Folded plate electrode assemblies for battery cathodes

An electrode assembly in embodiments of the invention can include a unitary member formed from an electrically conductive material having a central portion, and tab and plate portions extending radially outward from the central portion. The unitary member can be folded to configure the plate portions in a stacked configuration, thereby providing an electrically connected support structure for a cathode and/or anode assembly without individual connections/welds of plates to a common connection. The elimination of multiple welds lowers the internal resistance of the electrode assembly, and improves the structural integrity. Embodiments of the invention include batteries and implantable medical devices (IMDs) which incorporate the design flexibility in the shape and contour of the electrode assembly and hence, the overall shape and design of batteries and IMDs.

FIELD OF THE INVENTION

The invention relates generally to electrode assemblies for use in applications such as batteries in implantable medical devices.

BACKGROUND OF THE INVENTION

Implantable medical devices are used to deliver therapy to patients suffering from a variety of conditions. Examples of implantable medical devices are implantable pacemakers and implantable cardioverter-defibrillators (ICDs), which are electronic medical devices that monitor the electrical activity of the heart and provide electrical stimulation to one or more of the heart chambers as needed. For example, a pacemaker senses an arrhythmia, i.e., a disturbance in heart rhythm, and provides appropriate electrical stimulation pulses, at a controlled rate, to selected chambers of the heart in order to correct the arrhythmia and restore the proper heart rhythm. The types of arrhythmias that may be detected and corrected by pacemakers include bradycardias, which are unusually slow heart rates, and certain tachycardias, which are unusually fast heart rates.

Implantable cardioverter-defibrillators (ICDs) also detect arrhythmias and provide appropriate electrical stimulation pulses to selected chambers of the heart to correct an abnormal heart rate or rhythm. In contrast to pacemakers, however, an ICD can deliver cardioversion and high energy defibrillation pulses that are much stronger than typical pacing pulses. This is because ICDs are generally designed to correct fibrillation and tachycardia episodes. To correct such arrhythmias, an ICD delivers a low, moderate, or high-energy therapy.

Modern pacemakers and ICDs are designed with ergonomic shapes that are relatively compliant with a patient's implant location and tend to minimize patient discomfort. As a result, the corners and edges of the devices are typically designed with relatively generous radii to present a device having smoothly contoured exterior surfaces. It is also desirable to minimize the volume occupied by the devices as well as their mass to further limit patient discomfort.

The electrical energy for the therapy delivered by an ICD is generated by delivering electrical current from a power source (battery) to charge capacitors to store energy. The capacitors are capable of rapidly discharging under computer control to deliver one or more appropriate waveforms that deliver energy via electrodes disposed in communication with a patient's heart. In order to provide timely therapy to the patient after the detection of ventricular fibrillation, for example, it is necessary to charge the capacitors with the required amount of energy as quickly as possible. Thus, the battery in an ICD must have a high rate capability to provide the necessary current to charge the capacitors. In addition, since ICDs are implanted in patients, the battery must be able to accommodate physical constraints on size and shape.

Batteries or cells are volumetrically constrained systems. The size or volume of components that go into a battery (cathode, anode, separator, current collectors, electrolyte, etc.) cannot exceed the available volume of the battery case. The arrangement of the components affects the amount or density of active electrode material contained within the battery case.

One battery suitable for use in ICDs is disclosed in U.S. Pat. No. 4,830,940 to Keister et al, which patent is incorporated herein by reference. As disclosed therein, the anode material of the battery comprises lithium and the reactive cathode material comprises silver vanadium oxide. The anode is constructed in a serpentine-like configuration with cathode plates inserted between each of the convolutions thereof on both sides thereof. The electrolyte for a lithium battery or cell is a liquid organic type which comprises a lithium salt and an organic solvent. Both the anode and the cathode plates are encapsulated in an electrically insulative separator material. An improvement to this design is disclosed in U.S. Pat. No. 5,147,737 to Post et al., in which the active material on the serpentine-type electrode is positioned so that the sections of the serpentine-like structure which do not face cathode plates do not contain anode active material.

Known high current power sources used in ICDs employ deep, prismatic, six-sided rectangular solid shapes in packaging of the electrode assemblies. Examples of such deep package shapes can be found in, e.g., U.S. Pat. No. 5,486,215 to Kelm et al., and U.S. Pat. No. 6,040,082 to Haas et. al. These prismatic cases have proven effective for housing and electrically insulating the electrode assemblies.

