Halide ions-contained polysulfides as cathode materials for aqueous zinc-sulfur batteries with improved cycling performance

Abstract

Organic sulfur-based cathode materials for aqueous zinc-sulfur batteries have garnered significant attention, however, insufficient sulfur content, and sluggish redox kinetics hinder their application. To overcome these challenges, polysulfides SZIM-X (X = Cl, Br, I) were synthesized via inverse vulcanization of sulfur with ZnX₂ coordinated 1-vinylimidazole. Carbon nanotubes composited SZIM-X (SZIM-X@CNTs) featuring imidazole-Zn²⁺ coordination bonds exhibited high sulfur content (>64 wt%) and exceptional volume-change tolerance. The SZIM-Cl@CNTs-50 cathode delivered a high capacity of 690 mAh g^-1 at 0.5 A g^-1 with 53% retention after 100 cycles (35 A g^-1). Similarly, the SZIM-Br@CNTs-50 cathode exhibited a capacity of 356 mAh g^-1 with 55% retention after 100 cycles. In contrast, the SZIM-I@CNTs-50 achieved 420 mAh g^-1 at 0.5 A g^-1 with 77% retention even after 500 cycles. Ex situ XPS and in situ Raman analyses confirmed highly reversible redox transitions between S^2-↔S⁰↔S⁴⁺ and I^-↔I₃^- in Zn(ClO₄)₂ electrolyte. The findings provided a strategy and insight for practical applications of organic electrode materials in zinc-sulfur batteries.