Abstract: Disclosed are positive electrode active material particles having both high-capacity and cycling properties. The positive electrode active material particles of the present disclosure have an O2-type structure, and comprise: at least one element selected from Mn, Ni and Co; Li; an element M; and O, wherein the element M is at least one selected from B, Mg, Al, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo and W, and the molar concentration of the element M in the surface layer portion of the particles is higher than the molar concentration of the element M in the central portion of the particles.

Abstract: A major object is to provide a method of producing a cathode active material having a high average discharge potential, and a high degree of stability at high potential. The method includes: a step of preparing a Na-doped precursor of making a sodium-containing transition metal oxide having the P2 structure belonging to a space group of P63/mmc; and an ion exchange step of substituting lithium for at least part of sodium contained in the sodium-containing transition metal oxide by the ion exchange method, wherein in the ion exchange step, at least lithium iodide is used as a Li ion source.

Abstract: A main object of the present disclosure is to provide a cathode active material having excellent capacity properties. The present disclosure achieves the object by providing a method for producing a cathode active material including an O2-type structure, the method comprising: a preparing step of preparing a transition metal oxide containing Na and including a P2-type structure; and an ion exchanging step of exchanging a Na ion included in the transition metal oxide with a Li ion; wherein temperature for the ion exchanging is 350° C. or more and 600° C. or less.

Abstract: A main object is to provide a method of producing a cathode active material having a high average discharge potential, and a high degree of stability at high potential. A step of preparing a Na-doped precursor of making a transition metal oxide having a P2 structure belonging to a space group of P63/mmc; and an ion exchange step of substituting lithium for at least part of sodium contained in the transition metal oxide by an ion exchange method are included, wherein the transition metal oxide has the composition represented by NaaMnx-pNiy-qCoz-rM1p+q+rO2, where 0.5?a?1, x+y+z=1, 3?4x+2y+3z?3.5, and 0.05?p+q+r<0.25, M1 is Al or Mo, when M1 is Al, p is not equal to q, and any one of p and q is not 0.

Abstract: A major object is to provide a method of producing a cathode active material having a high average discharge potential, and a high degree of stability at high potential. The method includes: a step of preparing a Na-doped precursor of making a sodium-containing transition metal oxide having the P2 structure belonging to a space group of P63/mmc; and an ion exchange step of substituting lithium for at least part of sodium contained in the sodium-containing transition metal oxide by the ion exchange method, wherein in the ion exchange step, at least lithium iodide is used as a Li ion source.