Positive active material, method of preparing the same, and lithium battery including the positive active material

1. A positive active material comprising:

a lithium-containing oxide; and

a lithium-intercalatable phosphate compound disposed on the lithium-containing oxide,

wherein the phosphate compound includes both primary particles and secondary particles including the primary particles,

wherein the primary particles of the phosphate compound have an average particle diameter of from about 0.01 nanometers to about 1,000 nanometers,

wherein the secondary particles of the phosphate compound have an average particle diameter of from about 0.02 nanometers to about 15 micrometers,

wherein at least some of the phosphate compound is in a form of a coating on at least a portion of a surface of a particle of the lithium-containing oxide, and the phosphate compound is further disposed inside a particle of the lithium-containing oxide,

wherein the phosphate compound is a compound represented by Formula 1:

MOPO 4   Formula 1

wherein, in Formula 1,

M is at least one selected from a transition metal having an ionic diameter of from about 60 angstroms to about 90 angstroms and an oxidation number of +5, and

wherein the lithium-containing oxide comprises at least one compound selected from compounds represented by Formulas 2 to 4:

x Li[Li 1/3 Me 2/3 ]O 2 -(1 −x )LiMe′O 2   Formula 2

wherein, in Formula 2,

0< x< 0.9;

Me is at least one element selected from manganese, molybdenum, tungsten, vanadium, titanium, zirconium, ruthenium, rhodium, palladium, osmium, iridium, and platinum; and

Me′ is at least one element selected from nickel, manganese, and cobalt;

y Li[Li 1/3 ((M1) a (M2) b (Mn) c ) 2/3 ]O 2 -(1 −y )LiMe′O 2   Formula 3

wherein in Formula 3,

0 ≦a≦ ⅓;

0 ≦b≦ ⅓;

a+b+c= 1;

0 <y< 0.9; and

M1 is at least one element selected from nickel, copper, zinc, cobalt, chromium, iron, and magnesium; and

M2 is at least one element selected from molybdenum, tungsten, vanadium, titanium, zirconium, ruthenium, rhodium, palladium, osmium, iridium, and platinum;

Li d Co 1-e-g Ni e (M3) g O 2-j (X1) j   Formula 4

wherein, in Formula 4,

0.8 <d≦ 1.6;

0 ≦e≦ 1;

0 ≦g≦ 0.5;

0 ≦j≦ 1;

M3 is at least one element selected from nickel, cobalt, copper, magnesium, sodium, calcium, titanium, zinc, gallium, germanium, aluminum, chromium, magnesium, strontium, molybdenum, tungsten, vanadium, titanium, zirconium, ruthenium, rhodium, palladium, osmium, iridium, silver, gold, hafnium, tin, and platinum; and

X1 is at least one element selected from oxygen, fluorine, sulfur, and phosphorus.

2. The positive active material of claim 1 , wherein the phosphate compound comprises at least one selected from MoOPO 4 , TiOPO 4 , VOPO 4 , TaOPO 4 , and NbOPO 4 .

3. The positive active material of claim 1 , wherein the phosphate compound has a layered structure or a tunneled structure.

4. The positive active material of claim 1 , wherein the phosphate compound has a single crystalline structure.

5. The positive active material of claim 1 , wherein the phosphate compound has a crystalline structure of at least one selected from an α I phase, α II phase, β phase, γ phase, δ phase, ε phase, and a ω phase.

6. The positive active material of claim 1 , wherein an amount of the phosphate compound is from about 0.001 parts to about 30 parts by weight, based on 100 parts by weight of the lithium-containing oxide.

7. The positive active material of claim 1 , wherein the coating has a thickness of from about 0.01 nanometers to about 9.99 micrometers.

8. The positive active material of claim 1 , wherein an amount of the phosphate compound is from about 0.001 parts to about 10 parts by weight, based on 100 parts by weight of the lithium-containing oxide.

9. The positive active material of claim 1 , wherein an amount of the phosphate compound is from about 0.001 parts to about 5 parts by weight, based on 100 parts by weight of the lithium-containing oxide.

10. A lithium battery comprising: a positive electrode; an electrolyte; and a negative electrode, wherein the positive electrode comprises the positive active material of claim 1 .

11. The lithium battery of claim 10 , wherein an operating voltage of the positive active material is in the range of 4.3 Volts±0.1 Volts versus lithium or greater.

12. A method of preparing a positive active material, the method comprising:

heating a transition metal precursor to prepare a lithium-intercalatable phosphate compound; and

contacting the phosphate compound with a lithium-containing oxide to prepare the positive active material, which comprises a mixture of the lithium-containing oxide and the phosphate compound, wherein:

the phosphate compound includes both primary particles and secondary particles, the secondary particles including the primary particles,

the primary particles of the phosphate compound have an average particle diameter of from about 0.01 nanometers to about 1,000 nanometers,

the secondary particles of the phosphate compound have an average particle diameter of from about 0.02 nanometers to about 15 micrometers,

at least some of the phosphate compound is in a form of a coating on at least a portion of a surface of a particle of the lithium-containing oxide, and the phosphate compound is further disposed inside a particle of the lithium-containing oxide,

the phosphate compound is a compound represented by Formula 1:

MOPO 4   Formula 1

wherein, in Formula 1,

M is at least one selected from a transition metal having an ionic diameter of from about 60 angstroms to about 90 angstroms and an oxidation number of +5, and

the lithium-containing oxide comprises at least one compound selected from compounds represented by Formulas 2 to 4:

x Li[Li 1/3 Me 2/3 ]O 2 -(1 −x )LiMe′O 2   Formula 2

wherein, in Formula 2,

0< x< 0.9;

Me is at least one element selected from manganese, molybdenum, tungsten, vanadium, titanium, zirconium, ruthenium, rhodium, palladium, osmium, iridium, and platinum; and

