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 H 2 O 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 H 2 O and microstructural parameters in organic-aqueous electrolytes. A more positive solvation power difference value between ether and H 2 O is appealing to drive enhanced microheterogeneity, which accordingly lowers the average Li + coordination number and reduces H 2 O cluster size. A small and isolated H 2 O cluster, which bridges the microstructural parameters and macroscopic electrolyte performance, is critical to suppress long-range H 2 O diffusion, thereby enhancing the electrochemical stability of the electrolyte. Diethyl ether with an optimal positive solvation energy difference with H 2 O forms minimal [Li(H 2 O) 4 ] + clusters and moderate anion aggregation, simultaneously enabling fast Li + ion diffusion and an expanded electrochemical window. LiMn 2 O 4 ||Li 4 Ti 5 O 12 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.