Co-extrusion method of fabricating electrode structures in honeycomb substrates and ultracapacitor formed thereby
A method for fabricating electrode structures within a honeycomb substrate having a plurality of elongated channels is provided that is particularly adaptable for producing an ultracapacitor. In this method, the nozzle of a co-extrusion device simultaneously feeds a current collector along a central axis of one of the channels while simultaneously injecting a paste containing an electrode material so that the interior of the channel becomes completely filled with electrode paste at the same rate that the current collector is fed. Such co-extrusion as performed simultaneously at both sides of the ceramic substrate to rapidly form electrode structures within substantially all the channels of the substrate. The resulting ultracapacitor is capable of storing large amounts of electrical energy per unit volume in a structure which is relatively quick and easy to manufacture.
This application claims the benefit of U.S. Provisional Application No. 60/809,582, filed May 30, 2006, entitled “Co-Extrusion Method of Fabricating Electrode Structures in Honeycomb Substrates and Ultracapacitor Formed Thereby.”
FIELD OF THE INVENTIONThis invention generally relates to ultracapacitor energy storage devices, and is particularly concerned with a method for forming electrode structures within the channels of a honeycomb substrate, and the ultracapacitor formed thereby.
BACKGROUND OF THE INVENTIONElectric double layered capacitors (EDLC), commonly known as ultracapacitors, are known in the prior art. Such devices are capable of storing larger amounts of electrical energy per unit volume than the traditional capacitors, generating much higher power in a short instant than many types of chemical batteries, and may be charged and discharged a large number of times with virtually no energy losses due to chemical reaction. Ultracapacitors having capacitances of thousands of Farads are already commercially available, and are being used as energy storage devices for providing back-up currents for microcomputers, clock radios, and other consumer electronics, as well as actuators or primary power sources capable of providing sufficient current for automobile engine cranking, as well as power sources for hybrid and electrical vehicles.
Such devices achieve their relatively high capacitances by virtue of a high-area electrode microstructure. In conventional capacitors, the electrodes are typically metallic plates separated by a dielectric material. As capacitance is dependent upon the area of the electrode, such plate-type electrode structures must be made very large to obtain capacitances in excess of one F. Ultracapacitors circumvent this limitation by means of electrodes formed from very fine, particulate materials, such as activated carbon, having surface area to mass ratios on the order of 1,000 to 3,000 m2/gm. The resulting high surface area per unit volume that such electrode structures provide allow much higher capacitances to be stored in the resulting ultracapacitor than could possibly be stored in a capacitor using conventional, plate type electrodes.
In the simplest design of an ultracapacitor, two high-area electrodes are separated a short distance from one another via a dielectric material. Current collectors (which may be in the form of either wires or plates) are centrally provided within each of the particulate carbon electrode structures. The electrodes and the dielectric separating them are soaked in an electrolyte, which is preferably non-aqueous in order to avoid limitations on the charging voltage that are inherent with aqueous-type electrolytes. A charging voltage is then applied across the current collectors of the two opposing electrodes, which in turn allows a relatively large amount of positive and negative charges to migrate from the current collectors to the surfaces of the mutually contacting carbon particles forming the electrode structures. The charging process is complete when the capacitor is saturated. Electrical power may then be tapped from the current collectors as needed.
Unfortunately, such a simplistic, two-electrode carbon-based design does not yield efficient electrical power. While the power output may be increased by shortening the distance between the current collectors and the particulate carbon, the resulting lower volume of electrodes would of course reduce the available electrode area and hence the capacitance.
To overcome these limitations, ultracapacitors having multiple electrodes connected in parallel have been constructed. In one such design, an extruded honeycomb substrate formed from a conductive carbon-based material forms the first set of electrodes of the ultracapacitor, while monolithic carbon rods disposed in the hollow channels of the honeycomb structure form the other set of electrodes. To prevent short circuiting between the two sets of electrodes, the interior walls of the channels of the honeycomb structure are coated with a dielectric polymer film prior to the insertion or manufacture of the rod-like electrode structures within the honeycomb channels.
