A lithium secondary battery including a positive electrode, a negative electrode comprising a negative electrode current collector, and an electrolyte interposed between the positive electrode and negative electrode. The lithium metal is formed on the negative electrode current collector by lithium ions migrating toward the negative electrode current collector after charge. The electrolyte comprises a sacrificial salt having an oxidation potential of 5 V or less with respect to lithium. The lithium secondary battery forms lithium metal while being blocked from the atmosphere, and thereby improves an existing problem caused by high reactivity of lithium metal. By including a sacrificial salt in an electrolyte, lithium consumption caused by an irreversible reaction of a negative electrode is reduced, which may prevent decline in the battery capacity and lifetime properties.