Organic ionic plastic crystals (OIPCs) have been focused as new solid electrolytes because they have some unique properties such as nonflammability, nonvolatility, plasticity and relatively high ionic conductivity at room temperature. Recently, we reported that 1-ethyl-1-methylpyrrolidinium bis(fluorosulfonyl)amide ([P12][FSA]) showed a high melting point (Tm) with a OIPC behavior in a wide temperature range (-20 - 205°C) and a high ionic conductivity value reaching 1.23x10-6 S cm-1 at 25°C. In this study, three kinds of pyrrolidinium-based OIPCs with various side chain length were synthesized. OIPC/Li salt composites were prepared by doping lithium bis(fluorosulfonyl)amide (LiFSA) or lithium bis(trifluoromethylsulfonyl)amide (LiTFSA). The DSC heating trace of all the OIPCs synthesized in this study exihited the solid-solid phase transitions in the range of -40°C and -20°C, and their Tm values were over 100°C with a small entropy change of fusion (&lt; 20 J K-1 mol-1). The OIPC with two ethyl side chains, 1,1-diethylpyrrolidinium bis(fluorosulfonyl)amide ([P22][FSA]), exhibited the lowest Tm value among those. The X-ray diffraction patterns of neat OIPCs suggested the lattice spacing was increased as the side chains were lengthened. The ionic conductivity value of [P22][FSA] was 8.44x10-6 S cm-1 at 25°C, which was higher than that of [P12][FSA]. The ionic conductivity of OIPCs was improved by adding Li salts. The ionic conductivity value of [P22][FSA]/LiTFSA composite was 1.19x10-4 S cm-1 at 25°C, which was about twice as high as that of [P22][FSA]/LiFSA (6.40x10-5 S cm-1). However, [P22][FSA]/LiTFSA exhibited much lower Tm value than [P22][FSA]/LiFSA. [P22][FSA]/LiFSA was more studied as a solid electrolyte material because of its promising thermal property and high ionic conductivity. In spite of its low mole fraction of lithium-ion (0.025), lithium transference number of [P22][FSA]/LiFSA was estimated 0.26. This result indicated lithium-ions were preferentially transferred in [P22][FSA]. In the results of cyclic voltammetry, stable lithium plating/stripping cycling behavior was observed in [P22][FSA]/LiFSA.

Development of flexible solid electrolytes composed of plastic crystals (III): Effect of lithium salt species on ionic conductivity

255th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.