Investigation of Imidazole-Based Lithium Conducting Materials

This study aims to develop novel polyelectrolytes including lithiated imidazole heterocycles for use in lithium ion rechargeable batteries. Lithium ion local mobility in these materials is characterized by 6.7Li solid-state NMR. By comparing these results with macroscopic ionic conductivity, measured by impedance spectroscopy, we will be able to develop a picture of the ionic conductivity at the microscopic level. Multinuclear solid state NMR provides information on microscopic interactions including ionic mobility and ring reorientations which govern the efficiency of conductivity. Our research includes 6.7Li variable MAS NMR studies at intermediate spinning speeds, relaxation investigations to determine spin-lattice relaxation times (T1) of lithium ion hopping, and 2D exchange spectroscopy to determine possible chemical exchange processes. A very long T1(135 s at ambient temperature) and an activation energy Ea = 17.2 kJ/mol suggests rigid molecule structure and the absence of the ring reorientation of the model compound, lithium imidazolium (LiIm). We compare this to the behavior of LiIm doped with lithium methanesulfonate, which we show to form a new ionic complex with lower T1 and corresponding lower activation energy. With the goal of creating new polyelectrolytes, we have synthesized electrolytes incorporating lithiated imidazole rings, where lithium transport may be independent of polymer-backbone flexibility, and thus polymers with high Tg may be viable. Such materials are highly desirable for secondary lithium polymer battery applications.