Patent Publication Number: US-8988859-B2

Title: Sintered capacitor electrode including a folded connection

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 12/968,555, issued as U.S. Pat. No. 8,619,408, entitled “Sintered Capacitor Electrode Including a Folded Connection,” filed Dec. 15, 2010, which claims the benefit of U.S. Provisional Application No. 61/288,076, filed on Dec. 18, 2009, under 35 U.S.C. §119(e), each of which is incorporated herein by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     This document relates generally to energy storage and particularly to sintered electrodes to store energy in an implantable medical device. 
     BACKGROUND 
     Electrical stimulation therapy has been found to benefit some patients. For example, some patients suffer from an irregular heartbeat or arrhythmia and may benefit from application of electrical stimulation to the heart. Some patients suffer from a particular type of arrhythmia called a fibrillation. Fibrillations may affect different regions of the heart, such as the atria or the ventricles. When a fibrillation occurs in the ventricles, the heart&#39;s ability to pump blood is dramatically reduced, putting the patient at risk of harm. It has been found that applying an electrical stimulation to the patient can effectively treat patients suffering from disorders such as from fibrillation by restoring a regular heartbeat. 
     Because disorders such as fibrillations can happen at any time, it is helpful to have a device that is easily accessible to treat them. In some cases, it is helpful if that device is portable or implantable. In developing a device that is portable or implantable, it is helpful to have access to subcomponents that are compact and lightweight and that can perform to desired specifications. 
     SUMMARY 
     This document provides apparatus related to energy storage devices having folded portions to couple electrodes of the devices. One apparatus embodiment includes a hermetically sealed capacitor case sealed to retain electrolyte, a first electrode disposed in the capacitor case, a second electrode disposed in the capacitor case in a stack with the first electrode, the second electrode including sintered material disposed on a flexible unitary substrate, with the flexible unitary substrate included a connection portion that is flexed and coupled to the first electrode. The apparatus includes, a third electrode disposed in the capacitor case in the stack, a first terminal coupled to the first electrode, and a second terminal coupled to the third electrode, the second terminal electrically isolated from the first terminal. 
     This Summary is an overview of some of the teachings of the present application and not intended to be an exclusive or exhaustive treatment of the present subject matter. Further details about the present subject matter are found in the detailed description and appended claims. Other aspects of the invention will be apparent to persons skilled in the art upon reading and understanding the following detailed description and viewing the drawings that form a part thereof. The scope of the present invention is defined by the appended claims and their legal equivalents. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings illustrate generally, by way of example, various embodiments discussed in the present document. The drawings are for illustrative purposes only and may not be to scale. 
         FIG. 1  is a schematic of a medical system including a sintered capacitor, according to some embodiments. 
         FIG. 2  is an implanted medical system including a sintered capacitor, according to some embodiments. 
         FIG. 3  shows a capacitor according to some embodiments of the present subject matter. 
         FIG. 4A  shows an isometric view of a capacitor element according to some embodiments of the present subject matter. 
         FIG. 4B  shows an isometric view of a capacitor element according to some embodiments of the present subject matter. 
         FIG. 5  shows a side view of a capacitor element according to some embodiments of the present subject matter. 
         FIG. 6  shows a side view of a capacitor element according to some embodiments of the present subject matter. 
         FIG. 7  shows a side view of a capacitor element according to some embodiments of the present subject matter. 
         FIGS. 8A and 8B  show side views of a capacitor element according to some embodiments of the present subject matter. 
         FIG. 9  shows a capacitor element according to some embodiments of the present subject matter. 
         FIGS. 10A and 10B  show a capacitor element according to some embodiments of the present subject matter. 
         FIG. 11  shows a side view of a capacitor element according to some embodiments of the present subject matter. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description of the present invention refers to subject matter in the accompanying drawings which show, by way of illustration, specific aspects and embodiments in which the present subject matter may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the present subject matter. References to “an”, “one”, or “various” embodiments in this disclosure are not necessarily to the same embodiment, and such references contemplate more than one embodiment. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope is defined only by the appended claims, along with the full scope of legal equivalents to which such claims are entitled. 
