Method of preparing positive electrode active material

A method of preparing a positive electrode active material comprising:

• introducing a reaction mixture including a lithium source material and a nickel-manganese-cobalt precursor into a continuous firing furnace and performing primary heat treatment, thereby preparing a fired mixture;
• subjecting the fired mixture to pulverization or size classification;
• and
• introducing the fired mixture having been pulverized or size-classified into a rotary kiln and performing secondary heat treatment, thereby forming a lithium nickel manganese cobalt-based positive electrode active material,
• wherein the continuous firing furnace is a roller hearth kiln;
• wherein the fired mixture is a mixture of spinel structured lithium nickel cobalt manganese-based oxide seeds and laminar-structured lithium nickel cobalt manganese-based oxide seeds,
• wherein the primary heat treatment is performed under an oxygen atmosphere or an air atom sphere, and
• wherein the secondary heat treatment is performed under an inert nitrogen atmosphere or a vacuum atmosphere;
• wherein the lithium nickel manganese cobalt-based positive electrode active material is represented by the following Chemical Formula 1:
• Li1+x[NiaMnbCocM11−a−b−c]1−xO2 [Chemical Formula 1]
• wherein, in Chemical Formula 1, −0.2≤x≤0.2, 0<a<1, 0<b<1, 0<c<1, and M1 is one or more selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo.