A positive active material composition for a rechargeable battery includes a positive active material selected from compounds represented by formulas 1 to 13, and at least one semi-metal, metal or oxides thereof: Li.sub.xMnA.sub.2 (1) Li.sub.xMnO.sub.2-zA.sub.z (2) Li.sub.xMn.sub.1-yM'.sub.yA.sub.2 (3) Li.sub.xMn.sub.2A.sub.4 (4) Li.sub.xMn.sub.2O.sub.4-zA.sub.z (5) Li.sub.xMn.sub.2-yM'.sub.yA.sub.4 (6) Li.sub.xBA.sub.2 (7) Li.sub.xBO.sub.2-zA.sub.z (8) Li.sub.xB.sub.1-yM''.sub.yA.sub.2 (9) Li.sub.xB.sub.1-yM''.sub.yO.sub.2-zA.sub.z (10) Li.sub.xNiCoO.sub.2-zA.sub.z (11) Li.sub.xNiCoO.sub.2-zA.sub.z (12) Li.sub.xNi.sub.1-y-zCo.sub.yM''.sub.zA.sub.2 (13) where 1.0.ltoreq.x.ltoreq.1.1, 0.01.ltoreq.y.ltoreq.0.1, 0.01.ltoreq.z.ltoreq.0.5, M' is at least one transition metal or lanthanide metal selected from Al, Cr, Co, Mg, La, Ce, Sr, or V, M'' is at least one transition metal or lanthanide metal selected from Al, Cr, Mn, Fe, Mg, La, Ce, Sr or V, A is selected from 0, F, S or P, and B is Ni or Co.