Importance of glassy fragility for energy applications of ionic liquids

TL;DR

This paper explores how the glassy fragility of ionic liquids influences their conductivity, which is crucial for their application in energy storage and conversion devices like batteries and supercapacitors.

Contribution

It demonstrates that ionic liquids' conductivity depends systematically on their glass temperature and fragility, providing new insights into their physical properties for energy applications.

Findings

Conductivity correlates with glass temperature and fragility.

Fragility affects ionic mobility in ionic liquids.

Understanding fragility can improve energy device performance.

Abstract

Ionic liquids (ILs) are salts that are liquid close to room temperature. Their possible applications are numerous, e.g., as solvents for green chemistry in various electrochemical devices, and even for such "exotic" purposes as spinning-liquid mirrors for lunar telescopes. Here we concentrate on their use for new advancements in energy-storage and -conversion devices: Batteries, supercapacitors or fuel cells using ILs as electrolytes could be important building blocks for the sustainable energy supply of tomorrow. Interestingly, ILs show glassy freezing and the universal, but until now only poorly understood dynamic properties of glassy matter, dominate many of their physical properties. We show that the conductivity of ILs, an essential figure of merit for any electrochemical application, depends in a systematic way not only on their glass temperature but also on the so-called fragility, characterizing the non-canonical super-Arrhenius temperature dependence of their ionic mobility.