Aqueous Zn-I2 batteries are gaining attention as next-generation energy storage systems due to their safety, low cost, and high energy density. However, their practicality is limited by interfacial instabilities at the anode, such as hydrogen evolution, corrosion, and dendritic Zn growth, as well as slow I2/I- conversion and polyiodide shuttling at the cathode. Here, 4-aminobutyric acid (AB), a commercially available amino acid derivative, is utilized as a functional electrolyte additive possessing a push-pull dipolar structure. Unlike conventional additives that adopt folded or congested structures, AB maintains an extended conformation that maximizes its dipole moment and polarizability. This extended structure strongly binds Zn2+ ions, promoting rapid desolvation, inducing (002) directional Zn deposition and suppressing parasitic reactions. Simultaneously, AB selectively interacts with iodine species, inhibiting the formation and migration of polyiodides while accelerating redox reaction rates. Consequently, the Zn||Zn symmetric cell operates stably for over 1000 h at 3 mA cm-2 and 3 mAh cm-2, while the Zn-I2 full cell with a high-capacity cathode (5 mAh cm-2) retains 95.8% capacity after 900 cycles. This study demonstrates that controlling the molecular structure to implement extended dipolar structures is a universal strategy for achieving interfacial stabilization and enhanced kinetics in aqueous Zn-I2 batteries.
Kim et al. (Thu,) studied this question.