Conventional lithium batteries can also employ an electrode configuration sometimes referred to as the “jelly roll” design, in which the anode, cathode and separator elements are overlaid and coiled up in a spiral wound form. A strip sheet of lithium or lithium alloy comprises the anode, a cathode material supported on a charge collecting metal screen comprises the cathode, and a sheet of non-woven material separates the anode and cathode elements. These elements are combined and wound to form a spiral. Typically, the battery configuration for such a wound electrode would be cylindrical. An advantage of this design is that there need not be anode material which is not mated to cathode material in the jelly roll electrode configuration. Such designs therefore have the potential for an improved match between the cathode and anode components and improved uniformity of anode and cathode utilization during discharge.

It has also been known to adapt wound electrodes to a prismatic case configuration by departing from a true spiral winding. For example, U.S. Pat. No. 2,928,888 discloses inFIGS. 5aand5btherein an oblong electrode assembly wound on an elongated mandrel for use in a rectangular case. Also, U.S. Pat. No. 4,051,304 discloses inFIG. 2therein another oblong wound electrode assembly for use in a rectangular case.

U.S. Pat. No. 4,761,352 to Bakos et al. discloses yet another electrode assembly design comprising an accordion folded electrode assembly with unitary members for both the anode and cathode electrode strips. The cathode strip is approximately half the length of the anode strip and the anode strip is folded over the cathode strip to “sandwich” the cathode between two layers of the anode. The resulting form is then manually folded in an alternating series of “V” folds (best shown inFIG. 4of the '352 patent).

There exists a need for a battery for implantable medical devices which optimizes volumetric efficiency while allowing for flexibility in designing the shape of the battery to match the contours of an implantable medical device and to fit within the available device space.

BRIEF SUMMARY OF THE INVENTION

The present invention provides an electrode assembly and methods of fabrication that in certain embodiments can include a unitary member formed from an electrically conductive material having a central portion, and tab and plate portions extending radially outward from the central portion. The unitary member can be folded to configure the plate portions in a stacked configuration, thereby providing an electrically connected support structure for a cathode and/or anode assembly without individual connections/welds of plates to a common connection. The elimination of multiple welds lowers the internal resistance of the electrode assembly, and improves the structural integrity. Embodiments of the invention include batteries and implantable medical devices (IMDs) which incorporate the design flexibility in the shape and contour of the electrode assembly and hence, the overall shape and design of batteries and IMDs.

In one embodiment, an electrode assembly is provided having a first electrode, a second electrode, a separator layer located between the first and second electrodes to prevent contact therebetween; and at least one of the first and second electrodes being formed of an electrically conductive material folded into a compact configuration, the electrically conductive material having a central portion and a plurality of generally planar tab portions extending outwardly from the central portion when the electrically conductive material is unfolded, and the central portion being folded in the compact configuration such that the tab portions generally overlap in a stacked arrangement, and the tab portions being folded in the compact configuration such that the stacked tab portions are spaced apart from each other.

In another embodiment, electrode assembly is provided having a first electrode, a second electrode, a separator located between the first and second electrodes to prevent contact therebetween, at least one of the first and second electrodes including an electrically conductive material folded into a compact configuration, the electrically conductive material having a central portion and a plurality of tab portions extending outwardly from the central portion when the electrically conductive material is unfolded, the tabs each extending into generally planar plate portions; and the central portion being folded in the compact configuration such that the plate portions are positioned to generally overlap each other in a stacked arrangement, and the tab portions being folded in the compact configuration such that the stacked plate portions are spaced apart from each other.

In one embodiment of a fabrication technique, a method of forming an electrode assembly is provided that employs the following steps. Providing an electrically conductive material having a central portion and a plurality of tab portions extending outwardly from the central portion, the tabs each having a generally planar portion. Then folding the electrically conductive material at fold locations in the central portion such that plate portions are generally overlapping with each other in a stacked arrangement, and folding the electrically conductive material at fold locations in the tab portions such that the tab portions are spaced apart from each other and are generally parallel to each other.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The following discussion is presented to enable a person skilled in the art to make and use the invention. Various modifications to the illustrated embodiments will be readily apparent to those skilled in the art, and the generic principles herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention as defined by the appended claims. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein. The following detailed description is to be read with reference to the figures, in which like elements in different figures have like reference numerals. The figures, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of the invention. Skilled artisans will recognize the examples provided herein have many useful alternatives which fall within the scope of the invention.

Embodiments of the invention are not limited to implantable cardioverter defibrillators (“ICDs”), and may be employed in many various types of electronic and mechanical devices for treating patient medical conditions such as pacemakers, neurostimulators, and therapeutic substance delivery systems. However, for purposes of illustration only, the invention is described below in the context of ICDs. It is to be further understood that the present invention is not limited to high current batteries and may be utilized for low or medium current batteries. For purposes of illustration only, however, the present invention is below described in the context of high current batteries.

