Conditions Extrêmes et Matériaux : Haute Température et Irradiation

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Ghenima Oukali, 'Étude par résonance magnétique nucléaire du transfert des ions lors de la charge et la décharge de supercondensateurs', These 1-165 (2019)

Supercapacitors (Electrochemical Double Layer Capacitors) are powerful energy storage devices. The actual challenge for the development of supercapacitors on a larger scale is to increase the stored energy density. The full understanding of the molecular processes that contribute to the charging mechanism is essential to overcome the current limits. We use Nuclear Magnetic Resonance (NMR), a technique that is sensitive to the local environment of the atoms, to study the charge mechanisms in supercapacitors. In situ measurements are essential to follow the ionic movements in the electrolyte during the charge and discharge, but regular spectroscopy offers little insight due to the overlap of the signals of the ions in both electrodes of the supercapacitor. We demonstrated that the electrode design modifications proposed in the literature degrade the electrochemical performances of supercapacitors, and we developed a new tool for the in situ study of supercapacitors with a realistic configuration. Nuclear magnetic imaging (MRI) allows for the segregation of the signals of ions in each electrode of a supercapacitor, placed in an electrochemical cell especially designed for NMR measurements. The charge storage mechanism in carbon-based supercapacitors was determined and the effect of various parameters on this mechanism, such as pore size distribution and electrolyte concentration, were investigated.