Interaction‐Matched Protonated Aminopyridine Additives for Highly Reversible Aqueous Zinc Metal Anodes and Zn–I 2 Batteries

ABSTRACT In aqueous zinc‐ion batteries, electrolyte additives stabilize Zn anodes through interfacial adsorption, suppressing corrosion and parasitic reactions while regulating Zn deposition. However, although enhanced zincophilicity and hydrophobicity improve interfacial protection, whether strengthened adsorption promotes long‐term Zn reversibility and interfacial Zn 2+ dynamics remains unclear. Herein, protonated aminopyridine derivatives with progressive methyl substitution are employed to elucidate the structure–adsorption–kinetics relationship. Electron‐donating, hydrophobic methyl groups strengthen adsorption and reconstruct a more hydrophobic anode/electrolyte microenvironment, enhancing interfacial protection. However, excessive adsorption reduces the accessibility of Zn deposition sites and increases barriers to Zn 2+ interfacial migration and nucleation, imposing kinetic penalties and promoting coarser deposits, thereby reducing Zn reversibility. Protonated 4‐aminopyridine (APH + ) achieves the most favorable balance between interfacial protection and deposition kinetics, enabling reversible Zn plating/stripping for over 700 cycles with 99.37% Coulombic efficiency (CE). This interaction‐matching principle further extends to Zn||I 2 full cells, where overly strong additive–I 3 − interactions suppress polyiodide shuttling but partially immobilize iodine species, compromising iodine redox accessibility and accelerating capacity decay. Consequently, APH + retains 96.63% capacity after 2000 cycles. This work demonstrates that additive interactions with both Zn anodes and active cathode species should be appropriately matched rather than maximized, providing a design principle for durable aqueous Zn batteries.