Thermodynamic Studies of Li‐Ge Alloys: Application to Negative Electrodes for Molten Salt Batteries

Abstract

The use of germanium as an alloying agent for lithium negative electrodes in molten salt cells was studied in a cell of the typebetween 360° and 440°C. The Li‐Ge electrode could be charged and discharged reversibly with lithium. Five distinct two‐phase plateau regions, together with a suspected sixth region, were identified by coulometrically charging and discharging the cell. The five distinct two‐phase plateau regions are believed to occur during the formation of,,,, and. The Gibbs free energies of formation for these alloys were determined by integrating the coulometric titration curve to the appropriate lithium composition. EMF temperature dependencies of the four most negative two‐phase plateau regions were measured between 360° and 440°C, and the entropy of formation was calculated for each alloy associated with these plateaus. EMF measurements also allowed the determination of the partial molar Gibbs free energy and the corresponding activities of lithium and germanium in the observed plateaus. Preliminary corrosion tests of low‐carbon steel toward germanium were conducted. A comparison of lithium‐germanium alloys was made with the two dominant alloys used in the lithium‐alloy/metal sulfide battery: lithium‐aluminum and lithium‐silicon.