Li x Ni1/3Mn2/3O2 (x > 2/3) compounds have been synthesized from P3 type Na2/3Ni1/3Mn2/3O2 precursor through a new reduction-ion exchange method. The XRD patterns of Li x Ni1/3Mn2/3O2 show superlattice peak around 2θ = 20°, which is similar to that of the lithium-excess manganese based cathode materials. In contrast to sample obtained from traditional ion exchange method, the Li x Ni1/3Mn2/3O2 compound delivers LiNi1/2Mn1/2O2–Li2MnO3 solid solution type potential profiles and higher capacity than that of Li2/3Ni1/3Mn2/3O2, especially for the capacity delivered in high potential region. Moreover, it exhibits extremely small irreversible capacity at the initial cycle and small capacity loss during cycling in the voltage range 4.7–2.5 V. The structure and electrochemical properties of metallic elements substituted Li x Ni2/9M1/9Mn2/3O2 (M = Al, Co, Fe, Mg) were also studied. XRD and Raman spectra results suggest that small amount substitution of Ni with other metal ions does not affect the main structure of Li x Ni2/9M1/9Mn2/3O2 compounds. For Mg substituted compound, Li x Ni2/9Mg1/9Mn2/3O2, it exhibits improved cycleability compared with the other samples.