Nanocomposite electrodes and related devices

• US 20100075225A1
• Filed: 09/05/2006
• Published: 03/25/2010
• Est. Priority Date: 09/02/2005
• Status: Active Grant

• Current Assignee: A123 Systems Incorporated
• Original Assignee: A123 Systems Incorporated
• Inventors: Wilkins, Ronnie, Shiao, Hung-Chieh, Gozdz, Antoni S.
• Granted Patent: US 8,323,831 B2
• Time in Patent Office: Days
• US Class Current: 429/212
• CPC Class Codes: H01M 2004/021 Physical characteristics, e.g. porosity, surface area
• CPC Class Codes: H01M 4/0404 by coating on electrode collectors
• CPC Class Codes: H01M 4/0409 by a doctor blade method, slip-casting or roller coating
• 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 4/1397 of electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
• CPC Class Codes: H01M 4/621 Binders
• CPC Class Codes: H01M 4/625 Carbon or graphite
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

A nanocomposite electrode that includes a current collector, an electroactive layer a conductive adhesive contacting the surface of the current collector and an interlayer region in electrical communication with the current collector and the electroactive material. The interlayer region is interposed between the current collector and the electroactive layer and includes a portion of the conductive adhesive intermixed with a portion of the electroactive layer. The electroactive layer includes electroactive material having a surface area of at least about 10 m²/g. The conductive adhesive may be at least partially soluble in electrode casting solvent. Electrochemical devices, such as lithium secondary cells, containing an electrode with an interlayer region are also provided, as are processes for making such electrodes and electrochemical devices.

Claims

1. A nanocomposite electrode, comprising:

a current collector;

an electroactive layer comprising an electroactive material having a surface area of at least about 10 m²/g and a first polymer;

wherein the first polymer is selected from a group consisting of a polyvinylidene fluoride polymer, a copolymer thereof, and a terpolymer thereof; and

a conductive adhesive layer contacting the surface of the current collector, wherein the conductive adhesive layer comprises a second polymer selected from the group consisting of a polyolefin, a polyurethane, a polyacrylic acid, a polyacrylic ester, a polyether, a polyacrylate, a polystyrene, a copolymer thereof, a terpolymer thereof, and a mixture thereof; and

an interlayer region interposed between the conductive adhesive layer and the electroactive layer and in electrical communication with the current collector and the electroactive layer, the interlayer region comprising a portion of the conductive adhesive layer intermixed with a portion of the electroactive material.

2. The electrode of claim 1, wherein the conductive adhesive layer further comprises a conductive material and wherein a portion of the conductive material is located in the interlayer region.

3. The electrode of claim 1, wherein the electroactive layer is cast from a solvent-based composition and wherein the conductive adhesive layer is at least partially soluble in the casting solvent.

4. The electrode of claim 1, wherein the conductive adhesive layer comprises a carbon-based composite.

5. The electrode of claim 4, wherein the carbon-based composite comprises conductive material and the second polymer.

6. The electrode of claim 5, wherein the conductive material is selected from one or more of carbon black, natural and artificial graphite, partially graphitized coke, carbon fiber, vapor-phase grown carbon fibers, and carbon nanotubes and mixtures thereof.

8. The electrode of claim 1 wherein the second polymer is an acrylic acid and styrene copolymer.

9. The electrode of claim 1 wherein the second polymer is an acrylic acid, isobutyl acrylate styrene copolymer.

10. The electrode of claim 3, wherein the casting solvent is selected from the group consisting of NMP, gamma-butyrolactone, dimethylformamide, acetone, methyl ethyl ketone and mixtures thereof.

11. The electrode of claim 1, wherein the electroactive material has a surface area of at least about 15 m²/g.

12. The electrode of claim 1, wherein the electroactive material is an olivine compound having a composition Li_xM′

_yM″

_a(PO₄), wherein M″

is selected from the group consisting of Group HA, IIIA, IVA, VA, VIA, and IIIB and metals having an ionic radius less than the ionic radius of Fe²⁺, x is equal to or greater than 0, and a and y are greater than 0.

13. The electrode of claim 12, wherein M′

is Fe²⁺.

14. The electrode of claim 12, wherein M″

is one or more metals selected from the group consisting of aluminum, titanium, zirconium, niobium, tantalum, tungsten, and magnesium.

15. The electrode of claim 12, wherein the compound is Li_xFe_yM″

_aPO₄, wherein x, y, and a are greater than 0.

16. The electrode of claim 12, wherein the compound is any of Li_x(M′

_1-aM″

_a)PO₄, (Li_1-aM″

_a)_xM′

_yPO₄, Li_xM″

_aM′

PO₄, Li_x(M′

_1-a-yM″

_aLi_y)PO₄, or Li_x-aM″

_aM′

_1-aLi_yPO₄, wherein 0.0001<

a≦

0.1.

