Ionic conductivity and molecular dynamic behavior in supramolecular ionic networks; the effect of lithium salt addition

• Novel amorphous and semicrystalline supramolecular ionic networks, iNets, have been synthesised by self-assembly of dicationic and dianionic molecules.
• Significant enhancement of conductivity of the semicrystalline iNets has been achieved upon doping with LiTFSI.
• Solid state NMR of the semicrystalline iNets shows narrower lines upon doping due to increased mobility in the network.

Supramolecular ionic networks combine singular properties such as self-healing behaviour and ionic conductivity. In this work we present an insight into the ionic conductivity and molecular dynamic behaviour of an amorphous and semicrystalline supramolecular ionic networks (iNets) that were synthesised by self-assembly of difunctional imidazolium dicationic molecules coupled with (trifluoromethane-sulfonyl) imide dianionic molecules. Relatively low ionic conductivity values were obtained for the semicrystalline iNet below its melting point (Tm = 101 °C) in comparison with the amorphous iNet for which the conductivity significantly increased (∼3 orders of magnitude) above 100 °C. Upon LiTFSI doping, the semicrystalline iNet reached conductivity values ∼ 10−3 S cm−1 due to enhanced mobility of the network which was supported by solid-state static NMR. Furthermore, the overlapping of 19F and 7Li resonance lines from both the semicrystalline network and the LiTFSI suggests fast molecular motions.

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