     This document concerns sintered electrodes for use in an electrical energy storage device. Specific examples include sintered anodes formed of aluminum or its alloys. Certain examples are for use in aluminum electrolytic capacitors. Examples include electrodes with a sintered portion disposed onto at least one side of a substrate. Some examples include a stack of electrodes in which the substrates of multiple electrodes are interconnected. This interconnection method improves upon energy storage devices using etched electrodes because the foils may be bent together for interconnection with a low risk of breakage, whereas etched materials often break. Additional benefits stem from an increased surface area that is a product of sintering. 
     Sintering results in many interstices (i.e., spaces) between grains of the electrode. Sintered electrodes resemble crushed grains with interstices between the grains. The interstices are filled with electrolyte, thereby increasing capacitance per unit of volume, as capacitance is proportional to a surface area exposed to electrolyte. An electrode with such interstices offers improved lateral or parallel movement of electrons in relation to a major surface of a flat electrode layer, as etched electrodes restrict lateral movement because the etchings result in voids that are typically perpendicular to the major surface of the flat layer. Accordingly, some examples have a lower ESR (equivalent series resistance) compared to etched foils due to this enhance ionic flow. 
     Overall, an energy storage device using the sintered electrodes described here is well suited for use in an implantable medical device such as a defibrillator. Because sintering can produce a variety of shapes, sintered electrodes can be used to create energy storage devices such as capacitors that have custom shapes versus simple cylinders or a prism having a parallelogram as its base. In some examples, manufacturing efficiency is improved, such as by allowing electrodes to be nested on a web before they are excised from the web and stacked into a capacitor. In other words, nesting reduces waste by allowing more of the web to be converted into electrodes. The interstices are very small, making the electrodes rigid and able to withstand handling by a machine or assembly personnel. These electrodes demonstrate an improved energy density over etched electrodes and are therefore useful to make smaller implantable devices that are able to deliver an amount of energy for a particular therapy. 
       FIG. 1  is a schematic of a medical system  100  including a sintered capacitor, according to some embodiments. The medical system  100  represents any number of systems to provide therapeutic stimulus, such as to a heart. Examples of medical systems include, but are not limited to, implantable pacemakers, implantable defibrillators, implantable nerve stimulation devices and devices that provide stimulation from outside the body, including, but not limited to, external defibrillators. 
     Electronics  104  are to monitor the patient, such as by monitoring a sensor  105 , and to monitor and control activity within the system  100 . In some examples, the electronics  104  are to monitor a patient, diagnose a condition to be treated such as an arrhythmia, and control delivery of a stimulation pulse of energy to the patient. The electronics  104  can be powered wirelessly using an inductor. Alternatively, the electronics  104  can be powered by a battery  106 . In some examples, electronics  104  are to direct small therapeutic bursts of energy to a patient from the battery  106 . 
     For therapies, such as defibrillation, that use energy discharge rates exceeding what battery  106  is able to provide, a capacitor  108  is used. Energy from the battery  106  is controlled by the electronics  104  to charge the capacitor  108 . The capacitor  108  is controlled by the electronics  104  to discharge to a patient to treat the patient. In some examples, the capacitor  108  completely discharges to a patient, and in additional examples, the capacitor is switched on to provide therapeutic energy and switched off to truncate therapy delivery. 
     Some examples of a medical system  100  include an optional lead system  101 . In certain instances, after implantation, the lead system  101  or a portion of the lead system  101  is in electrical communication with tissue to be stimulated. For example, some configurations of lead system  101  contact tissue with a stimulation electrode  102 . The lead system  101  couples to other portions of the system  100  via a connection in a header  103 . Examples of the lead system  101  use different numbers of stimulation electrodes and/or sensors in accordance with the needs of the therapy to be performed. 
     Additional examples function without a lead  101 . Leadless examples can be positioned in contact with the tissue to be stimulated, or can be positioned proximal to tissue to shock the tissue to be stimulated through intermediary tissue. Leadless examples can be easier to implant and can be less expensive as they do not require the additional lead components. The housing  110  can be used as an electrode in leadless configurations. 
