In this work, we present a comparative study of physical properties and CO2 solubility of two ionic liquids (ILs), protic trimethylammonium bis­[(trifluoromethyl)­sulfonyl]­imide and aprotic trimethylsulfonium bis­[(trifluoromethyl) sulfonyl]­imide in mixture with glutaronitrile (GLN). The effect of temperature on density and viscosity of mixtures was studied and discussed in terms of intra- and intermolecular interactions. Applying Glasser’s theory, standard molar entropy, S 0, and the crystal energy, U POT, of the IL/GLN mixtures were estimated, showing a positive contribution of ILs to these quantities. This positive contribution to the entropy variation by the addition of an IL is because of the fact that it destroys GLN–GLN interactions, replacing them with new cation–GLN and anion–GLN interactions. The deconstructing effect of S111 is greater because there are no strong S111–GLN interactions, unlike the ammonium cation which can establish H-bonds with CN groups. The CO2 solubilities in both (IL/GLN) mixtures expressed by CO2 molar fractions, x CO2 , or the Henry constant K H/MPa showed that the [S111]­[TFSI]/GLN solubilizes more CO2 than the [HN111]­[TFSI]/GLN throughout the temperature range. The solubility of CO2 is sensitive to the cation nature and temperature. The sulfonium cation promotes CO2 solubility because it is less cluttered than the ammonium cation unlike HN111, which is the hydrogen-binding seat (NH–GLN) with GLN. Finally, the thermodynamic parameters such as the standard enthalpy Δdiss H 0, the free enthalpy Δdiss G 0, and the entropy Δdiss S 0 of CO2 dissolution were calculated. They showed that the dissolution of CO2 did not depend on the molecular organization (small variation in entropy) but that it is linked to the intermolecular interactions in the IL/GLN mixture, as shown by the difference in Δmix H.

Aqueous solutions are crucial to most domains in biology and chemistry, including in energy fields such as catalysis and batteries. Water‐in‐salt electrolytes (WISEs), which extend the stability of aqueous electrolytes in rechargeable batteries, are one example. While the hype for WISEs is huge, commercial WISE‐based rechargeable batteries are still far from a reality, and there remain several fundamental knowledge gaps such as those related to their long‐term reactivity and stability. Here, we propose a comprehensive approach to accelerating the study of WISE reactivity by using radiolysis to exacerbate the degradation mechanisms of concentrated LiTFSI‐based aqueous solutions. We find that the nature of the degradation species depends strongly on the molality of the electrolye, with degradation routes driven by the water or the anion at low or high molalities, respectively. The main aging products are consistent with those observed by electrochemical cycling, yet radiolysis also reveals minor degradation species, providing a unique glimpse of the long‐term (un)stability of these electrolytes.