MANUFACTURING ENHANCED GRAPHITE METALLIC BIPOLAR PLATE MATERIALS

Abstract

The present invention includes methods of manufacturing a metal infused graphitic material. Also described is how this device may be rendered impermeable. The present invention includes the electroplating/electroless deposition of metal on exposed internal and external surfaces of a porous graphitic substrate. The deposition of metal on the internal structure is accomplished by replacing the void space in the porous substrate with an electrolyte solution containing dissolved metallic species. The plating is initiated either through electrochemical means, electroless means, chemical vapor deposition means, or other means obvious to one familiar in the art of metal plating. A post-deposition bath is also described wherein the plating may be removed from one or both sides of the external surface without impacting the internal pore plating.

Claims

1. A device comprising, a first part comprised of a porous graphitic material; and a second part comprised of a metallic material plated upon the exposed surfaces of the first part.

2. The device according to claim 1, wherein the first part comprises one of a group including a compressed expanded-graphite foil, a sintered body graphite element, or any combination thereof, with opposed planar porous surfaces.

3. The device according to claim 1, wherein the second part comprises a metal configured to improve an electrical conductivity of the device.

4. The device according to claim 1, wherein the second part comprises a metal configured to improve a strength-to-weight ratio of the device.

5. The device according to claim 1, wherein the metallic materials of the second part are configured to improve chemical stability of the device in an alkaline environment.

6. The device according to claim 1, wherein the metallic materials of the second part are configured to provide chemical stability in a secondary battery.

7. The device according to claim 1, further comprising a third part comprised of a non-polar compound that fills and seals a void space in the device.

8. The device according to claim 1, wherein the second part is removed from the exterior surfaces of the first part via an etching process.

9. The device according to claim 7, wherein the third part is constructed from a compound that is chemically stable in an acidic environment.

10. The device according to claim 1, wherein the first and second parts are chosen to improve thermal conductivity of the device for use as a heat spreader.

11. A device according to claim 1, wherein the first part and the second part are a bipolar plate configured to be used in a redox flow battery, and a fuel cell.

12. A device according to claim 3, wherein the first and second parts are chosen to enable the device for use as a conductive layer in a semiconductor assembly.

13. A method of manufacturing a metal hybrid infrastructure bipolar materials from porous graphite materials, comprising the steps of: providing a raw material comprising: a flexible graphite foil produced by compressing expanded graphite, a sintered body graphite element, or a composite of the flexible graphite foil and the sintered body graphite element; immersing the raw material in deposition bath and subjecting the material to an electrochemical or electroless deposition treatment process.

14. The method of claim 13 further comprising the step of, drawing a vacuum around the raw material prior to immersing the raw material in the deposition bath.

15. The method of claim 13, wherein the raw material is immersed in the deposition bath for a period between 1 second and 1 minute.

16. The method in claim 13, wherein the raw material is immersed in the deposition bath for a period greater than 1 minute.

17. The method of claim 13 further comprising the step of, wherein the immersed raw material is pulled from the deposition bath and subsequently moved to an acid or base wash.

18. The method of claim 13 further comprising the step of, wherein the immersed raw material is pulled from the deposition bath and subsequently moved to a gaseous etching system.

19. The method of claim 13, wherein the raw material is immersed in the deposition bath via a batch process.

20. The method of claim 13, wherein the steps are carried out in an environment chamber configured to control temperature and pressure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. 1 is a conceptual illustration of expanded graphite pre- and post-compression showing the residual discontinuity in the graphite material.

[0020] FIG. 2 is a schematic of illustrating open porosity (left), surface porosity (middle), and internal porosity (right) of expanded graphite material.

[0021] FIG. 3 is a schematic of a pore structure similar to FIG. 3 once metallic deposition has occurred. Tree branch like growths coming from within the pores represent dendrite formation of the application.

[0022] FIG. 4 is a schematic illustrating the deposition and impregnation process of expanded graphite foil.

[0023] FIG. 5 is a schematic illustrating a batch process for processing porous graphite materials and doctoring process.

