The performances of lithium-ion batteries are set by the electrodes materials
capacity to exchange lithium ions and electrons faster and reversibly. To this
goal Ni-rich layered metal oxides, especially LiNiO2, are attractive electrode
candidate to achieve both high voltage and capacities. Despite its
attractiveness, several drawbacks for its industrialization are related to
different form of surface and bulk instabilities. These instabilities are due
to redox process involving the charge transfer between cations and anions.
Therefore, a fundamental understanding based on further experimental evidence
is required to resolve of charge transfer between the cation and anion from the
surface to the bulk in LiNiO2. Herein, we resolve the role of nickel and oxygen
in the charge compensation process in LixNiO2 electrodes from the extreme
surface down to 30 nm by energy-dependent core-level HAXPES supported by ab
initio simulation. We emphasize the central role of oxygen in the bulk charge
compensation mechanism from LiNiO2 to NiO2 due to the negative charge transfer
and bond/charge-disproportionation characters of LiNiO2. This bulk behavior is
in turn responsible for surface deoxygenation and nickel reduction upon
delithiation