FERRIC PHOSPHATE AND METHODS OF PREPARATION THEREOF

• US 20110068295A1
• Filed: 09/20/2010
• Published: 03/24/2011
• Est. Priority Date: 09/18/2009
• Status: Active Grant

• Current Assignee: A123 Systems Incorporated
• Original Assignee: A123 Systems Incorporated
• Inventors: BECK, Larry W., SOLTANI, Mahrokh, WANG, Liya
• Granted Patent: US 9,174,846 B2
• Time in Patent Office: Days
• US Class Current: 252/182.1
• CPC Class Codes: C01B 25/375 of iron
• CPC Class Codes: H01M 10/052 Li-accumulators
• CPC Class Codes: H01M 4/136 Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
• CPC Class Codes: H01M 4/5825 Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
• CPC Class Codes: Y02E 60/10 Energy storage using batteries
• CPC Class Codes: Y02P 70/50 Manufacturing or production processes characterised by the final manufactured product

Abstract

High-purity crystalline ferric phosphate material with desirable characteristics for use in synthesis of nano-sized LFP cathode material are described. The ferric phosphate dihydrate material has as disclosed herein has a molar ratio of phosphorous to iron is from about 1.001 to about 1.05, a surface area of from about 25 m²/g to about 65 m²/g, and is substantially free of metallic or magnetic impurities. Methods of synthesizing high-purity crystalline ferric phosphate material with desirable characteristics for use in synthesis of nano-sized LFP cathode material are also described. In some embodiments, one or more magnetic traps are used during the reaction process and/or after the formation of the final product to remove magnetic impurities. In some embodiments, a synthetic method of ferric phosphate using multiple steps is described, wherein the intermediate of the synthesis is isolated and purified to improve the purity of the ferric phosphate material. In some embodiments, an iron compound is added to an aqueous solution of phosphoric acid. The solution pH and temperature are controlled to ensure the complete dissolution of the iron compound. The desired iron phosphate crystalline material can be obtained with high purity and high crystalline phase purity by controlling the pH and temperature of the solution.

Claims

1. A crystalline ferric phosphate material, comprising:

less than about 1000 ppm sulfate ion;

wherein

the molar ratio of phosphorous to iron is from about 1.001 to about 1.05;

the ferric phosphate material has a surface area of from about 25 m²/g to about 65 m²/g; and

the ferric phosphate material comprises less than 0.8 wt % metallic or magnetic impurities.

2. The crystalline ferric phosphate material of claim 1, wherein

the ferric phosphate material comprises ferric phosphate dihydrate;

and the ferric phosphate dihydrate comprises;

from about 28.3 wt % to about 29.6 wt % iron;

from about 16.0 wt % to about 16.9 wt % phosphorous; and

less than about 700 ppm sulfate ion; and

the ferric phosphate dihydrate material has a surface area of from about 30 m²/g to about 55 m²/g.

3. The crystalline ferric phosphate material of claim 2, wherein the crystalline ferric phosphate dihydrate material comprises less than about 100 ppm metallic or magnetic impurities.

4. The crystalline ferric phosphate material of claim 2, wherein the crystalline ferric phosphate dihydrate material comprises less than about 10 ppm metallic impurities.

5. The crystalline ferric phosphate material of claim 2, wherein the crystalline ferric phosphate dihydrate material comprises less than about 1 ppm magnetic impurities.

6. The crystalline ferric phosphate material of claim 2, wherein the crystalline ferric phosphate dihydrate material comprises less than about 100 ppb magnetic impurities.

7. The crystalline ferric phosphate material of claim 2, wherein a solution of 1 g of the crystalline ferric phosphate dihydrate material in 20 ml of deionized water has a pH value of between about 1 and about 5.

8. The crystalline ferric phosphate material of claim 2, wherein a solution of 1 g of the crystalline ferric phosphate dihydrate material in 20 ml of deionized water has a pH value of between about 2 and about 3.

9. The crystalline ferric phosphate material of claim 2, wherein the crystalline ferric phosphate dihydrate material comprises less than about 100 ppm sulfate ion.

10. The crystalline ferric phosphate material of claim 2, wherein the crystalline ferric phosphate dihydrate material comprises less than about 0.5 wt % other alkali or prevalent anion or other salt impurities.

11. The crystalline ferric phosphate material of claim 2, wherein the crystalline ferric phosphate dihydrate material comprises less than about 0.02 wt % nitrate or chloride.

12. The crystalline ferric phosphate material of claim 2, wherein the crystalline ferric phosphate dihydrate material comprises about 19.3 wt % to about 20.8 wt % water.

13. The crystalline ferric phosphate material of claim 2, wherein the crystalline phase of the crystalline ferric phosphate dihydrate is selected from a group consisting of strengite, meta-strengite (I), meta-strengite (II), and mixtures thereof.

14. The crystalline ferric phosphate material of claim 2, wherein the ferric phosphate dihydrate material has a surface area of from about 30 m²/g to about 55 m²/g.

