Phase and microstructure stabilities of LiAlO2 in molten Li/Na carbonate for molten carbonate fuel cells

The phase and microstructure stabilities of LiAlO2 for improving the matrix reliability of molten carbonate fuel cells are investigated. The phase transformation and particle growth of LiAlO2 are examined via immersion tests of pure gamma-LiAlO2,an alpha-/gamma-LiAlO2 mixture and pure alpha-LiAlO2 in molten carbonate at 650 deg C in an air atmosphere. Dissolution of Li+ ions occurs mainly from gamma-LiAlO2 over an 18000h period, and the dissolved Li+ ions precipitate as LiNaCO3 and alpha-LiAlO2. Particle growth takes place continuously from an early stage of heat-treatment and quickly progresses by the accelerated dissolution and precipitation of Li+ ions after 10000h. By contrast, the particle size and the crystalline phase of alpha-LiAlO2 do not change during 3000h of immersion. These results show that alpha-LiAlO2 is less soluble than gamma-LiAlO2 and is more stable in molten carbonate.