Achieve an atomic-level understanding of the anion/concentration effect on transport properties for aqueous zinc halide electrolytes

Abstract

Despite the growing research interest in aqueous zinc-ion batteries (AZIBs), the detailed atomic-level understanding of the structure-property relationship in AZIBs electrolytes remains incomplete. In this study, we employ molecular dynamics simulations to study the properties of three zinc halide salt electrolytes (ZnCl₂, ZnBr₂, and ZnI₂) at concentrations ranging from 0.44 m to 4 m. We observed the diffusion coefficients decrease as the concentration increases, and the overall diffusion coefficients follow the sequence of ZnI₂ > ZnBr₂ > ZnCl₂. Further study revealed that this is attributed to the different degrees of ion clustering and the resultant disruption of the water network across different systems. Furthermore, we found that ionic conductivities of all three salts increase first and then decrease beyond an inflection point as the concentration rises, which is closely associated with the proportion of Zn²⁺ in solvent-separated ion pairs. This work aims to deepen the understanding of aqueous zinc salt electrolytes and inform the design of high-performance AZIBs.