15. The crystalline ferric phosphate material of claim 2, wherein the primary particle size of the ferric phosphate dihydrate material is between about 1 nm to about 100 nm.

16. The crystalline ferric phosphate material of claim 2, wherein the primary particle size of the ferric phosphate dihydrate material is between about 20 nm to about 40 nm.

17. The crystalline ferric phosphate 2 material of claim 2, wherein the medium size of the aggregate particle of the ferric phosphate dihydrate material is between about 1 μ

m to about 4 μ

m.

18. The crystalline ferric phosphate material of claim 2, wherein the medium size of the agglomerated particle of the ferric phosphate dihydrate material is between about 4 μ

m to about 10 μ

m.

24. The method of claim 18, wherein the iron (II) salt is step a) comprises iron (II) sulfate, iron (II) chloride, iron (II) nitrate, any hydrate thereof, or a mixture thereof.

25. The method of claim 18, wherein the phosphate salt in step a) comprises diammonium phosphate.

26. The method of claim 18, wherein step a) further comprises adding ammonium hydroxide to the solution.

27. The method of claim 26, wherein the pH of the resulting solution in step a) is between about 4 to about 5.

28. The method of claim 18, wherein the oxidizing agent comprises hydrogen peroxide.

29. The method of claim 18, wherein step b) further comprises adding phosphorous acid.

30. The method of claim 18, wherein step b) further heating the solution at a temperature of between about 35 to about 65°

C.

31. The method of claim 18, wherein the method further comprises:

c) heating the solution at a temperature of between about 85 to about 100°

C.

32. The method of claim 18, wherein the method further comprises washing the resulting crystalline ferric phosphate dihydrate material to a purity level of about 95% to about 99%.

19. A method of synthesizing crystalline ferric phosphate material, comprising:

a) introducing an iron (II) salt and a phosphate salt into an aqueous solution to form a ferrous phosphate material and washing the ferrous phosphate to remove impurities; and

b) oxidizing the ferrous phosphate from step a) with an oxidizing agent to form a ferric phosphate material.

20. The method of claim 19, wherein the ferric phosphate material comprises ferric phosphate dihydrate.

21. The method of claim 19, wherein the ferrous phosphate material compromises ferrous phosphate octahydrate.

22. The method of claim 19, further comprises:

using one or more metallic traps to remove metallic or magnetic impurities in step a), step b), after step b), or any combination thereof.

23. The method of claim 22, wherein the magnetic trap comprises rare-earth magnets.

33. The method of claim 19, wherein the synthesized crystalline ferric phosphate dihydrate material comprises:

from about 28.3 wt % to about 29.6 wt % iron;

from about 16.0 wt % to about 16.9 wt % phosphorous; and

less than about 0.8 wt % sulfate ion;

wherein

the molar ratio of phosphorous to iron is from about 1.001 to about 1.05;

the ferric phosphate dihydrate material has a surface area of from about 25 m²/g to about 65 m²/g; and

the ferric phosphate dihydrate material is substantially free of metallic or magnetic impurities.

34. A method of synthesizing crystalline ferric phosphate material, comprising:

a) combining iron (II) compound and an oxidizing agent in an aqueous solution and forming amorphous ferric phosphate and washing the amorphous ferric phosphate to remove impurities; and

b) crystallizing the amorphous ferrous phosphate from step a) to form a crystalline ferric phosphate material.

35. The method of claim 34, wherein one or more metallic traps are used to remove metallic or magnetic impurities in step a), step b), after step b), or any combination thereof.

36. The method of claim 34, wherein the ferric phosphate material comprises ferric phosphate dihydrate.

37. The method of claim 34, wherein the magnetic trap comprises rare-earth magnets.

38. The method of claim 34, wherein the iron (II) phosphate is formed by combining an iron (II) salt and a phosphate salt.

39. The method of claim 38, wherein the iron (II) salt comprises iron (II) sulfate, iron (II) chloride, iron (II) nitrate, any hydrate thereof, or a mixture thereof.

40. The method of claim 39, wherein the iron (II) salt comprises iron (II) sulfate heptahydrate.

41. The method of claim 39, wherein the phosphate salt comprises diammonium phosphate.

42. The method of claim 34, wherein the oxidizing agent comprises hydrogen peroxide.

43. The method of claim 34, wherein step a) further comprises heating the solution at a temperature between about 30 to about 65°

C.

44. The method of claim 34, wherein step b) further comprises adding phosphoric acid.

45. The method of claim 34, wherein step b) further comprises:

heating the solution at a temperature between about 85 to about 100°

C.

46. The method of claim 34, wherein the method further comprises washing the resulting crystalline ferric phosphate material.

47. The method of claim 36, wherein the synthesized crystalline ferric phosphate dihydrate material comprises:

from about 28.3 wt % to about 29.6 wt % iron;

from about 16.0 wt % to about 16.9 wt % phosphorous; and

less than about 0.8 wt % sulfate ion;

wherein

the molar ratio of phosphorous to iron is from about 1.001 to about 1.05;

the ferric phosphate dihydrate material has a surface area of from about 25 m²/g to about 65 m²/g; and

the ferric phosphate dihydrate material is substantially free of metallic or magnetic impurities.

