Sulphate-based solid electrolytes: properties and applications

Abstract

Sulphate-based solid electrolytes can have conductivities as high as 3 (Ω cm) −1, as is the case in pure Li 2SO 4 at a temperature of 800°C. For binary systems highly conducting phases can be found down to at least 415°C. If additional components are added conductivities exceeding 10 −3 (Ω cm) −1 can be obtained at room temperature. The conductivity is due to cation mobility and, in contrast to other solid electrolytes such as beta-alumina and AgI-based double salts, both mono- and divalent cations are mobile. Phase diagrams for the systems containing Li 2SO 4 combined with Na 2SO 4, K 2SO 4, Rb 2SO 4, Cs 2SO 4, MgSO 4, CaSO 4, and ZnSO 4 have been constructed. A number of galvanic cells using anodes made from Mg, Ca, and Zn have been tested at elevated temperatures. A Mg|Li 1.72Mg 0.14SO 4|MnO 2 cell gave an open-circuit voltage of 2.3 V and a power density of 400 W/kg at 745°C. Ag|electrolyte|I 2 cells have been tested at room temperature.