Ionic Glass Electrolytes—The Role of Medium Range Order in Mechanics and Ion Conduction

One of the most intriguing classes of solid-state electrolytes is the family of ionic glasses. Ionic glasses are glasses that are primarily bound together with ionic bonds such as amorphous Li₃PO₄ and amorphous Li₄SiO₄ of which LiPON is the most well-known. Here we provide an in-depth structural characterization of the amorphous ionic glasses LiPON and LiSiPON with high Li content. Based on ab-initio molecular dynamics simulations, the structure of these materials is identified as an inverted glass structure with either isolated polyanion tetrahedra or polyanion dimers suspended in a Li⁺ matrix. Based on neutron scattering data, this type of inverted structure leads to a significant amount of medium-range ordering as demonstrated by neutron total scattering. Further analysis highlights correlations between the degree of medium range order and the ionic conductivity and mechanical ductility. The combination of tunable ionic conductivity and ductility, has significant implications for solid electrolyte design that can enable next generation high-energy high-power solid state-batteries.