Reducing Overpotential of Solid-State Sulfide Conversion in Potassium-Sulfur Batteries

Abstract

Improving kinetics of solid-state sulfide conversion in sulfur cathodes can enhance sulfur utilization and promote Coulombic efficiency of secondary metal-sulfur batteries. However, fundamental mechanisitic understanding of the solid-state conversion in metal-sulfur batteries remains to be achieved. Here, taking potassium-sulfur batteries as a model system, we for the first time report the reducing overpotential of solid-state K2S3 to K2S conversion via the meta-stable S2-3 intermediates on a range of transition metal single-atom catalytic sulfur hosts. The resultant catalytic sulfur host containing Cu single atoms demonstrate high discharge capacities of 1,595 and 1226 mAh g-1 at specific current densitieis of 335 and 1675 mA g-1, respectively, with stable Coulombic efficiency of ~100% during cycling. Combined spectroscopic characterizations and density functional theory computations reveal that the Cu single atom catalyst exhibits a relatively weak Cu-S bonding during sulfur redox conversion, resulting in low overpotential of solid-state K2S3-K2S conversion and high sulfur utilization. The elucidation of reaction mechanism of solid-state sulfide conversion can direct the exploration of highly efficient metal-sulfur batteries.