Patent Application
20080090146
Aspects of the disclosure may be more fully understood from the following description when read together with the accompanying drawings, which are to be regarded as illustrative in nature, and not as limiting. The drawings are not necessarily to scale, emphasis instead being placed on the principles of the disclosure. In the drawings:
While certain embodiments depicted in the drawings, one skilled in the art will appreciate that the embodiments depicted are illustrative and that variations of those shown, as well as other embodiments described herein, may be envisioned and practiced within the scope of the present disclosure.
Aspects and embodiments of the present disclosure are directed to bipolar electrode structures, related assembly methods, and resulting bipolar battery assemblies.
Referring to
Depicted in
The sealing ring 10 is a thermoplastic component manufactured by injection molding or casting, which has a substantially ‘L’ shaped cross section. The bottom leg of the ‘L’ has a protrusion of circular cross section, which provides a locking snap feature during assembly of the bipolar electrode assembly 4.
In exemplary embodiments, a second electrode substrate 12 can have a flat metallic, electrically conductive plate, having one side spray coated with a thermoplastic layer of suitable thickness, e.g., 0.0002″ to 0.006″ thick. At least one or more circular areas 21 can be excluded from the spray coating by masking or removal of the coating in diameter and pattern to match the stamped offset areas 14 of the first electrode substrate 9 and which match the pattern of the punched through holes of the support plate 11.
Referring to
The second electrode substrate 12 can be placed and held flat with the previously spray-coated surface facing upward. The support plate 11, previously coated, with fill tube/vent 20 previously installed, can be placed on top of the second electrode substrate 12 with the circular holes 17 of the support plate 11 aligned with the circular coating free areas 21 of the second electrode substrate 12. Next the sealing ring 10 can be pressed into place along the inside surface of the support plate 11 vertical wall. The first electrode substrate 9, having aligned the stamped offsets 14 with the through holes 17 of the support plate 11, can then be pressed into the inside of the sealing ring 10 until the bottom surface of the first electrode substrate 9 makes contact with the surface of the support plate 11.
The drafted vertical wall of the first electrode substrate 9 will deform the leg of the “L” shaped sealing ring 10, causing the top edge of the first electrode substrate 9 to snap into contact with the inside vertical wall of the seal ring 10. In the assembled position the draft angle of the drafted wall of the first electrode substrate 9 is substantially reduced, creating a permanent outward compressive force on the sealing ring 10.
Welding or brazing the first electrode substrate 9 and the second electrode substrate 12 in the uncoated circular contacting areas electrically and mechanically connects the first and second electrode substrates. The welding can be accomplished by suitable techniques, e.g., resistance welding, ultrasonic welding, laser welding, electron beam welding or brazing.
The resulting assembly can then be heated to near the thermoplastic melting point, thermally bonding the contacting coated surfaces of the first electrode substrate 9, support plate 11, second electrode substrate 12 and the sealing ring 10, creating a liquid tight seal between the inside surface of the first electrode substrate 9 and the outside of the bipolar plate assembly 4, while maintaining electrical isolation between the two electrode substrates and the support plate 11.
This design is applicable to many different primary and secondary electrochemical systems currently being employed, such as Lithium primary batteries, Nickel-Metal Hydride and Lithium Ion rechargeable batteries for example. The selection of materials will be determined by performance, cost and chemical compatibility considerations for any particular battery chemistry system utilized.
For a Nickel Metal Hydride bipolar battery with aqueous KOH electrolyte, the first and second electrode substrates are selected from Nickel, Nickel-plated steel or stainless steel. The polymer coating and sealing ring are selected from Nylon or Polypropylene. The first electrode 8 can be a plastic bonded Nickel Oxide powder, pasted onto metallic foam, expanded metal grid or directly onto the first electrode substrate 9. The second electrode 13 can be a Misch-metal hydrogen absorbing alloy powder pasted onto metallic foam, expanded metal grid or directly onto the second electrode substrate 12. A separator 22 of non-woven or micro-porous polyolefin sheet can be present to provide electrical and mechanical isolation between the first and second electrodes while allowing ionic current to flow during battery charge and discharge.
In a Lithium Ion rechargeable bipolar battery embodiment, utilizing an organic solvent based electrolyte, the first electrode 8 is graphite and carbon powder with plastic binder pasted onto an expanded metal grid or directly onto the first electrode substrate 9. The first electrode substrate 9 can be Copper. The second electrode 13 would be a mixture of lithiated Cobalt Oxide, Carbon and plastic binder or a mixture of lithiated Iron Phosphate, carbon and plastic binder, pasted onto an expanded metallic grid or directly onto the second electrode substrate 12.
The second electrode substrate 12 can be, in exemplary embodiments, made of Aluminum or an Aluminum alloy. The support plate 11 is also Aluminum or Aluminum alloy, allowing effective edge welding of the first electrode substrate 9 and support plate 11. The separator 22 is a micro-porous polyethylene. The polymer coatings and sealing ring 10 are a thermoplastic compatible with the electrolyte solution such as Tefzel (ETFE), polyamide or polyethylene.
The detailed description herein provided describes a cylindrical bipolar electrode assembly 4 and a bipolar battery assembly 1. This design approach is also applicable to bipolar batteries of other shapes, such as rectangular, square or ‘D’ shape. The cylindrical shape was chosen for convenience of communication of the design approach and key features and does not imply any limitation of the application of this invention to other geometrical shapes.
