Patent Application
20170110255
The present invention relates generally to the field of electrolytic capacitors and batteries.
Compact, high voltage capacitors are utilized as energy storage reservoirs in many applications, including implantable medical devices. These capacitors are required to have a high energy density, since it is desirable to minimize the overall size of the implanted device. This is particularly true of an Implantable Cardioverter Defibrillator (ICD), also referred to as an implantable defibrillator, since the high voltage capacitors used to deliver the defibrillation pulse can occupy as much as one third of the ICD volume.
Stacked electrolytic capacitors are typically constructed with a plurality of anodes and cathodes, which must be separated by a liquid absorbent insulative material, and are impregnated by an electrically conductive electrolyte. If the separator is not present as a line of sight barrier between any anode and adjacent cathode, there exists a danger of physical contact, as well as electrical breakdown of any incidental gasses present in the completed capacitor. Either of these scenarios would result in an undesirable partial or complete discharge event with a high probability of device failure.
Stacked electrolytic capacitors have utilized physical features in the constituent components of assembly with the aim of assuring precision of physical alignment such that the dimensions of those components leave physical margins that assure adequate separator coverage between all anodes and cathodes. Historically, those features have included holes in the separators, anodes, and cathodes in order to align with features on stacking fixtures when being assembled. These holes constitute undesirably lost surface area in each anode and cathode, which in turn requires compensation either in numbers of anodes and cathodes, or overall physical outline of those components in order to achieve a given design capacitance in the finished part.
The stacked alignment holes result in an undesirably larger overall finished part than would otherwise be required. The stacked alignment holes also create isolated cavities in the finished part which can lead to gas rich, electrolyte starved regions ripe for latent failure. The edges of the holes or other features necessarily create more edge length and complexity of shape for each anode, which increases the challenge of removing them flaw-free from the source anode sheet material.
Device designs are presented that include a cathode subassembly for protecting the device from unwanted discharge, and aiding in alignment of the cathodes and anodes within a device.
According to an embodiment, a device includes a conductive anode (e.g., an anode foil), a dielectric material disposed on a surface of the conductive anode, a conductive cathode (e.g., a cathode foil), and an electrolyte disposed between the anode and the cathode. The conductive cathode is sandwiched between two separator sheets, the two separator sheets being adhered together along a peripheral area outside of a perimeter of the conductive foil.
According to an embodiment, a cathode for use in an electrolytic capacitor includes a conductive foil, a first separator sheet, and a second separator sheet. The first separator sheet has a shape corresponding to a shape of the conductive foil and is disposed over a first face of the conductive foil. The second separator sheet has a shape corresponding to the shape of the conductive foil and is disposed over an opposite face of the conductive foil. The first separator and the second separator are adhered together along a peripheral area outside of a perimeter of the conductive foil.
Further embodiments, features, and advantages of the present invention, as well as the structure and operation of the various embodiments of the present invention, are described in detail below with reference to the accompanying drawings.
The accompanying drawings, which are incorporated herein and form part of the specification, illustrate a cathode assembly with an integrated separator and a capacitor formed therefrom. Together with the detailed description, the drawings further serve to explain the principles of and to enable a person skilled in the relevant art(s) to make and use the methods and systems presented herein. In the drawings, like reference numbers indicate identical or functionally similar elements. Further, the drawing in which an element first appears is typically indicated by the leftmost digit(s) in the corresponding reference number.
The following detailed description of capacitor and battery designs refers to the accompanying drawings that illustrate exemplary embodiments consistent with these devices. Other embodiments are possible, and modifications may be made to the embodiments within the spirit and scope of the methods and systems presented herein. Therefore, the following detailed description is not meant to limit the devices described herein. Rather, the scope of these devices is defined by the appended claims.
Electronic component 100 may be, for example, an electrolytic capacitor or a battery. When electronic component 100 is used as a capacitor, example materials for plurality of cathodes 104 include aluminum, titanium, stainless steel, while example materials for plurality of anodes 108 include aluminum and tantalum. When electronic component 100 is used as a battery, example materials for plurality of cathodes 104 include silver vanadium oxide, carbon fluoride, magnesium oxide, or any combination thereof, while example materials for plurality of anodes 108 include lithium metal.
Spacer 106 may be provided to maintain a given separation between each cathode 104 and an adjacent anode 108 within housing 102. Additionally, spacer 106 may be provided to prevent arcing between cathode 104 and anode 108 in spaces where dielectric 110 may be very thin or nonexistent, and/or where a void within electrolyte 112 exists between cathode 104 and anode 108.
Aligning each cathode 104, spacer 106, and anode 108 together in a stack is typically performed using physical features on each element that fit together (such as a peg-in-hole arrangement). As discussed above, this reduces the total usable surface area, which in turn reduces the overall energy density of electronic component 100.
It should be understood that the various elements and dimensions of electronic component 100 are not drawn to scale. Although each of cathode 104, separator 106, and anode 108 are illustrated as being apart from one another for the convenience of illustration and labeling, it would be understood by one skilled in the art that such elements may also be stacked together in close physical contact with one another.