FIG. 1is a simplified schematic view of an example of an implantable medical device (“IMD”)10, in accordance with an exemplary embodiment of the present invention. The IMD10is shown inFIG. 1as a pacemaker/cardioverter/defibrillator (PCD) with a relationship to the human heart. However, IMD10may assume a wide variety of forms. For example, IMD10may be an implantable cardiac defibrillator (ICD as is known in the art). Alternatively, or in addition, IMD10may be an implantable cardiac pacemaker, such as that disclosed in U.S. Pat. No. 5,158,078 to Bennett et al.; U.S. Pat. No. 5,312,453 to Shelton et al.; or U.S. Pat. No. 5,144,949 to Olson, all hereby incorporated by reference, each in its entirety. Even further, IMD10may be an implantable neurostimulator, such as that described, for example, in U.S. Pat. No. 5,342,409 to Mullet; or an implantable drug pump; a cardiomyostimulator; a biosensor; and the like.

IMD10includes associated electrical leads14,16and18, although it will be appreciated that IMD10may include any number of leads suitable for a particular application. Leads14,16and18are coupled to IMD10by means of a multi-port connector block20, which contains separate ports for each of the three leads14,16, and18. Lead14is coupled to a subcutaneous electrode30, which is intended to be mounted subcutaneously in the region of the left chest. Alternatively, or additionally, an active “can” configuration may be employed in which the housing of IMD10may serve as an electrode. Lead16is a coronary sinus lead employing an elongated coil electrode that is located in the coronary sinus and great vein region of a heart12. The location of the electrode is illustrated in broken line format at32, and extends around heart12from a point within the opening of the coronary sinus to a point in the vicinity of the left atrial appendage.

Lead18may be provided with elongated electrode coil28, which may be located in the right ventricle of heart12. Lead18may also include a helical stimulation electrode34, which takes the form of an advanceable helical coil that is screwed into the myocardial tissue of the right ventricle. Lead18may also include one or more additional electrodes for near and far field electrogram sensing.

In the system illustrated, cardiac pacing pulses are delivered between the helical electrode34and the elongated electrode coil28. The electrodes28and34are also employed to sense electrical signals indicative of ventricular contractions. As illustrated, it is anticipated that the right ventricular electrode28will serve as the common electrode during sequential and simultaneous pulse multiple electrode defibrillation regimens. For example, during a simultaneous pulse defibrillation regimen, pulses would simultaneously be delivered between electrode28and electrode30, and between electrode28and electrode32. During sequential pulse defibrillation, it is envisioned that pulses would be delivered sequentially between subcutaneous electrode30and electrode28, and between coronary sinus electrode32and right ventricular electrode28. Single pulse, two electrode defibrillation pulse regimens may also be provided, typically between electrode28and coronary sinus electrode32. Alternatively, single pulses may be delivered between electrodes28and30. The particular interconnection of the electrodes to the IMD10will depend somewhat on which specific single electrode pair defibrillation pulse regimen is believed more likely to be employed.

As previously described, IMD10may assume a wide variety of forms as are known in the art. One example of various components of an IMD10is shown inFIG. 2. IMD10includes a case50(the right-hand side of which is shown inFIG. 2), an electronics module52, a battery or electrochemical cell54, and capacitor(s)56. Each of the components of the IMD10is preferably configured for the particular end-use application. Thus, the electronics module52is configured to perform one or more sensing and/or stimulation processes. Electrochemical cell54includes an insulator58disposed therearound. Electrochemical cell54provides the electrical energy to charge and re-charge the capacitor(s)56, and also powers the electronics module52.

With reference toFIG. 3, an exploded perspective view of a deep drawn battery case in an embodiment according to the present invention is shown. A battery40according to the present invention includes a long drawn battery case42and an electrode assembly44. Case42is generally made of a medical grade titanium, however, it is contemplated that case42could be made of almost any type of metal such as aluminum and stainless steel, as long as the metal is compatible with the battery's chemistry in order to prevent corrosion. Further, it is contemplated case42could be manufactured from most any process including but not limited to machining, casting, drawing, or metal injection molding. In some embodiments, case42is made of non-conductive materials, such as plastic. Case42is designed to enclose electrode assembly44and be sealed by a battery cover46. While sides48of case42are generally planar it is contemplated sides48could be generally arcuate in shape. This construction would provide a number of advantages including the ability to accommodate a curved or arcuate electrode assembly44. Arcuate sides could also nest within an arcuate edge of an implantable medical device such as an implantable cardiac defibrillator.

In contrast to deep cases, battery case42may also be manufactured using a shallow form process. With reference toFIG. 6, an exploded perspective view of a shallow drawn battery according to an embodiment of the present invention is shown. Battery310is comprised of a shallow drawn battery case312, electrode assembly314, insulator cup316, battery cover318, coupling320, headspace cover322, feedthrough assembly324, and battery case liner331. The battery case312is designed to enclose the electrode assembly314and be hermetically sealed with battery cover318. Embodiments of the invention may be used in either deep cases or shallow drawn cases without departing from the scope of the invention.

