Plastic Crystals Utilising Small Ammonium Cations and Sulfonylimide Anions as Electrolytes for Lithium Batteries

Ruhamah Yunis, Danah Al-Masri, Anthony F. Hollenkamp, Cara M. Doherty, Haijin Zhu, Jennifer M. Pringle

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28 Scopus citations


Organic ionic plastic crystals (OIPCs) are increasingly promising as a class of solid-state electrolyte for developing safer lithium batteries. However, their advancement relies on expanding the range of well-characterised cation/anion combinations. Here, we report the synthesis and characterization of OIPCs utilising small ammonium cations tetramethylammonium ([N1111]+), triethylmethylammonium ([N1222]+) and tetraethylammonium ([N2222]+), chosen to encourage significant rotational and translational motion, with the charge-diffuse and electrochemically stable bis(fluorosulfonyl)imide ([FSI]) and bis(trifluoromethanesulfonyl)imide ([NTf2]) anions. To investigate the physico-chemical properties of the OIPCs, the free volume was measured by positron annihilation spectroscopy (PALS) and correlated with the ionic conductivity and thermal analysis (DSC). Solid-state NMR analysis of the salts, is also reported. The salts with the less symmetric cation, [N1222][FSI] and [N1222][NTf2], were identified as the most promising electrolyte materials, and thus the electrochemical properties after mixing with 10 and 90 mol% lithium bis(fluorosulfonyl)imide (LiFSI) or lithium bis(trifluoromethanesulfonyl)imide (LiNTf2), respectively, were investigated. This study demonstrates the efficacy of these OIPC materials as new quasi-solid state electrolytes with advantageous properties such as high conductivity, good thermal and electrochemical properties, the ability to incorporate high lithium salt concentrations and support efficient lithium electrochemistry.

Original languageEnglish
Article number070529
JournalJournal of the Electrochemical Society
Issue number7
StatePublished - 5 Jan 2020
Externally publishedYes


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