Water or Anion? Zn2+ Solvation Environment in Mixed Zn2+/Li+ Water-in-Salt Electrolytes

Combined experimental and molecular simulation studies show that Zn2+ are predominately solvated by six water molecules in the mixed Zn(TFSI)2/LiTFSI water-in-salt electrolytes (WISE)

Scientific Achievement

Zn2+ cations are mainly solvated by six waters in their first solvation shell, while TFSI- anions are excluded from solvation in the WISE electrolyte consisting of 1 m Zn(TFSI)2 and 20 m LiTFSI although the TFSI- concentration is as high as 22 m.

Significance and Impact

The results shown here suggest that the unusual high stability of the Zn2+/Li+ WISE electrolytes is not due to the changes in the Zn2+ solvation environment in the bulk and additional work needs to be performed to explain the underlying mechanisms.

Research Details

▪Mixed Zn(TFSI)2/LiTFSI WISE electrolytes were studied using multimodal X-ray total scattering, X-ray absorption spectroscopy (XANES & EXAFS), FTIR experiments, and classical molecular dynamics (MD) simulations.

▪MD simulations were validated against X-ray total scattering and FTIR experiments.

▪EXAFS results were fit to model clusters that satisfy the symmetric octahedral coordination environment suggested by XANES.

▪All techniques point to the same Zn(H2O)62+ solvation environment.

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DOI: 10.1021/acsenergylett.1c01624

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