Ionic Conductivity in Solid Electrolytes Based on Lithium Aluminosilicate Glass and Glass‐Ceramic

Abstract

Ionic conductivity measurements on , i.e., , glass and glass‐ceramic have shown these materials to be good lithium ion conducting solid electrolytes at high temperatures. This composition crystallizes in the β‐eucryptite structure which is attractive for solid electrolyte applications because of its low thermal expansion. The glasses were prepared by quenching from the melt and were annealed to remove strain. The glass‐ceramic (β‐eucryptite) samples were crystallized (aided by and nucleating agents) by using a heat‐treatment determined through differential thermal analysis. The conductivity (σ) was measured (to 650°C) with a variety of techniques, including 2‐terminal a.c., 3‐terminal guarded a.c., 4‐terminal a.c., 2‐terminal d.c., and a pulsed method. Vapor‐deposited Cr contacts were used. Different sample geometries, contact geometries, and measurement circuitries were employed. The results from the various measurements are in excellent agreement. The a‐c techniques appear to be the most versatile and accurate of the methods examined. In these materials the conductivity is thermally activated with typical values of and for the glasses, and and for the glass‐ceramics. The and nucleating agents [concentrations up to 2.8 mole per cent (m/o)] did not appear to influence the ionic conductivity. Data were also taken on a (β‐eucryptite) glass‐ceramic with a composition near the β‐eucryptite/β‐spodumene phase boundary. The ionic conductivity of this material is lower than that of the materials. Data are also provided on β‐spodumene material.