Expanding the Electrochemical Stability Window: Unraveling the Role of Solvent Polarity and a WiSE-Compatible Strategy

Expanding the electrochemical stability window (ESW) of aqueous batteries significantly enhances their safety and energy density, addressing performance limitations and elevating their position in energy storage systems. Over the past decade, water-in-salt electrolyte (WiSE) has led to groundbreaking advancement in this field. However, a pressing question arises: can we further broaden the ESW through novel approaches? This study delves into this question, leveraging atomistic simulation along with ESW estimation and WiSE continuum theory to uncover that interfacial solvent polarity, subtly modulated by adding minor organic solvents, expands the ESW as well as promotes ion intercalation and transport. The strategy of incorporating minor organic solvents is compatible with WiSE, which not only advances our comprehension but also forges new research paths for post-WiSE era aqueous battery innovation. More importantly, our study provides a systematic way for theoretically estimating ESW and analyzing its enhancement mechanism in aqueous batteries.