Smart hydrogel electrodes: stretchable, eco-friendly, and tunable platforms for next-generation energy storage devices

Conductive hydrogels have surfaced as potential electrode and electrolyte materials for batteries and supercapacitors owing to their special blend of mechanical flexibility, strong ionic conductivity, and tunable porous networks. By integrating conductive fillers and polymer matrices, they enable efficient charge transport, long-term cycling stability, and potential applications in innovative wearable and flexible energy storage technologies. When combined, the elevated electrical conductivity, quick ion transport, mechanical flexibility, and large surface area of materials like polyaniline, polypyrrole, polythiophene, and carbon based such as CNTs, Graphene, as well as MXene-based conductive hydrogels improve battery performance by increasing capacity, cycling stability, safety, and suitability pertaining to wearable and flexible energy storage systems. The review explores the conductive hydrogels based on ionic, electronic, and polymer electrolyte and their interaction, crosslinking methods, electrode materials, as well as their materials for batteries and supercapacitors and emerging functionalities and applications, challenges and limitations, as well as future direction. Among sodium-ion, lithium-ion, and zinc-ion batteries integrated upon conductive hydrogels, lithium-ion systems currently offer the highest energy density and overall performance, sodium-ion systems distinguish themselves by being affordable and sustainable in large-scale storage, and zinc-ion systems are the most promising for safe, flexible, and wearable applications.