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

The use of Ge as an alloying agent for Li negative electrodes in molten salt cells was studied in a cell of the type LiAl/LiCl + KCl/Li--Ge alloy between 360 and 440 deg C. The Li--Ge electrode could be charged and discharged reversibly with Li. 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 LiGe, Li sub 9 Ge sub 4 , Li sub 16 Ge sub 5 , Li sub 15 Ge sub 4 and Li sub 22 Ge sub 5 . The Gibbs free energies of formation for these alloys were determined by integrating the coulometric titration curve to the appropriate Li composition. EMF temp. dependencies of the four most negative two-phase plateau regions were measured between 360 and 440 deg 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 Li and Ge in the observed plateaus. Preliminary corrosion tests of low-carbon steel toward Ge were conducted. A comparison of Li--Ge alloys was made with the two dominant alloys used in the Li alloy/metal sulfide battery: Li--Al and Li--Si. 33 ref.--AA