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Competitive Salt Precipitation/Dissolution During Free-Water Reduction in Water-in-Salt Electrolyte |
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| Authors: | Dr Roza Bouchal Dr Zhujie Li Chandra Bongu Steven Le Vot Dr Romain Berthelot Dr Benjamin Rotenberg Dr Frederic Favier Dr Stefan A Freunberger Prof Mathieu Salanne Dr Olivier Fontaine |
| Institution: | 1. ICGM, Univ. Montpellier, CNRS, Montpellier, France;2. Sorbonne University, vUPMC Univ. Paris 06, CNRS, Laboratoire PHENIX, 75005 Paris, France
Maison de la Simulation, CEA, University Paris-Saclay, 91191 Gif-sur-Yvette, France Réseau sur le Stockage Electrochimique de l'Energie (RS2E), CNRS FR3459, 33 rue Saint Leu, 80039 Amiens Cedex, France;3. ICGM, Univ. Montpellier, CNRS, Montpellier, France Réseau sur le Stockage Electrochimique de l'Energie (RS2E), CNRS FR3459, 33 rue Saint Leu, 80039 Amiens Cedex, France;4. Institute for Chemistry and Technology of Materials Graz, Stremayrgasse 9, 8010 Graz, Austria |
| Abstract: | Water-in-salt electrolytes based on highly concentrated bis(trifluoromethyl)sulfonimide (TFSI) promise aqueous electrolytes with stabilities nearing 3 V. However, especially with an electrode approaching the cathodic (reductive) stability, cycling stability is insufficient. While stability critically relies on a solid electrolyte interphase (SEI), the mechanism behind the cathodic stability limit remains unclear. Now, two distinct reduction potentials are revealed for the chemical environments of free and bound water and that both contribute to SEI formation. Free water is reduced about 1 V above bound water in a hydrogen evolution reaction (HER) and is responsible for SEI formation via reactive intermediates of the HER; concurrent LiTFSI precipitation/dissolution establishes a dynamic interface. The free-water population emerges, therefore, as the handle to extend the cathodic limit of aqueous electrolytes and the battery cycling stability. |
| Keywords: | electrochemistry electrolytes interfaces salt effect water-in-salt |