Fabrication and Characteristics of Electrolyte Combined α-LiAlO2 Matrices for Molten Carbonate Fuel Cells

A key component in MCFC is the porous matrix filled with electrolyte providing both ionic conduction and gas sealing. The matrix, which acts as an electrolyte retainer, has an impact on both cell life and performance because its cracking results in degradation of the electrodes and gas cross leakage. During initial start-up and operation at 650 ^oC of a MCFC stack, the matrix experiences both mechanical and thermal stresses due to the difference in thermal expansion coefficients between the LiAlO₂ ceramic particle and the carbonate electrolyte, and than the matrix might be cracked. Also, the decrease of the unit-cell thickness by the suction of the liquid electrolyte layer in electrolyte support matrix can depreciate the stability of the stack. In this study, to maintain the stability of the stack height and to improve mechanical strength and microstructure stability of the matrices, the manufacturing process of the electrolyte combined α-LiAlO₂ matrices was developed using the mixture of synthetic α-LiAlO₂ (11~50μm) and Li/K carbonate powders. The content of Li/K carbonate powders is optimized by using the porosity of the pure α-LiAlO₂ matrix and microstructure stability of the electrolyte combined matrix. The suitable electrolyte content fixed at 45~50 vol.% for the homogeneously filled up pores of the pure α-LiAlO₂ matrix after heat-treatment at 650 ^oC for 1 h. In unit-cell and thermal-cycling tests, the optimized matrices kept up stable state over 20 times. Furthermore, aluminum-reinforced α-LiAlO₂ composite matrices are also fabricated and their properties are compared with Al-free matrices.