Novel Fe-Mn oxide positive electrode materials with high capacity (150mAh/g) and superior high temperature (60 °C) cycle performance has been developed through the combination of material design fully utilizing Fe ion with novel synthetic route for getting homogeneous and fine particles (<100nm). The material belongs a LiFeO₂-Li₂MnO₃ solid solution and could be expressed as Li_1+x(Fe_0.5-yMn_0.5-yNi_2y)_1-xO₂ (0<x<1/3, y=0 or 0.1). The synthetic route consists of three steps; coprecipitation, hydrothermal and post heat-treatment processes for complete mixing of two or three transition metal ions. As iron resource is available abundantly, it will open the way to the development of low cost lithium ion battery.