17. The electrode of claim 1, wherein the electroactive layer further comprises a conductivity-enhancing additive.

18. The electrode of claim 17, wherein the conductivity-enhancing additive comprises carbon.

19. The electrode of claim 1, wherein the conductive adhesive covers about 20% to about 100% of the current collector surface.

20. The electrode of claim 1, wherein the conductive adhesive has a thickness from about 0.1 μ

m to about 20 μ

m.

21. The electrode of claim 1, wherein the interlayer region forms a gradient, wherein the concentration of the conductive adhesive layer is greater at the interface with the current collector than at the interface with the electroactive layer.

22. The electrode of claim 1, wherein the interlayer region forms a discreet layer interposed between the current collector and the electroactive layer.

23. The electrode of claim 1, wherein the electroactive layer has a thickness from about 50 μ

m to about 125 μ

m.

89. The electrode of claim 3, wherein about 10% to about 90% of the conductive adhesive is extractable into the casting solvent.

7. (canceled)

24-44. -44. (canceled)

45. A lithium secondary cell, comprising:

a lithium-containing positive electrode in electronic contact with a positive electrode current collector, the positive electrode current collector in electrical connection with an external circuit;

a negative electrode in electronic contact with a negative electrode current collector, the negative electrode current collector in electrical connection with an external circuit; and

an electrolyte in ionic contact with the positive and negative electrodes, wherein

the positive electrode comprises

an electroactive layer comprising an electroactive material having a surface area of at least about 10 m²/g and a first polymer;

wherein the first polymer is selected from a group consisting of a polyvinylidene fluoride polymer, a copolymer thereof, and a terpolymer thereof;

a conductive adhesive layer contacting the surface of the positive current collector, wherein the conductive adhesive layer comprises a second polymer selected from the group consisting of a polyolefin, a polyurethane, a polyacrylic acid, a polyacrylic ester, a polyether, a polyacrylate, a polystyrene, a copolymer thereof, a terpolymer thereof, and a mixture thereof; and

an interlayer region interposed between the conductive adhesive layer and the electroactive layer and in electrical communication with the positive current collector and the electroactive layer, the interlayer region comprising a portion of the conductive adhesive intermixed with a portion of the electroactive material.

46. The lithium secondary cell of claim 45, wherein the conductive adhesive layer further comprises a conductive material and wherein a portion of the conductive material is located in the interlayer region.

47. The lithium secondary cell of claim 45, wherein the electroactive material is cast from a solvent-based composition and wherein the conductive adhesive layer is at least partially soluble in the casting solvent.

48. The lithium secondary cell of claim 45, wherein the conductive adhesive layer comprises a carbon-based composite.

49. The lithium secondary cell of claim 48, wherein the carbon-based composite comprises conductive material and the second polymer.

50. The lithium secondary cell of claim 49, wherein the conductive material is selected from one or more of carbon black, natural and artificial graphite, partially graphitized coke, carbon fiber, vapor-phase grown carbon fibers, and carbon nanotubes and mixtures thereof.

52. The lithium secondary cell of claim 49, wherein the second polymer is an acrylic acid/styrene copolymer.

53. The lithium secondary cell of claim 47, wherein the casting solvent is selected from the group consisting of NMP, gamma-butyrolactone, dimethylformamide, acetone, methyl ethyl ketone and mixtures thereof.

54. The lithium secondary cell of claim 45, wherein the electroactive material is an olivine compound having a composition Li_xM′

_yM″

_a(PO₄), wherein M″

is selected from the group consisting of Group HA, IIIA, IVA, VA, VIA, and IIIB and metals having an ionic radius less than the ionic radius of Fe²⁺;

x is equal to or greater than 0; and

a and y are greater than 0.

55. The lithium secondary cell of claim 54, wherein M′

is Fe²⁺.

56. The lithium secondary cell of claim 45, wherein M″

is one or more metals selected from the group consisting of aluminum, titanium, zirconium, niobium, tantalum, tungsten, and magnesium.

57. The lithium secondary cell of claim 54, wherein x has a value between zero and about 1, and y is about 1.

58. The lithium secondary cell of claim 54, wherein the compound is any of Li_x(M′

_1-aM″

_a)PO₄, (Li_1-aM″

_a)_xM′

_yPO₄, Li_xM″

_aM′

PO₄, Li_x(M′

_1-a-yM″

_aLi_y)PO₄, or Li_x-aM″

_aM′

_1-aLi_yPO₄, wherein 0.0001<

a≦

0.1.

59. The lithium secondary cell of claim 54, wherein the compound is Li_xFe_yM″

PO₄.

60. The lithium secondary cell of claim 45, wherein the electroactive layer further comprises a conductivity-enhancing additive.

61. The lithium secondary cell of claim 60, wherein the conductivity-enhancing additive comprises carbon.

62. The electrode of claim 45, wherein the conductive adhesive covers about 20% to about 100% of the current collector surface.

