Power source for an implantable medical device

A battery having an electrode assembly located in a housing that efficiently utilizes the space available in many implantable medical devices is disclosed. The battery housing includes a cover and a case. The electrode assembly includes an anode tab and a cathode tab that are coupled to the cover and to a feedthrough pin disposed on the cover. The coupling of the anode tab to the cover defines an anode terminal while the coupling of the cathode tab to the feedthrough pin defines the cathode terminal. The anode and cathode tabs are aligned with the feedthrough pin and the connection point at the cover such that the tabs and feedthrough pin overlap each other along a common plane that is perpendicular to a plane that is defined by a major surface of the cover.

FIELD

The disclosure relates to implantable medical devices and, more particularly to power sources, such as batteries, that are used to power implantable medical devices.

BACKGROUND

The human anatomy includes many types of tissues that can either voluntarily or involuntarily, perform certain functions. After disease, injury, or natural defects, certain tissues may no longer operate within general anatomical norms. For example, after disease, injury, time, or combinations thereof, the heart muscle may begin to experience certain failures or deficiencies. Some of those maladies can be corrected or treated with implantable medical devices (IMDs), such as implantable pacemakers, implantable cardioverter defibrillator devices, cardiac resynchronization therapy defibrillator devices, or combinations thereof. The electrical therapy produced by an IMD may include, for example, pacing pulses, cardioverting pulses, and/or defibrillator pulses to reverse arrhythmias (e.g. tachycardias and bradycardias) or to stimulate the contraction of cardiac tissue (e.g. cardiac pacing) to return the heart to its normal sinus rhythm.

The IMDs are preferably designed with shapes that are easily accepted by the patient's body while minimizing patient discomfort. As a result, the corners and edges of the devices are typically designed with generous radii to present a package having smoothly contoured surfaces. It is also desirable to minimize the volume and mass of the devices to further limit patient discomfort. As such, efforts towards miniaturization of the IMD package also require a reduction in the sizes and form factors of the components housed within the package.

In general, the IMDs include a power source (battery) and electronic circuitry, such as a pulse generator and/or a processor module, which are hermetically sealed within a housing (can). The electrical energy for the electrical therapy delivered by IMDs is generated by delivering electrical current from the battery. The battery is a volumetrically constrained system. The sizes or volumes of components that are contained within a battery (cathode, anode, separator, current collectors, electrolyte, etc.) cannot in total exceed the available volume of the battery case. The arrangement of the components affects the amount or density of active electrode material, which can be contained within the battery case.

Typically, a battery includes corrosive material (e.g., the electrolyte). Any leakage of the corrosive material may undesirably damage the battery and/or the electrical components of the device (e.g., the implantable medical device) that the battery is used with. Such damage may generally cause the device to function improperly or otherwise cause it to cease operating altogether. In addition, if used in a medical device surgically implanted within a patient's body, as described above, accessibility to the device may be difficult for repair or replacement.

One approach to isolating the corrosive material involves using an electrical feedthrough arrangement for the battery to function as an intermediary. The feedthrough arrangement is designed to provide electrical connection between the battery and the other electrical components of the implantable medical device, and to maintain environmental isolation between the corrosive material within the battery and the other electrical components within the device. This isolation is, in part, achieved by using feedthrough pins that are generally corrosion resistant. However, effectively coupling these pins to the one or more of the electrodes in contact with the corrosive material within the battery can be difficult.

Therefore, there remains a need for improvements to methods of constructing power sources.

SUMMARY

In general, the disclosure is directed to articles of an implantable medical device that include a weld that bonds a first component and a second component of the article. In accordance with some embodiments, the articles of the implantable medical device include a battery. The battery for an implantable medical device comprises an electrode assembly enclosed in a battery case. The battery includes a cathode tab and an anode tab that are coupled to the electrode assembly.

In one aspect, the disclosure describes coupling techniques that facilitate miniaturization of the battery. The techniques enable construction of a battery with a tight form factor that enables a reduction in the overall volume of the battery.

