Role of Exposure Atmospheres on Particle Coarsening and Phase Transformation of LiAlO2

Abstract

The phase transformation and particle coarsening of lithium aluminate (α-LiAlO2) in electrolyte are the major causes of degradation affecting the performance and the lifetime of the molten carbonate fuel cell (MCFC). The stability of LiAlO2 has been studied in Li2CO3-Na2CO3 electrolyte under accelerated conditions in reducing and oxidizing gas atmospheres at temperatures of 650 and 750 for up to 500 hours. X-ray diffraction analyses show that the progressive transformation of α-LiAlO2 to γ-LiAlO2 phase proceeds with increasing temperature in lower PCO2 and lower PO2 environments. Spherical LiAlO2 particles were transformed to coarsened pyramid-shape particles in 4% H2-3% H2O-N2 and 100% N2 (∼10 ppm PO2) atmospheres. Under CO2-rich atmospheres (4% H2-30% CO2-N2 and 70% air-30% CO2), both phase and particle size remained unchanged at 650 and 750°C. Selected area electron diffraction (SAED) pattern analysis indicated that the large pyramidal shape particles (∼30 μm) were γ-LiAlO2 phase. Experimental observations and related simulation results pertaining to particle coarsening and phase transformation behavior of LiAlO2 are presented.