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.

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