An O2-type layered LiNi0. 5 Mn0. 5 O2 was prepared by rapidly-quenched method, and the structural feature was studied by X-Ray Diffraction. The material synthesized at 950℃ was with a single O2-type structure. Charge and discharge in a voltage range of 2.0-4.35V, the discharge specific capacity of material at the 1st cycle is 143.1 mAh/g in a current density of 0.5 mA/cm2 , and the plot of discharge was with two voltage plat at 3.6 V and 2.8V.