As used herein, the terms battery or batteries include a single electrochemical cell or cells. Batteries are volumetrically constrained systems in which the components in the case of the battery cannot exceed the available volume of the battery case. Furthermore, the relative amounts of some of the components can be important to provide the desired amount of energy at the desired discharge rates. A discussion of the various considerations in designing the electrodes and the desired volume of electrolyte needed to accompany them in, for example, a lithium/silver vanadium oxide (Li/SVO) battery, is discussed in U.S. Pat. No. 5,458,997 (Crespi et al.). Generally, however, the battery must include the electrodes and additional volume for the electrolyte required to provide a functioning battery.

Most embodiments of the present invention are particularly directed to high current batteries that are capable of charging capacitors with the desired amount of energy, typically between about 20 joules to about 35 joules, in the desired amount of time, (e.g., about 10–15 seconds or less). As a result, the batteries must typically deliver up to about 5 amps at about 1.5 to about 2.5 volts, in contrast to low rate batteries that are typically discharged at much lower currents. Furthermore, batteries providing this high current must be able to provide these amounts of energy repeatedly, separated by about 30 seconds or less or, in some cases within about 10 seconds or less.

Electrode assemblies44and314may include spirally-wound, stacked plate, or serpentine electrodes of the type disclosed, for example, in U.S. Pat. Nos. 5,312,458 and 5,250,373 to Muffuletto et al. for “Internal Electrode and Assembly Method for Electrochemical Cells;” U.S. Pat. No. 5,549,717 to Takeuchi et al. for “Method of Making Prismatic Cell;” U.S. Pat. No. 4,964,877 to Kiester et al. for “Non-Aqueous Lithium Battery;” U.S. Pat. No. 5,147,737 to Post et al. for “Electrochemical Cell With Improved Efficiency Serpentine Electrode;” and U.S. Pat. No. 5,468,569 to Pyszczek et al. for “Use of Standard Uniform Electrode Components in Cells of Either High or Low Surface Area Design,” the disclosures of which are hereby incorporated by reference herein in their respective entireties. Alternatively, electrochemical cell54can include a single cathode electrode as described, for example, in U.S. Pat. No. 5,716,729 to Sunderland et al. for “Electrochemical Cell,” which is hereby incorporated by reference in its entirety. The composition of the electrode assemblies can vary. One illustrated electrode assembly includes a core of lithium/silver vanadium oxide (Li/SVO) as discussed in, e.g., U.S. Pat. No. 5,458,997 (Crespi et al.). Other battery chemistries are also anticipated, such as those described in U.S. Pat. No. 5,180,642 (Weiss et al) and U.S. Pat. Nos. 4,302,518 and 4,357,215 (Goodenough et al).

With reference toFIG. 4, a cutaway perspective view of the electrode assembly as shown inFIG. 3is shown. Electrode assembly44generally includes a first electrode82, a second electrode80, and a porous, electrically non-conductive separator material84encapsulating either or both of the electrodes80,82. These three components are generally placed together to form electrode assembly44. Second electrode80of electrode assembly44can comprise a number of different materials including second electrode active material located on a second electrode conductor element or current collector.

In one embodiment, the second electrode is an anode in the case of a primary cell or the negative electrode in the case of a rechargeable cell. Examples of suitable electrode active materials include, but are not limited to: alkali metals, materials selected from Group IA of the Periodic Table of Elements, including lithium, sodium, potassium, etc., and their alloys and intermetallic compounds including, e.g., Li—Si, Li—B, and Li—Si—B alloys and intermetallic compounds, insertion or intercalation materials such as carbon, or tin-oxide. Examples of suitable materials for the anode current collector include, but are not limited to: stainless steel, nickel, titanium, or aluminum. Further, the current collector may have a grid configuration, a perforated pattern, or a “solid grid” design. In one embodiment, the anode is comprised of lithium with a titanium current collector. In various embodiments, the anode active material can be pressed into a mesh or etched current collector, or onto the surface of a current collector, or be of pure lithium and have no current collector. In one embodiment, a sheet of lithium is attached to a current collector and then die cut to the desired shape.

First electrode portion82of electrode assembly44generally includes a first electrode active material located on a first electrode current collector, which also conducts the flow of electrons between the first electrode active materials, and first electrode terminals of electrode assembly44. In one embodiment, the first electrode is a cathode in the case of a primary cell or the positive electrode in the case of a rechargeable cell. Examples of materials suitable for use as first electrode active material include, but are not limited to: a metal oxide, a mixed metal oxide, a metal, and combinations thereof. Suitable first electrode active materials include silver vanadium oxide (SVO), copper vanadium oxide, copper silver vanadium oxide (CSVO), manganese dioxide, titanium disulfide, copper oxide, copper sulfide, iron sulfide, iron disulfide, and fluorinated carbon, and mixtures thereof, including lithiated oxides of metals such as manganese, cobalt, and nickel.

