Local Li cation coordination and dynamics in novel solid electrolytes

Van Wüllen L., Echelmeyer T., Voigt N., Köster T.K.-J., Schiffmann G.

Abstract

Research on solid ionic conductors for use as electrolytes in all solid state batteries still constitutes a rather vivid branch of today´s materials science. Despite enormous efforts, neither the development of a solid electrolyte fulfilling the key requirements such as mechanical stability and high ionic conductivity at ambient temperature has been successful nor has an extended understanding of the local Li coordination motifs in the often amorphous systems been obtained. In this contribution, recent progress both in the development of novel solid state electrolytes with high ionic conductivity and mechanical stability and in the characterization of the local Li coordination motifs in these electrolytes from our laboratory is presented. The work was performed as a project within the framework of the Collaborative Research Centre SFB 458 "Ionic Motion in Materials with Disordered Structures - From Elementary Steps to Macroscopic Transport". Results will be given for polymer electrolytes based on polyethylene oxide (PEO), polyphosphazene (PPZ) and polyacrylonitrile (PAN) with various Li salts, nano-composites of these polymer electrolytes and Al2O3 as a ceramic filler, novel inorganic/organic hybrid electrolytes, in which a mixture of an ionic liquid and Li salt is confined within the pore system of a SiO2 glass, and a crystalline electrolyte, Li5La3Nb2O12. Employing a range of advanced solid state NMR methodologies including dipolar based NMR techniques and pulsed field gradient (PFG) NMR and impedance spectroscopy we were able to obtain a detailed knowledge about the local Li cation coordination motifs and the mechanism of Li transport in these electrolytes. Especially the hybrid electrolytes and the salt rich PAN based polymer electrolytes were identified as rather promising materials which combine a high ionic conductivity and mechanical stability.