We have investigated the effect of dopants on the electrochemical and thermal properties of layered Li(Ni0.5−x Mn0.5−x M2x ′) materials (M′=Mg, Al, Co, Ni, Ti; x=0,0.025) that were prepared using a manganese–nickel hydroxide precursor. Li(Ni0.5Mn0.5)O2 exhibited discharge capacities of ca. 120 and 150mAh/g at 2.8–4.3 and 2.8–4.6V, respectively, with slight capacity fades; the addition of 5mol% Al, Co, Ni, and Ti increased discharge capacity by 10–30% and improved capacity retention. X-ray photoelectron spectroscopy data suggested that Ni and Mn exist as Ni2+ and Mn4+ so that only Ni is electrochemically active in the layered structure. Differential scanning calorimetry (DSC) data showed that exothermic reactions of Li y (Ni0.5−x Mn0.5−x M2x ′)O2 charged to 4.3V versus Li started at higher temperatures (270–290°C) than LiNiO2-based cathode materials (e.g. 200°C for LiNi0.8Co0.2O2), which indicates that the thermal stability of Li(Ni0.5−x Mn0.5−x M2x ′) is superior to that of LiNiO2-based cathode materials.