Process for producing cathode active material for lithium ion secondary battery, cathode for lithium ion secondary battery, and lithium ion secondary battery
To provide a cathode active material for a lithium ion secondary battery, and its production process. A lithium-containing composite oxide containing a transition metal element and a composition (1) are contacted to obtain particles (I) having a compound containing a metal element (M) attached, which are mixed with a compound which generates HF by heating, and the mixture is heated to obtain particles (III) having a covering layer (II) containing the metal element (M) and fluorine element formed on the surface of the lithium-containing composite oxide. Composition (1): a composition having a compound containing no Li element and containing at least one metal element (M) selected from Mg, Ca, Sr, Ba, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Ni, Pb, Cu, Zn, Al, In, Sn, Sb, Bi, La, Ce, Pr, Nd, Gd, Dy, Er and Yb dissolved or dispersed in a solvent.
1. A process for producing a cathode active material for a lithium ion secondary battery, comprising:
contacting a lithium-containing composite oxide containing Li element and a transition metal element with a composition (1) such that particles (I) are obtained and that the particles (I) comprises the lithium-containing composite oxide and a compound containing a metal element (M) attached to the lithium-containing composite oxide;
mixing the particles (I) and a compound (2) such that a mixture is formed; and
heating the mixture such that particles (III) comprising the lithium-containing composite oxide and a covering layer (II) formed on a surface of the lithium-containing composite oxide are obtained and that the covering layer (II) comprises the metal element (M) and a fluorine element,
wherein the composition (1) comprises a compound containing no Li element and containing the metal element (M),
the metal element (M) is at least one selected from the group consisting of Mg, Ca, Sr, Ba, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Ni, Pb, Cu, Zn, Al, In, Sn, Sb, Bi, La, Ce, Pr, Nd, Gd, Dy, Er and Yb dissolved or dispersed in a solvent,
the compound (2) is a compound which generates HF by heating, and
the mixing of the particles (I) and the compound (2) comprises mixing the particles (I) and a solid form of the compound (2).
2. The process according to claim 1 , wherein the compound (2) is ammonium fluoride or ammonium bifluoride.
3. The process according to claim 1 , wherein the metal element (M) is at least one of Al, Nb and Zr.
4. The process according to claim 1 , wherein the heating is carried out at a temperature of from 250 to 700° C.
5. The process according to claim 1 , wherein, in the contacting, the lithium-containing composite oxide and the composition (1) are contacted such that a molar amount of the metal element (M) in the particles (I) is from 0.001 to 0.05 time of a molar amount of the transition metal element in the lithium-containing composite oxide.
6. The process according to claim 1 , wherein, in the mixing and the heating, the particles (I) and the compound (2) are mixed and heated such that an amount of the fluorine element in the covering layer (II) is from 0.05 to 3 mass % based on the total mass of the cathode active material.
7. The process according to claim 1 , wherein the solvent of the composition (1) is water.
8. The process according to claim 1 , wherein the contacting of the lithium-containing composite oxide and the composition (1) comprises adding the composition (1) to the lithium-containing composite oxide, and stirring and mixing the lithium-containing composite oxide and the composition (1).
9. The process according to claim 1 , wherein the contacting of the lithium-containing composite oxide and the composition (1) comprises spraying the composition (1) to the lithium-containing composite oxide.
10. The process according to claim 1 , wherein the lithium-containing composite oxide is represented by formula (C-1):
Li(Li x Mn y Me′ z )O p F q(C- 1)
where Me′ is at least one element selected from the group consisting of Co, Ni, Cr, Fe, Al, Ti, Zr, and Mg, and x, y, z, p and q satisfy 0.09<x<0.3, y>0, z>0, 1.9<p<2.1, 0≦q≦0.1, 0.4≦y/(y+z)≦0.8, x+y+z=1, and 1.2<(1+x)/(y+z).
11. The process according to claim 10 , wherein x, y, and z in formula (C-1) satisfy 1.25≦(1+x)/(y+z)≦1.75.
12. The process according to claim 1 , wherein the lithium-containing composite oxide has an average particle size (D 50 ) of from 3 to 30 μm.
13. The process according to claim 1 , wherein the lithium-containing composite oxide has an average particle size (D 50 ) of from 4 to 25 μm.
14. The process according to claim 1 , wherein the heating comprises heating the mixture for 1 to 10 hours.
15. The process according to claim 1 , further comprising:
drying the particles (I) at a temperature of from 40 to 200° C. prior to the mixing of the particles (I) and the compound (2).