sustainable large-scale energy-storage system due to their high energy density and low cost. Nevertheless, practical applications of RT Na-S batteries are still prevented by the shuttle effect of sodium polysulfides (NaPS), slow reaction kinetics of S, and incomplete conversion process of NaPS. Here, Mo₂ N-W₂ N heterostructures embedded in a spherical carbon superstructure (Mo₂ N-W₂ N@PC) are designed to efficiently suppress the "polysulfide shuttle" and promote NaPS redox reactions. The designed Mo₂ N-W₂ N@PC heterostructure with abundant heterointerfaces, high conductivity, and porosity can facilitate electron/ion diffusion and provide high catalytic activity for efficient NaPS conversion. The obtained Na-S battery delivers high reversible capacity with superior long-term cyclability (517 mAh g^-1 at 1 A g^-1 after 400 cycles) and unprecedented rate capability (417 mAh g^-1 at 2 A g^-1 ). Furthermore, the electrocatalysis mechanism is revealed by combining in situ X-ray diffraction (XRD), ex situ X-ray photoelectron spectroscopy (XPS), UV-vis spectra, and precipitation experiments. This work demonstrates a novel heterostructure design strategy that enables high-performance Na-S batteries.