A key component in molten carbonate fuel cells (MCFCs) is the electrolyte matrix, which provides both ionic conduction and gas sealing. During initial MCFC stack start-up and operation (650 degrees C), the matrix experiences both mechanical and thermal stresses as a result of the difference in thermal expansion coefficients between the LiAlO2 ceramic particles and the carbonate electrolyte that causes cracking of the matrix. A pure gamma-LiAlO2 matrix, however, has poor mechanical strength and low thermal expansion coefficients. In this study, fine gamma-LiAlO2 powders and pure Al (3/20/50 mu m)/Li2CO3 particles are used as a matrix and as reinforcing materials, respectively. The Al phase transforms completely into gamma-LiAlO2 at 650 degrees C within 10 h. The mechanical strength of these matrices (283.48 gf mm(-2)) increases nearly threefold relative to that of a pure gamma-LiAlO2 matrix (104.01 gfmm(-2)). The mismatch of the thermal expansion coefficient between the matrix and electrolyte phases can be controlled by adding Al particles, which results in improved thermal stability in the initial heating-up step. In unit-cell and thermal-cycling tests, the optimized matrix demonstrates superior performance over pure gamma-LiAlO2 matrices. (C) 2008 Elsevier B.V. All rights reserved.