Generally, cathode or positive electrode active material comprises a mixed metal oxide formed by chemical addition, reaction or otherwise intimate contact or by thermal spray coating process of various metal sulfides, metal oxides or metal oxide/elemental metal combinations. The materials thereby produced contain metals and oxides of Groups IB, IIB, IIIB, IVB, VB, VIIB, VIIB, and VIII of the Periodic Table of Elements, which includes noble metals and/or their oxide compounds.

First cathode and positive electrode materials can be provided in a binder material such as a fluoro-resin powder, generally polyvinylidine fluoride or polytetrafluoroethylene (PTFE) powder also includes another electrically conductive material such as graphite powder, acetylene black powder, and carbon black powder. In some cases, however, no binder or other conductive material is required for the first electrode. In one embodiment, the cathode material can be a powder which is pressed into a mesh current collector. In one embodiment, a cathode paste can be provided which can be laminated, pressed, rolled, or otherwise mounted onto the surface of a current collector. The cathode current collector may be comprised of the same materials and configured similar to that described above for the anode current collector.

It is to be understood that electrochemical systems other than those set forth explicitly above may also be employed in conjunction with the present invention, including, but not limited to, cathode/anode systems such as: silver oxide/lithium; manganese oxide/lithium; V2O5/lithium; copper silver vanadium oxide/lithium; copper oxide/lithium; lead oxide/lithium; carbon monofluoride/lithium; chromium oxide/lithium; bismuth-containing oxides/lithium; copper sulfate/lithium; mixtures of various cathode materials listed above such as a mixture of silver vanadium oxide and carbon monofluoride; and lithium ion rechargeable batteries, to name but a few.

Separator material84electrically insulate second electrode80from first electrode82. The material is generally wettable by the cell electrolyte, sufficiently porous to allow the electrolyte to flow through separator material84, and maintain physical and chemical integrity within the cell during operation. Examples of suitable separator materials include, but are not limited to: polyethylenetetrafluoroethylene, ceramics, non-woven glass, glass fiber material, polypropylene, and polyethylene. As illustrated, separator84includes three layers. A polyethylene layer is sandwiched between two layers of polypropylene. The polyethylene layer has a lower melting point than the polypropylene and provides a shut down mechanism in case of cell over heating. The electrode separation is different than other lithium-ion cells in that two layers of separator are used between second electrode80and first electrode82.

As illustrated, the electrolyte solution can be an alkali metal salt in an organic solvent such as a lithium salt (i.e. 1.0M LiClO4or LiAsF6) in a 50/50 mixture of propylene carbonate and dimethoxyethane.

As best seen inFIG. 5, an insulator354is located on electrode assembly44when assembled, which is discussed in more detail below. Insulator354includes slits356and358to accommodate first electrode tab352and second electrode tab350. As detailed below, tabs350,352may connect to an electrically connected support structure for the electrodes without requiring individual connections/welds of the electrodes to a common connection. Insulator354further includes aperture61allowing electrolyte to enter and surround electrode assembly44. Generally insulator354is comprised of ETFE, however, it is contemplated other materials could be used such as HDDE, polypropylene, polyurethane, fluoropolymers, and the like. Insulator354performs several functions including working in conjunction with case liner60to isolate case42and cover46from electrode assembly44. It also provides mechanical stability for electrode assembly44.

Electrode assembly44is also generally inserted into an electrically non-conductive case liner60during assembly. Case liner60generally extends at its top edge above the edge of electrode assembly44to overlap with insulator354. Case liner60is generally comprised of ETFE, however, other types of materials are contemplated such as polypropylene, silicone rubber, polyurethane, fluoropolymers, and the like. Case liner60generally has substantially similar dimensions to case42except case liner60would have slightly smaller dimensions so it can rest inside of battery case42.

FIGS. 3 and 5also depict battery cover46and a headspace insulator62along with case42and electrode assembly44. Similar to case42, cover46is comprised of medical grade titanium to provide a strong and reliable weld creating a hermetic seal with battery case42. However, it is contemplated cover46could be made of any type of material as long as the material was electrochemically compatible. Illustrated battery cover46includes a feedthrough aperture64through which feedthrough assembly68is inserted. Feedthrough assembly contains a ferrule67, an insulating member65, and a feedthrough pin66. Feedthrough pin66is comprised of niobium; however, any conductive material could be utilized without departing from the spirit of the invention. Niobium is generally chosen for its low resistivity, its material compatibility during welding with titanium, and its coefficient of expansion when heated. Niobium and titanium are compatible metals, meaning when they are welded together a strong reliable weld is created.

