A Mo(5)N(6) electrocatalyst for efficient Na(2)S 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 Mo(5)N(6) cathode material that enables efficient Na(2)S 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 Na(2)S(2) dissociation free energy for Mo(5)N(6). This promotes Na(2)S electrodeposition, and thereby favours long-term cell cycling performance.