Lithium-containing composite oxide and its production process

1. A process for producing a lithium-containing composite oxide represented by the formula Li p N x M y O z F a , where

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 Co, Mn and Ni,

0.9≦p≦1.2, 0.95≦x<2.00, 0<y≦0.05, 1.9≦z≦4.2 and 0≦a≦0.05, the process comprising

a step 1 of mixing a lithium source, an N element source, an M element source containing at least Al, and if necessary, a fluorine source, and firing the mixture in an oxygen-containing atmosphere at from 700 to 1,100° C. to obtain a fired powder; and

a step 2 of mixing the fired powder obtained in step 1, an M element salt aqueous solution containing at least Zr and/or Ti, and if necessary, a fluorine source, and firing the mixture in an oxygen-containing atmosphere at from 300 to 1,100° C. to produce the lithium-containing composite oxide, wherein

the amount of Zr and/or Ti contained in the lithium-containing composite oxide powder obtained in step 2 is from 0.1 to 30 weight % based on the M elements.

2. The process according to claim 1 , wherein in the above step 1, the M element source is an M element source in the form of an aqueous solution of an M element-containing carboxylate containing at least Al, and the M element-containing carboxylate is a carboxylate having at least two carboxyl groups or having at least two carboxyl group(s), hydroxyl group(s) or carbonyl group(s) in total.

3. The process according to claim 2 , wherein the M element-containing carboxylate is a salt of at least one acid selected from the group consisting of citric acid, maleic acid, lactic acid and tartaric acid.

4. The process according to claim 2 , wherein the M element-containing carboxylate aqueous solution has a pH of from 2 to 12.

5. The process according to claim 1 , wherein the N element source and the M element source in the above step 1 are an N-M element coprecipitate precipitated by adding a pH adjustor and an alkali to an aqueous solution having an M element salt containing at least Al and an N element salt dissolved therein.

6. The process according to claim 1 , wherein the M element source in step 1 contains at least Al and Mg.

7. The process according to claim 1 , wherein

the lithium-containing composite oxide powder obtained in step 2 comprises particles each having a particle surface and a particle center; and

the Zr and/or Ti concentration in the vicinity of the particle surface is higher than the Zr and/or Ti concentration in the vicinity of the particle center.

8. The process according to claim 1 , wherein in step 2 the M element salt aqueous solution is an aqueous solution containing zirconium ammonium carbonate and/or a zirconium ammonium halide.

9. The process according to claim 1 , wherein in step 2 the M element salt aqueous solution is an aqueous solution containing titanium lactate.

10. The process according to claim 1 , wherein in step 2 the M element salt aqueous solution further contains magnesium.

11. The process according to claim 1 , wherein the N element source is at least one member selected from the group consisting of a nickel salt, a cobalt salt, a nickel-cobalt coprecipitate and a nickel-cobalt-manganese coprecipitate.

12. 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.

13. The process according to claim 1 , wherein the M element contains Al, Zr and/or Ti, and at least one element selected from the group consisting of Hf, Nb, Ta, Mg, Sn and Zn.

14. The process according to claim 1 , wherein the M element contains Al, and Zr and/or Ti, in an Al/(Zr and/or Ti) atomic ratio of from 1/2 to 40/1.