LiNiO 2 with theoretical capacity of 275 mAh g −1 is regarded as a promising cathode material for Li-ion batteries, but its potential capacity has not been fully realized due to the severe capacity loss in the first charge/discharge cycle. Via co-precipitation method, we synthesized Li[Ni 0.90 Co 0.05 Mn 0.05 ]O 2, Li[Ni 0.95 Co 0.025 Mn 0.025 ]O 2 , and LiNiO 2 which delivered 221, 230, and 240 mAh g −1 , respectively, when cycled from 2.7 to 4.3 V vs. Li 0 /Li + at 0.1 C and retained ∼70% of the initial capacity after 100 cycles. To date, such high reversible capacities are not yet to be reported from the Ni-rich Li[Ni 1−x−y Co x Mn y ]O 2 cathodes. The observed high capacities were attributed to the presence of a rock salt phase from severe cation mixing and excess Li ions in the host structure. It is believed that the rock salt phase stabilized the host structure in the delithiated state while the excess Li allowed the Li ions percolated through the rock salt phase which would be electrochemically inactive otherwise.Lithium nickel oxide, LiNiO 2 , with isostructural with NaFeO 2 , was firstly reported by Dyer et al. in 1954. 1 Since the commercialization of lithium-ion battery by Sony in 1991, LiNiO 2 has been extensively studied to replace LiCoO 2 because of its higher capacity and lower cost. However, it has been well-known that synthesis of stoichiometric LiNiO 2 is very difficult since Ni 2+ with similar ionic radius as Li + ends up in the Li + sites to form of Li 1-x Ni 1+x O 2 (0.0 ≤ x ≤ 0.2), or more precisely [Li 1-x Ni x ]3a[Ni]3b[O 2 ]6c 2,3 during the high temperature calcination of stoichiometric LiNiO 2 . The substituted Ni in the lithium layer hinders the Li + diffusion and thus greatly decreases electrochemical performances. 4 Ohzuku et al. reported that an integrated intensity ratio of I(003)/I(104) had a strong relation with the displacement of nickel ions and lithium ions which was correlated to the electrochemical reactivity of the LiNiO 2 ; 5 the higher intensity ratio of the I(003)/I(104) reduced the cation mixing and thus results in a high capacity and good Li + intercalation stability. A stoichiometric LiNiO 2 synthesized by excess Li method showed discharge capacity of more than 200 mAh g −1 when cycled between 3.0 and 4.5 V. 2,6 However, all the synthesized LiNiO 2 have exhibited reduction in capacity and poor cycling performance when the upper cutoff potential was reduced to 4.3 V. 7 It is likely that a high concentration of unstable Ni 4+ in the highly delithated Li x NiO 2 was easily transformed to more stable and insulting NiO phase, leading to high interfacial impedance and thus resulting in poor electrochemical performance. 2,7,8 The structural changes of Li 1-x NiO 2 occurring during charging and discharging were intensively studied by X-ray diffraction analysis to identify the relationship between the phase transition and the Li + intercalation stability. 2,6,8,9 Ohzuku et al. did ex-situ XRD study on the Li 1-x NiO 2 on 1 st charge and discharge processes and reported that t...

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