Salt nanoconfinement in zirconium-based metal organic frameworks leads to pore-size and loading-dependent ionic conductivity enhancement

Schematic representation of the disruption of salt structure due to the confinement of salt in the pores of a metal organic framework (MOF), resulting in the increase of ion mobility.

Scientific Achievement

The nanoscale confinement of [NEt4][TFSI] in three isostructural MOFs enhanced the conductivity of composites relative to neat [NEt4][TFSI] by up to a factor of 50. The conductivity increases with the increase in pore size and maximum conductivity was achieved with a salt loading slightly less than that required for complete filling of the MOF pores.

Significance and Impact

Spatially confining [NEt4][TFSI] in isoreticular, microporous, Zr-based stable and insulating MOFs leads to pore-size and loading-dependent enhancement of ionic conductivity. The melt loading of salt under solvent-free conditions provides a means to study the solid-state ionic conductivity of the salt-MOF composites in the absence of competing solvent-mediated pathways. [NEt4][TFSI] serves as a model for other salts such as LiTFSI, Mg(TFSI)2, etc. that are of interest for solid electrolytes in metal-ion batteries.

Research Details

  • The salt loading was monitored via PXRD and DSC.
  • AC electrochemical impedance spectroscopy was used to determine the ionic conductivity of several MOF-[NEt4][TFSI] composites, with varying composition, as a function of temperature. The conductivity for all composites increased as a function of temperature.

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DOI: 10.1039/D0CC03147J

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