Chain Length Dependent Structural Organization of Imidazolium Ionic Liquids for Potassium-Ion Electrolytes

Understanding how molecular architecture influences the local structure and dynamics in ionic liquid electrolytes is critical for advancing potassium-ion battery technologies. We employed all-atom molecular dynamics simulations to investigate a series of TFSI⁻-based imidazolium ionic liquids with systematically varied alkyl chain lengths, enabling direct assessment of their impact on electrolyte structure and K⁺ dynamics. Radial distribution functions reveal strengthened K⁺-TFSI⁻ correlations and progressive reorganization of cation-cation interactions with increasing nonpolar character. Static structure factor analysis shows enhanced intermediate-range ordering, consistent with the emergence of nanoscale polar-nonpolar segregation. Dynamical analyses, including velocity autocorrelation functions and probe-accessible free-volume distributions, demonstrate that longer alkyl chains induce stronger and longer-lived caging environments, leading to slower structural relaxation and reduced K⁺ mobility. These findings establish a direct link between cation alkyl chain length, mesoscale organization, and ion transport behaviour, providing molecularlevel design insights for developing stable and high-performance ionic liquid electrolytes for potassium-ion batteries.