The positive electrode active material according to the present invention may: comprise lithium, a transition metal, and oxygen; comprise a layered crystalline structure in which a lithium layer comprising the lithium and a transition metal layer comprising the transition metal are alternately and repeatedly arranged; and have provided, in the lithium layer or the transition metal layer, a partially regular mixed structure in which a unit arrangement is repeatedly provided in one direction, the unit arrangement having any one of the transition metal and the lithium arranged twice in a row in the one direction, and then the other arranged one time in the one direction.

The positive electrode active material according to the present invention may: comprise lithium, a transition metal, and oxygen; comprise a layered crystalline structure in which a lithium layer comprising the lithium and a transition metal layer comprising the transition metal are alternately and repeatedly arranged; and have provided, in the lithium layer or the transition metal layer, a partially regular mixed structure in which a unit arrangement is repeatedly provided in one direction, the unit arrangement having any one of the transition metal and the lithium arranged twice in a row in the one direction, and then the other arranged one time in the one direction.

An electrode active material in the present disclosure has at least one O2-like structure selected from among of an O2-type structure, a T#2-type structure, and an O6-type structure. The crystallite size of the O2-like structure that is measured by XRD is 400 or more and 1000 or less.

An electrode active material in the present disclosure has at least one O2-like structure selected from among of an O2-type structure, a T#2-type structure, and an O6-type structure. The crystallite size of the O2-like structure that is measured by XRD is 400 or more and 1000 or less.

An electrode active material in the present disclosure has at least one O2-like structure selected from among an O2-type structure, a T#2-type structure, and an O6-type structure, and has a chemical composition shown as Li.sub.aNa.sub.bNi.sub.x-pCO.sub.y-qMn.sub.z-rM.sub.p+q+rO.sub.2(0<a1.00, 0b0.20, 0.15<x<0.35, 0.15<y<0.45, 0.25<z<0.50, x+y+z=1, and 0p+q+r<0.17 are satisfied, and an element M is at least one element selected from among B, Mg, Al, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W).

An electrode active material in the present disclosure has at least one O2-like structure selected from among an O2-type structure, a T#2-type structure, and an O6-type structure, and has a chemical composition shown as Li.sub.aNa.sub.bNi.sub.x-pCO.sub.y-qMn.sub.z-rM.sub.p+q+rO.sub.2(0<a1.00, 0b0.20, 0.15<x<0.35, 0.15<y<0.45, 0.25<z<0.50, x+y+z=1, and 0p+q+r<0.17 are satisfied, and an element M is at least one element selected from among B, Mg, Al, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W).

A positive electrode active material comprises a first active material represented by a formula (I) and a second active material represented by a formula (II). The formula (I) and the formula (II) are as specified in the claims. Each of the first active material and the second active material is secondary particles each consisting of 50 or more primary particles aggregated together. An average particle size (D.sub.150) of the first active material is smaller than an average particle size (D.sub.250) of the second active material.

A positive electrode active material comprises a first active material represented by a formula (I) and a second active material represented by a formula (II). The formula (I) and the formula (II) are as specified in the claims. Each of the first active material and the second active material is secondary particles each consisting of 50 or more primary particles aggregated together. An average particle size (D.sub.150) of the first active material is smaller than an average particle size (D.sub.250) of the second active material.

A positive electrode active material comprises a first active material represented by a formula (I) that is secondary particles each consisting of 50 or more primary particles aggregated together, as well as a second active material represented by a formula (II) that is at least one of single particles and secondary particles each consisting of 2 to 10 primary particles aggregated together. The formula (I) and the formula (II) are as specified in the claims. A content of the first active material in the positive electrode active material is from 20 to 70 mass %. A ratio (D.sub.150/D.sub.250) of an average particle size (D.sub.150) of the first active material to an average particle size (D.sub.250) of the second active material is from 2.45 to 5.95.

A positive electrode active material comprises a first active material represented by a formula (I) that is secondary particles each consisting of 50 or more primary particles aggregated together, as well as a second active material represented by a formula (II) that is at least one of single particles and secondary particles each consisting of 2 to 10 primary particles aggregated together. The formula (I) and the formula (II) are as specified in the claims. A content of the first active material in the positive electrode active material is from 20 to 70 mass %. A ratio (D.sub.150/D.sub.250) of an average particle size (D.sub.150) of the first active material to an average particle size (D.sub.250) of the second active material is from 2.45 to 5.95.