Because honeycomb substrate having relatively high channel densities of between 400 and 2,000 channels per square inch may be manufactured with existing extrusion technology, an ultracapacitor having hundreds or even thousands of electrodes are possible with this approach. The relatively small cross section where the cross sectional area of the resulting electrodes provides short distances between the centrally disposed current collectors, and the surrounding matrix of particulate carbon, allowing electrical charges to migrate to the surfaces of the particulate carbon with relatively small internal resistance, thereby resulting in an ultracapacitor that is chargeable within a matter of a few seconds, and which has a highly usable discharge energy.
Unfortunately, such honeycomb-type ultracapacitors have not yet realized their full potential in providing a low-cost, high energy storage device. It has been proven very difficult to install the rod-like, carbon electrode structures within the channels of the ceramic substrate. No practical and time-efficient method has yet been found to produce such rod-like electrode structures and to insert the hundreds or thousands required into the small, individual openings of the honeycomb channels. While extrusion techniques have been attempted, the small cross-sections of the channels and their close distances together has made it difficult to reliably and rapidly form electrode structures with current collectors within the channels without the formation of void spaces which compromises the performance and capacity of the resulting ultracapacitor. It has also proven difficult and time consuming to uniformly and reliably apply a coat of dielectric, insulating polymer over the interior walls of the hundreds or thousands of small channels within such honeycomb structures. Finally, the carbon based honeycomb substrates tend to be brittle and fragile, and thus prone to cracking or breakage during the installation of the rod-like electrode structures. The resulting cracks or other discontinuities create electrical leakages in the final ultracapacitor, which in turn degrade its performance.
Clearly, what is needed is an ultracapacitor capable of exploiting all the advantages of extruded honeycomb substrates without the accompaniment of any of the aforementioned disadvantages. In particular, a technique for manufacturing a honeycomb based ultracapacitor is needed wherein electrode structures are quickly and easily formed within each of the channels of the substrate without potentially wall-breaking forces and without the formation of performance compromising voids that reduce both energy and power performance. Ideally, the design of the honeycomb based ultracapacitor would obviate the need for coating the interior walls of the channels with a dielectric polymer. Finally, it would be desirable if the honeycomb substrate could be formed from a material stronger and more robust than carbon-based conductive compounds, and hence less apt to form internal cracks or other discontinuities that would compromise the performance of the final device.
SUMMARY OF THE INVENTIONGenerally speaking, the invention is a method of fabricating electrode structures within the channels of honeycomb substrates that overcomes or at least ameliorates all of the aforementioned shortcomings associated with the prior art. To this end, the method comprises the steps of providing a honeycomb substrate having a plurality of channels, and then simultaneously feeding a current collector along a central portion of at least one of the channels while injecting a paste containing an electrode material such that the interior of the channel becomes completely filled with electrode paste at substantially the same rate that the current collector is fed into the channel. The electrode paste is preferably extrudable, and the current collector and electrode paste may be simultaneously fed into the channel of the substrate by the nozzle of a co-extrusion device by inserting the nozzle to the far end of the channel, and commencing the simultaneous feeding of the current collector and extrudable electrode paste from the nozzle while withdrawing the nozzle from the channel at a same rate that the current collector and extrudable electrode paste are fed.
The current collector may be, for example, a wire or strand formed from an electrically conductive metal or polymer. The electrode paste may include, for example, particulate carbon having a relatively high surface area per weight, e.g. 1,000-3,000 m2/gm. Preferably, the dielectric honeycomb substrate may be of a form used in diesel particulate filters, wherein each of the elongated channels has a plugged end, and an open end, and wherein the plugging pattern on both ends of the substrate is a checkerboard pattern. Such a checkerboard plugging pattern not only provides an optimal distribution of three-dimensional interleaving electrode structures for ultracapacitator purposes, but further facilitates the simultaneous fabrication of an electrode structure in a plurality of channels that are all plugged at the same ends by allowing a wider spacing apart of the nozzles of a co-extrusion device than would otherwise occur if simultaneous co-extrusion were attempted within a plurality of mutually contiguous channels.
