Microscopic Understanding of the Ionic Networks of “Water-in-Salt” Electrolytes

(a) SAXS profile of LiTFSI aqueous electrolytes at different concentrations under room temperature. The data is offset for clarity. (b) d spacing is plotted as a function of LiTFSI concentrations at room temperature. d spacing is calculated by d = 2π/q. Three concentration regimes are divided: (I) low concentration, (II) medium concentration, and (III) high concentration.

Scientific Achievement

We conduct  SAXS study to investigate the solvation behavior of LiTFSI aqueous solutions in a wide range of concentration from 1 to 20 m. Also, the stability of these samples under different temperatures is studied by in situ SAXS measurements.

Significance and Impact

The paper shows that TFSI- solvated  structure and TFSI- network can coexist at a particular concentration, and temperature changes will lead to one structure’s formation or disappearance. Also, the TFSI- network is the key to obtain a stable electrochemical window under relatively high temperatures.

Research Details

  • TFSI- anions can form two different structures, TFSI- solvated structure and TFSI- network.
  • At low concentrations, the TFSI- solvated structure is the main solvated structure. TFSI- solvated structure and TFSI- network coexist as the concentration increases to the medium concentration. At high concentrations, only the TFSI- network remains.
  • Increasing temperature may promote the conversion between bulk water and interfacial water. The structural changes caused by the temperature are the reversible process.

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DOI: 10.34133/2021/7368420

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