     In certain embodiments, the electronics  104  include an electronic cardiac rhythm management circuit coupled to the battery  106  and the capacitor  108  to discharge the capacitor  108  to provide a therapeutic defibrillation pulse. In some examples, the system  100  includes an anode and a cathode sized to deliver a defibrillation pulse of at least approximately 50 joules. Other configurations can deliver larger amounts of energy. Some configurations deliver less energy. In some examples, the energy level is predetermined to achieve a delivered energy level mandated by a governing body or standard associated with a geographic region, such as a European country. In an additional embodiment, the anode and cathode are sized to deliver a defibrillation pulse of at least approximately 60 joules. In some examples, this is the energy level is predetermined to achieve an energy level mandated by a governing body of another region, such as the United States. In some examples, electronics  104  are to control discharge of a defibrillation pulse so that the medical system  100  delivers only the energy mandated by the region in which the system  100  is used. In some examples, a pulse of 36 joules is delivered. 
     Packaging anodes and cathodes can reduce their efficiency. Interconnections between conductors coupled to electronics and to the electrodes of the capacitor  108  decrease efficiency, for example. Accordingly, anodes and cathodes are sized to compensate for decreases in efficiency. As such, in some embodiments, the capacitor  108  includes anodes and cathodes sized and packaged to deliver a defibrillation pulse of at least approximately 50 joules. Some are sized and packaged to deliver a defibrillation pulse of at least approximately 60 joules. 
     One characteristic of some sintered electrode examples is that at least one anode and a cathode have a DC capacitance that is approximately 23% greater than a AC capacitance for the at least one anode and the cathode of an etched capacitor that has 74.5 microfarads per cubic centimeter. In some examples, the at least one anode and the cathode have an AC capacitance of at least 96.7 microfarads per cubic centimeter at 445 total voltage. In some examples, this is comparable to an operating voltage of about 415 volts. This is a 30% improvement over an etched capacitor that has 74.5 microfarads per cubic centimeter. Total voltage is the voltage that allows 1 milliamp of leakage per square centimeter. Some examples are aged to 415 volts. 
     In certain examples, the capacitor  108  includes a capacitor case  112  sealed to retain electrolyte. In some examples, the capacitor case  112  is welded. In some instances, the capacitor case  112  is hermetically sealed. In additional examples, the capacitor case  112  is sealed to retain electrolyte, but is sealed with a seal to allow flow of other matter, such as gaseous diatomic hydrogen or a helium molecule. Some of these examples use an epoxy seal. Several materials can be used to form case  112 , including, but not limited to, aluminum, titanium, stainless steel, nickel, a polymeric material, or combinations of these materials. The case  112  is sealed to retain electrolyte. Various electrolytes can be used including, but not limited to, Suzuki-Techno Corporation electrolyte model 1184. The case  112  includes a seal, such as a resin based seal including but not limited to epoxy, in some examples. Some examples include a rubber seal to seal case portions to one another, or to seal subcomponents such as a feedthrough to one or more case portion. In some examples, case  112  is welded together from subcomponents. Some examples include a case that includes one or more backfill ports, but the present subject matter is not so limited. 
     A hermetically sealed device housing  110  is used to house components, such as the battery  106 , the electronics  104 , and the capacitor  108 . Hermeticity is provided by welding components into the hermetically sealed device housing  110 , in some examples. Other examples bond portions of the housing  110  together with an adhesive such as a resin based adhesive such as epoxy. Accordingly, some examples of the housing  110  include an epoxy sealed seam or port. Several materials can be used to form housing  110 , including, but not limited to, titanium, stainless steel, nickel, a polymeric material, or combinations of these materials. In various examples, the housing  110  and the case  112  are biocompatible. 
