Method of producing cathode active material, and method of producing lithium ion battery

A method of producing a lithium ion battery, the method comprising:

• a step of making a cathode active material layer containing a cathode active material;
• and
• a step of using the cathode active material layer, an anode active material layer containing an anode active material, and an electrolyte layer containing an electrolyte, to arrange the electrolyte layer between the cathode active material layer and the anode active material layer,
• wherein the cathode active material is produced by a method comprising:
• 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,
• 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, and
• a O2 structure and a O3 structure coexist in a single particle of the cathode active material obtained by the ion exchange step, and
• wherein an initial average discharge potential of the cathode active material is at least 3.76V.