Coupling hydration continuity with coordination-hopping transport regulates interfacial Zn²⁺ flux in gel electrolytes

Densely cross-linked hydrogel electrolytes often suffer from tortuous ion pathways, disrupted hydration continuity, and severe concentration polarization, which collectively hinder Zn²⁺ interfacial transport in aqueous Zn batteries. Herein, we report a low-cross-linking polyacrylamide/sodium alginate (PAM/SA) hydrogel that couples continuous hydration-rich channels with transient coordination sites to regulate Zn²⁺ migration and deposition behavior. In this structure, the reduced cross-linking density preserves hydrated transport domains, while carboxylate groups from sodium alginate and carbonyl groups from PAM provide alternating short-residence coordination sites for Zn²⁺ relay transport. Spectroscopic analyses, electrochemical measurements, and simulations consistently indicate that this coupling of hydration continuity and reversible coordination suppresses interfacial ion depletion, homogenizes ion flux and electric field, and promotes dense Zn deposition. As a result, the hydrogel exhibits an ionic conductivity of 6.49 mS cm^-1 and a Zn²⁺ transference number of 0.88, together with robust mechanical properties. Zn||NVO full cells further deliver prolonged cycling stability at both 10 and 25 A g^-1. This work provides mechanistic insight into how cross-linking density, hydration structure, and transient coordination jointly govern ion transport in hydrated polymer electrolytes.