A lithium secondary battery, comprising: a cathode; an anode; and an electrolyte between the cathode and the anode, wherein the cathode comprises a cathode active material represented by Formula 1, and the electrolyte includes a lithium salt, a non-aqueous solvent, and a compound represented by Formula 2: Formula 1> Li x Ni y M 1-y O 2-z A z wherein, in Formula 1, 0.9≤x≤1.2, 0.6≤y≤0.98, and 0≤z≤0.2 are satisfied, M is at least one element selected from Al, Mg, Mn, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, and Bi, and A is an element having an oxidation number of -1 or -2; and wherein, in Formula 2, L 1 is selected from a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, and a heptylene group; and a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, and a heptylene group, each of which is substituted with at least one selected from a methyl group, an ethyl group, a propyl group, a vinyl group, -F, -Cl, - Br, -I, a cyano group, a hydroxy group, and a nitro group, a1 is 1 or 2, and the L 1 s are the same as or different from each other when a1 is 2, R 1 to R 4 are each independently selected from hydrogen, a substituted or unsubstituted C 1 -C 30 alkyl group, a substituted or unsubstituted C 2 -C 30 alkenyl group, and a substituted or unsubstituted vinyl group, at least one of R 1 to R 4 is selected from a substituted or unsubstituted C 1 -C 30 alkyl group, a substituted or unsubstituted C 2 -C 30 alkenyl group, and a substituted or unsubstituted vinyl group, and each of substituents of the substituted C 1 -C 30 alkyl group, the substituted C 2 -C 30 alkenyl group, the substituted C 2 -C 30 alkynyl group, the substituted C 2 -C 30 alkoxyalkyl group, and the substituted vinyl group is at least one selected from a C 1 -C 20 alkyl group, a C 2 -C 20 alkenyl group, a C 2 -C 20 alkynyl group, a C 1 -C 20 alkoxy group, a vinyl group, a halogen, a cyano group, a hydroxyl group, and a nitro group. a cathode; an anode; and an electrolyte between the cathode and the anode, wherein the cathode comprises a cathode active material represented by Formula 1, and the electrolyte includes a lithium salt, a non-aqueous solvent, and a compound represented by Formula 2: Formula 1> Li x Ni y M 1-y O 2-z A z wherein, in Formula 1, 0.9≤x≤1.2, 0.6≤y≤0.98, and 0≤z≤0.2 are satisfied, M is at least one element selected from Al, Mg, Mn, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, and Bi, and A is an element having an oxidation number of -1 or -2; and wherein, in Formula 2, L 1 is selected from a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, and a heptylene group; and a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, and a heptylene group, each of which is substituted with at least one selected from a methyl group, an ethyl group, a propyl group, a vinyl group, -F, -Cl, - Br, -I, a cyano group, a hydroxy group, and a nitro group, a1 is 1 or 2, and the L 1 s are the same as or different from each other when a1 is 2, R 1 to R 4 are each independently selected from hydrogen, a substituted or unsubstituted C 1 -C 30 alkyl group, a substituted or unsubstituted C 2 -C 30 alkenyl group, and a substituted or unsubstituted vinyl group, at least one of R 1 to R 4 is selected from a substituted or unsubstituted C 1 -C 30 alkyl group, a substituted or unsubstituted C 2 -C 30 alkenyl group, and a substituted or unsubstituted vinyl group, and each of substituents of the substituted C 1 -C 30 alkyl group, the substituted C 2 -C 30 alkenyl group, the substituted C 2 -C 30 alkynyl group, the substituted C 2 -C 30 alkoxyalkyl group, and the substituted vinyl group is at least one selected from a C 1 -C 20 alkyl group, a C 2 -C 20 alkenyl group, a C 2 -C 20 alkynyl group, a C 1 -C 20 alkoxy group, a vinyl group, a halogen, a cyano group, a hydroxyl group, and a nitro group.