Quantitative Chemistry in Electrolyte Solvation Design for Aqueous Batteries

Aqueous electrolyte design is pivotal for boosting the energy density and lifespan of aqueous batteries, because it can expand the electrochemical stability window and also mitigate the parasitic side reactions. Until now, three main kinds of electrolytes, i.e., water-in-salt, eutectic, and additives-modified electrolytes, have been developed by which the activity of H2O can be lowered and/or the formed specific solid–electrolyte interphase (SEI) can mitigate the decomposition of H2O. However, there is still a lack of a universal model to elucidate the reason for the improved performance, especially as the SEI interpretation becomes ever more controversial. Herein, we present a quantitative and graphical model of the electrolyte solvation structure and metal-ion (de)solvation process (i.e., interfacial model) to summarize a relationship between the electrolyte–electrode interfacial chemistry and electrode performance. This Focus Review extends the solvation structure and interfacial model into the field of aqueous electrolytes, revealing the essential influence of the solvation structure's properties on electrolyte stability and electrode performance, by which electrode performance and electrolyte design can be more quantitatively and accurately understood.