Deciphering failure mechanisms of Zn–S batteries: anion–cation synergy for dual-interface stabilization toward dendrite-free zinc and reversible sulfur conversion

Rechargeable aqueous zinc–sulfur batteries (ZSBs) are promising candidates for large-scale energy storage due to their high theoretical capacity and cost-effectiveness. Generally, the reversible specific capacity of ZSBs can be enhanced by adding iodide catalysts, but their long-term cyclability remains an issue. Herein, this work comprehensively reveals that the loss of iodide ions (I⁻) on the cathode side is a major cause of limited cyclability. As a proof of concept, an anion–cation synergistic strategy is developed to effectively inhibit the loss of I⁻ on the cathode side by introducing a choline cation (Ch⁺) for enhanced ZSB performance. Systematic electrochemical analyses and theoretical computational studies reveal that Ch⁺ disrupts the hydrogen-bonding network of water, reduces reactive water activity, and modulates uniform Zn deposition, while Ch⁺ and I⁻ accelerate the redox kinetics of S through their synergistic action. Owing to the advantage of the strong adsorption of Ch⁺ on the electrode interface, it not only inhibits the shuttle effect of iodine and improves the reversibility of the S cathode, but also inhibits the corrosion of the Zn anode. The ZSB catalyzed by I⁻ with Ch⁺ as the medium delivers a high specific capacity of 1240 mAh g⁻¹ at 0.5 A g⁻¹, an enhanced cyclability (72% capacity retention after 2000 cycles at 5 A g⁻¹) and superior anti-self-discharge performance (98.91% coulombic efficiency after 48 h). The success of the ZSB study at high sulfur loading (4.5 mg cm⁻²) under lean electrolyte conditions (E/S = 10 μL mg_s⁻¹) demonstrates the potential practicality. This work establishes fundamental insights into the synergistic catalytic mechanisms of Ch⁺/I⁻ for high-performance ZSBs.