Water drives sequential breakdown of dynamic nanodomains in deep eutectic electrolytes

The rational design of functional materials hinges on understanding molecular interactions in complex hydrogen-bonded liquids like deep eutectic electrolytes (DEEs), where molecular structure governs ionic conductivity and electrochemical stability. Hydration levels critically influence these properties, yet the underlying mechanisms remain elusive, hindering systematic design. Using multidimensional NMR, 2D infrared spectroscopy, and molecular dynamics simulations, we studied choline chloride-malic acid DEEs at varying hydration levels. We show a sequential, component-specific breakdown of molecular nanodomains that overturns dilution models. This process proceeds in distinct stages: water first disrupts ionic domains at moderate hydration levels, while hydrogen-bonded organic networks persist until higher water content. These insights enabled us to design a DEE with enhanced electrolyte performance, achieving ionic conductivity of 13.0 mS cm^-1 and stable cycling over 1000 cycles while suppressing parasitic reactions. This work demonstrates how fundamental molecular insights can resolve critical bottlenecks in sustainable technology development, enabling systematic engineering of nanostructured liquids for energy storage, catalysis, and sustainable chemistry applications.