Process for producing lithium-containing composite oxide for positive electrode for lithium secondary battery
To provide a cathode active material for a lithium secondary battery, which is low in gas generation and has high safety and excellent durability for charge and discharge cycles even at a high charge voltage. A process for producing a lithium-containing composite oxide represented by the formula Li p L q N x M y O z F a (wherein L is at least one element selected from the group of B and P, N is at least one element selected from the group consisting of Co, Mn and Ni, M is at least one element selected from the group consisting of Al, alkaline earth metal elements and transition metal elements other than N, 0.9≦p≦1.1, 1.0≦q<0.03, 0.97≦x<1.00, 0≦y≦0.03, 1.9≦z≦2.1, q+x+y=1 and 0≦a≦0.02), wherein a lithium-containing composite oxide powder containing an N element and, if necessary, an M element and fluorine, is preliminarily prepared; the lithium-containing composite oxide powder is mixed with an aqueous solution containing the L element source; from the obtained mixture, an aqueous medium is removed, followed by the firing in an oxygen-containing atmosphere at from 300 to 1,050° C.
1. A process for producing a lithium composite oxide, represented by the formula Li p L q N x M y O z F a wherein L is at least one element selected from the group consisting of B and P, N is at least one element selected from the group consisting of Co, Mn and Ni, M is at least one element selected from the group consisting of Al, alkaline earth metal elements and transition metal elements other than N, 0.9≦p≦1.1, 0.0<q≦0.03, 0.97≦x<1.00, 0≦y≦0.03, 1.9≦z≦2.1, q+x+y=1 and 0≦a≦0.02, which comprises
preparing a lithium composite oxide powder comprising an N element and, optionally an M element and fluorine,
mixing the lithium composite oxide powder with an aqueous solution containing an L element source to obtain a first mixture, wherein the aqueous solution comprising an L element source is an aqueous solution comprising boric acid and/or phosphoric acid and a compound having at least two carboxylic acid groups, or carboxylic acid groups and hydroxyl groups, or mixtures thereof;
removing an aqueous medium from the first mixture to obtain a second mixture and
firing said second mixture in an oxygen-containing atmosphere at from 300 to 1,050° C.
2. The process according to claim 1 , wherein the aqueous solution comprising an L element source is an aqueous solution comprising boric acid and a compound having at least two in total of carboxylic acid groups, or carboxylic acid groups and hydroxyl groups, or mixtures thereof.
3. The process according to claim 1 , wherein the aqueous solution comprising an L element source is an aqueous solution comprising phosphoric acid and a compound having at least two in total of carboxylic acid groups, or carboxylic acid groups and hydroxyl groups, or mixtures thereof.
4. The process according to claim 1 , wherein the aqueous solution comprising an L element source has a pH of at most 3.
5. The process according to claim 1 , wherein the M element is at least one element selected from the group consisting of Zr, Hf, Ti, Nb, Ta, Mg, Cu, Sn, Zn and Al.
6. The process according to claim 1 , wherein the M element comprises at least Al and Mg, the atomic ratio of Al/Mg is from 1/3 to 3/1, and 0.005≦y≦0.025.
7. The process according to claim 1 , wherein the M element comprises Mg and M2, wherein M2 is at least one element selected from the group consisting of Zr, Nb, Ta and Ti, the atomic ratio of M2/Mg is from 1/40 to 2/1, and 0.005≦y≦0.025.
8. The process according to claim 1 , wherein the integral breadth of the diffraction peak of (110) plane at 2θ=66.5±1° of the lithium composite oxide is from 0.08 to 0.14° as measured by means of powder X-ray diffraction analysis using CuKα rays, the surface area is from 0.2 to 0.7 m 2 /g, and the heat generation starting temperature is at least 160° C.
9. The process according to claim 1 , wherein N is cobalt and a source of N is cobalt carbonate, cobalt hydroxide, cobalt oxyhydroxide or cobalt oxide, or mixtures thereof.
10. The process according to claim 1 , wherein N is nickel and a source of N is nickel hydroxide or nickel carbonate, or mixtures thereof.
11. The process according to claim 1 , wherein N is manganese and a source of N is manganese carbonate.
12. The process according to claim 1 , wherein a source of the M element is in powder form with an average particle size of from 0.1 to 20 μm.
13. The process according to claim 1 , wherein the aqueous solution comprising an L element source comprises carboxylic acid in an amount of from 1 to 20 mass %, based on the mass of the aqueous solution.
14. The process according to claim 13 , wherein the carboxylic acid is at least one carboxylic acid selected from the group consisting of citric acid, oxalic acid, lactic acid, tartaric acid, maleic acid, malonic acid, and succinic acid.
15. The process according to claim 13 , wherein the carboxylic acid is citric acid.
16. The process according to claim 1 , wherein the removing an aqueous medium from the first mixture comprises drying said aqueous solution at a temperature of from 80 to 120° C.
17. The process according to claim 1 , wherein the firing is performed at a temperature of from 400 to 700° C.