Exploration of phase diagram, structural and dynamic behavior of [HMG][FSI] mixtures with NaFSI across an extended composition range

Karolina Biernacka, Faezeh Makhlooghiazad, Ivan Popov, Haijin Zhu, Jean Noël Chotard, Luke A. O’Dell, Alexei P. Sokolov, Jennifer M. Pringle, Maria Forsyth*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

5 Scopus citations

Abstract

Hexamethylguanidinium bis(fluorosulfonyl)imide ([HMG][FSI]) has recently been shown to be a promising solid state organic ionic plastic crystal with potential application in advanced alkali metal batteries. This study provides a detailed exploration of the structural and dynamic behavior of [HMG][FSI] mixtures with the sodium salt NaFSI across the whole composition range from 0 to 100 mol%. All mixtures are solids at room temperature. A combination of differential scanning calorimetry (DSC), synchrotron X-ray diffraction (SXRD) and multinuclear solid state NMR spectroscopy is employed to identify a partial phase diagram. The 25 mol% NaFSI/75 mol% [HMG][FSI] composition presents as the eutectic composition with the eutectic transition temperature at 44 °C. Both DSC and SXRD strongly support the formation of a new compound near 50 mol% NaFSI. Interestingly, the 53 mol% NaFSI [HMG][FSI] composition was consistently found to display features of a pure compound whereas the 50 mol% materials always showed a second phase. Many of the compositions examined showed unusual metastable behaviour. Moreover, the ion dynamics as determined by NMR, indicate that the Na+ and FSI anions are signifcantly more mobile than the HMG cation in the liquid state (including the metastable state) for these materials.

Original languageEnglish
Pages (from-to)16712-16723
Number of pages12
JournalPhysical Chemistry Chemical Physics
Volume24
Issue number27
DOIs
StatePublished - 18 Jun 2022
Externally publishedYes

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