Abstract
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.
Highlights
Metal sulfides electrodeposition in sulfur cathodes mitigates the shuttle effect of polysulfides to achieve high Coulombic efficiency in secondary metal-sulfur batteries
Progress in density functional theory (DFT) computations that takes into account the geometric/electronic structure of the sulfur cathode materials is essential in investigating metal sulfides electrodeposition kinetics[25]
A series of molybdenum nitrides with varying atomic structure were selected as model cathode materials for investigation of correlation between the atomic structure, electronic structure and electrochemical performance in room-temperature sodium–sulfur (RT Na–S) batteries
Summary
Metal sulfides electrodeposition in sulfur cathodes mitigates the shuttle effect of polysulfides to achieve high Coulombic efficiency in secondary metal-sulfur batteries. 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. Sluggish SRR kinetics leads to incomplete conversion of the sulfur and “shuttle effect” of the polysulfides This limits Coulombic efficiency (CE) and cycle-life and is a deterrent to practical application[6]. Progress in density functional theory (DFT) computations that takes into account the geometric/electronic structure of the sulfur cathode materials is essential in investigating metal sulfides electrodeposition kinetics[25]. With this research work we shed some light on the origin of high Na2S electrodeposition reactivity and high SRR efficiency of this cathode material
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