Ultracapacitor package design having slideably engagable bent tabs

A terminal plate for an ultracapacitor package is formed from a single sheet of conductive material and comprising a plurality of bent tabs extending in a direction substantially orthogonal to a first main surface of the terminal plate. The terminal plate is configured to provide direct metallurgical contact between external terminals of the ultracapacitor package and the respective terminals of an electrode set that is incorporated into the package.

FIELD OF THE DISCLOSURE

The disclosure relates to a low cost package design for electrochemical double layer capacitors, and more particularly to a terminal plate design for providing an all-metal, electrically-conductive path between the electrodes and the capacitor terminals in an EDLC.

BACKGROUND

Energy storage devices such as ultracapacitors may be used in a variety of applications where a discrete power pulse is required. Such applications range from cell phones to hybrid vehicles. Ultracapacitors can include two or more carbon-based electrodes separated by a porous separator and an organic electrolyte. The foregoing active components can be arranged in a variety of designs, which can include parallel plate and jellyroll configurations. The active components are contained within a housing or package.

Important characteristics of an ultracapacitor are the energy density and the power density that it can provide. The energy density and the power density are largely determined by the properties of the active components. A further important characteristic is cost. Factors that impact the cost of the device include the cost of the raw materials, as well as the direct and indirect costs of the associated packaging, which can impact performance, manufactureabilty and reliability. It is desirable to make an ultracapacitor package simple and inexpensive while simultaneously robust and efficient.

One aspect of an ultracapacitor package is the means by which internal electrical connections are made. Approaches for forming electrical connections between the active components of the device (e.g., jellyroll) and the package terminals include welding, crimping and interference fits. Conventional designs that utilize the foregoing approaches, however, can have issues with long-term performance and reliability.

In view of the foregoing, there is a need for a simple, economical and robust package design for ultracapacitors.

SUMMARY

The disclosure relates to a terminal plate for an ultracapacitor package. In an embodiment, the terminal plate is formed from a single sheet of conductive material and comprises a plurality of bent tabs extending in a common direction substantially orthogonal to a first main surface of the terminal plate.

An ultracapacitor package can include one or more terminal plates. In a further embodiment, an ultracapacitor package comprises a housing having an end wall that includes a first package terminal. The housing defines an interior volume that can be closed using an end cap that includes a second package terminal. An electrode set comprising first and second electrodes can be incorporated into the interior volume. First and second terminal plates can also be incorporated into the interior volume to provide an electrical connection between the capacitor electrodes and the package terminals. In an example configuration, a first main surface of a first terminal plate is in electrical contact with the first electrode, and bent tabs formed in the first terminal plate are in electrical contact with the first package terminal. In a similar manner, a first main surface of a second terminal plate is in electrical contact with the second electrode, and bent tabs formed in the second terminal plate are in electrical contact with the second package terminal.

DETAILED DESCRIPTION

An ultracapacitor package includes a terminal plate that provides an all metallurgical connection along a current flow path between capacitor electrodes and the electrical terminals of the device. The terminal plate, which can improve the current density distribution and provide low resistance during charge/discharge cycles, is simple and economical to manufacture, and can be incorporated easily into the disclosed ultracapacitor package. The terminal plate and resulting ultracapacitor package can provide enhanced reliability with respect to conventional ultracapacitor packages.

An example ultracapacitor package100is illustrated schematically in cross-section inFIG. 1. The ultracapacitor package100includes a housing110defining an interior volume112. The housing110comprises an end wall116, side walls118, and an end cap130configured to sealably engage with the side walls118to enclose the interior volume112. The end wall116and the end cap130comprise respective package terminals126,136. Conventional methods can be used to form the housing including, for example, impact extrusion.

An electrode set such as a jellyroll electrode set can be incorporated into the interior volume112. In embodiments, the electrode set150can adopt a conventional construction comprising, for example, electrodes divided by at least one separator layer. Each of the electrodes can include a carbon-based layer formed over a conductive foil. As used herein, a layer that is “formed over” another layer will be in electrical contact but not necessarily in direct physical contact with the other layer.

In an example design, a pair of electrodes and two separator layers are stacked in an alternating manner and rolled along an axis into a “jelly-roll” cylinder. Once formed, the jelly-roll can have, for example, a circular or an oval cross section. Prior to rolling, the electrodes can be configured and arranged such that portions of each respective conductive foil extend beyond the other components of the electrode set in opposite directions to form first and second capacitor terminals154,158. Thus, when the electrodes and the separators are rolled, the capacitor terminals154,158at opposing ends of the cylinder provide a means to connect the resulting jellyroll capacitor to the package terminals126,136. In some designs, the extended portions of each conductive foil can be pressed or matted together to facilitate robust electrical connections.