In another aspect, the battery is configured having the anode tab and the cathode tab being positioned in an overlapping orientation such that the tabs are generally parallel along a common plane in relation to a major planar surface of the cover. A feedthrough pin is disposed on the cover for providing a terminal for connection of the battery to circuitry of the implantable medical device. The anode tab is electrically coupled to the cover and the cathode tab is electrically coupled to the feedthrough pin.

In another aspect, methods for fabrication of batteries for implantable medical devices include the tasks of: providing an electrode assembly that includes a first tab and a second tab, providing a battery cover having a feedthrough assembly that includes a feedthrough pin, aligning the electrode assembly with the battery cover such that the feedthrough pin intersects the first tab at a first connection point and the second tab intersects the battery cover at a second connection point such that the second connection point is oriented to overlap with the first connection point, and connecting the electrode assembly to the battery cover to form a joint unit whereby the feedthrough pin is electrically coupled to the first tab at the first connection point and the second tab is electrically coupled to the cover at the second connection point.

In another aspect, a resistance spot welding manufacture includes a first set of components and a set of components, wherein each set of components is oriented to overlap in a common lateral axis. The resistance spot welding manufacturing includes a first weld joint bonding the first set of components and a second weld joint bonding the second set of components. In some embodiments, at least one of the components in the first set of components and at least one of the components in the second set of components is formed from a dissimilar material.

In an additional aspect, a method of forming a resistance spot weld includes aligning a first set of components and a second set of components such that at least a portion of the components overlap along a common lateral axis. The method includes delivering a current through the first set of components and the second set of components to simultaneously form a first weld joint and a second weld joint between the first set of components and the second set of components, respectively. In some embodiments, the current delivered through the first set of components may be different from the current delivered through the second set of components.

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 present teachings. Skilled artisans will recognize the examples provided herein have many useful alternatives and fall within the scope of the present teachings.

DETAILED DESCRIPTION

In general, the disclosure is directed to articles of an implantable medical device that include a weld that bonds a first component and a second component of the article. For example, an article of the implantable medical device includes a battery.

The disclosure is not limited to any one type of application for the coupling techniques. For example, while embodiments are described and shown herein illustrating batteries in implantable medical devices with respect to medical applications, the disclosure should not be limited as such.

As used herein, the terms battery or batteries include a single electrochemical cell or cells. Batteries are volumetrically constrained systems in which the components 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. In certain embodiments, the battery is hermetically sealed.

In certain embodiments, the batteries are directed to high current batteries that are capable of charging capacitors with the desired amount of energy in the desired amount of time. In certain embodiments, the desired amount of energy is typically at least about 20 joules. Further embodiments involve the energy amount being about 20 joules to about 40 joules. In certain embodiments, the desired amount of time is no more than about 20 seconds. Further embodiments involve the desired amount of time being no more than about 10 seconds. These energy and time values can typically be attained during the useful life of the battery as well as when the battery is new. As a result, in certain embodiments, the batteries 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, the batteries are able to provide these amounts of energy repeatedly. In certain embodiments, the battery can provide these amounts of energy with a time delay of no more than about 30 seconds. Further embodiments involve the time delay being no more than about 10 seconds.

FIG. 1is a simplified schematic view of an implantable medical device (“IMD”)10. The IMD10is shown with a relationship to a human heart12. However, the IMD10shown may assume a wide variety of forms. For example, the IMD10may be an implantable neurostimulator, or an implantable drug pump, a cardiomyostimulator; a biosensor, and the like.

The IMD10includes associated electrical leads14,16and18, although it should be appreciated that the IMD10can include any number of leads suitable for a particular application. The leads14,16and18are coupled to the IMD10by means of a multi-port connector block20, which contains separate ports for each of the leads14,16, and18. The leads14,16, and18may be implanted in any known implantation location including, inside the heart12, or externally such as in contact with the heart12tissue or over the ribcage. In the illustration, electrical therapy is delivered between any one of the electrodes22,24,26, and28. The electrodes22-28are also employed to sense electrical signals indicative of cardiac contractions.