In a preferred embodiment of the method, two opposing arrays of co-extrusion nozzles are simultaneously inserted in all of the open ends of the channels on either end of the honeycomb substrate until the nozzles are adjacent to the plugged ends of the channels. All of the nozzles are then simultaneously actuated, and the two arrays of nozzles of the co-extrusion device are withdrawn as the current collectors and electrode paste are simultaneously extruded at such a rate that the channels become completely filled with electrode paste as the current collectors are fed along the central axis of the elongated channels. Extrusion of the electrode past ceases when the nozzles are withdrawn from the open ends of the channels. However, the feeding of the current collectors continues to provide a terminal portion of the current collector that extends out of each of the elongated channels of the substrate. The distal ends of the terminal portions are then cut, and all the terminal portions on either side of the honeycomb substrate are interconnected by means of collector plates.
The method is particularly adapted to forming an ultracapacitor having a high energy storage capacity per unit volume and a relatively low weight. The high processing speeds made possible by the inventive method and the use of low-cost materials advantageously result in a low-cost energy storage device. When the honeycomb substrate is formed from a dielectric ceramic material, the resulting structure is more robust than ultracapacitors utilizing a carbonaceous honeycomb substrate, and hence is less prone to breakage or manufacturing faults that can lead to power leakage during use. The co-extruded current collectors and electrode paste deposited within the channels of the dielectric ceramic substrate provides an electrode structure without the need for the deposition or coating of insulating films over the channel walls, and the terminal portions of the current collectors formed outside of the channels provides a convenient and robust means for interconnecting all of the electrodes on each side of the substrate via a conductive collector plate. Finally, the ability to manufacture channels in such ceramic honeycomb substrate having small cross sections (i.e., having a density of between 200 and 2,000 channels per square inch) provides an ultracapacitor which may be quickly charged, and which discharges at voltages comparable to those commonly associated with chemical batteries (i.e., between two and four volts).
With reference to
With particular reference to
As is shown in
After the co-extrusion nozzle 40 has been positioned toward the closed end of the channel 7 as illustrated in
In operation, a honeycomb substrate 1 is placed between the opposing nozzle arrays 60 of the two co-extrusion assemblies 62a, b as shown in
Claims
1. A method for fabricating an electrode structure within channels of a honeycomb substrate, said method being particularly adapted for producing an ultracapacitor, and comprising the steps of:
- providing a honeycomb substrate having a plurality of channels, and
- simultaneously feeding a current collector along a central portion of at least one of said channels while injecting a paste containing an electrode material such that the interior of said channel becomes completely filled with said electrode paste at substantially a same rate that said current collector is fed into said channel.
2. The method defined in claim 1, wherein said electrode paste is extrudable, and said current collector and said electrode paste are simultaneously fed into said channel by the nozzle of a co-extrusion device.
3. The method defined in claim 2, further comprising the steps of inserting said nozzle of said co -extrusion device to one end of said channel, commencing the feeding of said current collector and extrudable electrode paste from said nozzle, and withdrawing said nozzle from said channel at a same rate that said current collector and said extrudable electrode paste are fed into said channel.
4. The method defined in claim 1, wherein said current collector is a wire formed from an electrically conductive material.
5. The method defined in claim 1, wherein the electrode paste includes particulate carbon.
6. The method defined in claim 1, wherein the honeycomb structure is formed from a dielectric and thermally stable ceramic material.
7. The method defined in claim 3, further including the step of plugging one end of said channel and inserting said nozzle into an opposite, unplugged end prior to commencing the feeding of said current collector and extrudable electrode paste.
8. The method defined in claim 7, wherein said co-extrusion device has a plurality of nozzles, each of which is simultaneously inserted, and simultaneously actuated to feed said current collector and extrudable electrode paste into its respective channel, and then simultaneously withdrawn, such that an electrode structure is simultaneously produced in a plurality of channels.
