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 1x2006;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. Incomplete conversion of sodium polysulfides represents a significant issue in room-temperature sodium-sulfur batteries. Here, the authors propose Mo5N6 as an electrocatalyst for efficient Na2S electrodeposition and improved cell cycling performances.

Automated summary

The Mo5N6 cathode material enables efficient Na2S electrodeposition, improving cycling performance in room-temperature sodium-sulfur batteries.