Nanoheterogeneity of LiTFSI Solutions Transitions Close to a Surface and with Concentration

Interfacial structures of 1-3 nm in force curves from surface force apparatus (SFA) measurements in LiTFSI/H2O systems of various concentrations on a mica surface

Scientific Achievement

The interfacial structure of the water-in-salt electrolytes (WiSE) on a mica surface is investigated. Nanostructures of 1nm to 3 nm are observed. The size of the nanostructure varies depending on the concentration of the LiTFSI/H2O system.

Significance and Impact

Our study suggests the nanoheterogeneity of the WiSE at the solid/electrolyte interfacial region, and corresponds with previous computational and experimental studies on the bulk nanoherterogeneity of the electrolyte.

Research Details

  • WiSE/mica surface structure is studied with AFM and surface force apparatus (SFA).
  • Smaller layered structures are observed in AFM (< 1nm), at a closer distance to the mica surface (D < 4 nm).
  • Larger nanostructures are observed in SFA farther from the mica surface (D > 4 nm), ranging from 1 nm to 3 nm.
  • The nanostructure size increases with higher concentration.
  • In 18 m-21 m system, Li(H2O)x+, H2O, [Li(H2O)x]+[TFSI]-)y, and nanoclusters of 2nm-3nm are observed respectively from the mica surface to the bulk electrolyte.
  • The interfacial structure exhibits a hysteresis for 8 m, possibly due to the breakdown of nanostructure with a lower salt-to-water ratio.

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DOI: 10.1021/acs.nanolett.1c00167

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