9. The method defined in claim 8, wherein said co-extrusion device has first and second sets of nozzles disposed on opposite sides of said honeycomb substrate, the total number of nozzles being the same or nearly the same as the total number of channels in the honeycomb substrate, and wherein said first and second sets of nozzles are simultaneously inserted, actuated, and withdrawn such that an electrode structure is simultaneously formed in substantially all of the channels.
10. The method defined in claim 1, wherein the honeycomb substrate is formed from one of the group consisting of cordierite, mullite, aluminum titanate, silicon carbide, alumina and silicone alumina.
11. A method for forming electrode structures within a dielectric honeycomb substrate, said method being particularly adapted for producing an ultracapacitor, and comprising the steps of:
- providing a honeycomb substrate having a plurality of elongated channels, and
- simultaneously feeding a wire-like current collector along a central axis of at least one of said channels while injecting a paste containing an electrode material such that the interior of the channel becomes completely filled with said electrode paste at a same rate that said current collector is fed into said channel.
12. The method defined in claim 11, wherein said electrode paste is extrudable, and said wire-like current collector and said electrode paste are simultaneously fed into said channel by the nozzle of a co-extrusion device.
13. The method of claim 11, wherein the electrode paste includes activated particulate carbon.
14. The method of claim 13, wherein the surface area of the activated particulate carbon is between about 1000 to 3000 m2/gm.
15. The method of claim 11, wherein the current collector is a wire formed from a conductive metal.
16. The method of claim 11, wherein the current collector is a wire having a diameter of between about 0.10 and 0.30 mm.
17. The method of claim 12, further including the step of plugging one end of said at least one channel and inserting said nozzle into an opposite, unplugged end prior to commencing the feeding of said current collector and extrudable electrode paste.
18. The method of claim 12, wherein said co-extrusion device has a plurality of nozzles, each of which is simultaneously inserted, and simultaneously actuated to feed said current collector and extrudable electrode paste into its respective channel, and then simultaneously withdrawn, such that an electrode structure is simultaneously produced in a plurality of channels.
19. The method of claim 18, wherein said co-extrusion device has first and second sets of nozzles disposed on opposite sides of said ceramic honeycomb structure, the total number of nozzles being the same or nearly the same as the total number of channels in the ceramic substrate, and wherein said first and second sets of nozzles are simultaneously inserted, actuated, and withdrawn such that an electrode structure is simultaneously formed in substantially all of the channels.
20. The method of claim 11, wherein the channel density of said honeycomb substrate is between about 400 and 2000 per square inch.
21. An ultracapacitor, comprising:
- a dielectric ceramic honeycomb substrate having a plurality of elongated channels, wherein at least one channel contains an electrode structure including a current collector disposed along a central axis of the channel, and wherein the balance of said channel is completely filled with electrode paste such that substantially no air voids are present within said channel.
22. The ultracapacitor of claim 21, wherein said current collector is formed from a wire of electrically conductive material, and said honeycomb structure has a channel density of between about 400 and 2000 per square inch.
23. The ultracapacitor of claim 21, wherein said electrode paste includes activated particulate carbon having a surface area of between about 1000 to 3000 m2/gm.
24. The ultracapacitor of claim 21, wherein a plurality of said channels include said electrode structure, and wherein said current collector of each electrode has a portion that extends beyond one end of its respective channel.
25. The ultracapacitor of claim 24, wherein the channels of said dielectric honeycomb structure are plugged in a checkerboard pattern at either end of said structure such that each channel has one plugged end and one open end, and wherein substantially all of said channels include said electrode structure, and further comprising conductive plates on either end of said structure that electrically connect said extending portions of said current collectors.
Type: Application
Filed: Apr 26, 2007
Publication Date: Dec 6, 2007
Inventors: William James Miller (Horseheads, NY), Huan-Hung Sheng (Horseheads, NY)
Application Number: 11/789,860
International Classification: H01G 9/155 (20060101);