DETAILED DESCRIPTION OF THE INVENTION

[0024] This invention pertains to the manufacturing process and novelty therein for generating metal-graphite hybrid infrastructure bipolar current collector electrodes and comparable materials. This process can be modified for metal deposition on any graphite material that is porous in nature, including, but not limited to sintered body graphite plates, sheets, rods, bars of the same, compressed expanded graphite, or calendared expanded graphite foil.

I. Terms and Definitions

[0025] The following explanations of terms and abbreviations are provided to better describe the present invention and to guide those of ordinary skill in the art in the practice of the present invention. As used herein, the singular forms a or an or the include plural references unless the context clearly dictates otherwise. The term or refers to a single element of stated alternative elements or a combination of two or more elements, unless the context clearly indicates otherwise.

[0026] Unless explained otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. The materials, methods, and examples are illustrative only and not intended to be limiting. Other features of the invention are apparent from the following detailed description and the claims.

[0027] Unless otherwise indicated, all numbers expressing quantities of components, percentages, temperatures, times, and so forth, as used in the specification or claims are to be understood as being modified by the term about. When directly and explicitly distinguishing embodiments from discussed prior art, the embodiment numbers are not approximations unless the word about is recited.

[0028] For the purposes of this patent, a deposition bath is defined as a solution with metal ion species dissolved in a solvent. Open pores are defined as void spaces that consist of continuous uninterrupted flow paths through the bulk material, with an opening on first and second opposing surfaces. Surface pores are defined as void space in the substrate material with at least one opening on the first or second opposing surface of the substrate, but not both. Internal pores are defined as void spaces which do not have any continuous uninterrupted flow path to any exterior surface of the substrate.

II. Devices Comprising a Bipole

[0029] Embodiments of a device, or a component of a device, including at least one bipole prepared by the proposed methods are disclosed.

[0030] In a Proton-Exchange Membrane fuel cell (PEMFC) hydrogen is adopted as fuel source to generate electricity from energy released in hydrogen's electrochemical reaction with oxygen. Two main materials are key in PEMFC's. The first is the membrane, which must be ionically conductive to move protons, but not electrically conductive so as to prevent the electrical shorting of the cell. Second is the bipolar electrode materials, which must be electrically conductive to act as a current collector for the electrochemical reaction. These electrode materials would be a direct application of this invention.

[0031] In a redox flow battery electrical energy is converted and stored as chemical potential energy in ions dissolved in the electrolyte. Within this system, there are two electrolyte tanks in a redox flow battery, one containing an analyte and the other a catholyte. Both electrolytes are kept in separate flow circuits while they are pumped through a stack of electrochemical reaction cells. It is critical that the two electrolytes do not mix while flowing through the reaction cells, as this causes the system to self-discharge, resulting in poor efficiency and energy losses. This loss is called cross-over and is managed within these systems by carefully selecting the proton/ion exchange membrane and bipole materials that are used to separate each individual cell within the stack of electrochemical reaction cells. The proposed invention can produce a device capable of satisfying the requirements of a bipole material for a redox flow battery system akin to that described here.

III. Preparation of a Metallic Bipole

[0032] Expanded graphite foil is permeable to fluids and ions as part of an electrolyte solution. Insight to this porous structure can be derived from its manufacturing, which is essentially the compression of many graphite flakes, illustrated in FIG. 1. The pores of the graphite foil are essentially void spaces throughout the bulk of the material, and comprise three types of pores illustrated in FIG. 2: open (12), surface (13), and internal (14). These void spaces are filled by air or other gas. When a porous material like the one described is immersed in a liquid, the gas particles will tend to evacuate the void space in all the accessible pores through diffusion into the liquid. The diffusion process may be aided by adding energy into the system by heating the liquid, agitation, or both. The void space is back filled with the surrounding fluid, allowing a solvent to now occupy these pores. This access of the solvent allows for subsequent deposition of metal into the internal pore surface. The electrochemical, electroless, or similar deposition process precipitates the solute metal, resulting in a plated metal surface throughout the internal pore structure of the bulk material. The result of this process is presented visually in FIG. 3.

