In order to provide a 3V level non-aqueous electrolyte secondary battery with a flat voltage and excellent cycle life at a high rate with low cost, the present invention provides a positive electrode represented by the formula: Li.sub.2.+-..alpha.[Me].sub.4O.sub.8-x, wherein 0.ltoreq..alpha.<0.4, 0.ltoreq.x<2, and Me is a transition metal containing Mn and at least one selected from the group consisting of Ni, Cr, Fe, Co and Cu, said active material exhibiting topotactic two-phase reactions during charge and discharge.