Thermophysical characterization of ionogels of ethylamonium nitrate as advanced electrolytes for electrochemical devices

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 [1].

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.

Gelation process has been performed following Negre et al. methodology [2]. Essentially, a solid ionogel-based electrolyte was synthetized using two different sol-gel agents and the IL.

Differential Scanning Calorimetry was employed to determine the melting and freezing temperatures [3], 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 [3]. 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.

Acknowledgements

This work was developed within the scope of the projects EM2013/031 and GRC ED431C 2016/001 and by the network REGALIS ED431D 2017/06 (Xunta de Galicia, Spain). The financial support of the Spanish Ministry of Economy and Competitiveness through grants MAT2014-57943-C3-1-P, MAT2014-57943-C3-2-P and MAT2014- 57943-C3-3-P is also gratefully acknowledged.

 Refs.

[1] S. Menne, J. Pires, M. Anouti, A. Balducci, Electrochem. Commun. 31, 39 (2013).

[2] L. Negre, B. Daffos, V. Turq, P.L. Taberna P. Simon, Electrochim Acta 206, 490 (2016).

[3] M. Villanueva, J. J. Parajó, P.B. Sánchez, J. García, J. Salgado, J. Chem. Thermodyn. 91, 127 (2015).

[4] T. Méndez-Morales, J. Carrete, S. Bouzón-Capelo, M. Pérez-Rodríguez, O. Cabeza, L. J. Gallego, L.M. Varela, J. Phys. Chem. B 117, 3207 (2013).