Potential-Dependent Layering in the Electrochemical Double Layer of Water-in-Salt Electrolytes

Ruixian Zhang, Mengwei Han, Kim Ta, Kenneth E. Madsen, Xinyi Chen, Xueyong Zhang, Rosa M. Espinosa-Marzal, Andrew A. Gewirth

Research output: Contribution to journalArticlepeer-review


Water-in-salt electrolytes (WiSE) are concentrated aqueous electrolytes recently developed that are of great interest because of their possible relevance for batteries. The origin for their promising application has been ascribed to the formation of percolating nanodomains in the bulk. However, the interfacial structure of WiSE still remains to be understood. In this paper, we characterize the potential-dependent double layer of a LiTFSI-based electrolyte on a charged electrode surface. Ultramicroelectrode (UME) measurements reveal a surface-confinement effect for a ferricyanide redox species at the electrode/WiSE interface. Potential-dependent atomic force microscopy (AFM) shows the presence of layers, the structure of which changes with the applied potential. Thicker layers (6.4 and 6.7 Å) are observed at positive potentials, associated with [Li(H2O)x]+([TFSI]-)y ion pairs, while thinner layers (2.8 and 3.3 Å) are found at negative potentials and associated with [Li(H2O)x]+ alone. Vibrational spectroscopy shows that the composition of the double layer also changes with potential, where [TFSI]- is enriched at positive and [Li(H2O)x]+ enriched at negative potentials.

Original languageEnglish (US)
Pages (from-to)8086-8094
Number of pages9
JournalACS Applied Energy Materials
Issue number8
StatePublished - Aug 24 2020


  • aqueous electrolytes
  • atomic force microscopy
  • batteries
  • concentrated electrolytes
  • double layer

ASJC Scopus subject areas

  • Chemical Engineering (miscellaneous)
  • Energy Engineering and Power Technology
  • Electrochemistry
  • Materials Chemistry
  • Electrical and Electronic Engineering


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