Tailoring interfacial and bulk solvation environments through molecular crowding for high-performance aqueous batteries

Abstract Aqueous batteries represent a compelling frontier for safe and sustainable large-scale energy storage. However, the narrow electrochemical stability window and complex interfacial side reactions of water fundamentally limit their energy density and cycle life. In biological cells, the highly crowded intracellular environment governs vital biochemical processes by restricting water mobility. Inspired by this natural mechanism, molecular crowding electrolytes (MCEs) have been developed to manipulate the hydrogen-bonding network of aqueous electrolytes. This review provides a systematic overview of aqueous lithium-ion, sodium-ion, zinc-ion, iron-metal, aluminum-metal, and proton batteries. By introducing proper crowding agents, MCE effectively sequesters water molecules into localized coordination environments, thereby suppressing water-driven parasitic reactions without relying on extreme salt concentrations. The adoption of MCE could enable next-generation aqueous batteries with high energy density and prolonged cycling stability.