Positive electrode active material, positive electrode, nonaqueous electrolyte cell, and method of preparing positive electrode active material

1. A positive electrode active material prepared by:

mixing a lithium-containing compound, a compound containing a transition metal M1 to be involved in a solid solution, and a compound containing a metallic element M2 different from the transition metal M1, and firing the mixture to form composite oxide particles having a laminar rock salt structure and an average composition represented by Chemical formula 1:

Li a A b M 1-b O c   Chemical formula 1

where A represents at least one element selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn) and iron (Fe); M represents at least one element selected from the group consisting of manganese (Mn), magnesium (Mg), aluminum (Al), nickel (Ni), boron (B), titanium (Ti), cobalt (Co) and iron (Fe); and a, b and c are numbers in the ranges of 0.2≦a≦1.4, 0≦b≦1.0, and 1.8≦c≦2.2;

depositing a compound containing at least one element selected from among sulfur (S), phosphorus (P) and fluorine (F) on surfaces of the composite oxide particles; and

firing the composite oxide particles with the compound containing at least one element selected from among sulfur (S), phosphorus (P) and fluorine (F) deposited thereon;

whereby each of the composite oxide particles is provided with a concentration gradient such that the concentration of the metallic element M2 increases from the center toward the surface of the composite oxide particle, and

at least one element selected from among sulfur (S), phosphorus (P) and fluorine (F) is made present in the form of being aggregated at the surfaces of the composite oxide particles.

2. The positive electrode active material according to claim 1 , wherein the transition metal M1 is at least selected one element selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn) and iron (Fe).

3. The positive electrode active material according to claim 1 , wherein the metallic element M2 is at least one element selected from among manganese (Mn), magnesium (Mg), aluminum (Al), nickel (Ni), boron (B), titanium (Ti), cobalt (Co) and iron (Fe).

4. The positive electrode active material according to claim 1 , wherein the firing of the composite oxide particles with the compound containing at least one element selected from among sulfur (S), phosphorus (P) and fluorine (F) deposited thereon is conducted in the co-existence of a lithium-containing compound.

5. The positive electrode active material according to claim 1 , wherein the compound containing at least one element selected from among sulfur (S), phosphorus (P) and fluorine (F) or the thermally decomposed product of said compound has a melting point of 70° C. or more and 600° C. or less.

6. The positive active material according to claim 1 , wherein the compound containing at least one element selected from among sulfur (S), phosphorus (P) and fluorine (F) or the thermally decomposed product of said compound preferably has an average diameter of 30 μm or less.

7. A positive electrode comprising a positive electrode material which is prepared by:

mixing a lithium-containing compound, a compound containing a transition metal M1 to be put into a solid solution, and a compound containing a metallic element M2 different from the transition metal M1, and firing the mixture to form composite oxide particles having a laminar rock salt structure and an average composition represented by Chemical formula 1:

Li a A b M 1-b O c   Chemical formula 1

where A represents at least one element selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn) and iron (Fe); M represents at least one element selected from the group consisting of manganese (Mn), magnesium (Mg), aluminum (Al), nickel (Ni), boron (B), titanium (Ti), cobalt (Co) and iron (Fe); and a, b and c are numbers in the ranges of 0.2≦a≦1.4, 0≦b≦1.0, and 1.8≦c≦2.2;

depositing a compound containing at least one element selected from among sulfur (S), phosphorus (P) and fluorine (F) on surfaces of the composite oxide particles; and

firing the composite oxide particles with the compound containing at least one element selected from among sulfur (S), phosphorus (P) and fluorine (F) deposited thereon;

whereby each of the composite oxide particles is provided with a concentration gradient such that the concentration of the metallic element M2 increases from the center toward the surface of the composite oxide particle, and

at least one element selected from among sulfur (S), phosphorus (P) and fluorine (F) is made present in the form of being aggregated at the surfaces of the composite oxide particles.

8. A nonaqueous electrolyte cell comprising a positive electrode, a negative electrode, and an electrolyte,

wherein the positive electrode include a positive electrode active material which is prepared by:

mixing a lithium-containing compound, a compound containing a transition metal M1 to be put into a solid solution, and a compound containing a metallic element M2 different from the transition metal M1, and firing the mixture to form composite oxide particles having a laminar rock salt structure and an average composition represented by Chemical formula 1:

Li a A b M 1-b O c   Chemical formula 1

where A represents at least one element selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn) and iron (Fe); M represents at least one element selected from the group consisting of manganese (Mn), magnesium (Mg), aluminum (Al), nickel (Ni), boron (B), titanium (Ti), cobalt (Co) and iron (Fe); and a, b and c are numbers in the ranges of 0.2≦a≦1.4, 0≦b≦1.0, and 1.8≦c≦2.2;

depositing a compound containing at least one element selected from among sulfur (S), phosphorus (P) and fluorine (F) on surfaces of the composite oxide particles; and

firing the composite oxide particles with the compound containing at least one element selected from among sulfur (S), phosphorus (P) and fluorine (F) deposited thereon;

whereby each of the composite oxide particles is provided with a concentration gradient such that the concentration of the metallic element M2 increases from the center toward the surface of the composite oxide particle, and

at least one element selected from among sulfur (S), phosphorus (P) and fluorine (F) is made present in the form of being aggregated at the surfaces of the composite oxide particles.

