Process for producing cathode active material for lithium ion secondary battery

A process for producing a cathode active material for a lithium ion secondary battery, comprising the following steps (I), (II) and (III) in this order:

• step (I):
• a step of bringing a lithium-containing composite oxide (I) containing Li element and a transition metal element into contact with a washing liquid and then separating it from the washing liquid to obtain a lithium-containing composite oxide (II),
• step (II):
• a step of bringing the lithium-containing composite oxide (II) into contact with the following composition (1) and composition (2) to obtain a lithium-containing composite oxide (III), and
• step (III):
• a step of heating the lithium-containing composite oxide (III),
• composition (1):
• an aqueous solution containing a monoatomic or polyatomic anion (A) containing at least one element (a) selected from the group consisting of S, P, F and B,
• composition (2):
• an aqueous solution containing a monoatomic or complex cation (M) of at least one metal element (m) selected from the group consisting of Li, Mg, Ca, Sr, Ba, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Zn, Al, Ga, In, Sn, Sb, Bi, La, Ce, Pr, Nd, Gd, Dy, Er and Yb.