The road ahead for hydrogel electrolytes in aqueous zinc metal batteries

Hydrogel electrolytes, enabled by tunable polymer networks, mechanical robustness, and water confinement, provide a promising platform for stabilizing Zn metal anodes in aqueous zinc metal batteries. Progress can be broadly viewed through three coupled modules: microenvironment control to regulate water activity and Zn2+ solvation, bulk transport engineering to sustain selective Zn2+ delivery, and interfacial design to tune desolvation, nucleation, and growth. Our perspective is that the central challenge is not the independent optimization of these modules, but the rate mismatch that can emerge among them under practical conditions: suppressing water activity alone may not sustain Zn2+ supply, improving bulk transport alone may not resolve interfacial kinetic barriers, and interfacial stabilization alone may remain ineffective if local ion delivery is insufficient. As a result, the practical operating window is often governed by how well these three processes are temporally and spatially coordinated, especially at high current densities and areal capacities. Additionally, scalable fabrication, full-cell architectures that accommodate electrode asymmetry, and sealed-cell management of gas evolution and pressure are needed.