A lithium secondary battery includes a positive electrode; a negative electrode; and an electrolyte disposed between the positive electrode and the negative electrode, wherein the positive electrode includes a positive active material represented by Formula 1, and the electrolyte includes a lithium salt; a non-aqueous solvent; and a phosphite compound represented by Formula 2, wherein the phosphite compound is present in amount of about 0.1 wt % to about 5 wt % based on a total weight of the electrolyte: LixNiyM1-yO2-zAz  Formula 1 wherein, in Formula 1, 0.9≤x≤1.2, 0.7≤y≤0.98, and 0≤z