Preparation and Characterization of LiCoO2 and LiMg0.05Co0.95O2 Thin Films on Porous Ni/NiO Cathodes for MCFC by Complex Sol-Gel Process (CSGP)

The major disadvantage of Ni/NiO cathodes for a Molten Carbonate Fuel Cells (MCFC) application is dissolution of NiO in K/Li electrolyte that significantly decreases the cell lifetime. Thin films of LiCoO2 or LiMg0.05Co0.9502 were prepared on a cathode body in order to protect them against dissolution. For preparation of starting sols the Complex Sol-Gel Process (CSGP) has been applied. These sols have been prepared by adding of LiOH to aq. acetates solution of Co 2+(Mg2+) with ascorbic acid and then by alkalizing them with aqueous ammonia to pH=8. The cathode plates of various dimensions (to several hundreds cm2) have been dipped in these sols and withdrawn at rate a 1.7 cm/s. Commercially sintered Ni plates were always initially oxidized by heating at various temperatures. Their microstructure and mechanical properties as a function of temperature were observed. Heat treatment should be carried out under the dead load of the ceramic plates in order to avoid their waving. The best non-folded plates were obtained by treating them for lh at 550°C. The covered substrates were calcined for lh at 650°C, using low heating ratel°C/min. The presence of LiCoO2 in a deposited coating has been proved by EDS patterns. The resultant film thicknesses were measured by scanning electron microscopy (SEM) on the fractured cross-sections; they ranged from 0.5 to 2νm and depended on sol concentration and viscosity. A 350 hundred hours test in molten carbonates, proved that the cathode bodies covered with LiCoO2 are completely prevented from dissolution of Ni in a molten K/Li electrolyte. Dissolution of LiCoO2 coating was not observed as well. After treatment in a molten electrolyte SEM observations did not show any changes in microstructures and morphology of the covered cathodes.