Micro–Macro Hierarchical Hydrogel Architectures with Dual‐Scale Polyanionic Networks for High Energy Density PBA||Zn Batteries

Hydrogel electrolytes are promising for aqueous zinc metal batteries but face challenges in suppressing Zn dendrites and cathode dissolution. This study develops a polyanionic hydrogel electrolyte, poly(2-acrylamido-2-methyl-1-propanesulfonic acid-co-acrylamide) (P(AMPS-co-AM)), featuring a dense porous structure that enables a higher Zn²⁺ transference number (t_Zn ²⁺ = 0.81) and homogeneous zinc deposition. Additionally, the dense porous structure further reduces the proportion of free water molecules, thereby suppressing side reactions. Based on the benefits of the hydrogel, the Zn||Zn symmetric cell demonstrates over 3000 h of continuous cycling, and the Zn||Cu asymmetric cell exhibits an exceptional Coulombic efficiency of 99.29% in the first cycle. Benefiting from the fixation of transition metals by polyanionic groups and the reduced content of free water molecules within a densely packed porous architecture, the PBA||Zn full cell achieves a high energy density of 267 Wh kg^-1. This hydrogel electrolyte design strategy provides significant insights for achieving long cycle life through both the microscale and macroscale structure design to achieve low cost and high energy density of aqueous zinc-metal batteries (AZMBs).