Recent progress in hydrogel electrolytes for advanced flexible zinc-ion batteries

Flexible zinc-ion batteries (ZIBs) are emerging as a highly promising energy storage technology for wearable electronics due to their intrinsic safety, low cost, abundant materials, and environmental friendliness. However, persistent challenges in aqueous ZIBs—such as dendrite growth, parasitic reactions on the zinc anode, and the dissolution of cathode materials—continue to hinder their practical implementation. Hydrogel electrolytes, functioning as quasi-solid-state ionic conductors, not only impart outstanding mechanical flexibility and processability but also effectively stabilize the electrode–electrolyte interfaces, positioning them as ideal candidates for next-generation wearable electronics. This review offers a comprehensive summary of recent advancements in hydrogel electrolytes for flexible ZIBs. Initially, the fundamental working principles and material challenges of ZIBs are discussed. The physicochemical properties, synthesis approaches, and structural design strategies for hydrogel electrolytes are then thoroughly examined. Next, we highlight cutting-edge strategies aimed at stabilizing both the zinc anode and various cathode materials by rationally tailoring hydrogel chemistry. Particular attention is given to multifunctional hydrogels engineered to operate under diverse conditions, including low/high-temperature tolerance, self-healing, and biocompatibility. Furthermore, the integration of hydrogel electrolytes into ZIBs and their potential applications in wearable sensors, electronic skin, and flexible touch interfaces are reviewed. Lastly, we provide a critical outlook on current challenges and future research directions, emphasizing the urgent need for enhanced multifunctionality, scalability for pouch cells, and standardized testing protocols. This comprehensive review is intended not only to elucidate the state of the art, but also to inspire innovative strategies, thereby facilitating the transition of hydrogel-based flexible ZIBs from laboratory research to real-world applications