A porous electrode of nickel covered by a thin film of lithium cobaltite doped with magnesium (LiMg0.05Co0.95O2) was prepared in order to protect nickel cathode against dissolution into the molten carbonate. A sol impregnation technique was used to deposit gel precursors on the porous surface of the substrate; the covered substrate was submitted to thermal treatments, which produced a lithium cobaltite layer. The cathode was characterized by the following measurements: biaxial bending test, SEM/EDX analysis, which demonstrated the uniformity of the lithium cobaltite layer and the presence of cobalt homogeneously distributed over the nickel particles, electrical conductivity. To test the cathodic performance of the material under study a cell was assembled and tested in a 10cm×10cm electrodes area plant. The cell performance during the time was studied carrying out polarization curves for many hours (more than 1000h). To determine the influence of the cathodic gas composition on the electrode performance the atmosphere was changed maintaining alternatively at a constant value the partial pressure of CO2 and O2. In such a way the kinetic effect of the single gas was studied. By the technique of IR interruption the internal resistance of the cell was measured.