Thermophysical and Dynamics Perspective of Ions and Microstructures in Binary Salt K-Ion Battery Electrolytes

Potassium-ion batteries have gained much attention as alternatives to lithium-ion batteries. As electrolytes play an essential part in a battery's performance, we used classical molecular dynamics to understand the solvation structures and dynamics of different K-ion electrolytes. We also applied different static electric fields to the electrolytes to study their structural and dynamic changes. We investigated seven electrolytes by changing the concentrations (0.75 and 1.0 m) and molar ratios of KPF₆ and KFSA salts. The qualitative and quantitative results of different interactions were obtained from structural analyses. We distinguished different microstructures present in the electrolytes based on various interactions. The highest contact ion pair (CIP) percentage is observed for a higher KPF₆ molar ratio. The potential of mean force calculations reveals that a higher KPF₆ molar ratio has a more stable CIP and a higher KFSA molar ratio has a less stable CIP. The diffusion coefficients of cations and anions allow us to gain insight into ion dynamics in electrolytes. The anions have higher diffusion than cations. We have established a correlation between the potential mean force and conductivity. An electrolyte with higher conductivity has a higher value of the potential mean force at CIP. The lifetimes for different interactions led us to understand the most and least common interactions. K⁺-PF₆^- has a higher lifetime among cation-anion interactions, while K⁺-DEC has a higher lifetime among cation-solvent interactions.