Cosolvent-involved hybrid solvation models for aqueous Zn-ion electrolytes: a case study of ethylene glycol-H2O-ZnSO4 system

Tuning electrolyte bulk properties, fundamentally the Zn-ion solvation structures, is key to addressing degradation issues in aqueous Zn-ion batteries (AZIBs). The common practice is to add water-soluble organics as a cosolvent. However, a comprehensive fundamental understanding of the cosolvent effect on electrolyte bulk properties is still lacking. In this work, using ethylene glycol (EG) as the cosolvent and 2M ZnSO4 as the base aqueous Zn-ion electrolyte, we report from a computational perspective how the cosolvent affects aqueous electrolyte bulk properties such as conductivity and pH. To ensure reliability of the computational results, we have used experimental ion conductivity data to validate our computing methods. Further, we show new hybrid solvation models that encompass H2O, cosolvent and anion, e.g., EG-Zn(H2O)52+ and EG-Zn(H2O)42+-SO42-. Based on these cosolvent-involved Zn-ion solvation models, the experimental pH trending has been successfully explained. Our work offers new insights into the cosolvent effect on aqueous Zn-ion electrolyte bulk properties and solvation structures.