As previously described, the IMD10can assume a wide variety of forms as are known in the art. Generally, IMDs include one or more of the following elements: (a) a device housing (e.g., a case), (b) one or more capacitors disposed within the device housing, (c) a battery disposed within the device housing and operatively connected to the capacitor, and (d) circuitry disposed within the device housing providing electrical connection between the battery and the capacitor.

FIG. 2depicts exemplary illustrations and general locations of elements of an IMD30. As shown, the IMD30includes a device housing or case32(having two halves), an electronics module34(the circuitry), capacitor(s)36, and an electrochemical cell38(the battery). Each of these components of the IMD30is preferably configured for one or more particular end-use applications. For example, the electronics module34is configured to perform one or more sensing and/or stimulation processes. The electrochemical cell38provides the electrical energy to charge and re-charge the capacitor(s)36, and to also power the electronics module34. According to certain embodiments, the electrochemical cell38may take the form of a rechargeable (secondary) lithium-ion battery, which may incorporate a negative active material comprised of Carbon, a positive active material of a lithium transition metal oxide, such as LiCoO2, for example, and a lithium containing salt, such as LiPF6 and an appropriate organic solvent for the LiPF6 salt, for example. In other certain embodiments, the electrochemical cell38may be provided as a non-rechargeable (primary) lithium battery. It should be appreciated that the electrochemical cell38may take the form of various other battery types or electrochemical cells, either active or passive (battery packs), and, thus need not necessarily be limited to the aforementioned examples.

Electrochemical cells generally include one or more of the following components: (a) an electrode assembly including one or more of an anode and a cathode, (b) an electrolyte, and (c) a housing within which the electrode assembly and the electrolyte are disposed. In certain embodiments, the housing includes one or more of the following elements: (a) a cover, (b) a case with an open top to receive the cover, (c) at least one feedthrough assembly providing electrical communication from a first electrode of the electrode assembly and the implantable medical device circuitry (e.g., the electronics module34), (d) a coupling providing electrical connection between the at least one feedthrough assembly and a first electrode of the electrode assembly, and (e) a coupling providing electrical connection between the case (or another feedthrough assembly) and a second electrode of the electrode assembly. The housing may optionally include one or more insulators including (a) a case liner adjacent to the case providing a barrier between the electrode assembly and the case, and (b) a head space insulator adjacent to the electrode assembly (e.g., proximate to the insulator adjacent to the cover) providing a barrier between the electrode assembly and the case.

FIGS. 3 and 4illustrate an assembly of a battery in accordance with an exemplary embodiment of the present disclosure. A battery38is illustrated having a shallow drawn battery case42and an electrode assembly44. The battery case42is generally made of a medical grade titanium; however, it is contemplated that the 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. The battery case42is designed to enclose the electrode assembly44and be sealed with a battery cover46. A headspace43region may be included in the battery case42for housing insulators and the connector tabs (discussed below) that transfer electrical energy from electrode assembly44to the implantable medical device circuitry.

The battery case42is formed having a planar bottom portion, an open top to receive the cover46, and at least two sides45a,45bextending from the bottom portion that may be radiused at intersections with the bottom portion. The planar bottom portion may define a plane along the (lateral) x-axis that is parallel to the plane defined by a major surface of the cover46.

The battery cover46is held in place by a lip47that prevents the cover46from dropping within battery case42. In an alternative embodiment, the lip may be located on the cover46to engage with the case42. The cover46is welded to the case42, such as through laser welding, although other methods of attachment are contemplated. For example, resistance welding, brazing, soldering and similar techniques may be employed and/or adhesive materials may be used to couple the cover46to the case42.