Feedthrough pin66is generally conductively insulated from cover46by feedthrough assembly68where it passes through cover46. Insulating member65is comprised of CABAL-12 (calcium-boro-aluminate), TA-23 glass or other glasses, which provides electrical isolation of feedthrough pin66from cover46. The pin material is in part selected for its ability to join with insulating member65, which results in a hermetic seal. CABAL-12 is very corrosion resistant as well as a good insulator. Therefore, CABAL-12 provides for good insulation between pin66and cover46as well as being resistant to the corrosive effects of the electrolyte. However, other materials besides glass can be utilized, such as ceramic materials, without departing from the spirit of the invention. Battery cover46also includes a fill port70used to introduce an appropriate electrolyte solution after which fill port70is hermetically sealed by any suitable method.

Headspace insulator62is generally located below battery cover46and above insulator354, i.e., in the headspace above electrode assembly44and below the cover46. Generally, headspace insulator62is comprised of ETFE (Ethylene Tetrafluoroethylene), however, other insulative materials are contemplated such as polypropylene. ETFE is stable at both second electrode80and first electrode82potentials and has a relatively high melting temperature. Headspace insulator62preferably covers distal end72of feedthrough pin66, first electrode tab352, and second electrode tab350. While electrode assembly44is described as having a first and second electrode tab, it is fully contemplated each electrode could have a plurality of tabs without departing from the spirit of the invention. Insulator62is designed to provide thermal protection to electrode assembly44from the weld joining case42and cover46by providing an air gap between the headspace insulator and the cover in the area of the case to cover weld. Insulator62prevents electrical shorts by providing electrical insulation between the first electrode tab352, second electrode tab350, and bracket74and their conductive surfaces. Illustrated weld bracket74serves as conductor between first electrode tab352and battery cover46. Weld bracket74is a nickel foil piece that is welded to both cover46and first electrode tab352.

Battery40inFIGS. 3 and 5can be thought of as including three major functional portions. They are the encasement, insulation, and active component portions. The encasement or closure portion comprises of case42, cover46, feedthrough assembly68, fillport70, ball112, button114, and electrical connections. The major functions of the encasement are to provide a hermetic seal, a port for adding electrolyte and isolated electrical connections. The major function of the insulators is to prevent electrical shorts. The insulators include headspace insulator62, coil insulator354, and case liner60. The active portion of the cell is where the electrochemistry/energy storage occurs. It includes the electrolyte and electrode assembly44. Electrode assembly44includes second electrode80, first electrode82, and two layers of separator84.

The resulting battery40may be formed as a case negative electrical configuration, i.e. the second electrode80(anode) may be electrically connected to the conductive casing42serving as the negative polarity external electrical connection for the battery40, and feedthrough terminal pin66may be connected to the first electrode82(cathode) serving as the positive external electrical connection for the battery40. Alternately, the first and second electrode82,80connections can be reversed, resulting in a case positive electrical configuration. Also, a case neutral configuration may be obtained by using two feedthrough pins66for the first and second electrode82,80connections. In the case neutral configuration, the case may be made of conductive materials or non-conductive materials.

As noted above, the first and second electrode82,80portions may each include a current collector portion to which active anode or active cathode material may be applied. In accordance with an embodiment of the invention, a current collector is described which allows multiple plates of an anode and/or cathode to be electrically connected, eliminating the need for multiple welds and the problems associated therewith (higher internal resistance, weaker structural integrity, etc.), while allowing great flexibility in the design of the shape of an electrochemical cell.

Referring now toFIGS. 7(a) and (b), a current collector100for supporting and/or connecting a plurality of cathode or anode plate portions in a stacked configuration is illustrated in accordance with one embodiment of the invention. The current collector may be formed from a single piece of a conductive material, such as a metal, which may be folded as shown inFIGS. 8(a)–(c) to form a stacked electrode assembly configuration. Titanium may be suitably employed as the material for the current collector100, although any conductive material with the desired mechanical and electrical properties will suffice. Partial etching of one or both sides of the current collector100may be employed to facilitate bending and folding of the current collector100at predetermined locations.

FIG. 7(a) shows an embodiment of the invention in which the current collector100includes a central portion110, a plurality of tab portions120extending generally radially outwardly from the central portion110, and a plurality of plate portions130extending from the tab portions120. In one embodiment, the central portion110, tab portions120, and plate portions130are formed from a single piece of a conductive material, cut to the desired size and shape. A metal, such as titanium, may be used for this purpose.

