Electric Dipoles and Ionic Conductivity in a Na+ Glass Electrolyte

Abstract

Glass, unlike a crystalline solid, contains atoms and molecules that do not occupy fixed positions. A glass that contains molecules that attract one another can age with time. We report such a glass that contains A2O and (OA)− electric dipoles (A = Li or Na). At a temperature T < 1.2Tg ≈ 110°C (Tg is the glass transition temperature) the electric dipoles coalesce with time into clusters within which, unlike in ice, some dipoles condense into ferroelectric, negatively charged molecules locally charge-compensated by weakly attracted A+ ions. In an applied electric field, the dipoles are oriented and, over time depending on the T < 110°C, are aligned parallel to the field axis to yield a solid A+ electrolyte with an ionic conductivity σi > 10−2 S cm−1 and a huge dielectric constant that makes it suitable for many applications, including safe rechargeable batteries of high energy density and long cycle life.