To elucidate the mechanism of Li incorporation into NiO in molten carbonates, the open-circuit potential of the cell: O-2 + CO2 (g) \ Ni or Co oxide (s) \ Li2CO3 + Na2CO3 (1) \ Au (s) \ O-2 + CO2 (g) was examined for porous LixNi1-xO (0 less than or equal to x less than or equal to 0.5), LiCoO2 and Co3O4 electrodes. These studies and X-ray diffraction examination of the samples before and after submersion in carbonate melt indicated that LiNiO2 is formed in small amounts as an ultimate product of the reaction. Consequent extraction of Li+ ions from LiNiO2 formed this way occurs due to polarisation of the electrode by the electro-reduction of oxygen dissolved in molten carbonates and results in turn in partial decomposition of LiNiO2.