63. The electrode of claim 45, wherein the conductive adhesive has a thickness from about 0.1 μ

m to about 20 μ

m.

64. The electrode of claim 45, wherein the interlayer region forms a gradient, wherein the concentration of the conductive adhesive is greater at the interface with the current collector than at the interface with the electroactive layer.

65. The electrode of claim 45, wherein the interlayer region forms a discreet layer interposed between the current collector and the electroactive layer.

66. The electrode of claim 45, wherein the electroactive layer has a thickness from about 50 μ

m to about 125 μ

m.

91. The electrode of claim 47, wherein about 10% to about 90% of the conductive adhesive is extractable into the casting solvent.

51. (canceled)

67. A process for preparing a lithium-containing electrode, comprising:

applying a conductive adhesive layer to one or more surfaces of a current collector, forming a current collector coated with an adhesive layer, wherein the conductive adhesive layer comprises a second polymer selected from the group consisting of a polyolefin, a polyurethane, a polyacrylic acid, a polyacrylic ester, a polyether, a polyacrylate, a polystyrene, a copolymer thereof, a terpolymer thereof, and a mixture thereof;

applying an electroactive layer composition to one or more surfaces of the coated current collector, the electroactive layer composition comprising electroactive material, a first polymer and electrode casting solvent, wherein the electroactive material has a surface area of at least about 10 m²/g and ther first polymer is selected from a group consisting of a polyvinylidene fluoride polymer, a copolymer thereof, and a terpolymer thereof;

wherein

a portion of the high surface area electroactive material intermixes with the adhesive to form an interlayer region interposed between the conductive adhesive layer and the electroactive layer and in electrical communication with the coated current collector and the remainder of the high surface area electroactive material, the interlayer region comprising a portion of the conductive adhesive layer intermixed with a portion of the electroactive material.

68. The process of claim 67, wherein the conductive adhesive layer is at least partially soluble in the casting solvent.

69. The process of claim 67, wherein the conductive adhesive layer further comprises a conductive material and wherein a portion of the conductive material is located in the interlayer region.

70. The process of claim 67, wherein the conductive adhesive layer comprises a carbon-based composite.

71. The process of claim 70, wherein the carbon-based composite comprises conductive material and the second polymer.

72. The process of claim 71, wherein the conductive material is selected from one or more of carbon black, natural and artificial graphite, partially graphitized coke, carbon fiber, vapor-phase grown carbon fibers, and carbon nanotubes and mixtures thereof.

74. The process of claim 71, wherein the second polymer is acrylic acid/styrene copolymer.

75. The process of claim 71, wherein the casting solvent is selected from the group consisting of NMP, gamma-butyrolactone, dimethylformamide, acetone, methyl ethyl ketone and mixtures thereof.

76. The process of claim 67, wherein the electrode casting solvent is selected from the group consisting of NMP, gamma-butyrolactone, dimethylformamide, acetone, methyl ethyl ketone and mixtures thereof.

77. The process of claim 71, wherein the electroactive material is an olivine compound having a composition Li_xM′

_yM″

_a(PO₄), wherein M″

is selected from the group consisting of Group HA, IIIA, IVA, VA, VIA, and IIIB and metals having an ionic radius less than the ionic radius of Fe²⁺;

x is equal to or greater than 0; and

a and y are greater than 0.

78. The process of claim 77, wherein M′

is Fe²⁺.

79. The process of claim 77, wherein M″

is one or more metals selected from the group consisting of aluminum, titanium, zirconium, niobium, tantalum, tungsten, and magnesium.

80. The process of claim 77, wherein the compound is Li_xFe_yM″

_aPO₄, wherein x, y, and a are greater than 0.

81. The process of claim 77, wherein the compound is any of Li_x(M′

_1-aM″

_a)PO₄, (Li_1-aM″

_a)_xM′

_yPO₄, Li_xM″

_aM′

PO₄, Li_x(M′

_1-a-yM″

_aLi_y)PO₄, or Li_x-aM″

_aM′

_1-aLi_yPO₄, wherein 0.0001<

a≦

0.1.

82. The process of claim 71, wherein the electroactive layer further comprises a conductivity-enhancing additive.

83. The process of claim 82, wherein the conductivity-enhancing additive comprises carbon.

84. The process of claim 71, wherein the conductive adhesive covers about 20% to about 100% of the current collector surface.

85. The process of claim 71, wherein the conductive adhesive has a thickness from about 0.1 μ

m to about 20 μ

m.

86. The process of claim 71, wherein the interlayer region forms a gradient, wherein the concentration of the conductive adhesive is greater at the interface with the current collector than at the interface with the electroactive layer.

87. The process of claim 71, wherein the interlayer region forms a discreet layer interposed between the current collector and the electroactive layer.

88. The process of claim 71, wherein the electroactive layer has a thickness from about 50 μ

m to about 125 μ

m.

73. (canceled)

90. (canceled)