Relationships among Electrochemical, Thermodynamic, and Oxygen Potential Quantities in Lithium‐Transition Metal‐Oxygen Molten Salt Cells

Abstract

The interdependence of thermodynamic parameters, phase equilibria, and electrochemical measurements can be used as a powerful tool in the development of high specific energy cells. These principles were used in the analysis of electrochemical experiments performed on ternary lithium‐transition metal‐oxide positive electrodes. The free energies of formation of , , , and were found to be −178.21, −399.88, −154.18, and −131.62 kcal/mol at 400°C. The electrochemical displacement reactions were found to be reversible in molten salt cells over a range of 0.0–3.0 Li equivalents per mol at current densities of 5–15 mA/cm². The equilibrium potential vs. Li was found to be a logarithmic function of the calculated oxygen partial pressure for any tie triangle in which is present, or for any tie triangle containing ternary oxide phases which are only marginally stable with respect to and the relevant binary oxides . Compounds with oxygen partial pressures above 10⁻²⁵ atm were found to be unstable in electrolyte at 400°C.