Electrode assembly and lithium secondary battery including the same

A secondary battery includes an electrode assembly including a positive electrode having a positive active material, a negative electrode including a negative active material, and a separator between the positive and negative electrodes. The positive active material includes a lithium composite oxide represented by LiCo 1-x-y Mg x Ti y O 2 where 0.0056¤x¤0.0089, and 0.0029¤y¤0.0045. The electrode assembly and the lithium secondary battery including the same show good discharge efficiency even with increases in C-rate, and substantially prevent reductions in battery capacity resulting from battery deterioration, thereby improving battery lifespan.