Molecular dynamics study of [EMIM][TFSI]/(Li/Na)TFSI ionic liquids confined in silica pores

Abstract

We investigate the effects of confinement in hydroxylated silica (MCM41) pores on [EMIM][TFSI] ionic liquids doped with Li⁺ and Na⁺ cations using molecular dynamics. By systematically varying both pore size and metal cation concentration, we characterise how confinement and interfacial effects influence the structure, dynamics, and transport properties of these ionogels. Our results show that, although the silica interface induces local changes in the ionic liquid, a bulk-like structure and dynamic behaviour are nevertheless recovered in the pore centre even for diameters as small as 8 nm, which is promising for the development of ionogels as electrolytes in solid energy storage devices. Our results reveal that the silica interface induces interesting local modifications in ionic liquid structure and dynamics, while bulk-like behaviour is recovered in the pore centre for diameters as small as 8 nm. This dual-region behaviour is promising for the development of ionogels as electrolytes in solid energy storage devices, offering both the advantages of interfacial effects and bulk transport properties. By analysing region-resolved diffusivity – distinguishing between interfacial and central regions, alongside ion correlations and conductivity contributions, we show how the interface affects local dynamics and modifies the microscopic mechanisms of charge transport. While the magnitude of the diffusivity and conductivity do not change significantly under hydroxylated silica confinement, the associated underlying correlations are different. These findings help clarify the interplay between confinement, structure, and dynamics in ionogels, and highlight the crucial role of the interface, opening perspectives for tailoring transport properties through interfacial engineering.