48. A method for manufacture of a crystalline ferric phosphate material having a reaction mixture, one or more reactants, one or more intermediate products, and a ferric phosphate dihydrate product, the method comprising:

using one or more magnetic traps to remove metallic or magnetic impurities from the reactant, the intermediate product, the reaction mixture, or the ferric phosphate dihydrate product.

49. The method of claim 48, wherein the method uses a starting material comprising an iron (II) or iron (III) compound.

50. The method of claim 48, wherein the ferric phosphate material comprises ferric phosphate dihydrate.

51. The method of claim 48, wherein the method comprises one or more synthetic steps and the one or more magnetic traps are used before, during, or after any one of the synthetic steps, or any combination thereof.

52. The method of claim 51, wherein the metallic trap comprises rare-earth magnets.

53. The method of claim 51, wherein the magnet trap has a magnetic strength in the range of 1 to 20 k Gauss.

54. The method of claim 51, wherein the magnet trap has a magnetic strength in the range of 8 to 14 k Gauss.

55. The method of claim 48, further comprising:

a) combining an iron (II) or iron (III) compound and phosphoric acid in an aqueous solution;

b) maintaining uniform pH and a temperature of the solution to ensure substantially all of the iron (II) or iron (III) compound is consumed by the reaction with phosphoric acid; and

c) controlling the pH and the temperature of the solution to form the ferrous phosphate material with substantially pure crystalline phase;

wherein the one or more metallic traps is used to remove metallic or magnetic impurities in step a), step b), step c), after step c), or any combination thereof.

56. The method of claim 55, wherein the ferric phosphate material comprises ferric phosphate dihydrate.

57. The method of claim 55, wherein the magnetic trap comprises rare-earth magnets.

58. The method of claim 55, wherein the iron (II) or iron (III) compound comprises iron (II) or iron (III) oxide, hydroxide, carbonate, or oxy-hydrate.

59. The method of claim 55, wherein the iron (II) compound is used and step a) further comprises adding an oxidizing agent.

60. The method of claim 59, wherein the oxidizing agent comprises hydrogen peroxide, dissolved air or oxygen, or other mild oxidant.

61. The method of claim 55, wherein the phosphoric acid aqueous solution has a water:

phosphoric acid ratio of about 1;

1 to about 10;

1.

62. The method of claim 55, wherein the phosphoric acid aqueous solution has a water:

phosphoric acid ratio of about 1;

1 to about 4;

1.

63. The method of claim 55, wherein the pH value of the solution in step b) is maintained as less than about 2.

64. The method of claim 55, wherein the pH value of the solution in step b) is maintained as less than about 1.

65. The method of claim 55, wherein the temperature of the solution in step b) is maintained above 65°

C.

66. The method of claim 55, wherein the temperature of the solution in step b) is maintained above 70°

C.

67. The method of claim 55, wherein the temperature of the solution in step b) is maintained above 75°

C.

68. The method of claim 55, wherein the temperature of the solution in step b) is maintained above 95°

C.

69. The method of claim 55, wherein the ferric phosphate material has a metallic or magnetic impurities of less than 100 ppm.

70. The method of claim 55, wherein the ferric phosphate material has a metallic or magnetic impurities of less than 10 ppm.

71. The method of claim 55, wherein the ferric phosphate material has a metallic or magnetic impurities of less than 1 ppm.

72. The method of claim 55, wherein the ferric phosphate material has a metallic or magnetic impurities of less than 100 ppb.

73. The method of claim 55, wherein the substantially pure crystalline phase of ferric phosphate is meta-strengite-I.

74. The method of claim 55, wherein the substantially pure crystalline phase of ferric phosphate is meta-strengite-II.

75. The method of claim 55, wherein the substantially pure crystalline phase of ferric phosphate is strengite.

76. The method of claim 55, wherein the pH value of the solution in step c) is controlled as less than about 1.

77. The method of claim 76, wherein the temperature of the solution in step c) is controlled at less that about 85°

C.

78. The method of claim 76, wherein the substantially pure crystalline phase of ferric phosphate is meta-strengite-II.

79. The method of claim 76, wherein the substantially pure crystalline phase of ferric phosphate is meta-strengite-II.

80. The method of claim 55, wherein the pH value of the solution in step c) is controlled in the range of between about 1 and about 2.

81. The method of claim 80, wherein the temperature of the solution in step c) is controlled at less that about 85°

C.

82. The method of claim 80, wherein the substantially pure crystalline phase of ferric phosphate is meta-strengite-I.

83. The method of claim 81, wherein the substantially pure crystalline phase of ferric phosphate is meta-strengite-I.

84. The method of claim 55, wherein the solution in step c) is passed through one or more high-strength magnetic flux traps.

85. The method of claim 55, wherein the magnetic trap comprises a strong magnet directly inserted into the solution to generate a magnetic field.