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Competitive Salt Precipitation/Dissolution During Free‐Water Reduction in Water‐in‐Salt Electrolyte
Author(s) -
Bouchal Roza,
Li Zhujie,
Bongu Chandra,
Le Vot Steven,
Berthelot Romain,
Rotenberg Benjamin,
Favier Frederic,
Freunberger Stefan A.,
Salanne Mathieu,
Fontaine Olivier
Publication year - 2020
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.202005378
Subject(s) - electrolyte , dissolution , salt (chemistry) , inorganic chemistry , chemistry , precipitation , aqueous solution , interphase , cathodic protection , electrochemistry , electrode , chemical engineering , organic chemistry , physics , biology , meteorology , engineering , genetics
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.