Modulating Molecular Microheterogeneity within Electrolytes Controls Macroscopic Battery Performance

Narrow electrochemical windows and high reactivity of aqueous solutions remain critical bottlenecks for the practical application of aqueous batteries. However, the mechanisms for tuning microscopic reactivity of H₂O molecules in aqueous electrolytes remain elusive. This study employs six ether molecules with distinct structures and solvation powers to regulate the microstructure of aqueous solutions. We reveal underlying correlations between the reactivity of H₂O and microstructural parameters in organic-aqueous electrolytes. A more positive solvation power difference value between ether and H₂O is appealing to drive enhanced microheterogeneity, which accordingly lowers the average Li⁺ coordination number and reduces H₂O cluster size. A small and isolated H₂O cluster, which bridges the microstructural parameters and macroscopic electrolyte performance, is critical to suppress long-range H₂O diffusion, thereby enhancing the electrochemical stability of the electrolyte. Diethyl ether with an optimal positive solvation energy difference with H₂O forms minimal [Li(H₂O)₄]⁺ clusters and moderate anion aggregation, simultaneously enabling fast Li⁺ ion diffusion and an expanded electrochemical window. LiMn₂O₄||Li₄Ti₅O₁₂ full cells achieved 200 cycles with 97.5% capacity retention at 1 C. Additionally, a 1 Ah aqueous pouch cell delivered a high energy density of 80.93 Wh kg^-1. This work provides valuable insights into electrolyte stabilization and the design of high-performance electrolytes for energy storage and conversion applications.