Me′ is at least one element selected from nickel, manganese, and cobalt;

y Li[Li 1/3 ((M1) a (M2) b (Mn) c ) 2/3 ]O 2 -(1 −y )LiMe′O 2   Formula 3

wherein, in Formula 3,

0 ≦a≦ ⅓;

0 ≦b≦ ⅓;

a+b+c= 1;

0 <y< 0.9; and

M1 is at least one element selected from nickel, copper, zinc, cobalt, chromium, iron, and magnesium; and

M2 is at least one element selected from molybdenum, tungsten, vanadium, titanium, zirconium, ruthenium, rhodium, palladium, osmium, iridium, and platinum;

Li d Co 1-e-g Ni e (M3) g O 2-j (X1) j   Formula 4

wherein, in Formula 4,

0.8 <d≦ 1.6;

0 ≦e≦ 1;

0 ≦g≦ 0.5;

0 ≦j≦ 1;

M3 is at least one element selected from nickel, cobalt, copper, magnesium, sodium, calcium, titanium, zinc, gallium, germanium, aluminum, chromium, magnesium, strontium, molybdenum, tungsten, vanadium, titanium, zirconium, ruthenium, rhodium, palladium, osmium, iridium, silver, gold, hafnium, tin, and platinum; and

X1 is at least one element selected from oxygen, fluorine, sulfur, and phosphorus.

13. The method of claim 12 , wherein the transition metal precursor is at least one selected from MoOPO 4 .2H 2 O, TiOPO 4 .2H 2 O, VOPO 4 .2H 2 O, VOHPO 4 .0.5H 2 O, VPO 4 .H 2 O, TaOPO 4 .3.4H 2 O, TaOPO 4 .2.1H 2 O, TaOPO 4 .2.3H 2 O, TaOPO 4 .1.3H 2 O, and NbOPO 4 .H 2 O.

14. The method of claim 12 , wherein the heating is performed at a temperature from about 500° C. to about 1,200° C. for about 12 hours to about 48 hours.

15. The method of claim 12 , wherein an amount of the phosphate compound is from about 0.001 parts to about 30 parts by weight, based on 100 parts by weight of the lithium-containing oxide.

16. A method of preparing a positive active material, the method comprising:

heating a transition metal precursor to prepare a lithium-intercalatable phosphate compound; and

forming a coating of the phosphate compound on at least a portion of a surface of a particle of a lithium-containing oxide by a surface-treatment method to prepare the positive active material, wherein:

at least some of the phosphate compound is further disposed inside a particle of the lithium-containing oxide,

the phosphate compound includes both primary particles and secondary particles, the secondary particles including the primary particles,

the primary particles of the phosphate compound have an average particle diameter of from about 0.01 nanometers to about 1,000 nanometers,

the secondary particles of the phosphate compound have an average particle diameter of from about 0.02 nanometers to about 15 micrometers,

the phosphate compound is a compound represented by Formula 1:

MOPO 4   Formula 1

wherein, in Formula 1,

M is at least one selected from a transition metal having an ionic diameter of from about 60 angstroms to about 90 angstroms and an oxidation number of +5, and

the lithium-containing oxide comprises at least one compound selected from compounds represented by Formulas 2 to 4:

x Li[Li 1/3 Me 2/3 ]O 2 -(1 −x )LiMe′O 2   Formula 2

wherein, in Formula 2,

0< x< 0.9;

Me is at least one element selected from manganese, molybdenum, tungsten, vanadium, titanium, zirconium, ruthenium, rhodium, palladium, osmium, iridium, and platinum; and

Me′ is at least one element selected from nickel, manganese, and cobalt;

y Li[Li 1/3 ((M1) a (M2) b (Mn) c ) 2/3 ]O 2 -(1 −y )LiMe′O 2   Formula 3

wherein, in Formula 3,

0 ≦a≦ ⅓;

0 ≦b≦ ⅓;

a+b+c= 1;

0 <y< 0.9; and

M1 is at least one element selected from nickel, copper, zinc, cobalt, chromium, iron, and magnesium; and

M2 is at least one element selected from molybdenum, tungsten, vanadium, titanium, zirconium, ruthenium, rhodium, palladium, osmium, iridium, and platinum;

Li d Co 1-e-g Ni e (M3) g O 2-j (X1) j   Formula 4

wherein, in Formula 4,

0.8 <d≦ 1.6;

0 ≦e≦ 1;

0 ≦g≦ 0.5;

0 ≦j≦ 1;

M3 is at least one element selected from nickel, cobalt, copper, magnesium, sodium, calcium, titanium, zinc, gallium, germanium, aluminum, chromium, magnesium, strontium, molybdenum, tungsten, vanadium, titanium, zirconium, ruthenium, rhodium, palladium, osmium, iridium, silver, gold, hafnium, tin, and platinum; and

X1 is at least one element selected from oxygen, fluorine, sulfur, and phosphorus.

17. The method of claim 16 , wherein the surface-treatment method is a dry surface treatment method and is at least one selected from planetary ball milling, low-speed ball milling, high-speed ball milling, hybridization, and mechanofusion.

18. The method of claim 16 , wherein the surface-treatment method is a wet surface treatment method and is at least one selected from spraying, co-precipitation, and dipping.

19. The method of claim 16 , wherein the coating has a thickness of from about 0.01 nanometers to about 9.99 micrometers.

20. The method of claim 16 , wherein an amount of the phosphate compound is from about 0.001 parts to about 10 parts by weight, based on 100 parts by weight of the lithium-containing oxide.

21. The method of claim 16 , wherein an amount of the phosphate compound is from about 0.001 parts to about 5 parts by weight, based on 100 parts by weight of the lithium-containing oxide.