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

The phase transformation and particle coarsening of lithium aluminate (alpha-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 alpha-LiAlO2 to gamma-LiAlO2 phase proceeds with increasing temperature in lower P-CO2 and lower P-O2 environments. Spherical LiAlO2 particles were transformed to coarsened pyramid-shape particles in 4% H-2-3% H2O-N-2 and 100% N-2 (similar to 10 ppm P-O2) atmospheres. Under CO2-rich atmospheres (4% H-2-30% CO2-N-2 and 70% air-30% CO2), both phase and particle size remained unchanged at 650 and 750 degrees C. Selected area electron diffraction (SAED) pattern analysis indicated that the large pyramidal shape particles (similar to 30 mu m) were gamma-LiAlO2 phase. Experimental observations and related simulation results pertaining to particle coarsening and phase transformation behavior of LiAlO2 are presented. (C) The Author(s) 2017. Published by ECS. All rights reserved.