Process for producing lithium-containing composite oxide for positive electrode for lithium secondary battery
To provide a process for producing a lithium-containing composite oxide for a positive electrode for a lithium secondary battery, which is excellent in the volume capacity density, safety, charge and discharge cycle durability and low temperature characteristics. A process for producing a lithium-containing composite oxide represented by the formula Li p N x M m O z F a (wherein 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≦1.2, 0.97≦x<1.00, 0<m≦0.03, 1.9≦z≦2.2, x+m=1 and 0≦a≦0.02), which process comprises firing a mixture of a lithium source, an N element source and an M element source, and if necessary, a fluorine source, in an oxygen-containing atmosphere, characterized in that as the M element source, an aqueous solution of a ketocarboxylate compound having the M element, at least one carboxyl group and at least one carbonyl group in its molecule, is used.
1. A process for producing a lithium-containing composite oxide represented by:
Li p N x M m O z F a
wherein
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≦1.2,
0.97≦x<1.00,
0<m≦0.03,
1.9≦z≦2.2,
x+m=1 and
0≦a≦0.02, which process comprises
firing a mixture comprising a lithium source, an N element source, and an M element source, and optionally a fluorine source, in an atmosphere comprising oxygen,
wherein said M element source is an aqueous solution of a ketocarboxylate compound having the M element, at least is one carboxyl group, and at least one carbonyl group present within the ketocarboxylate molecule.
2. The process according to claim 1 , wherein the N element source is a powder having an average particle size, D50, of from 1 to 25 μm.
3. The process according to claim 1 , wherein the ketocarboxylate is one having from 2 to 8 carbon atoms.
4. The process according to claim 1 , further comprising adjusting a pH of the aqueous solution of a ketocarboxylate compound to a value of from 2 to 12 by adding an alkali.
5. The process according to claim 4 , wherein the pH of the aqueous solution of a ketocarboxylate compound is from 4 to 10.
6. The process according to claim 5 , wherein said pH is obtained by adding ammonia as said alkali to said aqueous solution of a ketocarboxylate compound.
7. The process according to claim 1 , wherein the N element source is at least one member selected from the group consisting of cobalt hydroxide, cobalt oxyhydroxide, tricobalt tetroxide and cobalt carbonate.
8. The process according to claim 1 , wherein the N element source is at least one member selected from the group consisting of nickel-cobalt coprecipitated hydroxide, nickel-cobalt coprecipitated oxyhydroxide, nickel-cobalt coprecipitated oxide, nickel-manganese coprecipitated hydroxide, nickel-manganese coprecipitated oxyhydroxide, nickel-manganese coprecipitated oxide, nickel-cobalt-manganese coprecipitated hydroxide, nickel-cobalt-manganese coprecipitated oxyhydroxide and nickel-cobalt-manganese coprecipitated oxide.
9. The process according to claim 1 , wherein the M element is at least one member selected from the group consisting of Ti, Zr, Hf, Nb, Ta, Mg, Sn, Zn, Cu and Al.
10. The process according to claim 1 ,
further comprising mixing said aqueous solution of a ketocarboxylate compound, a powder of the N element source, and if necessary, a powder of the fluorine source to obtain a mixture;
removing the water from said mixture; and then,
mixing a powder of the lithium source and optionally a powder of the fluorine source with said mixture; wherein said firing is carried out at a temperature of from 800 to 1,050° C.
11. The process according to claim 1 ,
further comprising mixing said aqueous solution of a ketocarboxylate compound, a powder of the N element source, a powder of the lithium source and optionally a powder of the fluorine source to obtain a mixture, and;
removing the water from said mixture; wherein said firing is carried out at a temperature of from 800 to 1,050° C.
12. The process according to claim 1 , further comprising mixing a lithium-containing composite oxide powder obtained by said firing with an aqueous solution of a ketocarboxylate compound to obtain a mixture;
removing the water from said mixing; and then
firing said mixture at a temperature of from 300 to 1,050° C. in an atmosphere comprising oxygen.
13. The process according to claim 1 , further comprising mixing at least an N element source and an M element source so that the N element: the M element atomic ratio is from 0.95:0.05 to 0.9995:0.0005.
14. The process according to claim 13 , wherein the N element source is at least one member selected from the group consisting of a hydroxide, an oxyhydroxide, an oxide and a carbonate.
15. The process according to claim 10 , wherein said removing is carried out at a temperature of from 50 to 200° C. for a period of from 1 to 10 hours.
16. The process according to claim 1 , wherein said lithium source is selected from the group consisting of lithium carbonate and lithium hydroxide.
17. The process according to claim 1 , wherein said mixture comprises a fluorine source selected from the group consisting of LiF and MgF 2 .
18. The process according to claim 1 , wherein said firing is carried out at a temperature of from 800 to 1,050° C.