Lithium Secondary Battery

Provided is a lithium secondary battery having improved high-temperature cycle characteristics, and including a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode includes lithium iron phosphorous oxide as a positive electrode active material, and the electrolyte includes a lithium salt, a first organic solvent, a second organic solvent, and an additive, the first organic solvent is a cyclic lactone compound, the second organic solvent is a carbonate-based organic solvent, and the additive is lithium nitrate (LiNO), and satisfies Equation 1: