Alkali-ion-bridged crown ether-polyoxometalate coordination arrays for Lithium-sulfur batteries

Polyoxometalates (POMs) are attractive redox catalysts for lithium‑sulfur (LiS) batteries because of their multielectron transfer capability and strong affinity toward lithium polysulfides (LiPSs). However, partial reduction of POMs during cycling generates heteropoly blue (HPB) species that readily dissolve into the electrolyte, resulting in catalyst loss and poor reaction reversibility. Herein, we report a crown ether-directed coordination assembly in which 15-crown-5 (CR5) macrocycles are bridged to POM clusters by alkali metal ions, forming a robust supramolecular array that effectively suppresses HPB dissolution and improves redox stability. The CR5-POM assembly exhibits strong LiPSs adsorption and accelerates bidirectional sulfur redox by integrating synergistic catalytic sites with regulated ion-transport pathways. As a result, the corresponding cathode delivers enhanced cycling stability, improved rate capability, and reduced polarization compared with conventional POM-based systems. Notably, a reversible discharge capacity of 750 mAh g^-1 is achieved at 5.0C, while long-term cycling at 1.0C affords an initial discharge capacity of 958.9 mAh g^-1 with an ultralow capacity decay of only 0.067% per cycle. This work establishes a macrocycle-coordination strategy for stabilizing redox-active POM catalysts and provides new insight into the supramolecular regulation of catalytic polysulfide conversion in LiS batteries.