Gradient Hydrogel Electrolyte Enables High Ionic Conductivity and Robust Mechanical Properties for Dendrite‐Free Aqueous Zinc‐Ion Battery

Abstract

Abstract Rechargeable aqueous Zinc‐ion batteries (AZIBs) hold great promise for sustainable storage, yet their practical deployment is impeded by dendrite growth and hydrogen evolution reaction (HER). Hydrogel electrolytes offer a potential solution to stabilization but suffer from a trade‐off in ionic conductivity and mechanical robustness. Herein, by leveraging the Hofmeister effect, the way ions influence the solubility, stability, and structure of polymers in aqueous solutions, a concentration gradient hydrogel electrolyte (CGHE) is designed to reconcile these challenges. By integrating two hydrogels with high (1.5  m OAc − ) and low (0.3  m ) acetate concentrations, the CGHE achieves a high Zn 2 ⁺ transference number ( = 0.88) and excellent mechanical strength ( σ = 1.7 MPa, ɛ max = 310%). The quasi‐solid gradient architecture regulates Zn 2+  transport and cation selectivity, promoting uniform Zn (002) deposition while suppressing HER through reduced water activity in the networks. Consequently, symmetric Zn//Zn cells exhibit ultrastable cycling over 2,500 h at 1 mA cm −2 , and Zn//Cu asymmetric cells deliver a coulombic efficiency of 99.1%. The Zn//hydrogel//V 2 O 5 full batteries retain 91% of capacity after 500 cycles at 2 A g −1 , while the quasi‐solid electrolyte offers flexibility and flame resistance, enabling potential safe operation in wearable devices. The gradient electrolyte design provides  a general strategy for constructing advanced electrolytes in metal‐based energy systems.