The battery case42will also include a fillport49athat is used to route the electrolyte into battery38. The fillport preferably includes an opening that is formed on battery case42and is preferably hermetically sealed to ensure no electrolyte leakage. The fillport receives an electrolyte injection device that transfers electrolyte from the device to battery38. Once the electrolyte has been injected within battery38, a ball seal49bmay be placed within the opening to create a “press-fit” hermetic seal, which prevents any electrolyte from escaping through the opening. A secondary seal may subsequently be formed over the ball seal to provide a redundant seal. In yet another embodiment, a gasket seal or epoxy is utilized to plug the opening.

A case liner50may be provided to electrically isolate electrode assembly44from battery cover46. The case liner50may be configured in the shape of the case42with dimensions that are slightly smaller so as to fit within the case42. The walls of the case liner42define a hollow receptacle that receives the electrode assembly44. Liner50may include an open end at the head space region43that leads into the hollow receptacle. As shown inFIG. 3, the case liner50is configured with slits at the open end to accommodate cathode tab56and anode tab58. Case liner50is comprised of an electrically insulative material such as ETFE having a thickness of about 0.030 cm. (0.012 inches). However, it is contemplated that other thicknesses and materials could be used such as high density polyethylene (HDPE), polypropylene, polyurethane, fluoropolymers, and the like.

The battery38may also include a head space insulator54that is coupled at the open end of the case liner50so as to enclose the open end of the case liner50. Although not shown inFIG. 3, head space insulator54may include components that are formed to be positioned between the anode tab58and the cathode tab56. The components may be formed with a predetermined width such that a predetermined spacing is maintained between the cathode tab56and anode tab58.

Case liner50performs several functions including working in conjunction with the head space insulator54to isolate battery case42and battery cover46from electrode assembly44. Case liner50also provides mechanical stability for electrode assembly44. In addition, case liner50serves to hold the coil assembly together which substantially aids in the manufacturing of battery38. Since electrode assembly44is preferably a wound coil, case liner50also helps prevent assembly44from unwinding. Case liner50further provides protection for assembly44during handling and during the life of assembly44. Finally, case liner50provides a thermal barrier between assembly44and cover46during the laser welding procedure that joins cover46with case42.

FIG. 5illustrates a partial cutaway perspective view of the electrode assembly44of the battery38ofFIG. 3along the lines4-4. As illustrated, the electrode assembly44generally includes a first electrode80, a second electrode82, and a porous, electrically non-conductive separator material84encapsulating either one or both of the first electrode80and the second electrode82. These three components are generally placed together to form the electrode assembly44. As is known in the art, the first electrode80and second electrode82will form an anode and a cathode of the battery38.

The details regarding construction of the electrode assembly44, with respect to materials and techniques may correspond to those disclosed for example in U.S. Pat. No. 7,544,220 entitled “Welding Methods and Apparatus for Batteries” issued to Zhao et al. and incorporated herein by reference in its entirety. The electrode assembly44can be a wound or coiled structure similar to those disclosed for example in U.S. Pat. No. 5,486,215 (Kelm et al.). The electrode assembly44can also be part of batteries in which the electrode types include spirally-wound, stacked plate, or serpentine, as disclosed, for example, in U.S. Pat. Nos. 5,312,458 and 5,250,373. Alternatively, in certain embodiments, the battery38can include single cathode electrodes as described, for example, in U.S. Pat. No. 5,716,729. The composition of the electrode assembly44can include any known battery chemistry, including a wound core of lithium/silver vanadium oxide (Li/SVO) battery as discussed for example in U.S. Pat. No. 5,458,997.

With reference toFIGS. 6 and 7, a top and side profile of a battery cover46with a feedthrough assembly is shown. Battery cover46is comprised of an electrode assembly region60, a headspace region62, and a feedthrough assembly68. Battery cover46is designed to fit overtop the opening of a perimeter of the open end of battery case42. As previously mentioned, the battery cover46rests on the lip of the open end such that it is substantially flush with the top of the opening of the battery case42. As used in this disclosure, substantially flush may refer to the overlap between the battery cover and the battery case having a proportion of between 60% to 100%, and preferably about 98 to 100%. This provides for substantial ease of manufacturing when battery cover46is laser welded to battery case42.

