Activation methods of rechargeable lithium batteries and rechargeable lithium batteries

A method of activating a rechargeable lithium battery, the method comprising

• performing a first charging and discharging process on a rechargeable lithium battery;
• performing a second charging and discharging process on the rechargeable lithium battery after the first charging and discharging process,
• wherein the rechargeable lithium battery includes:
• a positive electrode including a positive electrode active material including a layered lithium nickel-manganese-based composite oxide,
• a negative electrode,
• a separator between the positive electrode and the negative electrode, and
• an electrolyte solution, and
• wherein an upper limit voltage of the second charging and discharging process is higher than an upper limit voltage of the first charging and discharging process.