The jellyroll can be formed by coiling the stack of materials around a mandrel. The mandrel, if used, can be removed after the jellyroll is formed, or left in place to function as, for example, a heat sink in the capacitor during operation.

In embodiments, the conductive foil can comprise any conductive material suitable for use in an electrochemical double layer capacitor. In one aspect, at least one of the conductive foils comprises a flexible conductive material that can be, for example, folded, rolled, or coiled. The conductive foil can be made from a metal such as, for example, aluminum.

The carbon-based layer can increase the surface area of the electrode set, and can include porous carbon or activated carbon. In various embodiments, one or both of the electrodes comprise activated carbon.

The separator layer can be a porous layer that allows a liquid electrolyte to permeate and/or diffuse there through. For example, the separator layer(s) can comprise paper, mica, glass, ceramic, aerogel, silica, non-conductive carbon, polymeric material, or a combination thereof.

Further details describing the electrode set, including the conductive foil, carbon layers, separator layers and liquid electrolyte are disclosed in commonly-owned US Patent Application Nos. 2010/0306979 and 2009/0320253, the entire contents of which are hereby incorporated by reference.

A terminal plate300can provide electrical contact between the capacitor terminals154,158and the respective package terminals126,136. Together with the electrode set150, a terminal plate300can be incorporated into the interior volume112of package100such that one surface318of the terminal plate makes physical and electrical contact with a capacitor terminal154or158while one or more bent tabs320that extend from the opposing surface316make physical and electrical contact with either the end wall116or the end cap130of the package, and thus provides an electrical connection to package terminals126,136. A single terminal plate can be incorporated at either end of the housing, or a package can comprise a pair of terminal plates.

A detailed view of a terminal plate according to one embodiment is shown inFIG. 2. The terminal plate300comprises a plate body310defined by a perimeter edge312and having substantially parallel opposing main surfaces316,318. A plurality of bent tabs320can be formed in the terminal plate300. In the illustrated embodiment, a pair of tabs is bent to extend in a common direction substantially orthogonal to main face316. In alternate embodiments, the terminal plate can have three or more bent tabs, which can be adapted to engage with a like number of slots formed in an end cap or end wall.

Optionally, each bent tab can include a pair of positioning notches322, which can provide a self-fixturing stop that can position a terminal plate with respect to the end wall116or end cap130of the package100. The positioning notches can limit the extent to which a bent tab passes through a slot to less than 0.1 inch (e.g., less than 0.1 or less than 0.05 inch).

Thinned regions330can be formed in the plate body310to enable welding (e.g., laser welding) of a main surface318to terminals154,158. The thinned regions330can be formed by coining a main surface. In embodiments, the thinned regions330are formed in a main surface316opposite to a main surface318where the terminal plate contacts terminals154,158.

The terminal plate can optionally be provided with a center hole340. The center hole340can be used to enable electrolyte filling of the ultracapacitor package. A center hole forms an open dead space that may serve as a gas generation buffer, and allows the use of a rod or mandrel during assembly to hold each terminal plate300in contact with the capacitor terminals154and/or158during welding.

The terminal plate, which comprises a unitary part, can be formed from a sheet of conductive material using any suitable method, including stamping, laser cutting, water jet cutting, coining, etc. In embodiments, a thickness of the terminal plate can range from 0.01 inch to 0.1 inch, where a thickness of the thinned regions can range from 0.005 to 0.05 inch. By way of example, thinned regions330of the terminal plate can have a thickness ranging from 25% to 75% (e.g., 50%) of the original terminal plate thickness.

In ultracapacitors comprising a pair of terminal plates, the design of each terminal plate may be substantially identical, or the terminal plates may be different. In an embodiment, one terminal plate may have longer bent tabs, which can cooperate with an extended end cap or an extended end wall to form a dead gas volume within the assembled housing.

According to further embodiments, end wall116and end cap130of housing110can independently comprise slots140that are configured to slideably engage with the bent tabs. A detailed view of one end of an example ultracapacitor package100is illustrated inFIG. 3. Terminal154of a jelly roll electrode set150is welded to surface318of terminal plate300and inserted into interior volume112. Bent tabs320extend through slots140formed in the end cap130and optionally protrude slightly. A hermetic and direct metallurgical joint is formed between terminal154and the end cap130by welding the bent tabs320to the end cap130where the bent tabs pass through slots140. The welding can comprise autogenous gas tungsten arc welding (GTAW), for example. A similar configuration can be formed at the opposite end (e.g., at the end wall116) of the package100.

