Process for producing cathode active material for lithium ion secondary battery

1. 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.

2. The process for producing a cathode active material for a lithium ion secondary battery according to claim 1 , wherein the metal element (m) contained in the composition (2) is Al.

3. The process for producing a cathode active material for a lithium ion secondary battery according to claim 1 , wherein in the step (II), the lithium-containing composite oxide (II) is brought into contact with the compositions (1) and (2) so that the sum of the products of the absolute value of the valence of each cation (M) and the molar ratio of the cation (M) contained in the composition (2) based on the total amount of the transition metal element contained in the lithium-containing composite oxide (I), is within a range of from 0.001 to 0.15.

4. The process for producing a cathode active material for a lithium ion secondary battery according to claim 1 , wherein the anion (A) contained in the composition (1) is F − .

5. The process for producing a cathode active material for a lithium ion secondary battery according to claim 1 , wherein in the step (II), the lithium-containing composite oxide (II) is brought into contact with the compositions (1) and (2) so that the sum of the products of the absolute value of the valence of each anion (A) and the molar ratio of the anion (A) contained in the composition (1) based on the total amount of the transition metal element contained in the lithium-containing composite oxide (I), is within a range of from 0.001 to 0.15.

6. The process for producing a cathode active material for a lithium ion secondary battery according to claim 1 , wherein in the step (I), the washing liquid is an aqueous acidic solution having a pH of from 0 to 6 at 25° C.

7. The process for producing a cathode active material for a lithium ion secondary battery according to claim 1 , wherein the lithium elution ratio is from 0.2 to 10% as represented by the proportion of the amount of lithium element dissolved in the washing liquid based on the entire lithium element contained in the lithium-containing composite oxide (I).

8. The process for producing a cathode active material for a lithium ion secondary battery according to claim 1 , wherein the lithium-containing composite oxide (I) contains Li element and at least one transition metal element selected from the group consisting of Ni, Co and Mn, and the molar amount of the Li element is more than 1.2 times the total molar amount of the transition metal element.

9. The process for producing a cathode active material for a lithium ion secondary battery according to claim 8 , wherein the lithium-containing composite oxide (I) is a compound represented by the following formula (1):

Li(Li x1 Mn y1 Me z1 )Me′ a O p F q   (1)

wherein Me is at least one element selected from the group consisting of Co and Ni, Me′ is at least one member selected from the group consisting of Al, Cr, Mg, Mo, Ru, Ti, Zr and Fe, 0.1<x 1 <0.25, 0.5≤y 1 /(y 1 +z 1 )≤0.8, 0≤a≤0.1, x 1 +y 1 +z 1 =1, 1.9<p<2.1 and 0≤q≤0.1.

10. The process for producing a cathode active material for a lithium ion secondary battery according to claim 1 , wherein the heating in the step (III) is carried out at from 250 to 700° C.

11. The process for producing a cathode active material for a lithium ion secondary according to claim 1 , wherein the solvent of each of the compositions (1) and (2) in the step (II) is only water.

12. The process for producing a cathode active material for a lithium ion secondary battery according to claim 1 , wherein in the step (II), the lithium-containing composite oxide (II) is brought into contact with the composition (1) and the composition (2) by spraying the composition (1) and the composition (2) to the lithium-containing composite oxide (II) by a spray coating method.

13. The process for producing a cathode active material for a lithium ion secondary battery according to claim 12 , wherein in the step (II), the lithium-containing composite oxide (II) is brought into contact with the composition (1) and the composition (2) by spraying the composition (1) and the composition (2) to the lithium-containing composite oxide (II) with stirring.

14. A process for producing a positive electrode for a lithium ion secondary battery, which comprises a step of producing a cathode active material for a lithium ion secondary battery by the production process as defined in claim 1 , and

a step of forming a cathode active material layer containing the cathode active material for a lithium ion secondary battery, a binder and an electrically conductive material on a cathode current collector.

15. A process for producing a lithium ion secondary battery, which comprises a step of producing a positive electrode for a lithium ion secondary battery by the production process as defined in claim 14 , and

a step of assembling a lithium ion secondary battery by using the positive electrode for a lithium ion secondary battery, a negative electrode, a non-aqueous electrolyte and a separator.