9. A method of preparing a positive electrode active material comprising:

mixing a lithium-containing compound, a compound containing a transition metal M1 to be put into a solid solution, and a compound containing a metallic element M2 different from the transition metal M1, and firing the mixture to form composite oxide particles having a laminar rock salt structure and an average composition represented by Chemical formula 1:

Li a A b M 1-b O c   Chemical formula 1

where A represents at least one element selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn) and iron (Fe); M represents at least one element selected from the group consisting of manganese (Mn), magnesium (Mg), aluminum (Al), nickel (Ni), boron (B), titanium (Ti), cobalt (Co) and iron (Fe); and a, b and c are numbers in the ranges of 0.2≦a≦1.4, 0≦b≦1.0, and 1.8≦c≦2.2;

depositing a compound containing at least one element selected from among sulfur (S), phosphorus (P) and fluorine (F) on surfaces of the composite oxide particles; and

firing the composite oxide particles with the compound containing at least one element selected from among sulfur (S), phosphorus (P) and fluorine (F) deposited thereon;

whereby each of the composite oxide particles is provided with a concentration gradient such that the concentration of the metallic element M2 increases from the center toward the surface of the composite oxide particle, and

at least one element selected from among sulfur (S), phosphorus (P) and fluorine (F) is made present in the form of being aggregated at the surfaces of the composite oxide particles.

10. The method of preparing a positive electrode active material according claim 9 ; wherein during firing, the compound containing at least one element selected from among sulfur (S), phosphorus (P) and fluorine (F) is melted or thermally decomposed and melted, and the melted compound uniformly coats the surface of the composite oxide particles.

11. The method of preparing a positive electrode active material according claim 10 , wherein cation from the deposited compound containing at least one element selected from among sulfur (S), phosphorus (P) and fluorine (F) is eliminated during firing, and anion from the deposited compound containing at least one element selected from among sulfur (S), phosphorus (P) and fluorine (F) reacts with an element included in the composite oxide particle.

12. The positive electrode active material according to claim 1 ,

wherein a ratio d(%)=[(mass of the transition metal M1)+(mass of the metallic element M2)]/(mass of whole particles),

wherein a molar fraction r=(mass of the metallic element M2)/[(mass of the transition metal M1)+(mass of the metallic element M2)], and

wherein the molar fraction r(%) satisfies the formula 0.20≦r≦0.80 in the range where the ratio d(%) from the surface to a certain depth satisfies 0.020≦d≦0.050.

13. A positive electrode active material comprising:

a composite oxide particle; and

a compound including at least one element selected from the group consisting of sulfur (S), phosphorus (P) and fluorine (F) on surfaces of the composite oxide particle,

wherein the composite oxide particle has a laminar rock salt structure and an average composition including a transition metal M1 and a metallic element M2 different from the transition metal M1, and is represented by Chemical formula 1:

Li a A b M 1-b O c   Chemical formula 1

where A represents at least one element selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn) and iron (Fe); M represents at least one element selected from the group consisting of manganese (Mn), magnesium (Mg), aluminum (Al), nickel (Ni), boron (B), titanium (Ti), cobalt (Co) and iron (Fe); and a, b and c are numbers in the ranges of 0.2≦a≦1.4, 0≦b≦1.0, and 1.8≦c≦2.2, and

wherein the composite oxide particle has a concentration gradient such that the concentration of the metallic element M2 increases from the center toward the surface of the composite oxide particle.

14. The positive electrode active material according to claim 13 , wherein the transition metal M1 is at least selected one element selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn) and iron (Fe).

15. The positive electrode active material according to claim 13 , wherein the metallic element M2 is at least one element selected the group consisting of manganese (Mn), magnesium (Mg), aluminum (Al), nickel (Ni), boron (B), titanium (Ti), cobalt (Co) and iron (Fe).

16. The positive electrode active material according to claim 13 , wherein the compound, containing at least one element selected from the group consisting of sulfur (S), phosphorus (P) and fluorine (F), or a thermally decomposed product of the compound, has a melting point of 70° C. or more and 600° C. or less.

17. The positive active material according to claim 13 , wherein the compound, containing at least one element selected from the group consisting of sulfur (S), phosphorus (P) and fluorine (F), or a thermally decomposed product of the compound, has an average diameter of 30 μm or less.

18. The positive active material according to claim 13 , wherein the at least one element of the compound, selected from the group consisting of sulfur (S), phosphorus (P) and fluorine (F), is aggregated on the surfaces of the composite oxide particle.

19. The positive active material according to claim 13 , wherein A includes Ni and Co.

20. The positive electrode active material according to claim 13 ,

wherein a ratio d(%)=[(mass of the transition metal M1)+(mass of the metallic element M2)]/(mass of whole particles),

wherein a molar fraction r=(mass of the metallic element M2)/[(mass of the transition metal M1)+(mass of the metallic element M2)], and

wherein the molar fraction r(%) satisfies the formula 0.20≦r≦0.80 in the range where the ratio d(%) from the surface to a certain depth satisfies 0.020≦d≦0.050.