Importance of liquid fragility for energy applications of ionic liquids

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.

Dielectric Properties of 3D Printed Polylactic Acid

“…The relaxation times (s), which are revealed by the temperature dependent peak position of , are illustrated in an Arrhenius representation in the inset of Figure 3. The dashed line represents a Vogel-Fulcher-Tammann (VFT) function [38][39][40][41], which is extrapolated to (s) = 100 s. This point corresponds to the glass transition temperature [40,42] = 330 K revealed from (s) and agrees well with measured from DSC. The Arrhenius representation also reveals that there is no significant change in temperature dependence of around the cold crystallization (cf.…”

Thermophysical and Electrochemical Properties of Ethereal Functionalised Cyclic Alkylammonium‐based Ionic Liquids as Potential Electrolytes for Electrochemical Applications

“…However, the larger differences between T g and the theoretical T o are considered to depend on the liquid fragility or strength. Furthermore, while lower values of T g would be expected to yield lower viscosity, or higher conductivity, it has been shown for ILs under ambient conditions that these properties are dependent on both fragility and T g . The concept of fragility, introduced by Angell, describes the rate at which the transport properties and relaxation dynamics of a glass‐forming material changes as the temperature approaches T g .…”

“…Conversely, strong materials are considered more impervious to structural changes upon heating above their T g . Ionic liquids, materials known for undergoing glass transitions and commonly inadequately described by normal Arrhenius‐type temperature dependence (in terms of transport properties), have been frequently described as exhibiting intermediate to high fragility, such that their transport and relaxation dynamics change several orders of magnitude over relatively small temperature deviations close to their T g …”

“…For each dataset, an additional point of η ( T g )=10 15 mPa s or σ ( T g )=10 −12 mS cm −1 was included in the correlation leading to slightly different correlation parameters. These values represent an approximation of the sample viscosity and conductivity, respectively, at the T g of the material . The correlation parameters of these fits, detailed in Table S8, are then used to extrapolate the temperature dependant behaviour of viscosity/conductivity towards the T g .…”

Lithiation and Delithiation Reactions of Binary Silicide Electrodes in an Ionic Liquid Electrolyte as Novel Anodes for Lithium‐Ion Batteries

“…An increase in the energy density of LIBs leads to a greater probability of combustion; hence, non‐flammable electrolytes should be used to enhance the safety of LIBs. Ionic liquids have excellent physicochemical properties as electrolyte solvents, such as negligible vapor pressure, non‐flammability, high conductivity, and wide electrochemical windows . We have reported that a Si‐anode exhibits a better electrochemical performance in some ionic liquid electrolytes compared to that in conventional organic electrolytes .…”