Effect of Organic Additives on Ionic Conductivity of Electrolyte in Zinc Ion Batteries: Insights from Molecular Dynamics Simulations

Although the introduction of organic molecules into electrolytes effectively suppresses dendrite formation, its adverse impact on ionic conductivity poses a critical challenge for implementing extreme fast charging technologies of aqueous zinc-ion batteries. The effects of addition of N, N-dimethylacetamide (DMA) or methanol (MeOH) on ionic conductivity of ZnSO4 aqueous electrolyte are studied using molecular dynamics simulations. The results show that both DMA and MeOH reduce ionic conductivity of electrolyte, and the reduction is more obvious in DMA systems compared with MeOH systems. The insights into ion conduction proposed mostly in organic electrolyte, such as viscosity, ion states, solvation structures and coordination stability are evaluated for aqueous electrolyte. It is found that the reduced ionic conductivity is related to the increased electrolyte viscosity and the reduced diffusion coefficient of the most abundant ion state. However, the amount of ion states, the size of solvation structures and the coordination stability has no effect on ionic conductivity. New insights into ion conduction are given from the perspective of molecular and ionic motions. A correlation between the reduced ionic conductivity and the weakened electrolyte disturbance, which stems from suppressed rotational and translational motion of additives, is highlighted. This study advances the understanding of ion conduction mechanisms in organic additive electrolytes while offering practical guidance for the selection of additives in electrolyte design.