Abstract: A positive electrode active material includes secondary particles obtained by aggregation of a plurality of primary particles. The primary particles include, core particles including a lithium composite oxide, and a layer that is provided on surfaces of the core particles and includes a lithium composite oxide. The lithium composite oxide included in the core particles and the lithium composite oxide included in the layer have the same composition or almost the same composition, and crystallinity of the lithium composite oxide included in the layer is lower than crystallinity of the lithium composite oxide included in the core particles.

Abstract: A positive electrode active material includes: a composite particle that includes a particle containing a lithium transition metal composite oxide of Li and Co and a layer that is provided on a surface of the particle and includes an oxide of Li, Ni and Mn. Ni and Mn have a concentration distribution centered on the center from a surface of the composite particle, in a depth range in which a ratio d (%) satisfies 0.04%?d?0.20%, a mole fraction rn of Ni and a mole fraction rm of Mn are within ranges of 0.05?rn and 0.05?rm, respectively, and a ratio rn2/rn1 and a ratio rm2/rm1 are within ranges of 0.85?rn2/rn1?1.0 and 0.85?rm2/rm1?1.0, respectively.

Abstract: A positive electrode active material includes: a particle including a lithium composite oxide; a first layer that is provided on a surface of the particle and includes a lithium composite oxide; and a second layer that is provided on a surface of the first layer. The lithium composite oxide included in the particle and the lithium composite oxide included in the first layer have the same composition or almost the same composition, the second layer includes an oxide or a fluoride, and the lithium composite oxide included in the first layer has lower crystallinity than the lithium composite oxide included in the particle.

Abstract: A secondary battery includes a positive electrode including a positive electrode active material which includes a center portion including a lithium composite oxide including cobalt and an element M, and a covering portion that is provided on at least a portion of a surface of the center portion and contains lithium, nickel, and manganese elements. A concentration thereof has a gradient in a direction from a surface toward a center of the positive electrode active material. A first molar fraction satisfies 0.03<R<0.13 at a first position within the covering portion where the proportion D satisfies D=0.05. A second molar fraction satisfies 0.01<R<0.13 at a second position within the center portion where the proportion D satisfies D=0.3. A ratio F of the second molar fraction to the first molar fraction satisfies 0.7?F?1.

Abstract: A secondary battery includes a positive electrode including a positive electrode active material which includes a center portion including a lithium composite oxide including cobalt and an element M, and a covering portion that is provided on at least a portion of a surface of the center portion and contains lithium, nickel, and manganese elements. A concentration thereof has a gradient in a direction from a surface toward a center of the positive electrode active material. A first molar fraction satisfies 0.03<R<0.13 at a first position within the covering portion where the proportion D satisfies D=0.05. A second molar fraction satisfies 0.01<R<0.13 at a second position within the center portion where the proportion D satisfies D=0.3. A ratio F of the second molar fraction to the first molar fraction satisfies 0.7?F?1.

Abstract: A positive electrode active material includes: a particle including a lithium composite oxide; a first layer that is provided on a surface of the particle and includes a lithium composite oxide; and a second layer that is provided on a surface of the first layer. The lithium composite oxide included in the particle and the lithium composite oxide included in the first layer have the same composition or almost the same composition, the second layer includes an oxide or a fluoride, and the lithium composite oxide included in the first layer has lower crystallinity than the lithium composite oxide included in the particle.

Abstract: A positive electrode active material includes: secondary particles obtained by aggregation of a plurality of primary particles. The primary particles include, core particles including a lithium composite oxide, and a layer that is provided on surfaces of the core particles and includes a lithium composite oxide. The lithium composite oxide included in the core particles and the lithium composite oxide included in the layer have the same composition or almost the same composition, and crystallinity of the lithium composite oxide included in the layer is lower than crystallinity of the lithium composite oxide included in the core particles.

Abstract: A positive electrode active material includes: a composite particle that includes a particle containing a lithium transition metal composite oxide of Li and Co and a layer that is provided on a surface of the particle and includes an oxide of Li, Ni and Mn. Ni and Mn have a concentration distribution centered on the center from a surface of the composite particle, in a depth range in which a ratio d (%) satisfies 0.04%?d?0.20%, a mole fraction rn of Ni and a mole fraction rm of Mn are within ranges of 0.05?rn and 0.05?rm, respectively, and a ratio rn2/rn1 and a ratio rm2/rm1 are within ranges of 0.85?rn2/rn1?1.0 and 0.85?rm2/rm1?1.0, respectively.