Comparative study of Li(Ni0.5−xMn0.5−xM2x′)O2 (M′ = Mg, Al, Co, Ni, Ti; x = 0, 0.025) cathode materials for rechargeable lithium batteries

We have investigated the effect of dopants on the electrochemical and thermal properties of layered Li(Ni0.5−xMn0.5−xM2x′) 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 150 mAh/g at 2.8–4.3 and 2.8–4.6 V, respectively, with slight capacity fades; the addition of 5 mol% 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 Liy(Ni0.5−xMn0.5−xM2x′)O2 charged to 4.3 V 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−xMn0.5−xM2x′) is superior to that of LiNiO2-based cathode materials.