Phase and Microstructural Stability of Electrolyte Matrix Materials for Molten Carbonate Fuel Cells

LiAlO2 powder is used as a material for molten-carbonate fuel cell (MCFC) matrices. The physical and chemical stabilities of LiAlO2 powder during MCFC operation determine the performance and lifetimes of the cells. Change to the phase and particle size in the allotropic phase of LiAlO2 was examined with long-term stability tests on pure α-LiAlO2 matrix, Al-reinforced α-LiAlO2 matrix, Al-reinforced γ-LiAlO2 matrix, aqueous γ-LiAlO2 matrix and an α-/β-LiAlO2 mixture powder in molten carbonate at 650 °C in air. In the γ-LiAlO2 and α-/β-LiAlO2 mixture, the particle growth was continuous from the early stages of heat-treatment to 20,000 h. Crystalline phase transformation (γ-LiAlO2 and β-LiAlO2 to α-LiAlO2 and γ-LiAlO2, respectively) of these powders and matrices also occurred, and γ-LiAlO2 made the third phase like LiAl5O8. By contrast, the sizes of these particles and the crystalline phase of α-LiAlO2 did not change during immersion tests. These results show that, among α-/β- and γ-LiAlO2, α-LiAlO2 is the most stable phase in molten carbonate.