The bipolar battery assembly 1, utilizes the previously described bipolar electrode assembly 4 as a fundamental building block.
After vertically stacking and aligning all the components, the entire assembly can be compressed and held to the final required assembly height using a hydraulic press or similar means. The contacting edges of the second electrode substrates 12 and the mechanical support plates 11 are then welded continuously around the perimeter, creating a hermetic seal between the support plates 11 and the second electrode substrates 12. Suitable techniques such as laser welding, electron beam welding, or tungsten-inert-gas (TIG) welding, etc., can accomplish the edge welding. The appropriate process can depend upon specific materials utilized for these two components. After welding, a suitable number of mechanical fasteners, e.g., three or more mechanical fasteners, 7 can be installed through the two external end support plates 2,6, so as to maintain the required stack height or amount of stack compression desired.
The top and bottom external supporting end plates 2,6 are made of molded high strength plastic, such as glass filled Valox (PBT) or similar engineering resin. The external support plates further may have stiffening ribs (not shown), running from the outside edge to the inside edge to provide high mechanical resistance to bending from internal pressure of the battery assembly. The outer periphery of the support plates 2,6 extend beyond the outer periphery of the bipolar electrode assemblies 4 and provide multiple through holes for the fasteners 7 which extend from the top support plate 2 to the bottom support 6, allowing compressive force to be applied to the entire assembly by controlled torque on the fasteners 7. Alternatively, the supporting end plates could be made of a lightweight metal, such as machined or cast Aluminum or Titanium alloy.
The foam spacers 23,26 are made of closed cell elastic foam, such as high-density polyethylene foam or alternatively, a low or medium hardness (durometer value) rubber. This compressible and elastic layer accommodates growth and shrinkage of the active electrodes during charge and discharge of the bipolar battery, while maintaining required axial compression on the stack. The thickness and durometer of the foam layers are selected to accommodate the expected electrode displacement and provide required compression force for a specific battery stack design.
The first polarity current collector 24 is a metallic electrically conductive flat plate with a conductive connector attached at its central portion. The example shown depicts a threaded circular connector welded to the center of the current collector. Alternative connectors, such as flat ribbon stock or welded circular wire could also be employed. The current collector plate 24 is of sufficient thickness and conductivity to provide low electrical resistance to current flow in the radial direction. The first polarity current collector 24 is fused to the first electrode substrate 9 of a partially assembled bipolar electrode assembly 4 by welding, brazing or soldering, prior to assembly of the bipolar battery stack, the first polarity current collector taking the place of the second electrode substrate 12.
The second polarity current collector 25 is of substantially identical construction as the first polarity current collector 24, though it may be desirable to make the electrical connector of different dimensions to prevent incorrect polarity connection during installation in the application. The second polarity current collector 25 is fused to a second electrode substrate 12 by welding, brazing or soldering prior to completing the assembly of the bipolar electrode assembly 4 to which is attached.
The assembly of the bipolar stack is completed by welding the periphery of the second polarity current collector 25 to the support plate 11 of the adjacent bipolar plate assembly 4. The bipolar battery can them be activated by vacuum filling each of the bipolar cells via the fill port 20 and then plugging the fill ports to prevent leakage.
An electronics module, not shown, may be attached to the exposed edges of the bipolar plates, via welding or soldering metal tabs, allowing monitoring of individual cell voltages and other electronic control functions such as charge balancing and or safety shut off to prevent over-charge or over-discharge of individual cells of the bipolar battery stack.
Further, a common pressure manifold connected to individual cells via the venting/fill tube 20, may be utilized to eliminate large pressure differences between cells of the battery stack, preventing mechanical damage to adjacent cells in the event of high pressure in any one cell of the bipolar battery assembly.
Lastly, the assembled bipolar battery 1 may be inserted and mounted within a battery housing 27. The cover plates 28,29 of the battery housing 26 having central holes 30, allow the current connectors of the bipolar battery stack to protrude through. The inside dimension of the battery housing 27 is closely matched to the outside dimension of the bipolar battery stack end plates 2,6, such that the stack end plates provide lateral support of the bipolar battery 1 within the housing 27 while maintaining electrical isolation between housing 27 and the bipolar battery assembly 1.
The battery housing 27 provides mechanical protection to the bipolar battery assembly 1 as well as providing mounting features to allow integration with the application system. For very high power batteries and battery chemistry systems which may generate large amounts of heat during high rate charging, such as Nickel-Metal Hydride or Nickel-Iron, an active cooling system may be required. By mounting the battery stack in a housing 27 that has an airflow manifold 31 and providing forced air flow into and out of the battery housing 27, very effective active cooling of the bipolar battery assembly 1 is accomplished. Effective cooling is provided for by the exposed edges of the bipolar electrode assemblies 4. These exposed edges act as heat exchange fins, greatly improving heat removal from the bipolar battery 1 using forced or natural convection.
While certain embodiments have been described herein, it will be understood by one skilled in the art that the methods, systems, and apparatus of the present disclosure may be embodied in other specific forms without departing from the spirit thereof.
Accordingly, the embodiments described herein, and as claimed in the attached claims, are to be considered in all respects as illustrative of the present disclosure and not restrictive.
This application is based upon and claims priority from U.S. Provisional Application 60/851,839 filed on Oct. 12, 2006, the contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60851839 | Oct 2006 | US |
