Photoelectron spectroscopic study of the reaction of Li and Na with NiCo2O4

The in situ chemical reaction of NiCo2O4 with Li and Na by physical vapor deposition is studied by using high-resolution X-ray photoelectron spectroscopy. The thermal decomposition of the mixed oxalate precursors at 320 degrees C allows the formation of NiCo2O4 as nanosized domains. The small particle size facilitates the reaction with Li and Na. During the first steps of the reaction of NiCo2O4 with both alkali metals, the reduction of both Ni3+ and Co3+ to the divalent state is demonstrated by XP spectroscopic data. The mechanism of the first steps of the reaction has been unfolded. A first intercalation reaction of the alkali ions in the spinel host structure occurs. In a second step, sodium oxide or lithium oxide is formed, as well as the monoxides.