Mechanical spectroscopy for the investigation of materials for energy applications

Reference Speaker Authors
Annalisa Paolone Paolone, A.(CNR-ISC); Palumbo, O.(CNR-ISC); Trequattrini, F.(Sapienza University of Rome); Storage and transformation of energy is one of the priorities for the future. The basis for improvements in this field is the synthesis and characterization of new materials with better performances in energy devices. In order to achieve optimized applications, a deep knowledge of the basic physical and chemical properties of these compounds is needed. In this framework, we conducted an investigation of many materials with potential applications in the field of energy storage and conversion by means of mechanical spectroscopy. Our investigations exploited the full potential of mechanical spectroscopy: in fact, both the real and the imaginary part of mechanical modulus can give useful information about applicative materials. Indeed, on one side, in applications there a need of optimized mechanical properties of materials; for example, we measured the tension modulus of polymeric membranes useful as polymeric electrolyte membranes of fuel cells and its evolution with the addition of inorganic fillers. Moreover, both the shear and tension modulus of cellulose based membranes, intended as water compatible, gel electrolytes, are reported. Finally, we investigated the changes induced by a hot pressing process of the tension modulus and of the electrolyte uptake of electrospun polymeric membranes used as separators in lithium batteries. On the other side, mechanical spectroscopy can provide useful parameters of the local motion of atoms and defects or of the occurrence of phase transitions. In the field of electrodes materials for lithium batteries, LiMn1.5Ni0.5O4 was investigated by mechanical spectroscopy in order to study the manganese dynamics. An intense thermally activated peak, detectable only in off-stoichiometric samples, was attributed to a polaronic conduction due to an electron transfer from Mn3+ to a Mn4+, and the consequent motion of the Jahn–Teller lattice distortion. In order to have a good fit of the experimental data, the Jonscher model for ionic dynamics was adopted for the first time in this spinel structure. A value of about 0.3 eV for the energy barrier of the polaronic conduction was obtained. Moreover, in the last years we investigated ionic liquids (ILs) by means of mechanical spectroscopy. ILs present peculiar physical and chemical properties: an extremely low vapor pressure, a high ionic conductivity, a high thermal, chemical and electrochemical stability, a high thermal capacity and a good solvent capacity. Due to these peculiarities, ILs have been proposed for a large variety of applications in chemistry and physics, such as electrolytes for electrochemical devices, lubricants, ingredients for pharmaceuticals and heat exchangers. By modifying the method of measurement of a Dynamical Mechanical Analyzer, we could measure relaxation processes occurring in the liquid phase, due to the internal movements of the composing ions. Moreover, one can easily detect phase transitions towards solid phases. Due to the occurrence of vitrification at low temperatures in most ILs, proper theoretical models for the relaxation peaks should be considered. A survey of the results obtained in this field will be presented. REFERENCES 1) R. Scipioni, D. Gazzoli, F. Teocoli, O. Palumbo, A. Paolone, N. Ibris, S. Brutti, M. A. Navarra Preparation and characterization of nanocomposite polymer membranes containing superacidic SnO2 additives. Membranes 4, 123 (2014) 2) M. A. Navarra, C. Dal Bosco, J. Serra Moreno, F. M. Vitucci, A. Paolone, S. Panero Synthesis and characterization of cellulose-based hydrogels to be used as gel electrolytes. Membranes 5, 810 (2015) 3) F. M. Vitucci, O. Palumbo, A. Paolone, R. Cantelli, S. Brutti, S. Panero Dynamics of Mn3+ in off-stoichiometric LiMn1.5Ni0.5O4. Journal of Alloys and Compounds 604, 83 (2014) 4) F. Trequattrini, A. Paolone, O. Palumbo, F.M. Vitucci, M. A. Navarra, S. Panero Low Frequency Mechanical Spectroscopy Study of Three Pyrrolidinium Based Ionic Liquids. Archives of Metallurgy and Materials 60, 385 (2015) 5) O. Palumbo, F. Trequattrini, F. M. Vitucci, A. Paolone Relaxation dynamics and phase transitions in ionic liquids: viscoelastic properties from the liquid to the solid state. Journal of Physical Chemistry B 119, 12905-12911 (2015)
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