--- res: bibo_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. Here, we reveal two distinct reduction potentials for the chemical environments of 'free' and 'bound' water and that both contribute to SEI formation. Free-water is reduced ~1V above bound water in a hydrogen evolution reaction (HER) and 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. @eng bibo_authorlist: - foaf_Person: foaf_givenName: Roza foaf_name: Bouchal, Roza foaf_surname: Bouchal - foaf_Person: foaf_givenName: Zhujie foaf_name: Li, Zhujie foaf_surname: Li - foaf_Person: foaf_givenName: Chandra foaf_name: Bongu, Chandra foaf_surname: Bongu - foaf_Person: foaf_givenName: Steven foaf_name: Le Vot, Steven foaf_surname: Le Vot - foaf_Person: foaf_givenName: Romain foaf_name: Berthelot, Romain foaf_surname: Berthelot - foaf_Person: foaf_givenName: Benjamin foaf_name: Rotenberg, Benjamin foaf_surname: Rotenberg - foaf_Person: foaf_givenName: Fréderic foaf_name: Favier, Fréderic foaf_surname: Favier - foaf_Person: foaf_givenName: Stefan Alexander foaf_name: Freunberger, Stefan Alexander foaf_surname: Freunberger foaf_workInfoHomepage: http://www.librecat.org/personId=A8CA28E6-CE23-11E9-AD2D-EC27E6697425 orcid: 0000-0003-2902-5319 - foaf_Person: foaf_givenName: Mathieu foaf_name: Salanne, Mathieu foaf_surname: Salanne - foaf_Person: foaf_givenName: Olivier foaf_name: Fontaine, Olivier foaf_surname: Fontaine bibo_doi: 10.1002/anie.202005378 bibo_issue: '37' bibo_volume: 59 dct_date: 2020^xs_gYear dct_identifier: - UT:000541488700001 dct_isPartOf: - http://id.crossref.org/issn/1433-7851 - http://id.crossref.org/issn/1521-3773 dct_language: eng dct_publisher: Wiley@ dct_title: Competitive salt precipitation/dissolution during free‐water reduction in water‐in‐salt electrolyte@ fabio_hasPubmedId: '32390281' ...