article published yes Roza Bouchal author Zhujie Li author Chandra Bongu author Steven Le Vot author Romain Berthelot author Benjamin Rotenberg author Frederic Favier author Stefan Alexander Freunberger author A8CA28E6-CE23-11E9-AD2D-EC27E66974250000-0003-2902-5319 Mathieu Salanne author Olivier Fontaine author StFr department Water-in-salt electrolytes based on highly concentrated bis(trifluoromethyl)sulfonimide (TFSI) promise aqueous electrolytes with stabilities approaching 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. https://research-explorer.ista.ac.at/download/8057/8401/2020_AngChemieDE_Bouchal.pdf application/pdfno https://creativecommons.org/licenses/by/4.0/ Wiley2020 eng 0044-8249 1521-375710.1002/ange.202005378 1323716047-16051 Bouchal, Roza, Zhujie Li, Chandra Bongu, Steven Le Vot, Romain Berthelot, Benjamin Rotenberg, Frederic Favier, Stefan Alexander Freunberger, Mathieu Salanne, and Olivier Fontaine. “Competitive Salt Precipitation/Dissolution during Free‐water Reduction in Water‐in‐salt Electrolyte.” <i>Angewandte Chemie</i>. Wiley, 2020. <a href="https://doi.org/10.1002/ange.202005378">https://doi.org/10.1002/ange.202005378</a>. R. Bouchal <i>et al.</i>, “Competitive salt precipitation/dissolution during free‐water reduction in water‐in‐salt electrolyte,” <i>Angewandte Chemie</i>, vol. 132, no. 37. Wiley, pp. 16047–16051, 2020. R. Bouchal, Z. Li, C. Bongu, S. Le Vot, R. Berthelot, B. Rotenberg, F. Favier, S.A. Freunberger, M. Salanne, O. Fontaine, Angewandte Chemie 132 (2020) 16047–16051. Bouchal R, Li Z, Bongu C, Le Vot S, Berthelot R, Rotenberg B, Favier F, Freunberger SA, Salanne M, Fontaine O. 2020. Competitive salt precipitation/dissolution during free‐water reduction in water‐in‐salt electrolyte. Angewandte Chemie. 132(37), 16047–16051. Bouchal R, Li Z, Bongu C, et al. Competitive salt precipitation/dissolution during free‐water reduction in water‐in‐salt electrolyte. <i>Angewandte Chemie</i>. 2020;132(37):16047-16051. doi:<a href="https://doi.org/10.1002/ange.202005378">10.1002/ange.202005378</a> Bouchal, R., Li, Z., Bongu, C., Le Vot, S., Berthelot, R., Rotenberg, B., … Fontaine, O. (2020). Competitive salt precipitation/dissolution during free‐water reduction in water‐in‐salt electrolyte. <i>Angewandte Chemie</i>. Wiley. <a href="https://doi.org/10.1002/ange.202005378">https://doi.org/10.1002/ange.202005378</a> Bouchal, Roza, et al. “Competitive Salt Precipitation/Dissolution during Free‐water Reduction in Water‐in‐salt Electrolyte.” <i>Angewandte Chemie</i>, vol. 132, no. 37, Wiley, 2020, pp. 16047–51, doi:<a href="https://doi.org/10.1002/ange.202005378">10.1002/ange.202005378</a>. 80572020-06-29T16:15:49Z2023-09-05T15:47:50Z