Current electrolytes for electrochemical energy storage devices are made of solvents, which often present problems of flammability, corrosion and high toxicity. Ionic liquids and mixtures with metal salts are proposed as a good selection for safer electrolytes due to their properties such as, among others, non-flammability, negligible vapor pressure, high ionic conductivity and wide electrochemical window. In this work, the electrical conductivity of solutions of the ionic liquid 1-ethyl-3-methylimidazolium nitrate ([EIm][NO3]) with lithium nitrate salt in three different concentrations is analyzed for liquid and gel states. The temperature and salt concentration dependences of electrical conductivity are studied for liquid and gel states. As expected, an increase in conductivity with temperature and a decrease with salt concentration were observed, except for the case of gel [EIm][NO3] with a salt concentration of 0.5 m, which shows a small increase in conductivity compared to the pure gel. Comparison of the conductivity of the liquid and gel states shows a significant increase for the gel state at low concentrations of the added salt.
Abstract:Among the multiple applications of ionic liquids (ILs) and ionogels, electrolytes for electrochemical devices have a highlighted position. The interest in mixtures of ILs with alkaline metals salts has increased in the last years, since the presence of some electrochemically active species, is required for any electrochemical application of these designer solvents, e.g. in batteries.Although physical characterization of common ILs, as ethylammonium nitrate (EAN), is extensively performed and published, thermophysical characterization of its ionogels is not yet well developed.In this work, the liquid range and thermal stability of ionogels of EAN and its mixtures with lithium nitrate (LiNO3), an inorganic salt with a common anion, were measured. Differential Scanning Calorimetry was employed to determine the melting and freezing temperatures, observing that the pure IL and mixture melt at 12 ºC and 3 ºC, respectively, whereas no processes associated to the formation of a crystalline phase was observed for ionogels.Moreover, using a thermogravimetric analyzer operating in dynamic and isothermal modes under dry air and nitrogen atmospheres, thermal stability analysis was performed. Pure IL and ionogels showed similar thermogravimetric curves characterized by a loss mass in a single step starting at 200 ºC and finishing at 300 ºC, approximately.
Abstract:It has been frequently said that onset temperatures obtained from dynamic thermogravimetric analysis can be used to estimate the short-term thermal stability of materials and also the relative thermal stability.In this work the relative thermal stability was studied through dynamic analysis under the same experimental conditions for 50 Ionic Liquids (ILs). Several families with fixed anions and different cations and vice versa were chosen to have a comprehensive knowledge of thermal properties of ILs depending on the ions selection. Non-isothermal scans were performed under air atmosphere and a heating rate of 10 K · min -1 for all the selected ILs.It was observed that the anion influence on the thermal stability is stronger than the cation one,
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