Insights on lean-water hydrogel electrolyte designs for next-generation zinc batteries

Aqueous zinc-ion batteries (AZIBs) have emerged as promising large-scale energy storage devices owing to their intrinsic safety and low cost. Hydrogel electrolytes have been extensively studied for their ability to maintain excellent flexibility of zinc-based batteries while exhibiting superior electrochemical performance. However, traditional hydrogel electrolytes (THEs) typically suffer from narrow electrochemical stability potential windows (ESPWs) and poor cycling stability, primarily due to their high-water content. In recent years, lean-water hydrogel electrolytes (L-WHEs) have been developed to address these issues. By confining free water molecules and regulating ion transport within the hydrogel network, L-WHEs can efficiently suppress side reactions, widen ESPWs, and enhance interfacial stability. This review first systematically discusses the fundamental principles of L-WHEs, followed by summarizing strategies for developing practical L-WHEs and highlighting relevant research progress in recent years. Finally, based on the opportunities and challenges associated with high-performance L-WHEs, we propose perspectives for their future development.