On the role of lithium carbonate in the preparation of doped nickel oxide cathodes for molten carbonate fuel cells

Clear evidence was obtained by dilatation and density measurements that the amount of lithium carbonate in the starting mixture sensibly affects the sintering behaviour of mixed lithium-nickel oxide cathodes. Porosimetric, diffractometric and microscopic measurements were then performed to understand and put on a quantitative basis such an influence. It is shown that, when the sintering temperature is low enough to prevent lithium oxide loss from the mixed oxide, cathodes total porosity increases with increasing lithium content up to a limiting composition beyond which a porosity decrease takes place. Lithium oxide loss, on the other hand, leads to a total porosity decrease which is related both to the initial lithium content and to the amount of the lithium oxide lost. Such a behaviour can be explained on the basis of the different mechanism by which the mixed oxide is obtained depending on the relative amounts of nickel and lithium carbonate in the starting mixture. Moreover it is shown that the observed total porosity changes are mainly a consequence of microporosity changes.