Provided is a non-aqueous electrolyte-based, high-power lithium secondary battery having a long service life and superior safety at both room temperature and high temperature, even after repeated high-current charging and discharging. The battery comprises a mixture of a lithium/manganese spinel oxide having a substitution of a manganese (Mn) site with a certain metal ion and a lithium/nickel/cobalt/manganese composite oxide, as a cathode active material.