We investigated the oxygen contributions on delithiation process of different types of layered 3d transition metal oxides, Li TiO , Li MnO , and LiCoO , using X-ray spectroscopies with the aid of density functional theory calculations. In delithiatied LiCoO , electrons are extracted from highly hybridized Co 3d and O 2p orbitals without O loss. In Li TiO , the hybridized Ti 3d and O 2p orbitals at the valence band is mainly contributed by O 2p orbitals, and delithiated Li TiO loses oxygen as the electrons are extracted. Li MnO exhibits some hybridization. In delithiated Li MnO , a certain amount of oxygen is lost, but the large amount of oxidized O anions remains as peroxide and superoxide-like states, which would work as the redox active species. Therefore, the degree of hybridization between metal 3d and O 2p orbitals is a key factor to influence the stability of O anion redox during the oxidation process, which determines the electrode performance. 2 3 2 3 2 2 2 2 3 2 3 2 3 2 3