Zwitterion-mediated interface chemistry for practical Zn-iodine batteries

Aqueous zinc-iodine (Zn||I₂) batteries, recognized for their cost-effectiveness, safety, and environmental sustainability, are emerging as the next-generation energy storage technologies. However, capacity degradation arising from the detrimental parasitic reactions at both the negative electrode and positive electrode interfaces presents substantial challenges for the practical implementations of Zn||I₂ batteries. Herein, we develop zwitterion-mediated interface chemistry to modulate the interface reactions using the zwitterion of 1-butylsulfonate-3-methylimidazolium (BM) as an electrolyte additive. At the negative electrode, the alignment of electric field-oriented BM molecules creates a dynamic dual-asymmetry interface, facilitating homogeneous Zn deposition and protecting the Zn metal electrode from the water and corrosive polyiodides. At the positive electrode, the reconfigured solvation configuration of iodide ions, involved by BM molecules, deactivates the interface reaction associated with the I₂ dissolution and polyiodide formation. Consequently, Zn||I₂ batteries with BM additive demonstrate enhanced rate capability (135.5 mAh g^-1 at 20.0 A g^-1) and extended durability (capacity retention of 91.9% after 50,000 cycles at 10.0 A g^-1). The zwitterion-mediated interface chemistry effectively tackles the insurmountable challenges of aqueous Zn||I₂ batteries, facilitating their reliable and practical implementation.