Efficient Exploration of Highly Conductive Pyrrolidinium-based Ionic Plastic Crystals Using Materials Informatics

Ionic plastic crystals (IPCs), which are soft crystals with plasticity and ionic conductivity, are expected to be applied as solid electrolytes in battery applications. Further improvement of ionic conductivity is necessary for practical use as an electrolyte for energy storage devices. Materials Informatics (MI) is a method of incorporating information science in materials development. In this research, MI is being used to develop IPCs with high ionic conductivity. By using informatics science in addition to chemical knowledge, this research can be carried out efficiently and innovatively. The synthesis of eight new compounds resulted in six of them being solid at room temperature, while two of them were in a liquid state, namely ionic liquids. We evaluated the phase transition temperatures and ionic conductivity for each compound. Notably, N-ethyl-N-methylpyrrolidinium trifluoromethyltrifluoroborate ([C2mpyr][CF3BF3]) exhibited a high ionic conductivity of 1.75×10-4 S cm-1 at 25 oC, which is one of the highest values reported among IPCs to date. The combination of an experimental and MI based approach revealed an improved understanding of the relationship between ion size and ionic conductivity for a series of pyrrolidinium-based IPCs, and it is expected that further improvements to this approach will yield greater understanding of structure-property relationships.