Thermodynamic Properties of the Lithium‐Silicon System

The feasibility of using silicon as an alloying agent for the negative electrode in cells was determined by studying cells of the type The Li‐Si electrode was found reversible with respect to lithium between 650° and 725°K. The nonstoichiometry ranges of the respective Li‐Si compounds and electromotive forces (emf's) in the two‐phase regions of the Li‐Si phase diagram between 650° and 750°K were measured. These studies indicated a new compound, , which was confirmed by x‐ray diffraction, scanning electron microscope, and differential thermal analysis. The activities and relative partial molar properties of lithium and silicon in the two‐phase regions of the phase diagram were calculated from the emf's in the temperature range 650°–750°K, and the standard free energy of formation for the compounds , , , and , were also determined.