Fringe-field capacitor electrode for electrochemical device

• US 20040012913A1
• Filed: 04/02/2003
• Published: 01/22/2004
• Est. Priority Date: 10/02/2000
• Status: Active Grant

• Current Assignee: Biosource, Incorporated
• Original Assignee: Biosource, Incorporated
• Inventors: Andelman, Marc D.
• Granted Patent: US 6,781,817 B2
• Time in Patent Office: Days
• US Class Current: 361/503
• CPC Class Codes: C02F 1/4691 Capacitive deionisation
• CPC Class Codes: C02F 2001/46152 characterised by the shape or form electrodes in particulate form or with conductive or non-conductive particles between them C02F1/46114
• CPC Class Codes: H01G 11/24 characterised by structural features of the materials making up or comprised in the electrodes, e.g. form, surface area or porosity; characterised by the structural features of powders or particles used therefor
• CPC Class Codes: H01G 11/26 characterised by their structure, e.g. multi-layered, porosity or surface features
• CPC Class Codes: H01G 11/36 Nanostructures, e.g. nanofibres, nanotubes or fullerenes
• CPC Class Codes: H01G 11/38 Carbon pastes or blends; Binders or additives therein
• CPC Class Codes: H01G 11/42 Powders or particles, e.g. composition thereof
• CPC Class Codes: H01M 4/583 Carbonaceous material, e.g. graphite-intercalation compounds or CFx
• CPC Class Codes: H01M 4/8605 Porous electrodes
• CPC Class Codes: H01M 4/925 supported on carriers, e.g. powder carriers
• CPC Class Codes: H01M 4/96 Carbon-based electrodes
• CPC Class Codes: H01M 8/00 Fuel cells; Manufacture thereof
• CPC Class Codes: Y02E 60/10 Energy storage using batteries
• CPC Class Codes: Y02E 60/13 Energy storage using capacitors
• CPC Class Codes: Y02E 60/50 Fuel cells

Abstract

The invention features an electrochemical device which includes at least two capacitor electrodes 16, each of which includes a conductive material characterized in that at least ten percent (10%) of the overall surface area of the conductive material is an edge plane. In contrast to a basal plane, the electric field along an edge plane is distorted so as to exhibit an ‘edge effect or ‘fringe effect. Capacitor electrodes 16 with many edges, points, corners, or fractal surfaces exhibit greater capacitance per unit volume or mass amount of capacitor electrode material, than do materials in which the surface area of the material is predominately basal plane. An electrochemical device of the invention can be, for example, an electrochemical cell, e.g., a battery, a capacitor, or a flow-through capacitor.

Claims

1. An electrochemical device comprising at least two capacitor electrodes, each of said two capacitor electrodes comprising a conductive material characterized in that at least 10% of the surface area of said conductive material is an edge plane.

2. The electrochemical device of claim 1, wherein said electrochemical device is a flow-through capacitor.

3. The electrochemical device of claim 2, wherein said electrochemical device has a single electrode capacitance of at least 20 farads per cubic centimeter of electric material.

4. The electrochemical device of claim 2, wherein said electrochemical device has a single electrode capacitance of at least 5 microfarads per square centimeter of surface area.

5. The electrochemical device of claim 4, wherein said conductive material comprises particles of less than 10 microns in diameter.

6. The electrochemical device of claim 5, wherein said conductive material has a surface area of between 20 and 3000 square meters per gram material.

7. The electrochemical device of claim 5, wherein said conductive material is selected from the group consisting of pyrolytic graphite and graphite particles.

8. The electrochemical device of claim 5, wherein said conductive material is selected from the group consisting of nanofibers, nanotubes, and carbon fibers of less than 100 microns in diameter.

9. The electrochemical device of claim 5, wherein said conductive material is selected from the group consisting of carbon black and carbon nanoparticles.

10. The electrochemical device of claim 5, wherein said conductive material is selected from the group consisting of activated carbon and carbon powder.

11. The electrochemical device of claim 5, wherein said conductive material is selected from the group consisting of mechanically aligned graphite.

12. The electrochemical device of claim 2, wherein said capacitor electrode further comprises a binder material.

13. The electrochemical device of claim 12, wherein said binder material is selected from the group consisting of latex and a phenolic resin.

14. The electrochemical device of claim 12, wherein said binder material is a perfluorocarbon.

15. The electrochemical device of claim 12, wherein said binder material is a polymer fiber.

16. The electrochemical device of claim 12, wherein said binder material is a polytetrafluoroethylene (PTFE) polymer.

17. The electrochemical device of claim 12, wherein said binder material is in the form of a flexible sheet of less than 0.03 inches thick.

18. The electrochemical device of claim 4, wherein said edge planes are protected by boron or phosphorous.

19. The electrochemical device of claim 2, wherein said electrochemical device further comprises a current collector, and said capacitor electrode is either integral with, or in the same plane as, said current collector.

20. The electrochemical device of claim 4, wherein said conductive material is a nanofiber of less than 300 nanometers in diameter.

21. The electrochemical device of claim 2, wherein one or more of the edge planes of said conductive material are located on one or more of a branch, a dendrite, a fork, a jagged edge, a fractal edge, a point, a spine, or a protrusion in said conductive material.

22. The electrochemical device of claim 2, wherein said conductive material is a laminate comprising graphite, and said graphite is electrically integral with said current collector.

23. The electrochemical device of claim 2, wherein said electrochemical device further comprises a spacer layer, and said flow-through capacitor has a series resistance of less than 30 ohms per square centimeter of spacer layer.

24. The electrochemical device of claim 2, wherein said capacitor electrode comprises one or more pores through which an aqueous, conductive solution can pass through said capacitor electrode, and said edge planes of said conductive material are located on the surface of said pores.

25. The electrochemical device of claim 2, wherein said flow-through capacitor is used to remove ions from an aqueous medium so as to purify said aqueous medium, and said flow-through capacitor is able to remove at least 90% of said ions when said medium is a solution of 0.01M NaCl, said conductive material in said capacitor electrode is carbon, and said solution is allowed to flow through said flow-through capacitor at a flow rate of at least one milliliter per minute per gram of carbon at 2 volts.

26. A method of removing ions from an aqueous medium, said method comprising the steps of:

(a) providing the flow-through capacitor of claim 2;

(b) allowing an electric current to flow between two capacitor electrodes of said flow-through capacitor; and

(c) allowing a source of aqueous medium to flow through said flow-through capacitor so as to remove said ions from said medium.

27. The method of claim 26, wherein said method is able to remove at least 90% of said ions when said medium is a solution of 0.01M NaCl, said conductive material in said capacitor electrode is carbon, and said solution is allowed to flow through said flow-through capacitor at a flow rate of at least one milliliter per minute per gram of carbon at 2 volts.

28. A method of making an electrochemical device, said method comprising the steps of:

(a), providing at least two capacitor electrodes, wherein each of said two capacitor electrodes comprise a conductive material characterized in that at least 10% of the surface area of said conductive material is edge plane; and

(b) positioning a source of electrical current so as to provide electrical communication between each of said two capacitor electrodes.

29. The method of claim 28, wherein said capacitor electrode has a capacitance of at least 20 farads per cubic centimeter of electrical material.

30. The method of claim 28, wherein said capacitor electrodes have a single electrode capacitance of at least 5 microfarads per square centimeter of surface area.

31. The method of claim 28, further comprising the step of mixing said conductive material with a binder material.

32. The method of claim 31, further comprising the step of forming said binder material into a flexible sheet of less than 0.03 inch thickness, said forming selected from the group consisting of extruding, calendaring, pressing, adhering said sheet onto a current collector, and spray coating.