As shown in the side profile view ofFIG. 7, taken along lines7-7, the feedthrough assembly68contains a ferrule (not shown), an insulating member72, and a feedthrough pin74. In certain embodiments, the feedthrough pin74is formed of aluminum containing titanium alloy, as is described in U.S. Pat. No. 6,855,456, the disclosure of which is incorporated herein by reference. Accordingly, when such is used as the feedthrough pin74, the likelihood of the pin74corroding is reduced, and thus, the likelihood of the corrosive materials escaping from the battery housing is reduced as well. However, it should be appreciated that any conductive material could be utilized for the feedthrough pin74without departing from the spirit of the invention.

The feedthrough pin74is generally conductively insulated from the battery cover46by the insulating member72. The insulating member72, which is generally comprised of CABAL-12 (calcium-boron-aluminate), TA-23 glass or other glasses, provides electrical isolation of the feedthrough pin74from the battery cover46. The material of feedthrough pin74is in part selected for its ability to join with the insulating member72, which results in a hermetic seal. As mentioned above, the pin material is also selected to be corrosion resistant. CABAL-12 is also generally corrosion resistant and a good insulator. Therefore, CABAL-12 provides good insulation between the feedthrough pin74and the battery cover46and is 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.

Coupling between the electrodes and the externally accessible battery terminals such as feedthrough pin74and cover46, e.g., via electrical connection to the tabs extending from the electrodes, can be difficult for several reasons. One reason involves differences in the physical properties of the pins and the tabs. This dissimilarity in material properties can lead to brittle joints or other unacceptable performance-related problems. To address such problems, current coupling methods have often involved use of a coupling member or manipulating the tab and/or the feedthrough pin for initial retention purposes before using a coupling process to achieve a secure joint between the tab and the pin. Unfortunately, these methods have been found to be highly sensitive to manufacturing variability (e.g., weld damage, coil damage, tab damage and missed welds), resulting in unstable manufacturing yield. The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.

FIG. 8illustrates an exploded view of the battery38shown inFIG. 3. The battery38is shown with the electrode assembly44that includes first electrode tab56and second electrode tab58. While the electrode assembly44is described as having first and second electrode tabs56and58respectively, it is fully contemplated each electrode could have more than one tab without departing from the spirit of the invention. One such electrode configuration involves each of the electrodes being subdivided over one or more electrode plates connected together and each electrode plate includes at least one tab protruding therefrom. The tabs of each electrode are coupled together to provide electrical continuity throughout the respective electrodes.

As will be described in more detail, one of the battery electrodes is operatively coupled to a first feedthrough mechanism (e.g., a feedthrough pin74), while the other electrode is electrically coupled to the case42(e.g., via a direct connection to the cover46). Overall, these couplings are facilitated through the use of the electrode tabs. Thereafter, when the battery is subsequently used, current is able to flow from the electrode plates through the tabs to the corresponding battery electrical contact (e.g., feedthrough pin74, battery case42).

As mentioned above, the coupling of the tabs to the feedthrough pin74and the battery case42to provide an effective joint can be challenging, particularly if the feedthrough pin74and tabs are made of different materials. However, it is often a necessity to have the pin74and the tabs be made of different materials to ensure the battery remains hermetic.

The coupling techniques of the present disclosure facilitate miniaturization of the IMD10. In particular, the techniques enable construction of a battery with a tight form factor that enables a reduction in the overall volume of the battery of IMD10. As described in more detail in the '220 patent, the coupling techniques of conventional batteries allow for flexibility in determining weld position and weld size. In the construction of such exemplary batteries, the '220 patent describes positioning the tabs in a spaced apart orientation such that the tabs are generally parallel in relation to a major planar surface of the cover. This provides the benefit of flexibility of joining each of the tabs independently. Moreover, the requirement to position the tabs at laterally spaced apart locations, as shown generally in the '220 patent, allows for large tolerances with respect to positioning of the tab and feedthrough pin and hence affords increased manufacturability. Moreover, due to the dissimilar materials and the mismatched thicknesses of the tabs and feedthrough pin, the coupling techniques of the conventional batteries such as the '220 patent enable fabricating robust weld joints.