     The capacitor  108  is improved by the present electrode technology in part because it can be made smaller and with less expense. The improvement provided by these electrodes is pertinent to any application where high-energy, high-voltage, or space-efficient capacitors are desirable, including, but not limited to, capacitors used for photographic flash equipment. The present subject matter extends to energy storage devices that benefit from high surface area sintered electrodes including, but not limited to, aluminum. The electrodes described here can be incorporated into cylindrical capacitors that are wound, in addition to stacked capacitors. 
       FIG. 2  is an implanted medical system  200 , implanted in a patient  201 , and including a sintered capacitor, according to some embodiments. The system includes a cardiac rhythm management device  202  coupled to a first lead  204  to extend through the heart  206  to the right ventricle  208  to stimulate at least the right ventricle  208 . The system also includes a second lead  210  to extend through the heart  206  to the left ventricle  212 . In various embodiments, one or both of the first lead  204  and the second lead  210  include electrodes to sense intrinsic heart signals and to stimulate the heart. The first lead  204  is in direct contact (e.g., touching) with the right atrium  214  and the right ventricle  208  to sense and/or stimulate both those tissue regions. The second lead  210  is in direct contact with the left atrium  216  and the left ventricle  212  to sense and/or stimulate both those tissue regions. The cardiac rhythm management device  202  uses the lead electrodes to deliver energy to the heart, either between electrodes on the leads or between one or more lead electrodes and the cardiac rhythm management device  202 . In some examples, the cardiac rhythm management device  202  is programmable and wirelessly communicates  218  programming information with a programmer  220 . In some examples, the programmer  220  wirelessly  218  charges an energy storage device of the cardiac rhythm management device  202 . 
       FIG. 3  shows a capacitor  308  according to some embodiments of the present subject matter. In some examples, the capacitor  308  is flat. Various embodiments include a plurality of electrode layers. Some examples include a plurality of electrodes aligned in a stack. Although the illustrated capacitor is “D” shaped, in other embodiments, the capacitor is shaped differently, including but not limited to, rectangular, circular, oval, square or other symmetrical or asymmetrical shapes. In various embodiments, a stack defines a custom three-dimensional form factor shaped to conform to an interior volume of a case such as a capacitor case. In some embodiments, the capacitor case  312  is made from conductive material such as aluminum. In other embodiments, the case  312  is made from non-conductive material such as ceramic or plastic. 
     In some examples, the capacitor  308  includes a first terminal  322  and a second terminal  323  to connect the capacitor stack  321  to an electrical component, such as an electrical component included in an implantable medical device. In some embodiments, a first terminal  322  is a feedthrough terminal insulated from the case, while the second terminal  323  is directly connected to the case. Other embodiments may incorporate other connection methods including, but not limited to, a different number of terminations and a different number of feedthroughs. In certain examples, the capacitor stack  321  includes one or more capacitor elements such as elements discussed here. 
       FIG. 4A and 4B  show an isometric view of a capacitor element  430  according to some embodiments of the present subject matter. One or more capacitor elements may be used in forming a capacitor stack. A capacitor element  430  includes a first electrode layer  431 , separator material  432  proximate the first electrode layer, and a second electrode  433 . The second electrode includes a second electrode layer substrate  434 , a third electrode layer substrate  435  and a folded portion  436  coupling the second electrode layer substrate  434  and the third electrode layer substrate  435 . The folded portion  436  folded upon itself to couple the substrates  434 ,  435  in the stacked configuration. In some examples, the second and third electrode layers  438   a ,  438   b  include sintered material  439  disposed on a substrate that is unsintered. In various embodiments, the substrate includes aluminum. In various embodiments, the sintered portion includes aluminum. The folded portion  436 , in some embodiments, includes sintered material. In other embodiments, the folded portion includes one or more areas that are substantially free of sintering. 
     In some embodiments, the second electrode includes sintered material on one major surface  457  of the substrate. In various embodiments, the second electrode includes sintered material on both major surfaces  457 ,  459  of the substrate (see  FIG. 4B ). In various embodiments, the layers of the second electrode of a capacitor element are stacked such that perimeters of the substrate of each layer are substantially coextensive. In capacitors that may be made to fit a custom volume, the stacked electrodes may be offset to provide the desired shape. Some examples include a substantial overlap between adjacent electrodes. 
