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Recherche des causes du vieillissement de supercondensateurs à électrolyte organique à base de carbones activés

Abstract : The energy which is stored in electrochemical capacitors is proportional to the square of voltage. Consequently, the most attractive supercapacitors are those which operate in organic electrolyte medium, with an electrolyte potential window which theoretically can easily reach more than 3 V. However, even using lower values of voltage, there is a remarkable fading of the electrochemical characteristics with operating time, that is mainly characterized by capacitance loss and resistance increase. On a commercial point of view, these capacitors must be improved in order to reach the expected criterion of long operating life. In the presented work, we will determine some reasons of supercapacitors ageing in organic electrolyte (1M solution of Et4NBF4 in acetonitrile) and we will propose a treatment of activated carbon which noticeably improves the performance. A prolonged charging of electrochemical capacitors at 2.5 V, so called floating, results in gases formation and to a noticeable mass uptake of the electrodes. XPS and NMR analysis performed on carefully washed electrodes demonstrated the existence of decomposition products from the electrolyte, which are trapped in the pores of the activated carbon. These products block the pores, limiting the ions access to the active surface that causes the decay of electrochemical performances. Electrolyte decomposition is especially very high when the electrodes are constituted of carbons with a rich surface functionality, i.e. surface oxygenated groups and free radicals. Therefore, activated carbons have been submitted to thermal treatment, both in nitrogen and hydrogen atmosphere, allowing the oxygenated surface functionality to be noticeably depressed. Supercapacitors built with the treated materials have been submitted to floating during more than 2000 hours. Extremely good electrochemical performance are preserved with the electrodes obtained from activated carbons treated under hydrogen. It confirms that the surface functionality is the main origin of capacitance fading with time of operation, and that carbon materials containing essentially C-H surface groups are suitable for a durable utilisation of electrochemical capacitors.
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Contributor : Philippe Azais <>
Submitted on : Thursday, June 9, 2005 - 3:19:04 PM
Last modification on : Monday, October 19, 2020 - 11:06:13 AM
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  • HAL Id : tel-00009304, version 1


Philippe Azais. Recherche des causes du vieillissement de supercondensateurs à électrolyte organique à base de carbones activés. Matériaux. Université d'Orléans, 2003. Français. ⟨tel-00009304⟩



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