Adaptive Hydration Chemistry Enables Fast and Durable Zinc-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) are promising candidates for large-scale energy storage; however, uncontrolled interfacial water remains a major hurdle, limiting both anode stability and ion transport. In this study, 2-picolinaldehyde (2PA) was chosen as a reversible hydration modulator (RHM) that enables dynamic regulation of interfacial free water. Spectroscopic and computational analyses revealed that RHM captures excess water during plating to suppress hydrogen evolution and corrosion while releasing water during stripping to facilitate Zn²⁺ solvation and migration. In addition, RHM coordinates with Zn²⁺ and reorganizes its local coordination environment. Consequently, symmetric cells with the RHM-ZnSO₄ electrolyte deliver prolonged cycling exceeding 4000 h and excellent rate performance, with low voltage polarization even at a high current density of 20 mA cm^-2. The corresponding full cells demonstrate durable operation for over 5000 cycles at 5 A g^-1. This adaptive behavior satisfies the distinct interfacial water requirements during Zn plating and stripping, enabling interfacial stability and efficient ion transport, and provides a novel strategy for electrolyte design in AZIBs.