     In various embodiments, a layer may include a substantially sinter-free portion for connecting to other electrical components including other capacitor elements or other electrodes or electrode layers within the same capacitor element. 
       FIG. 4B  shows a capacitor element  480  with a sintered electrode substrate and an interconnect according to some embodiments of the present subject matter. In some embodiments, components of the capacitor element, such as the first electrode layer  431  and the separator material  432 , may be notched  448  to allow for connection to an adjacent element, other electronics or other capacitor elements. Such a notch  448  allows a connecting member  445  to be coupled to a target component without creating a bulge in components stacked onto the target component. 
     The illustrated embodiment of  FIG. 4B  shows a first electrode layer  431  and separator material  432  between a second electrode layer  438   a  and a third electrode layer  438   b . The first electrode layer  431  and separator materials  432  include a notch  448  to accommodate connecting members coupled to the second  438   a  and third  438   b  electrode layers without creating a bulge in the stacked capacitor element  480 . The second electrode layer illustrates a sinter-free area  449  for accommodating a connecting member to couple to the substrate of the second electrode layer  438   a . The third electrode layer  438   b  shows a connecting member  445 , such as a first clip, coupled to a sinter-free area of the third electrode layer  438   b . Various embodiments include a second clip coupled to the first electrode layer. In such embodiments the first and second clips may be coupled together to interconnect the electrode layers. The clips may be coupled together, for example, using a weld. Other forms of coupling connecting members together are possible without departing from the scope of the present subject matter including, but not limited to, laser welding, ultrasonic welding, using conductive adhesive or combinations thereof. In various embodiments, the first electrode layer is a cathode and the second and third electrode layers include a first and second anode plate. In some embodiments, a slotted interconnect may be used to couple sinter-free portions of two or more electrode layers together. In various embodiments, an electrode includes a tab extending from the perimeter of the substrate of the electrode. In some embodiments, more than one tab may extend from the perimeter of the substrate of an electrode. 
     In various embodiments, a capacitor stack may include many tabs. The tabs may include various alignment arrangements to provide for various connections to capacitor terminations. In some embodiments, the tabs may be aligned vertically to allow for efficient interconnection of the corresponding capacitor electrodes. In some embodiments, some tabs may be aligned but offset from other aligned tabs to allow for separate interconnection such as for a partitioned capacitor. In various embodiments, tabs of varying width may be used. Tabs of varying width may be stacked such that a first tab fully overlaps a wider adjacent tab. Such an arrangement allows for efficient connection of adjacent tabs such as by using a cold weld. Additionally, such an arrangement forms a more rigid composite connection tab as additional wider tabs are stacked together. 
       FIG. 5  shows a side view of a capacitor element according to some embodiments of the present subject matter. The capacitor element  530  includes a number of cathode stacks  537  and a number of anode plates  538 . Adjacent anode plates  538  are connected by a folding portion  536 , according to some examples. Each anode plate includes a sintered portion  539  disposed on a substrate  540 . In various embodiments, the substrate is a continuous, monolithic, solid, unitary piece of substrate material that forms a number of anode plates and folding portions of the capacitor element. In some embodiments, the substrate is a foil. In some examples, the substrate is an aluminum foil. Aluminum foil has a thickness of less than 0.008 inches/0.2 mm in various examples. Some aluminum foils are less than or equal to 0.005 inches thick. These foils are easily bent by hand and are easily torn by hand. Substrates that are thicker are additionally possible. 
     In some embodiments, the folding portion  536  connecting the anode plates  538  is separate from one or both of the anode plates it couples. In such embodiments, the folding portion  536  is coupled to an anode plate, for example using a weld, such as a cold weld, a laser weld or an ultrasonic weld or other coupling method. In some embodiments, the folding portion is coupled to a sinter free portion of the anode plate substrate. In various embodiments, one or more anode plates include sintered material disposed on both sides of the substrate. The cathode stack  537  includes a cathode. In various embodiments, the cathode stack  537  also includes separator material, such as separator material with absorbed or embedded electrolyte material. 
