LITHIUM SECONDARY BATTERY

The invention relates to a lithium secondary battery including a positive electrode, a negative electrode including a negative active material, and an electrolyte, wherein the positive electrode includes a first positive active material of a lithium manganese cobalt oxide in Chemical Formula 1, and a second positive active material of a lithium transition metal oxide that occludes and releases lithium ions; an average particle diameter (D50) of the first positive active material is smaller than an average particle diameter (D50) of the second positive active material; and the first positive active material has lower first charge/discharge efficiency than that of the negative active material and has an irreversible capacity during the first charge/discharge that is larger than an irreversible capacity during the first charge/discharge of the negative active material.