Understanding the Critical Bulk Properties of Zn-Salt Solution Electrolytes for Aqueous Zn-Ion Batteries

The unique technical merits of aqueous zinc-ion batteries (AZIBs) have attracted significant interest in the development of grid-scale energy storage technologies in the past decade. However, the development of AZIBs is severely hampered by the poor cycle stability, which exclusively stems from the electrolyte/electrode interactions. To address this issue, knowledge of the bulk properties of electrolytes, a pivotal component of AZIBs, is needed. Unfortunately, there still exists a significant gap in the data and understanding of these properties. This study investigates the concentration-dependent bulk properties of Zn-salt solution electrolytes through a combined experimental and theoretical approach. Key bulk properties such as pH, conductivity, water activity, hydrogen bonding, and electrochemical stability of five Zn-salt solutions are systematically studied as a function of concentration through a suite of experiments and theoretically interpreted by quantum chemistry calculations, molecular dynamics, and a tailored solvation model considering multispecies ion–ion and ion–molecule interactions. The model-produced theoretical results agree well with the experimental data. The revealed theoretical insights offer valuable fundamental guidance for future electrolyte discovery and understanding/mitigating degradation mechanisms in AZIBs.