A Mo5N6 electrocatalyst for efficient Na2S electrodeposition in room-temperature sodium-sulfur batteries

Metal sulfides electrodeposition in sulfur cathodes mitigates the shuttle effect of polysulfides to achieve high Coulombic efficiency in secondary metal-sulfur batteries. However, fundamental understanding of metal sulfides electrodeposition and kinetics mechanism remains limited. Here using room-temperature sodium-sulfur cells as a model system, we report a Mo₅N₆ cathode material that enables efficient Na₂S electrodeposition to achieve an initial discharge capacity of 512 mAh g⁻¹ at a specific current of 1 675 mA g⁻¹, and a final discharge capacity of 186 mAh g⁻¹ after 10,000 cycles. Combined analyses from synchrotron-based spectroscopic characterizations, electrochemical kinetics measurements and density functional theory computations confirm that the high d-band position results in a low Na₂S₂ dissociation free energy for Mo₅N₆. This promotes Na₂S electrodeposition, and thereby favours long-term cell cycling performance.