A 1:1 mixture of electrochemically active Li(Ni0.5Mn0.5)O2 and electrochemically inactive Li(Li1/3Mn2/3)O2, i.e. Li(Li0.17Ni0.25Mn0.58)O2, has been synthesized by a sol–gel method. The mixture was calcined at 900°C in air for 24h and cooled at three different rates: quenched into liquid nitrogen, 2°C/min, and 0.5°C/min. It was found that the crystallographic structure and electrochemical properties of Li(Li0.17Ni0.25Mn0.58)O2 highly depend on the cooling rate. The sample quenched into liquid nitrogen exhibited a long irreversible plateau at ca. 4.5V during the first charge, and the discharge capacity gradually increased from 170 to 210mAh/g after 40 cycles. The samples cooled at slower rates exhibited more monoclinic character and cubic spinel phase was observed; they showed no plateaus at 4.5V during the first charge and the discharge capacities also gradually increased from 80 and 55mAh/g to 130 and 85mAh/g for 2 and 0.5°C/min-cooled samples, respectively.