A cathode active material comprising: a lithium manganese-excess layered structure composite oxide represented by Formula Li[Li x-z (Ni a Co b Mn c) 1-x]O 2-y F y (here, a + b + c = 1, 0.05 ≤ x ≤ 0.33, 0 < y ≤ 0.08, and 0 < z ≤ 0.05), wherein the composite oxide before coating is a composite oxide consisting of rhombohedral LiMO 2 (here, M is Ni, Co, and Mn) and monoclinic Li 2 MnO 3 and the cathode active material further includes lithium manganese oxide (LiMn 2 O 4) having a cubic spinel structure, which is formed by a change in a part of the monoclinic Li 2 MnO 3 in the composite oxide in the vicinity of the composite oxide, and in this case, the composite oxide becomes a composite structure of rhombohedral LiMO 2 (R3m; here, M is Ni, Co, and Mn), monoclinic Li 2 MnO 3 (L2/m), and cubic spinel LiMn 2 O 4 (Fd3m); and a metal fluoride coating layer coated on a surface of the composite oxide; characterized in that a metal phosphate coating layer is coated on the metal fluoride coating layer, wherein (i) the metal fluoride coating layer consists of AlF 3 and the metal phosphate coating layer consists of AlPO 4, or wherein (ii) the metal fluoride coating layer consists of MgF 2 and the metal phosphate coating layer consists of Mg 3 (PO 4) 2, wherein a content of the metal phosphate coating layer is 0.2 wt% to 0.4 wt% based on a total weight of the cathode active material, a total content of the metal fluoride coating layer and the metal phosphate coating layer is 0.5 wt% to 2.0 wt% based on a total weight of the cathode active material and wherein a weight ratio of the metal fluoride coating layer and the metal phosphate coating layer is within a range of 1.0 < the metal fluoride coating layer / the metal phosphate coating layer < 5.0. a lithium manganese-excess layered structure composite oxide represented by Formula Li[Li x-z (Ni a Co b Mn c) 1-x]O 2-y F y (here, a + b + c = 1, 0.05 ≤ x ≤ 0.33, 0 < y ≤ 0.08, and 0 < z ≤ 0.05), wherein the composite oxide before coating is a composite oxide consisting of rhombohedral LiMO 2 (here, M is Ni, Co, and Mn) and monoclinic Li 2 MnO 3 and the cathode active material further includes lithium manganese oxide (LiMn 2 O 4) having a cubic spinel structure, which is formed by a change in a part of the monoclinic Li 2 MnO 3 in the composite oxide in the vicinity of the composite oxide, and in this case, the composite oxide becomes a composite structure of rhombohedral LiMO 2 (R3m; here, M is Ni, Co, and Mn), monoclinic Li 2 MnO 3 (L2/m), and cubic spinel LiMn 2 O 4 (Fd3m); and a metal fluoride coating layer coated on a surface of the composite oxide; characterized in that a metal phosphate coating layer is coated on the metal fluoride coating layer, wherein (i) the metal fluoride coating layer consists of AlF 3 and the metal phosphate coating layer consists of AlPO 4, or wherein (ii) the metal fluoride coating layer consists of MgF 2 and the metal phosphate coating layer consists of Mg 3 (PO 4) 2, wherein a content of the metal phosphate coating layer is 0.2 wt% to 0.4 wt% based on a total weight of the cathode active material, a total content of the metal fluoride coating layer and the metal phosphate coating layer is 0.5 wt% to 2.0 wt% based on a total weight of the cathode active material and wherein a weight ratio of the metal fluoride coating layer and the metal phosphate coating layer is within a range of 1.0 < the metal fluoride coating layer / the metal phosphate coating layer < 5.0.