Decomposition temperatures and vapour pressures of ionic liquids for electrochemical applications

Ionic liquids (ILs) are salts with melting temperatures below 100°C. Typically they are formed by organic cations, like imidazolium, pyrrolidinium, ammonium or alkyl phosphonium, and organic/inorganic anions, like hexafluorophosphate, tetrafluoroborate, triflate, dicyanamide, tetracyanamethanide, bis(trifluoromethanesulfonyl)imide (TFSI) or bis(fluorosulfonyl)imide (FSI). The presence of such bulky and asymmetric ions decreases the ion-ion interactions and lowers the melting point with respect to more classical salts. ILs present peculiar physical and chemical properties: extremely low vapour pressure, high ionic conductivity, a high thermal, chemical and electrochemical stability, a high thermal capacity and good solvent capacity. Due to these peculiarities, ILs have been proposed for a large variety of applications in chemistry and physics, such as, for example, green solvents, electrolyte components for electrochemical devices, lubricants, ingredients for pharmaceuticals and heat exchangers. Due to the possible applications of such materials, it is of great importance to investigate their decomposition temperatures and vapour pressures. In the present paper we report an investigation on these physical peculiarities for a few IL families based on the bis(trifluoromethanesulfonyl)imide or bis(fluorosulfonyl)imide anions and on quaternary ammonium or imidazolium cations. Ramp-temperature and isothermal thermogravimetric experiments were conducted in these compounds, after running a strict drying procedure, in order to ascertain their decomposition temperature and their vapour pressure in a wide temperature range, from 175 up to 325 °C, following well established procedures [1,2]. This Project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 814464.