Zinc-ion batteries based on lean-water hydrogel electrolytes and their application as flexible power source

Aqueous zinc-ion batteries, featuring intrinsic safety, the notable energy density of zinc anode, and cost-effectiveness, have emerged as promising candidates for flexible devices. As a key component of flexible zinc-ion batteries, the hydrogel electrolytes play a crucial role in achieving harmonious, balanced mechanical strength, flexibility, ionic conductivity, and interfacial stability. However, excessive water molecules in conventional hydrogels and their high electrochemical activity can induce undesired side reactions such as the hydrogen evolution reaction (HER), byproduct propagation, and dendrite growth, eventually resulting in short-circuit and battery failure. In this perspective, we summarize the recent progress in lean-water hydrogel electrolytes, showcasing their benefits, including enhanceable ion transport, restrained water-related side reactions, and mechanical integrity under deformation to cater to the demands of flexible zinc-ion batteries, followed by the key challenges and prospects of hydrogel strategies. This perspective offers guidance and inspiration for designing lean-water hydrogel electrolytes for flexible zinc-ion batteries.