Photoelectron Spectroscopic Study of the Reaction of Li and Na with NiCo 2 O 4

The in situ chemical reaction of NiCo 2 O 4 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 °C allows the formation of NiCo 2 O 4 as nanosized domains. The small particle size facilitates the reaction with Li and Na. During the first steps of the reaction of NiCo 2 O 4 with both alkali metals, the reduction of both Ni 3+ and Co 3+ 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.