FIG. 7(b) shows an alternate embodiment of the invention in which the central portion110and tab portions120of the current collector are formed from a single piece of a conductive material, and the plate portions (not shown) are connected to the tab portions120.FIG. 7(b) also illustrates the positioning of fold locations160,170on the central portion110and tab portions120, respectively.

FIGS. 8(a)–(c) illustrate current collector100being folded using fold locations160in the central portion110to form a stacked arrangement for the anode and/or cathode portions of an electrode assembly. As shown inFIGS. 9(a) and (b), folding the tab portions120at fold locations170may result in the tab portions120being generally parallel to each other and spaced apart in a stacked configuration. The tab portions120may be operatively connected to the cathode and/or anode plate portions (not shown). In one embodiment, a single-piece current collector construction includes integral plate portions130and thereby eliminates the need for multiple welds to electrically connect the plates. The elimination of welds reduces the resistance between plates and improves the reliability of the electrode assembly. The folded plate construction may also allow for more flexibility in designing the shape of an electrochemical cell, especially as compared to existing coiled electrode designs.

In one embodiment, the fold locations160,170may include etching of the current collector100to facilitate folding of the central portion110and tab portions120. For example,FIG. 22is an enlarged representation of the current collector shown inFIG. 7(a), indicating a pattern for etching the current collector100along the fold locations160,170. Etching may be performed, for example, by a chemical etching process whereby a mask is applied to one or both sides of the current collector, and a chemical is applied and washed away to remove a small amount of the surface of current collector100.FIG. 23shows an enlarged side view of a tab portion120which has mask material165applied to both sides, with exposed areas indicating fold locations170on tab portion120. The chemical etching on opposite sides of tab portion120as shown inFIG. 23facilitates folding in opposite directions, as may be desired to form a stacked configuration. In some embodiments, the etching process may be applied to both sides of a single fold location160,170, for example, to further facilitate the bending and folding of the current collector100material. As would be appreciated by one of ordinary skill in the art, the etching of fold locations160,170may be performed by a process other than chemical etching, such as laser etching, scoring or stamping of the current collector100material.

In the embodiments shown inFIGS. 7(a) and (b), current collector100has a central portion110with six sides, and six tab portions120extending radially outwardly. Some or all of the tab portions120may be adapted to include, or operatively connect to, plate portions130for supporting cathode or anode plates. In the embodiment illustrated inFIG. 9(b), the central portion110has six sides with six tab portions120extending radially outward therefrom, five of which are adapted to include or operatively connect to plate portions130, the sixth being adapted for welding to an electrical feedthrough terminal or to the battery case (shown inFIGS. 3 and 5). Alternatively, the embodiment illustrated inFIG. 9(a) uses all six of the tab portions120to support plate portions130, and may use the folded central portion110to make any necessary electrical connections.

As would be appreciated by a person having ordinary skill in the art, the number of plate portions130supported by the current collector100can be adjusted by varying the number of sides of the central portion110, and hence, the number of tab portions120that can support the plate portions130. In several possible embodiments, the central portion110may comprise a regular polygonal shape wherein all sides of the central portion110are of equal length and all internal angles are equal. SeeFIGS. 10(a)–(c) for examples of other shapes suitable for supporting various numbers of cathode and/or anode plates. As would be appreciated by a person having ordinary skill in the art, the invention is not limited to current collectors having symmetrical or regular polygonal shapes and includes current collectors with central portions which are irregularly shaped, as well as those that do not have tab portions evenly spaced radially about the central portion.

In one embodiment of the invention, the number of plate portions130in an electrode assembly may be adjusted by using more than one current collector100and electrically connecting the current collectors, for example by welding a connector115between the folded central portions110, as shown inFIG. 11.

As would also be appreciated by a person having ordinary skill in the art, the folded plate design described above may also be employed in the construction of analogous structures, such as the anode and cathode plates of a flat electrolytic capacitor (FEC), for example.

The current collector100embodiment discussed above may apply to the anode72, cathode76, or both in the electrode assembly of an electrochemical cell. For example,FIG. 12illustrates an electrode assembly200wherein the anode72and cathode76both incorporate the current collector100of an embodiment of the invention, and the respective current collectors100are oriented at an angle of approximately 90° with respect to each other. As shown, the plate portions130of the anode and cathode current collectors are interleaved.

FIG. 13shows electrode assembly200in accordance with an alternate embodiment of the invention wherein the current collectors100of both the anode72and cathode76are interleaved at approximately a 180° angle. As would be appreciated by one of ordinary skill in the art, the angles at which the anode and cathode current collectors are interleaved may be varied to provide the optimum utilization of available space within the housing50of electrochemical cell54.

