| Abstract
| - The electronic structures of NiO, LiNiO2, and NiO2 are studied by the electron energy loss spectroscopy atNi L2,3, Ni M2,3, and O K edges. The Ni L2,3 edge spectra suggest that the formal charge of nickel is +2 inNiO, +3 with a low-spin state in LiNiO2, and +4 with a low-spin state in NiO2. This is well confirmed byfirst-principles calculations. The Ni M2,3 edge spectra show similar chemical shifts to those of the Ni L2,3edge. Superposition of the Li K edge spectrum, however, hinders further analysis. Although the formal chargeof oxygen is −2 in all the three phases, the O K edge spectra indicate a more remarkable difference in theelectronic structure of the oxygen in NiO2 than that in either NiO or LiNiO2. The spectra suggest that lithiumextraction from LiNiO2 reinforces the covalent bonding between the oxygen and nickel atoms and causes anotable reduction in electron density at the oxygen atoms.
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