Cathode active material for non-aqueous electrolyte secondary battery and its production method
A cathode active material for a non-aqueous electrolyte secondary battery comprises a lithium-containing composite oxide powder, which is represented by the formula Li p N x M y O z F a wherein N is at least one element selected from the group consisting of Co, Mn and Ni, M is zirconium and optionally at least one element selected from the group consisting of Al, alkaline earth metal elements and transition metal elements other than the element N, 0.9≦p≦1.1, 0.965≦x≦1.00, 0≦y≦0.035, 1.9≦z≦2.1, x+y=1 and 0≦a≦0.02, an atomic ratio of zirconium/the element N is in a range of at least 1.0 to 4.0. A method to produce the cathode active material is provided.
1. A cathode active material comprising a lithium-containing composite oxide powder represented by the formula
Li p N x M y O z F a
wherein
N is Co,
M is zirconium and optionally at least one element selected from the group consisting of Al, alkaline earth metal elements and transition metal elements other than cobalt,
0.9≦p≦1.1,
0.965≦x≦1.00,
0≦y≦0.035,
1.9≦z≦2.1,
x+y=1 and
0≦a≦0.02, and
an atomic ratio of zirconium/cobalt in a surface layer within 5 nm of the surface is from 1.0 to 4.0, and
wherein the cathode active material is for a non-aqueous electrolyte secondary battery.
2. The cathode active material according to claim 1 , wherein the lithium-containing composite oxide powder comprises zirconium in an atomic ratio of from 0.00005 to 0.01 relative to a total of the element M and the cobalt.
3. The cathode active material according to claim 1 , wherein 0.975≦x≦0.995 and 0.005≦y≦0.025.
4. The cathode active material according to claim 1 ,
wherein the element M is zirconium and at least one element selected from the group consisting of magnesium and aluminum.
5. The cathode active material according to claim 1 , further comprising carbon in the surface layer within 5 nm.
6. A positive electrode for a lithium secondary battery comprising:
the cathode active material according to claim 1 ;
an electrical conducting material; and
a binder.
7. A lithium secondary battery comprising:
the positive electrode according to claim 6 ;
a negative electrode; and
a non-aqueous electrolyte.
8. A process for producing the cathode active material according to claim 1 , comprising:
applying a zirconium-containing aqueous solution to a lithium-containing composite oxide powder, with stirring under low shear;
to obtain a zirconium-added powder having a dense and uniform film of zirconium near the surface of the lithium-containing composite oxide powder, and
firing the zirconium-added powder in an atmosphere comprising oxygen.
9. The process according to claim 8 , wherein
a pH of the applied zirconium aqueous solution is from 3 to 12
the zirconium aqueous solution is applied to the lithium-containing composite oxide powder by spraying thereto, and
a temperature of the firing the zirconium-added powder is from 200 to 600° C.
10. The process according to claim 9 , wherein the zirconium aqueous solution comprises zirconium ammonium carbonate or a zirconium ammonium halide.