A lithium battery comprising: a cathode; an anode; and an electrolyte between the cathode and the anode, wherein the cathode includes a cathode active material represented by Formula 1, and the electrolyte includes a lithium salt, a non-aqueous solvent, and an unsaturated 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, 0.7≤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, wherein, in Formula 2, one of Q 1 and Q 2 is a group represented by -(L 1)-(R 1), and the other of Q 1 and Q 2 is a group represented by -(L 2)-(R 2), L 1 is selected from a substituted or unsubstituted C 2 -C 20 alkenylene group and a substituted or unsubstituted C 2 -C 20 alkynylene group, L 2 is a substituted or unsubstituted C 6 -C 60 arylene group, and R 1 and R 2 are each independently selected from hydrogen, a substituted or unsubstituted linear or branched alkyl group, and a substituted or unsubstituted C 6 -C 60 aryl group; wherein the substituent(s) of the substituted C 2 -C 20 alkenylene group, substituted C 2 -C 20 alkynylene group, substituted C 6 -C 60 arylene group, substituted linear or branched alkyl group and substituted C 6 -C 60 aryl group is selected from 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, a 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 heteroarylalkyl group, a C 6 -C 20 heteroaryloxy group, a C 6 -C 20 heteroaryloxyalkyl group and a C 6 -C 20 heteroarylalkyl group. a cathode; an anode; and an electrolyte between the cathode and the anode, wherein the cathode includes a cathode active material represented by Formula 1, and the electrolyte includes a lithium salt, a non-aqueous solvent, and an unsaturated 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, 0.7≤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, wherein, in Formula 2, one of Q 1 and Q 2 is a group represented by -(L 1)-(R 1), and the other of Q 1 and Q 2 is a group represented by -(L 2)-(R 2), L 1 is selected from a substituted or unsubstituted C 2 -C 20 alkenylene group and a substituted or unsubstituted C 2 -C 20 alkynylene group, L 2 is a substituted or unsubstituted C 6 -C 60 arylene group, and R 1 and R 2 are each independently selected from hydrogen, a substituted or unsubstituted linear or branched alkyl group, and a substituted or unsubstituted C 6 -C 60 aryl group; wherein the substituent(s) of the substituted C 2 -C 20 alkenylene group, substituted C 2 -C 20 alkynylene group, substituted C 6 -C 60 arylene group, substituted linear or branched alkyl group and substituted C 6 -C 60 aryl group is selected from 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, a 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 heteroarylalkyl group, a C 6 -C 20 heteroaryloxy group, a C 6 -C 20 heteroaryloxyalkyl group and a C 6 -C 20 heteroarylalkyl group.