Lithium-ion conduction in liquid-crystalline columnar Pd(II) nanoassemblies

Abstract

Liquid crystalline electrolytes are emerging as a promising class of functional materials for energy storage applications. They offer the ability to operate under anhydrous conditions without the presence of acids or flammable solvents, allowing high operating temperatures. Herein, the liquid crystalline phase of a bispyrazolate Pd(II) metallomesogen is used as a platform for Li-ion conduction, taking advantage of the existence of nanochannels in the hexagonal columnar mesophase. Li-doped liquid crystal composites have been prepared with different lithium content, and their mesomorphic properties and ionic conductivities were studied. It was found that the intercalation of lithium ions between molecules does not hinder the formation of the mesophase but rather extends the temperature range in which it is stable due to the existence of ion–dipole interactions between the lithium ions and the uncoordinated N-pyrazolic atoms, leading to lower melting and higher clearing temperatures. High Li-ion conductivity was found in the solid and liquid crystalline phases by complex impedance spectroscopy. The optimally doped composite with an 8:2 (metallomesogen:LiTFSI) molar ratio reaches conductivity values as high as 1.89 × 10–4 Ω–1 cm–1. The work presented is expected to pave the way for a promising class of liquid crystalline Li-ion electrolytes based on metallomesogens.