Aqueous Solid Electrolyte Interphases in Water‐in‐Salt Electrolytes and Beyond

The key issue with advancing aqueous batteries is the narrow electrochemical stability window (ESW) of the electrolyte; past efforts have focused on extending the water decomposition limits, principally using the highly concentrated water‐in‐salt electrolytes (WiSEs) with limited “free” water. Howev...

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Main Authors: Radhika Krishna Hema, Alberto Varzi
Format: Article
Language:English
Published: Wiley-VCH 2025-07-01
Series:ChemElectroChem
Subjects:
Online Access:https://doi.org/10.1002/celc.202500129
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author Radhika Krishna Hema
Alberto Varzi
author_facet Radhika Krishna Hema
Alberto Varzi
author_sort Radhika Krishna Hema
collection DOAJ
description The key issue with advancing aqueous batteries is the narrow electrochemical stability window (ESW) of the electrolyte; past efforts have focused on extending the water decomposition limits, principally using the highly concentrated water‐in‐salt electrolytes (WiSEs) with limited “free” water. However, the high salt content largely complicates practicability and long‐term performance, necessitating alternative strategies to enhance ESWs without relying entirely on huge amounts of salt. Forming stable, functional interphases on electrode surfaces can help realize this vision by masking the electrode from water, thereby inducing high overpotentials for hydrolysis. Solid electrolyte interphase (SEI) formation on the negative electrode has been observed to be particularly tricky to navigate through, due to the faster kinetics of water reduction or the hydrogen evolution reaction (HER), something popularly termed the “cathodic challenge.” We aim, through this concept review, to deliver a comprehensive overview of the mechanistic and electrochemical understandings that have been recognized over the years about the SEI formation in aqueous electrolytes. A broad analysis is drawn ranging from diluted to highly concentrated systems (WiSEs), while highlighting current challenges and limitations. The discussion is kept limited to Li‐based batteries, which however, in most cases, could also be extrapolated to Na and K‐based ones.
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spelling doaj-art-697c36758b6c4bfc9aebac973213133a2025-08-20T03:56:46ZengWiley-VCHChemElectroChem2196-02162025-07-011215n/an/a10.1002/celc.202500129Aqueous Solid Electrolyte Interphases in Water‐in‐Salt Electrolytes and BeyondRadhika Krishna Hema0Alberto Varzi1Helmholtz Institute Ulm (HIU) Helmholtzstraße 11 D‐89081 Ulm GermanyHelmholtz Institute Ulm (HIU) Helmholtzstraße 11 D‐89081 Ulm GermanyThe key issue with advancing aqueous batteries is the narrow electrochemical stability window (ESW) of the electrolyte; past efforts have focused on extending the water decomposition limits, principally using the highly concentrated water‐in‐salt electrolytes (WiSEs) with limited “free” water. However, the high salt content largely complicates practicability and long‐term performance, necessitating alternative strategies to enhance ESWs without relying entirely on huge amounts of salt. Forming stable, functional interphases on electrode surfaces can help realize this vision by masking the electrode from water, thereby inducing high overpotentials for hydrolysis. Solid electrolyte interphase (SEI) formation on the negative electrode has been observed to be particularly tricky to navigate through, due to the faster kinetics of water reduction or the hydrogen evolution reaction (HER), something popularly termed the “cathodic challenge.” We aim, through this concept review, to deliver a comprehensive overview of the mechanistic and electrochemical understandings that have been recognized over the years about the SEI formation in aqueous electrolytes. A broad analysis is drawn ranging from diluted to highly concentrated systems (WiSEs), while highlighting current challenges and limitations. The discussion is kept limited to Li‐based batteries, which however, in most cases, could also be extrapolated to Na and K‐based ones.https://doi.org/10.1002/celc.202500129aqueous batterieselectrochemical stability windowsolid electrolyte interphaseswater‐in‐salt electrolytes
spellingShingle Radhika Krishna Hema
Alberto Varzi
Aqueous Solid Electrolyte Interphases in Water‐in‐Salt Electrolytes and Beyond
ChemElectroChem
aqueous batteries
electrochemical stability window
solid electrolyte interphases
water‐in‐salt electrolytes
title Aqueous Solid Electrolyte Interphases in Water‐in‐Salt Electrolytes and Beyond
title_full Aqueous Solid Electrolyte Interphases in Water‐in‐Salt Electrolytes and Beyond
title_fullStr Aqueous Solid Electrolyte Interphases in Water‐in‐Salt Electrolytes and Beyond
title_full_unstemmed Aqueous Solid Electrolyte Interphases in Water‐in‐Salt Electrolytes and Beyond
title_short Aqueous Solid Electrolyte Interphases in Water‐in‐Salt Electrolytes and Beyond
title_sort aqueous solid electrolyte interphases in water in salt electrolytes and beyond
topic aqueous batteries
electrochemical stability window
solid electrolyte interphases
water‐in‐salt electrolytes
url https://doi.org/10.1002/celc.202500129
work_keys_str_mv AT radhikakrishnahema aqueoussolidelectrolyteinterphasesinwaterinsaltelectrolytesandbeyond
AT albertovarzi aqueoussolidelectrolyteinterphasesinwaterinsaltelectrolytesandbeyond