       FIG. 6  shows a side view of a capacitor element according to some embodiments of the present subject matter. The capacitor element  630  includes a number of cathode stacks  637 , anode plates  638 , folded portions  636  coupling anode plates, and anode tabs  641  coupled to the anode plates  638 . In the illustrated embodiment, a number of anode tabs  641  are gathered and welded  642  for connection to electronics, such as electronics related to an implantable medical device. In some embodiments, one or more tabs are coupled to a case of capacitor  643 . 
     The anode plates  638  include a sintered portion  639  disposed on a substrate  640 , such as an aluminum substrate in some examples. In various embodiments, the anode tabs  641  are extensions of the substrate  640 . In some embodiments, the anode tabs  641  are couple to the substrate, for example, the anode tabs may be coupled to the substrate of the anode plates at substantially sintering free portions of the substrate. In some embodiments, the tabs include sintered material disposed on a substrate. 
       FIG. 7  shows a side view of a capacitor element according to some embodiments of the present subject matter. The capacitor element  730  includes a number of cathode stacks  737 , a number of anode plates  738 , a number of folded portions  736  coupling anode plates, a number of folding portions  744  coupling cathode stacks and a number of tabs  741  for electrically coupling the anode plates  738  to each other using a clip  745 . The clip  745  may be used to couple to other electronics, such as electronics related to an implantable medical device. In some embodiments, the clip  745  is coupled to a conductive case. In some embodiments, the clip  745  is coupled to a feedthrough of a case, where the feedthrough insulates the clip from the case. The cathode stack includes a cathode electrode, and may include separator material, such as separator material with absorbed or imbedded electrolyte material. The anode plates include sintered material  739  disposed on at least one major surface of an anode plate substrate  740 . In various embodiments, sintered material is disposed on both major surfaces of an anode plate substrate. In various embodiments, the folded portions connecting the anode plates and the folded portions connecting the cathode stacks are continuous portions of the respective substrates of the anode plates and cathode stacks. Such an arrangement may provide efficiencies related to material and/or processing as each substrate can be excised from a continuous web of substrate material. It is understood that although the illustrated embodiment shows subsequent folding portions extending from opposite sides of the corresponding anode or cathode structure, other orientation arrangements are possible, as are other anode and cathode substrate shapes, without departing from the scope of the present subject matter. 
       FIGS. 8A and 8B  show side views of a capacitor element according to some embodiments of the present subject matter. The capacitor elements  830  include a number of cathode stacks  837 , a number of anode plates  838 , a number of folded portions  836  coupling anode plates, a number of tabs  841  each coupled to an anode plate, and a clip  845  coupled to each anode tab  841  for electrically coupling the anode plates  838  to each other and, in various embodiments, to other electrical components. Each anode plate  838  includes a sintered material  839  disposed on a substrate  840 . The anode plates  838  include sintered material  839  disposed on at least one major surface of an anode plate substrate  840 . In various embodiments, sintered material  839  is disposed on both major surfaces of an anode plate substrate  840 . In various embodiments, the folded portions  836  connecting the anode plates are continuous portions of the anode plate substrate  840 . It is understood that although the illustrated embodiment shows subsequent folding portions extending from opposite sides of the anode plate structure, other orientation arrangements and are possible, as are other anode substrate shapes, without departing from the scope of the present subject matter. The anode tabs  841  may be a continuous piece of the substrate material extending from the perimeter of the anode plate substrate  840 . In various embodiments, the tabs  841  may be separate pieces of material coupled to the anode plate, for example, a tab may be coupled to a substantially sintering free portion of the anode plate substrate. The clips  845  coupled to the tabs are welded together to electrically couple the anode plates. In the illustrated embodiment, the clips are coupled to a case  843  enclosing the capacitor element. The clips  845  are coupled to the case  843  using a conductive ribbon  846 . In some embodiments, the clips  845  are coupled to a feedthrough  847  of the case  843  using a conductive ribbon  846 , as is shown in  FIG. 8B . 
