Method for Manufacturing Lithium Secondary Battery Comprising Lithium-Rich Manganese Based Oxide

A method for manufacturing a lithium secondary battery includes preparing a battery cell, charging and discharging the battery cell under pressurization to activate the battery, and then charging is performed in a constant voltage mode. The battery cell includes a positive electrode, a negative electrode and an electrolyte, with the positive electrode containing lithium-rich manganese-based oxide in which the content of manganese in all metals excluding lithium is greater than 50 mol %, and the ratio of the number of moles of lithium to the number of moles of all metals excluding lithium (Li/Me) is greater than 1. The charging and discharging the battery cell under pressurization activates the battery. In the activating, the charging is performed in constant current mode until the charge cut-off voltage, and then the charging is performed in a constant voltage mode, and the charge cut-off voltage is greater than 4.35V.