A positive electrode material comprising: a spinel-structured lithium manganese-based first positive electrode active material and a lithium nickel-manganese-cobalt-based second positive electrode active material, wherein the first positive electrode active material comprises a lithium manganese oxide represented by Formula 1 and a coating layer which is disposed on a surface of the lithium manganese oxide and includes at least one element selected from the group consisting of aluminum, titanium, tungsten, boron, fluorine, phosphorus, magnesium, nickel, cobalt, iron, chromium, vanadium, copper, calcium, zinc, zirconium, niobium, molybdenum, strontium, antimony, bismuth, silicon, and sulfur, the second positive electrode active material is represented by Formula 2, and an average particle diameter D 50 of the second positive electrode active material is greater than an average particle diameter D 50 of the first positive electrode active material: [Formula 1] Li 1+a Mn 2-b M 1 b O 4-c A c wherein, in Formula 1, M 1 is at least one element selected from the group consisting of Al, lithium, Mg, Zn, B, W, Ni, Co, Fe, Cr, V, ruthenium, Cu, cadmium, silver, yttrium, scandium, gallium, indium, arsenic, Sb, platinum, gold, and Si, A is at least one element selected from the group consisting of F, chlorine, bromine, iodine, astatine, and S, 0≤a≤0.2, 0<b≤0.5, and 0≤c≤0.1, and [Formula 2] Li 1+x [Ni y Co z Mn w M 2 v]O 2-p B p wherein, in Formula 2, M 2 is at least one element selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, tantalum, Y, lanthanum, Sr, Ga, Sc, gadolinium, samarium, Ca, cerium, Nb, Mg, B, and Mo, B is at least one element selected from the group consisting of F, Cl, Br, I, At, and S, 0≤x≤0.3, 0.50≤y<1, 0<z<0.35, 0<w<0.35, 0≤v≤0.1, and 0≤p≤0.1, wherein the average particle diameters D 50 are determined as described in the specification, and wherein the lithium manganese-based first positive electrode active material comprises a lithium boron composite oxide and a lithium tungsten composite oxide. a spinel-structured lithium manganese-based first positive electrode active material and a lithium nickel-manganese-cobalt-based second positive electrode active material, wherein the first positive electrode active material comprises a lithium manganese oxide represented by Formula 1 and a coating layer which is disposed on a surface of the lithium manganese oxide and includes at least one element selected from the group consisting of aluminum, titanium, tungsten, boron, fluorine, phosphorus, magnesium, nickel, cobalt, iron, chromium, vanadium, copper, calcium, zinc, zirconium, niobium, molybdenum, strontium, antimony, bismuth, silicon, and sulfur, the second positive electrode active material is represented by Formula 2, and an average particle diameter D 50 of the second positive electrode active material is greater than an average particle diameter D 50 of the first positive electrode active material: [Formula 1] Li 1+a Mn 2-b M 1 b O 4-c A c wherein, in Formula 1, M 1 is at least one element selected from the group consisting of Al, lithium, Mg, Zn, B, W, Ni, Co, Fe, Cr, V, ruthenium, Cu, cadmium, silver, yttrium, scandium, gallium, indium, arsenic, Sb, platinum, gold, and Si, A is at least one element selected from the group consisting of F, chlorine, bromine, iodine, astatine, and S, 0≤a≤0.2, 0<b≤0.5, and 0≤c≤0.1, and [Formula 2] Li 1+x [Ni y Co z Mn w M 2 v]O 2-p B p wherein, in Formula 2, M 2 is at least one element selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, tantalum, Y, lanthanum, Sr, Ga, Sc, gadolinium, samarium, Ca, cerium, Nb, Mg, B, and Mo, B is at least one element selected from the group consisting of F, Cl, Br, I, At, and S, 0≤x≤0.3, 0.50≤y<1, 0<z<0.35, 0<w<0.35, 0≤v≤0.1, and 0≤p≤0.1, wherein the average particle diameters D 50 are determined as described in the specification, and wherein the lithium manganese-based first positive electrode active material comprises a lithium boron composite oxide and a lithium tungsten composite oxide.