Gradient interfacial water dynamics for stable aqueous metal anodes

The deployment of renewable energy necessitates reliable grid-scale storage technologies. Aqueous metal battery systems are one of the promising candidates due to high safety, low cost, and high theoretical capacity of metal anodes, yet their long-term stability is hindered by dendritic growth and parasitic water-induced side reactions. In particular, in the case of aqueous zinc (Zn) batteries, high water reactivity at the metal anode results in hydrogen evolution and corrosion in conventional ZnSO₄ aqueous electrolytes. However, restrained water activity often leads to slow charge transport kinetics of solvated cations, limiting the high-rate operation capability of aqueous batteries. Here, we report a gradient composite hydrogel interlayer incorporating vermiculite (VMT) nanosheets within a polyacrylamide polymer matrix to synergistically regulate interfacial water dynamics and stabilize Zn anodes. Abundant hydroxyl groups and negatively charged silicate layers in VMT nanosheets strongly interact with adjacent water molecules, converting free water into bound water to suppress its activity. Charge transport behaviors of Zn ions in the hydrogel interlayer are further improved by rationally tuning the water activity along the depth of the interlayer, resulting in high ion diffusion kinetics close to the bulk electrolyte. Therefore, such a design enables Zn||Zn symmetric cells to stably cycle for over 2,000 h at 5 mA cm^-2 and 5 mAh cm^-2, and sustain high current densities up to 40 mA cm^-2. This work brings critical scientific understanding on interfacial water dynamics and highlights its importance for durable metal anode during operation, advancing aqueous batteries toward practical grid-scale energy storage.