Characterization of Fragility in Silica-Based Ionogels

The present study examines the ionic conductivity and transport properties for ionic liquids confined within mesoporous materials. The fragility index was determined for several samples with varying microstructures and used to characterize performance as a pseudosolid electrolyte. The degree of microstructure complexity was characterized via the mass fractal dimension, which correlates with the fragility index in the pore size domain studied. We demonstrate for the materials studied here that the presence of the microporous matrix serves to inhibit ion mobility, and as the complexity of the matrix increases, the fragility index also increases, leading to lower conductivity materials. The microstructural features influencing conductivity were examined using Archie's law when assuming the matrix conductivity to be negligible. This type of analysis, previously validated for rock matrices, has now been extended to pseudosolid electrolyte materials. The results indicate that ionogel samples can approach the conductivity of the unconfined ionic liquid. These conclusions are applicable to a variety of pseudosolid electrolyte systems and have important implications for the design of electrochemical devices.