Particulate positive electrode active material for a lithium secondary cell
A particulate positive electrode active material for a lithium secondary cell which satisfies high charge and discharge cyclic durability, high safety, high temperature storage properties, a high discharge average voltage, large current discharge properties, a high weight capacity density, a high volume capacity density, etc. in a well-balanced manner is provided. A particulate positive electrode active material for a lithium secondary cell, which is represented by the formula Li p Co x M y O z F a (wherein M is at least one element selected from Groups 2 to 8, 13 and 14 of the Periodic Table, 0.9≦p≦1.1, 0.980≦x≦0.9999, 0.0001≦y≦0.02, 1.9≦z≦2.1, 0.9≦x+y≦1 and 0.0001≦a≦0.02), wherein fluorine atoms and element M are unevenly distributed on the particle surface, the atomic ratio of fluorine atoms to cobalt atoms (a/x) is from 0.0001 to 0.02, and in powder X-ray diffraction using CuKα-ray, the half value width of the angle of diffraction on (110) plane is from 0.06 to 0.13°, and the half value width of the angle of diffraction on (003) plane is from 0.05 to 0.12°.
1. A particulate positive electrode active material for a lithium secondary cell, which is represented by the formula Li p Co x M y O z F a (wherein M is at least one element selected from Groups 2 to 8, 13 and 14 of the Periodic Table, 0.9≦p≦1.1, 0.980≦x≦0.9999, 0.0001≦y≦0.02, 1.9≦z≦2.1, 0.9≦x+y≦1 and 0.0001≦a≦0.02), wherein fluorine atoms and element M atoms are unevenly distributed on the particle surface, the atomic ratio of fluorine atoms to cobalt atoms (a/x) is from 0.0001 to 0.008, and in powder X-ray diffraction using CuKα-ray, the half value width of the angle of diffraction on (110) plane is from 0.06 to 0.13°, and the half value width of the angle of diffraction on (003) plane is from 0.05 to 0.12° and wherein no crystal metal fluoride detectable by an X-ray diffraction method is present on the particle surface.
2. The particulate positive electrode active material for a lithium secondary cell according to claim 1 , wherein the fluorine atoms are unevenly distributed within 100 nm from the particle surface, and the element M atoms are unevenly distributed within 100 nm from the particle surface.
3. The particulate positive electrode active material for a lithium secondary cell according to claim 2 , wherein the element M is tetravalent, the ion radius is from 0.1 to 0.9 Å.
4. The particulate positive electrode active material for a lithium secondary cell according to claim 1 , wherein at least a part of the fluorine atoms is a solid solution replaced with oxygen atoms in the interior of the particles, and at least a part of the element M atoms is a solid solution which replaces cobalt atoms in the interior of the particles.
5. The particulate positive electrode active material for a lithium secondary cell according to claim 4 , wherein the element M is tetravalent, the ion radius is from 0.1 to 0.9 Å.
6. The particulate positive electrode active material for a lithium secondary cell according to claim 1 , wherein the element M is at least one member selected from Zr, Ti, V, Nb, Ge, Sn, Al, In, Y, Mo, W, Ga, Mg, Cr, Mn and Fe.
7. The particulate positive electrode active material for a lithium secondary cell according to claim 6 , wherein the element M is tetravalent, the ion radius is from 0.1 to 0.9 Å.
8. The particulate positive electrode active material for a lithium secondary cell according to claim 1 , wherein when the element M is bivalent, trivalent or tetravalent, the ion radius is from 0.3 to 0.9 Å.
9. The particulate positive electrode active material for a lithium secondary cell according to claim 1 , wherein the element M is tetravalent, the ion radius is from 0.1 to 0.9 Å.
10. A lithium secondary cell comprising, the particulate positive electrode active material as claimed in claim 9 .
11. A lithium secondary cell comprising, the particulate positive electrode active material as claimed in claim 1 .
12. A process for producing the particulate positive electrode active material for a lithium secondary cell as defined in claim 1 , which comprises firing a mixture of at least one member selected from an element M-containing oxide, an element M-containing hydroxide and an element M-containing oxyhydroxide, lithium fluoride, and cobalt hydroxide, cobalt oxyhydroxide or cobalt oxide, and lithium carbonate, at from 600 to 1050° C. in an oxygen-containing atmosphere for from 1 to 48 hours.
13. A process for producing the particulate positive electrode active material for a lithium secondary cell as defined in claim 1 , which comprises firing a mixture of an element M-containing fluoride, and cobalt hydroxide, cobalt oxyhydroxide or cobalt oxide, and lithium carbonate, at from 600 to 1050° C. in an oxygen-containing atmosphere for from 1 to 48 hours.
14. A process for producing the particulate positive electrode active material for a lithium secondary cell as defined in claim 1 , which comprises firing a mixture of at least one member selected from an element M-containing oxide, an element M-containing hydroxide element, an M-containing oxyhydroxide and an M-containing fluoride, lithium fluoride (except for a case where an element M-containing fluoride is used), cobalt hydroxide and/or cobalt oxyhydroxide formed by agglomeration of a large number of primary particles, and lithium carbonate, at from 600 to 1050° C. in an oxygen-containing atmosphere for from 1 to 48 hours.