Each separator sheet 202a and 202b may include a high density Kraft paper. Other example materials include woven textiles made of one or a composite of several nonconductive fibers such as aramid, polyolefin, polyamide, polytetrafluoroethylene, polypropylene, and glass. Separator sheets 202a and 202b should be porous enough such that an electrolyte can penetrate through each separator sheet 202a and 202b. Any insulating material that can be formed into a uniform, thin sheet with a porous structure may be used for separator sheet 202a and 202b. The material preferably shows no dissolution or shrinkage when introduced to the electrolyte. Similarly, the material preferably does not elute any chemicals when introduced to the electrolyte that would damage any part of the device over time (e.g., corrosives or, in the case of aluminum electrolytic capacitors, halides.)
An adhesive may be used at location 204 to bond separator sheet 202a and separator sheet 202b together. Example adhesives include UV curable polymers, acrylic polymers, silicones, polyurethanes, polysulfides and cyanoacrylates. According to an embodiment, the adhesive does not dissolve in the presence of an electrolyte and does not elute any chemicals when introduced to the electrolyte that would damage any part of the device over time (e.g., corrosives or, in the case of aluminum electrolytic capacitors, halides.). The adhesive is selected and configured to provide a permanent bond between separator sheet 202a and separator sheet 202b, according to an embodiment.
By sandwiching cathode 104 between separator sheets 202a and 202b, the entire surface area of cathode 104 is still usable, thereby promoting a higher energy density due to elimination of alignment center holes and/or circumscribed alignment features on the cathode. Relative surface area increase may be as much as 2% to 5% depending of the cathode geometry, resulting in an increase of between 0.1 J/cc (Joules per cubic centimeter) and 0.25 J/cc delivered energy capacity. Separator sheets 202a and 202b around cathode 104 eliminate the need for separator 106 in
It should be understood that only one cathode subassembly 200 is illustrated in
In another embodiment, a single separator sheet is used to encapsulate cathode 104 rather than using two separate sheets. In this embodiment, the single separator sheet is folded in half, with each half forming one of separator sheets 202a and 202b in
Electrical connection is made to cathode 104 via terminal 302. Terminal 302 may be an extension of the material of cathode 104, or terminal 302 may be a different material that is bonded to cathode 104. Cathode 104 is commonly formed from a metal foil or plate, such as aluminum, titanium, or stainless steel. Cathode 104 may be any electrically conductive material that can be formed into a uniform, thin sheet. As used herein, the terms “foil,” “sheet,” and “plate” are used interchangeably to refer to a thin, planar material.
Separator sheets 202a and 202b include corresponding (i.e., mating) indentations 304a and 304b, according to an embodiment. Indentations 304a and 304b may be configured to closely mate such that cathode 104 is enclosed or encapsulated, when separator sheets 202a and 202b are brought together on opposite sides of cathode 104 with cathode 104 sandwiched there between. An area of indentations 304a and 304b may be designed to be slightly larger than an area of cathode 104 to provide some tolerance when aligning separator sheets 202a and 202b over cathode 104.
An adhesive may be used within edge regions 306a and 306b to bond separator sheets 202a and 202b together, according to an embodiment. Edge region 306a may include the area between indentation 304a and an outermost edge of separator sheet 202a. Similarly, edge region 306b may include the area between indentation 304b and an outermost edge of separator sheet 202b. Edge regions 306a and 306b exist beyond a perimeter of cathode 104. In one example, edge regions 306a and 306b completely circumscribe cathode 104. The adhesive that bonds separator sheets 202a and 202b may extend all the way to the edges of separator sheets 202a and 202b.
According to an embodiment, each of the X and Y dimensions of cathode subassembly 200 is substantially the same as the X and Y dimensions of an anode that is stacked adjacent to cathode subassembly 200. This similarity in the footprint of each cathode subassembly 200 and each anode facilitates easier self-alignment of the various cathodes/anodes when constructing, for example, electronic component 100 of
Provided herein is one example of fabricating a cathode assembly 200, with reference to
At this point, an array of cathode subassemblies are formed and connected together along vertical scribe lines 506 and horizontal scribe lines 508. Each subassembly may be removed from bulk separator sheet 502 by cutting along vertical scribe lines 506 and horizontal scribe lines 508 using any number of known techniques, such as mechanical shearing, cleaving, or laser cutting. According to an embodiment, cutting along vertical scribe lines 506 and horizontal scribe lines 508 also cuts through the adhesive bonding the separator sheets together.
In one embodiment, portions of separator sheets 202a and 202b that cover terminal 302 of cathode 104 are removed to permit electrical connection to cathode 104. In another embodiment, cathode 104 is positioned in a cell 503 such that a distal (i.e., distal from the body of cathode 104) end of terminal 302 extends out from cell 503 and is not covered by separator sheets 202a and 202b. This eliminates need to remove separator sheets 202a and 202b material from terminal 302 when it is making electrical connection thereto.
It is to be appreciated that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the claims. The Summary and Abstract sections may set forth one or more but not all exemplary embodiments of the present system and method as contemplated by the inventors, and thus, are not intended to limit the present method and system and the appended claims in any way.
Moreover, while various embodiments of the present system and method have been described above, it should be understood that they have been presented by way of example, and not limitation. It will be apparent to persons skilled in the relevant art(s) that various changes in form and detail can be made therein without departing from the spirit and scope of the present system and method. Thus, the present system and method should not be limited by any of the above described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.
In addition, it should be understood that the figures, which highlight the functionality and advantages of the present system and method, are presented for example purposes only. Moreover, the steps indicated in the exemplary system(s) and method(s) described above may in some cases be performed in a different order than the order described, and some steps may be added, modified, or removed, without departing from the spirit and scope of the present system and method.
