A family of lithium-ion-conducting composite polymer-glass electrolytes containing the glass composition 14Li2O–9Al2O3–38TiO2–39P2O5 (abbreviated as (LiAlTiP) x O y ) with high ionic conductivity, an excellent electrochemical stability range, and high compatibility with lithium insertion anodes is described. An optimized composition has a room temperature conductivity of 1.7×10−4 Scm−1, an Li+ transference number of 0.39, and an electrochemical stability window to +5.1V versus Li/Li+. It also has good interfacial stability under both open-circuit and lithium metal plating–stripping conditions and provides good shelf-life.