In contrast with conventional assemblies, which use interference fits between parts in the electrical conductive paths, a welded fit has improved dimensional stability, greater mechanical robustness and, due to the hermetic nature of the weld joint, can provide enhanced resistance to interior corrosion and precipitation of salts from the electrolyte. Advantageously, the all metallurgical connection provided by the terminal plate can significantly lower the electrical resistance between the electrode set and the package terminals.

Thermal modeling and experimental testing were performed in order to assess the distribution of temperatures during welding. Excess heat may damage the jelly roll. Under welding conditions of 12 volts and 60 amps for 5 seconds, the modeling predicted a maximum temperature of 110° C. in the vicinity of the jelly roll, which is within acceptable range for the device.

FIGS. 4 and 5show a test device400. InFIG. 4, a terminal plate300abuts capacitor terminal154and the terminal plate is secured against the terminal154using a threaded tie rod410, washer415, and nut420. The plurality of portions of the conductive foil that form terminal154have been matted to provide a more robust interface between the terminal154and a main surface318of the terminal plate.

The terminal plate includes a pair of bent tabs320. Thermocouples450are positioned between the terminal plate300and the jelly roll terminal154in order to measure a local temperature during welding. As seen with reference toFIG. 5, a simulated end cap130having a pair of slots140is placed over the terminal plate300such that the bent tabs320extend through respective slots. The bent tabs pass through the slots and extend by approximately 0.03 inch.

The bent tabs are welded (e.g., gas tungsten arc welded) within the slots of the simulated end cap at welding conditions of 12 volts and 65 amps, which produced a measured temperature of 120° C. Helium leak testing confirmed that the weld joints are hermetic.

In an embodiment, bent tabs320can optionally include positioning notches322that are configured to limit the extent that the bent tabs engage with slots140. With reference again toFIG. 2, a bent tab having positioning notches322has an engagement segment326having a width w and depth d. A thickness of the engagement segment can be the same as the thickness of the bent tab, which can be the same as the thickness of the plate body310from which it was bent. A bent tab having such an engagement segment may slideably engage with a slot140having length and width dimensions slightly greater than wxd, where the bent tab will slide through such a slot only to a depth d whereupon a step328formed by notch322will engage with the body in which the slot is formed and seat the bent tab within the slot.

Positioning notches can be used to spatially offset an end cap or end wall away from the plate body310such that, in embodiments, a dead space390is formed between main surface316and an inner surface of the end cap or end wall. In embodiments, electrical contact between the terminal plate and the end cap or end wall is made only via bent tabs320, i.e., the plate body310does not make contact with an end cap130or end wall116. In addition to locating the fit between the terminal plate and the housing, the positioning notches can absorb external loads that would otherwise impact and potentially damage the weld joints.

A hermetic seal can be formed between the end cap130and the side walls118of the housing110in order to protect the contents of the housing from exposure to air or moisture, as well as to electrically isolate the end cap136(and the corresponding package terminal136) from the opposing end wall116(and the corresponding package terminal126).

A variety of approaches can be used to provide both hermetic sealing and electrical isolation between the end cap and the housing. Such approaches include the use of insulators, coatings, and polymer seals including O-rings.

The end cap joint can incorporate an O-ring370that can be positioned, for example between housing110and an inner surface of end cap130to provide a sealed interface. In an example embodiment, as illustrated inFIG. 4, an O-ring370can be incorporated as a face seal that engages housing110at an end face119of sidewall118. Example O-rings can have a high electrical resistance, and can be formed using a low carbon material.

In further embodiments, an adhesive seal can be used to electrically isolate the end cap from the housing, and hermetically seal the package against the ingress of air and/or moisture as well as prevent leakage of the liquid electrolyte. Tests have suggested that an adhesive seal can provide a more robust hermetic barrier than conventional polymer O-rings. For example, an epoxy resin could be used to seal the joint, and also to electrically isolate the housing from the end cap. An example epoxy is Loctite (Henkel, Dusseldorf, Germany).

An adhesive seal380, which can be used in addition to or in lieu of an O-ring, can be formed along a narrow interface between an outer surface of sidewall118and an inner surface of end cap130.

The disclosed ultracapacitor package includes low cost piece parts that are simple to assemble and which, when assembled, provide a low cost, robust and reliable package.

As used herein, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a “metal” includes examples having two or more such “metals” unless the context clearly indicates otherwise.

It is also noted that recitations herein refer to a component of the present invention being “configured” or “adapted to” function in a particular way. In this respect, such a component is “configured” or “adapted to” embody a particular property, or function in a particular manner, where such recitations are structural recitations as opposed to recitations of intended use. More specifically, the references herein to the manner in which a component is “configured” or “adapted to” denotes an existing physical condition of the component and, as such, is to be taken as a definite recitation of the structural characteristics of the component.

It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Since modifications combinations, sub-combinations and variations of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and their equivalents.