Process for production of cathode active material for lithiun ion secondary battery
To provide a process for producing a surface modified lithium-containing composite oxide, which is excellent in discharge capacity, volume capacity density, safety, durability for charge and discharge cycles and an excellent rate property, at a low production cost. The present invention is characterized in that a process for producing a surface modified lithium-containing composite oxide, wherein a lithium titanium composite oxide is contained in the surface layer of particles of 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, Sn, alkaline earth metal elements and transition metal elements other than Co, Mn and Ni, 0.9≦p≦1.3, 0.9≦x≦2.0, 0≦y≦0.1, 1.9≦z≦4.2, and 0≦a≦0.05, which comprises impregnating a solution having a lithium source and a titanium source dissolved therein, followed by heat treatment at a determined temperature, to obtain the surface modified lithium-containing composite oxide, wherein the titanium contained in the surface layer is from 0.01 to 1.95 mol %.
1. A process for producing a surface modified lithium-containing composite oxide for a cathode active material for a lithium ion secondary battery, wherein a lithium titanium composite oxide is contained in a surface layer of particles of 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, Sn, alkaline earth metal elements and transition metal elements other than Co, Mn and Ni, 0.9≦p≦1.3, 0.9≦x≦2.0, 0≦y≦0.1, 1.9≦z≦4.2, and 0≦a≦0.05,
which comprises impregnating a solution comprising a lithium source and a titanium source dissolved therein into a powder of the lithium-containing composite oxide, and subjecting obtained lithium titanium-impregnated particles to heat treatment at from 400 to 1,000° C., to obtain the surface modified lithium-containing composite oxide, wherein the amount of titanium contained in the surface layer is from 0.01 to 1.95 mol % to the amount of lithium-containing composite oxide used as a base material.
2. The process according to claim 1 , wherein the lithium titanium composite oxide is at least one member selected from the group consisting of Li 2 Ti 3 O 7 , Li(Li 1/3 Ti 5/3 )O 4 , LiTiO 2 , Li 2 (Li 1/3 Ti 5/3 )O 4 and Li 2 TiO 3 .
3. The process according to claim 1 , wherein the atomic ratio of lithium to titanium (Li/Ti) contained in the lithium titanium composite oxide is from 1/100 to 5/1.
4. The process according to claim 1 , wherein the solution having the lithium source and the titanium source dissolved therein contains a carboxylic acid having at least 2 carboxyl groups, or at least 2 in total of carboxyl groups and hydroxyl groups or carbonyl groups.
5. The process according to claim 1 , wherein the solution having the lithium source and the titanium source dissolved therein has a pH of from 1 to 7.
6. The process according to claim 1 , wherein the titanium source is titanium lactate.
7. The process according to claim 1 , wherein the solution having the lithium source and the titanium source dissolved therein is an aqueous solution.
8. The process according to claim 1 , wherein element M contains at least one element selected from the group consisting of Al, Ti, Zr, Hf, Nb, Ta, Mg, Sn and Zn.
9. The process according to claim 1 , wherein the lithium source is lithium carbonate.
10. The process according to claim 1 , wherein element N is Co.