       FIG. 9  shows a capacitor element according to some embodiments of the present subject matter. The capacitor element  930  includes a number of cathode stacks  937 , a number of anode plates  938  and folded portions  936  connecting the anode plates. The folded portion  941  of an anode plate interconnects each subsequent anode plate. A ribbon of conductive material  946  is used to interconnect the anode plates using the folded portions. The ribbon of conductive material  946  is coupled to a feedthrough  947  of a case  943  for connection to other electronics, such as electronics related to an implantable medical device. In various embodiments, the conductive material  946 , such as a ribbon, may be used to couple the anode plates to the case. In some embodiments, the ribbon interconnects anodes of a single capacitor element. In some embodiments, the ribbon interconnects multiple capacitive elements, for example, using the folded portions of anode plates of each element. In various embodiments, a ribbon is used to interconnect the anode plates  938  and a tab is used to connect the interconnected anode plates to the case or to a feedthrough of the case. In various embodiments, folded portions of the anode plates may be arranged such that additional conductive ribbons may be used to interconnect the anode plates. In some embodiments, the folded portions of the capacitor element, or multiple capacitor elements, are grouped at an offset to allow for partitioning of the capacitor. 
       FIGS. 10A and 10B  show a capacitor element according to some embodiments of the present subject matter.  FIG. 10A  shows a partially assembled stack of capacitor components including sintered anode plates  1038  and cathode stacks  1037 . Each anode plate and each cathode stack include a notch  1050  with an L-shaped tab extending from an interior side of the notch. When stacked, the legs of the L-shaped tabs of the anode plates overlap the legs of the L-shaped tabs of the cathode stacks. However, the L-shaped protrusions of the anode plates extend from the anode plate at the opposite end of the leg than do the L-shaped tabs extending from the cathode stacks. Once stacked, the legs of the L-shaped protrusions of the anode plates and the cathode stacks are coupled, such as by welding, to form a solid coupling of the tab legs. The middle section of the legs are then excised, such as by laser cutting, mechanical etching, chemical etching or grinding, for example.  FIG. 10B  shows the structure after the legs of the tabs have been excised. Excising the middle of the legs results in a pair of connected tabs  1051 ,  1052  forming somewhat rigid connections. A first set of connected tabs  1051  couples the anode plates together, and a second set of connected tabs  1052  couples the cathode stacks together. The above method of forming anode and cathode connection tabs uses materials of the initial anode and cathode structures to form the isolated tabs. The resulting tabs form a rigid stack when welded together. Such tabs provide robust connection points for additional electronics and reduce the risk of damaging the cathode substrate, for example, when handling the capacitor element during processing. Such substrates are often very thin and easily damaged during processing. 
       FIG. 11  shows side view of a capacitor element according to some embodiments of the present subject matter. The capacitor element  1130  includes a number of cathode stacks  1137 , a number of sintered anode plates  1138 , and a number of folded portions  1136  coupling anode plates stacked with the cathode stacks. Several of the anode plates include a tab  1153  extending from the anode plate. The tabs are rolled from a distal end back toward the anode plate from which each extends. The diameter of the rolled portion  1154  is approximately equal to the spacing of adjacent anode plates. The rolled portion  1154  of the tabs reduce stress on the tabs that may otherwise exist when connecting the tabs without the rolled portion. In various embodiments, the rolled portion  1154  of the tabs are coupled together, for example with a weld, to form an anode connection. In various embodiments, the tabs are formed from substrate material  1140  of the anode plate on which sintered material  1139  is disposed. In various embodiments, the rolled portion  1154  of the tabs in used to interconnect the anode plates and an unrolled tab  1141  is used for connecting the anodes of the capacitor element to other components of a device, such as an implantable medical device. In some embodiments, a conductive ribbon  1146  is used to couple the rolled tabs together. 
     This application is intended to cover adaptations or variations of the present subject matter. It is to be understood that the above description is intended to be illustrative and not restrictive. The scope of the present subject matter should be determined with reference to the appended claims, along with the full scope of legal equivalents to which such claims are entitled.