Novel Structural Janus Hydrogels for Battery Applications: Structure Design, Properties, and Prospects

Janus hydrogels, defined by their asymmetric architectures and bifunctional interfaces, have emerged as a transformative class of solid-state electrolytes in electrochemical energy storage. By integrating spatially distinct chemomechanical and ionic functionalities within a single matrix, they overcome the intrinsic limitations of conventional isotropic hydrogels, offering enhanced interfacial stability, directional ion transport, and dendrite suppression in lithium- and zinc-based batteries. This mini-review systematically highlights recent breakthroughs in Janus hydrogel design, including interfacial polymerization and layer-by-layer assembly, which collectively enable precise modulation of crosslinking gradients and ion transport pathways. This review uniquely frames Janus hydrogels from a battery-centric and interface-engineering perspective. It elucidates key structure–function correlations, identifies current limitations in scalable fabrication and electrochemical longevity, and outlines future directions toward intelligent, multifunctional platforms for next-generation flexible and biointegrated energy systems.