FIG. 14shows electrode assembly200in accordance with an embodiment of the invention wherein only one of either the cathode76or anode72utilizes the current collector100disclosed herein. As shown inFIG. 14, the cathode portion76of the electrode assembly200uses the folded current collector100of an embodiment of the invention, while the anode portion72is interleaved between the plates of the cathode76using a serpentine pattern220. In one embodiment, a long continuous anode material surrounded by a separator material weaves continuously between the plates of the cathode76. In an alternate embodiment of the invention, discrete anode plates are placed within a long continuous separator pouch that is interleaved between the plates of the cathode76in a similar manner. As would be appreciated by one of ordinary skill in the art, the anode72and cathode76portions inFIG. 14could be reversed without departing from the scope of the invention.

FIG. 15shows electrode assembly200in accordance with an embodiment of the invention wherein the cathode portion76includes the folded current collector100, while the anode portion72is folded in an accordion fashion230and inserted between the stacked plate portions of the cathode76such that alternating folds in the anode portion72interleave between the plates of the cathode portion76. In one embodiment, a long continuous anode material surrounded by separator material forms the folded accordion pattern230that is interleaved between the stacked plates of the cathode76. In an alternate embodiment of the invention, discrete anode plates are placed within a long continuous separator pouch that is interleaved between the plates of the cathode76in a similar manner. As would be appreciated by one of ordinary skill in the art, the anode72and cathode76portions inFIG. 15could be reversed without departing from the scope of the invention.

FIG. 16illustrates electrode assembly200in accordance with an embodiment of the invention wherein the cathode portion76includes the folded current collector100, while the anode portion72utilizes an arched, interleaved pattern240. This design offers potential advantages in terms of heat transfer characteristics, as well as structural integrity due to having fewer sharp folds. In one embodiment, a long continuous anode material surrounded by separator material forms the arched pattern240that is interleaved between the plates of the cathode76. In an alternate embodiment of the invention, discrete anode plates are placed within a long continuous separator pouch which is interleaved between the plates of the cathode76in a similar manner. As would be appreciated by one of ordinary skill in the art, the anode72and cathode76portions inFIG. 16could be reversed without departing from the scope of the invention.

FIG. 17shows electrode assembly200in accordance with an embodiment of the invention wherein the cathode portion76includes the folded current collector100, while the anode portion72is comprised of discrete plates250interleaved between the plates of the cathode portion76. Discrete plates250may have tabs joined welded together to electrically connect the plates together. As would be appreciated by one of ordinary skill in the art, the anode72and cathode76portions inFIG. 17could be reversed without departing from the scope of the invention.

Embodiments of the invention allow flexibility in the shape and size of the individual plates within the electrode assembly200. This flexibility allows for the design of electrochemical cells having three-dimensional or “contoured” shapes.FIGS. 18 and 19illustrate electrode assemblies200with anode and cathode plates having generally “D”-shaped configurations, with the size of adjacent plates being slightly smaller or larger, or with the positions slightly offset to produce a three-dimensional contoured surface configuration.FIGS. 18 and 19illustrate contoured shapes that may, for example, produce an overall design that is comfortable to a patient.

FIGS. 18(a) and19(a), for example, are top plan views of electrode assemblies200employing varying size and placement of the anode72and cathode76plates to produce a desired three-dimensional shape.

FIGS. 18(b) and19(b) illustrate current collector100configurations that may be able to produce the overall desired shape utilizing a single piece of material to form current collector100.

FIGS. 18(c) and19(c) are perspective views that illustrate how the electrode assemblies200may fit within a shaped case50.

FIGS. 20(a) and (b) show a front and side view, respectively, of an IMD10according to one possible embodiment of the invention. IMD10includes battery40generally having a “D”-shaped profile as seen in the front view (FIG. 20(a)), and also having a contoured shape with a rounded tapered lower front portion, as seen in the side view (FIG. 20(b)). Battery40may achieve this shape using the folded electrode assembly44in accordance with an embodiment of the invention.

FIGS. 21(a)–(c) provide additional detail regarding the shape of battery40shown inFIGS. 20(a) and (b). Again, this overall shape may be achieved employing the folded electrode assembly44as disclosed above in accordance with embodiments of the present invention. However, the particular shapes and contours depicted inFIGS. 20 and 21are provided for the purpose of illustration, not limitation, as many other shapes and contours may be achieved using embodiments of the invention.

Those skilled in the art will appreciate that while the invention has been described above in connection with particular embodiments and examples, the invention is not necessarily so limited and that numerous other embodiments, examples, uses, modifications and departures from the embodiments, examples and uses may be made without departing from the inventive concepts. For example, the invention should not be construed as limited to primary batteries; in fact, the present invention find application in primary and secondary batteries as well as capacitors. The actual metes and bounds of the invention are set forth in the appended claims which literally define the invention and set forth a basis for equivalents thereof.