A lithium battery comprising: a positive electrode; a negative electrode; and an electrolyte between the positive electrode and the negative electrode, wherein the positive electrode comprises a positive electrode active material represented by Formula 1A below, and the electrolyte comprises a lithium salt, a non-aqueous solvent, and an alkyl sulfonate compound represented by Formula 2 below: <Formula 1A> Li x Ni y M 1-y O 2-z A z wherein, in Formula 1A, 0.9≤x≤1.2, 0.88≤y≤0.98, and 0≤z<0.2 are satisfied, M is at least one element selected from the group consisting of aluminum (Al), magnesium (Mg), manganese (Mn), cobalt (Co), iron (Fe), chromium (Cr), vanadium, titanium (Ti), copper (Cu), boron, calcium (Ca), zinc (Zn), zirconium (Zr), niobium (Nb), molybdenum (Mo), strontium (Sr), antimony (Sb), tungsten, and bismuth (Bi); and A is an element having an oxidation number of -1 or -2; wherein, in Formula 2, Q 1 and Q 2 are each independently a substituted or unsubstituted C 1 -C 20 alkyl group, wherein an amount of the alkyl sulfonate compound is in a range of 0.005 parts by weight to 5 parts by weight with respect to 100 parts by weight of the electrolyte, and wherein substituted means that at least one hydrogen atom is substituted with a halogen atom, a C 1 -C 20 alkyl group substituted with a halogen atom, a C 1 -C 20 alkoxy group, a C 2 -C 20 alkoxyalkyl group, a hydroxyl group, a nitro group, a cyano group, an amino group, an amidino group, hydrazine, hydrazone, a carboxyl group or a salt thereof, a sulfonyl group, a sulfamoyl group, sulfonic acid group or a salt thereof, phosphoric acid or a salt thereof, 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 heteroalkyl group, a C 6 -C 20 aryl group, a C 6 -C 20 arylalkyl group, a C 6 -C 20 heteroaryl group, a C 7 -C 20 heteroarylakyl group, a C 6 -C 20 heteroaryloxy group, a C 6 -C 20 heteroaryloxyalkyl group, or a C 6 -C 20 heteroarylalkyl group. wherein the positive electrode comprises a positive electrode active material represented by Formula 1A below, and the electrolyte comprises a lithium salt, a non-aqueous solvent, and an alkyl sulfonate compound represented by Formula 2 below: <Formula 1A> Li x Ni y M 1-y O 2-z A z wherein, in Formula 1A, 0.9≤x≤1.2, 0.88≤y≤0.98, and 0≤z<0.2 are satisfied, M is at least one element selected from the group consisting of aluminum (Al), magnesium (Mg), manganese (Mn), cobalt (Co), iron (Fe), chromium (Cr), vanadium, titanium (Ti), copper (Cu), boron, calcium (Ca), zinc (Zn), zirconium (Zr), niobium (Nb), molybdenum (Mo), strontium (Sr), antimony (Sb), tungsten, and bismuth (Bi); and A is an element having an oxidation number of -1 or -2; wherein, in Formula 2, Q 1 and Q 2 are each independently a substituted or unsubstituted C 1 -C 20 alkyl group, wherein an amount of the alkyl sulfonate compound is in a range of 0.005 parts by weight to 5 parts by weight with respect to 100 parts by weight of the electrolyte, and wherein substituted means that at least one hydrogen atom is substituted with a halogen atom, a C 1 -C 20 alkyl group substituted with a halogen atom, a C 1 -C 20 alkoxy group, a C 2 -C 20 alkoxyalkyl group, a hydroxyl group, a nitro group, a cyano group, an amino group, an amidino group, hydrazine, hydrazone, a carboxyl group or a salt thereof, a sulfonyl group, a sulfamoyl group, sulfonic acid group or a salt thereof, phosphoric acid or a salt thereof, 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 heteroalkyl group, a C 6 -C 20 aryl group, a C 6 -C 20 arylalkyl group, a C 6 -C 20 heteroaryl group, a C 7 -C 20 heteroarylakyl group, a C 6 -C 20 heteroaryloxy group, a C 6 -C 20 heteroaryloxyalkyl group, or a C 6 -C 20 heteroarylalkyl group.