Positive electrode active material, positive electrode, and nonaqueous electrolyte cell

1. A positive electrode active material wherein at least one metallic element M 1 different from a principal transition metal element A is present at least at part of a surface of a lithium-containing transition metal oxide particle containing the principal transition metal element A, and

wherein a compound of a metallic element M 2 different from the metallic element M 1 is present in a coating manner or in the vicinity of the lithium-containing transition metal oxide particle, wherein the metallic element M 1 is at least one selected from the group consisting of Mn, Fe, Mg, Al, Ni, and Co, wherein the metallic element M 2 is at least one selected from the group consisting of Na, Li, Mg, Zr, Zn, Ba, Bi, Y, Ti, Al, and B, and wherein a concentration of the metallic element M 1 varies continuously from the surface towards a center of the lithium-containing transition metal oxide particle such that the metallic element M 1 has a continuous concentration gradient towards the center of the lithium-containing transition metal oxide particle, wherein the compound of the metallic element M 2 is a metallic salt,

wherein the metallic salt provides the positive electrode active material with an overall composition with atomic ratio of 0.001<(metallic element M 2 )/((metallic element M 2 )+(principal transition metal element A))<0.3, and has an average particle diameter of not more than 25 μm.

2. The positive electrode active material according to claim 1 , having an overall composition with atomic ratio of 0.001<(metallic element M 1 )/((metallic element M 1 )+(principal transition metal element A))<0.2.

3. The positive electrode active material according to claim 1 , wherein the compound of the metallic element M 2 contains phosphorus.

4. The positive electrode active material according to claim 3 , wherein the compound of the metallic element M 2 is at least one metallic salt represented by the formula: (M 2 )xPOyFz, where 0<x≦3, 0<y≦4, and 0≦z≦6.

5. The positive electrode active material according to claim 1 , wherein a metallic halide is used as the compound of the metallic element M 2 , and provides the positive electrode active material with an overall composition with atomic ratio of 0.001<(metallic element M 2 )/(((metallic element M 2 )+(principal transition metal element A))<0.15, and wherein the metallic halide has an average particle diameter of not more than 30 μm.

6. The positive electrode active material according to claim 5 , wherein the compound of the metallic element M 2 is a metallic fluoride.

7. The positive electrode active material according to claim 1 , wherein the lithium-containing transition metal oxide has a laminar rock salt structure.

8. The positive electrode active material according to claim 1 , wherein the principal transition metal element A is at least one selected from the group consisting of Ni, Co, and Mn.

9. The positive electrode active material according to claim 1 , wherein the metallic element M 1 is uniformly distributed on the surface of the lithium containing transition metal oxide particle, and wherein the metallic element M 2 is deposited on the surface of the lithium-containing transition metal oxide particle or is present between particles of the lithium-containing transition metal oxide.

10. The positive electrode active material according to claim 1 , wherein the compound of the metallic element M 2 does not contain the metallic element M 1 .

11. The positive electrode active material according to claim 1 , wherein the metallic element M 1 is diffused into an inside portion of the lithium-containing transition metal oxide particle.

12. A positive electrode comprising:

a positive electrode active material, wherein at least one metallic element M 1 different from a principal transition metal element A is present at least at part of a surface of a lithium-containing transition metal oxide particle containing the principal transition metal element A, and

wherein a compound of a metallic element M 2 different from the metallic element M 1 is present in a coating manner or in the vicinity of the lithium-containing transition metal oxide particle, wherein the metallic element M 1 is at least one selected from the group consisting of Mn, Fe, Mg, Al, Ni, and Co, wherein the metallic element M 2 is at least one selected from the group consisting of Na, Li, Mg, Zr, Zn, Ba, Bi, Y, Ti, Al, and B, and wherein a concentration of the metallic element M 1 varies continuously from the surface towards a center of the lithium-containing transition metal oxide particle such that the metallic element M 1 has a continuous concentration gradient towards the center of the lithium-containing transition metal oxide particle, wherein the compound of the metallic element M 2 is a metallic oxide,

wherein the metallic oxide provides the positive electrode active material with an overall composition with atomic ratio of 0.002<(metallic element M 2 )/((metallic element M 2 )+(principal transition metal element A))<0.15, and wherein the metallic oxide has an average particle diameter of not more than 20 μm.

13. The positive electrode according to claim 12 , having an overall composition with atomic ratio of 0.001<(metallic element M 1 )/((metallic element M 1 )+(principal transition metal element A))<0.2.

14. A nonaqueous electrolyte cell comprising:

a positive electrode having a positive electrode current collector provided thereon with a positive electrode active material layer containing a positive electrode active material, a negative electrode, and an electrolyte solution,

wherein the positive electrode active material contains a material in which at least one metallic element M 1 different from a principal transition metal element A is present at least at part of a surface of a lithium-containing transition metal oxide particle containing the principal transition metal element A, and

wherein a metallic element M 2 different from the metallic element M 1 is present in a coating manner or in the vicinity of the lithium-containing transition metal oxide particle, wherein the metallic element M 1 is at least one selected from the group consisting of Mn, Fe, Mg, Al, Ni, and Co, wherein the metallic element M 2 is at least one selected from the group consisting of Na, Li, Mg, Zr, Zn, Ba, Bi, Y, Ti, Al, and B, and wherein a concentration of the metallic element M 1 varies continuously from the surface towards a center of the lithium-containing transition metal oxide particle such that the metallic element M 1 has a continuous concentration gradient towards the center of the lithium-containing transition metal oxide particle, wherein the metallic element M 2 is a metallic salt,

wherein the metallic salt provides the positive electrode active material with an overall composition with atomic ratio of 0.001<(metallic element M 2 )/((metallic element M 2 )+(principal transition metal element A))<0.3, and has an average particle diameter of not more than 25 μm.

15. The nonaqueous electrolyte cell according to claim 14 , wherein the positive electrode active material has an overall composition with atomic ratio of 0.001<(metallic element M 1 )/((metallic element M 1 )+(principal transition metal element A))<0.2.

16. The nonaqueous electrolyte cell according to claim 15 , wherein the lithium-containing transition metal oxide has a laminar rock salt structure, and an upper limit of charging voltage is in the range of from 4.25 to 4.50 V, and a lower limit of discharging voltage is in the range of from 2.00 to 3.30 V.