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

LiAlO 2 powder is used as a material for molten‐carbonate fuel cell (MCFC) matrices. The physical and chemical stabilities of LiAlO 2 powder during MCFC operation determine the performance and lifetimes of the cells. Change to the phase and particle size in the allotropic phase of LiAlO 2 was examined with long‐term stability tests on pure α‐LiAlO 2 matrix, Al‐reinforced α‐LiAlO 2 matrix, Al‐reinforced γ‐LiAlO 2 matrix, aqueous γ‐LiAlO 2 matrix and an α‐/β‐LiAlO 2 mixture powder in molten carbonate at 650 °C in air. In the γ‐LiAlO 2 and α‐/β‐LiAlO 2 mixture, the particle growth was continuous from the early stages of heat‐treatment to 20,000 h. Crystalline phase transformation (γ‐LiAlO 2 and β‐LiAlO 2 to α‐LiAlO 2 and γ‐LiAlO 2 , respectively) of these powders and matrices also occurred, and γ‐LiAlO 2 made the third phase like LiAl 5 O 8 . By contrast, the sizes of these particles and the crystalline phase of α‐LiAlO 2 did not change during immersion tests. These results show that, among α‐/β‐ and γ‐LiAlO 2 , α‐LiAlO 2 is the most stable phase in molten carbonate.