Water-Responsive Molecule Realizes Stable Ah-Scale Zn–I2 Pouch Cells with High Zn Utilization

Abstract

Aqueous zinc–iodine (Zn–I2) batteries are promising candidates for large-scale energy storage due to inherent safety and environmental compatibility. However, their application is hindered by serious polyiodides shuttling, limited iodine conversion kinetics, and poor Zn anode reversibility. Here, we report a water-responsive molecular strategy to simultaneously address these challenges for advanced Zn–I2 batteries. When introduced into the electrolyte, Ectoine (Ect) spontaneously establishes localized dual-polarity charge centers. The positive center immobilizes polyiodides and mitigates their shuttling, while the negative site coordinates with Zn2+ to reshape its solvation environment and markedly improve Zn reversibility. Importantly, hydrogen bonding between Ect and polyiodides modulates the iodine conversion pathway and enhances its redox kinetics, even under high iodine loadings. Consequently, the Zn–I2 coin cell with Ect exhibits record cycling stability (60,000 cycles at 50 C) and high-rate capability (139.4 mAh g−1 at 50 C). The Zn–I2 pouch cell with high I2 loading of ~20 mgiodine cm−2 and 65% Zn utilization rate retains 80% of capacity after over 1,000 cycles. This finding offers a scalable electrolyte design for next-generation aqueous batteries, advancing their potential for practical large-scale energy storage.