[0033] To precipitate the metal, a graphite foil may be first soaked in an acidic metal salt solution, as mentioned above, to diffuse metal ions into the pore structure. After sufficient time is allowed for diffusion, plating may begin. To plate, a potentiostat may be used, attaching the working electrode lead to the graphite foil while submersing the counter and reference electrodes in the same solution. For this plating process, the potentiostat may be set up for cyclic step chronopotentiometry experiments and alternated between two galvanostat settings. In a first setting, the required potential to achieve 0 mA of current, thus holding equilibrium, is applied to the system, thereby allowing for further diffusion. In a second setting, a potential sufficient to reduce the metal ions inside of and around the foil is applied. By way of example, the potentiostat may be set to hold a current of 500 mA within the second setting to get functional samples of copper-graphite. After several cycles between the first and second setting, the potentiostat may be stopped, leads disconnected, and the plated sample rinsed off and dried in a vacuum oven.

IV. Impregnation

[0034] After the material has undergone metal deposition, the remaining void spaces may be filled to ensure impermeability of fluids. For acidic redox flow battery applications, this treatment may be preferred. The material may be sealed by a variety of composition polymer blends, including but not limited beeswax and/or other non-polar chemicals. The filling of these remaining voids spaces by this filling solution is accomplished by first melting the hydrophobic substrate to a point below the chemical's flash point but sufficiently high in temperature to minimize the solution's viscosity when in a liquid state, thereby aiding diffusion of the solution into the pores of the substrate. Finally, the metal-plated graphite substrate is submerged into a liquid bath of the solution, enabling the filling material to wick into the unfilled void spaces of the bulk material. The filled substrate is removed from the heated bath and allowed to cool, during which the filling solution changes phase back to a solid. The resultant device then provides hydrophobic and impermeable characteristics to the treated substrate. The resultant material will have no exposed metal at the surface, with the hydrophobic filler sealing off the metallic layers.

V. Large Scale Manufacturing

[0035] This process may be realized in a variety of embodiments at a manufacturing scale. One of these embodiments is a continuous roll-to-roll process depicted in FIG. 4, where a roll (i) is set on a spindle and unwound by the pre-calendaring rolls passed through a metal deposition bath (ii), and a subsequent impregnation bath (iv) and is then collected by the calendaring rolls. The now metal filled and impregnated material is fed through a cleaning system (v) to remove any excess material with the objective of exposing the exterior surface so that the only treatment left in the device is inside the pore structure of the material.

[0036] In another embodiment batch processing is adopted, illustrated in FIG. 5. Pieces of an expanded graphite foil are placed on a rack (8) and immersed into a metal deposition bath (9). The sheets are then transferred to a filling impregnation bath (not pictured), and finally they undergo a post-processing step similar to that described above (5,6,10).

VI. Examples

[0037] As mentioned above, the potential applications include, but are not limited to, use in redox flow batteries, Proton-Exchange membrane fuel cells and electrochemical processes. The claimed improvements in electrical conductivity and impermeability serve to both increase the lifespan of bipole parts in the applications and increase the efficiency with which they operate. The invention also serves to improve the materials resistance to oxidation or corrosion, which is a useful attribute in many other applications, including bur not limited to alkaline environments. The claimed increases in tensile strength and other mechanical properties of the material will reduce the chances that bipole plates become damaged by normal operations, and will allow for thinner plates to be used, thus further reducing overall resistance of the bipole. Finally, the invention and method of manufacturing this new composite material can be custom tailored to fit a variety of needs in other fields of application that include, but are not limited to: structural members for applications requiring high strength-to-weight ratios (e.g. aerospace, aeronautics, transportation), thermal heat sinks (e.g. electronics cooling, thermal management), heat spreaders (e.g. satellite thermal distribution, etc), non-secondary battery related electrochemical reaction chamber components, and high-frequency signal transmission.