However, the inventors discovered that these desirable properties in the conventional coupling techniques such as those in the '220 patent pose challenges when the overall dimensions of the battery38are reduced.

Aided by the disclosure of the '220 patent, those skilled in the art can appreciate that due to the nature of the coiling process of the electrode assembly, once unloaded coils will shrink in width and expand in thickness. This action is reversed when the coils are inserted and compressed inside the battery case. Therefore, the inventors of the present disclosure have found that a very accurate coil alignment relative to the header has to be maintained during formation of the cathode and anode weld joints with the aforementioned reduction in the overall dimensions of the battery components.

But even with adjustments to the coil alignment, the inventors of the present disclosure have found that as the dimensions of the overall battery are reduced, the conventional coupling techniques result in warped tabs and create buckling of the anode during the coupling between the cover and the electrode assembly.

The overall reduction in the volume of the battery means that a reduction occurs in the space that is required for the conventional coupling techniques of battery electrode assemblies. At the very least, the tabs of such conventional batteries cannot overlap each other as there must be enough clearance between the coupling locations.

In accordance with embodiments of the present disclosure, techniques have been developed that permit simultaneous coupling of the tab56to the feedthrough pin74and tab58to the battery cover46. The coupling techniques eliminate the need to manipulate the feedthrough pin or to utilize coupling components for forming the weld joints. The techniques enable the fabrication of a robust weld for a miniaturized battery.

FIG. 9illustrates a schematic diagram showing an embodiment of a coupling technique utilized for fabrication of battery38for the IMD10. As depicted, the feedthrough pin74is adjacent to tab56and the battery cover46is adjacent to the tab58. Unlike the conventional batteries, the orientation of these components is such that a portion of all four components, i.e., feedthrough pin74, tab56, tab58and the battery cover46will be oriented in an overlapping relationship such that the portions are positioned along a common plane along lines Y-Y that is perpendicular to the plane defined by the major surface of the battery case42(shown in phantom lines).

In the illustrative embodiment, a coupling technique is utilized to simultaneously couple the tab56to the feedthrough pin74and tab58to the battery cover46. As is shown inFIG. 8, the feedthrough pin74includes a first connection portion76and the anode tab includes a second connection portion78that are spaced apart, but overlap each other. As used in this disclosure, overlapped means that at least portions of the components, such as the tab56, feedthrough pin74, tab58and the battery cover46, are positioned along a plane with no lateral spacing. Returning toFIG. 9, both the first connection portion76and the second connection portion78are oriented along the common plane illustrated by lines Y-Y that is perpendicular to a plane defined by the major surface of the bottom end of the battery case42. Thus, a cathode weld joint is formed at the intersection of the tab56to the feedthrough pin74and an anode weld joint is formed at the intersection of the tab58to the battery cover46. Based on this configuration, the cathode weld joint and anode weld joint can be formed simultaneously through any known welding operation. While not shown, it should be appreciated that in alternative embodiments, the cathode weld joint may be formed at the intersection of the tab56to the battery cover46and an anode weld joint is formed at the intersection of the tab58to the feedthrough pin74.

In the illustrative embodiment ofFIG. 9, a coupling technique discussed in more detail inFIGS. 9 and 10is utilized to form the weld joints between the cathode tab56and the feedthrough pin74, and the anode tab58and the cover46. Briefly, the coupling technique utilizes resistance spot welding to form the mechanical connections that define the weld joints. However, aided with the benefit of this disclosure, it will be apparent to those skilled in the art that any suitable opposed welding process can be modified for the coupling process.

A coupling tool100having a set of electrodes102,104, and106is utilized in this embodiment for resistance spot welding. This process enables each of the electrodes102,104, and106to be dimensioned so as to provide adequate coverage over the weld location. Thus, the electrodes102,104, and106may be formed with dissimilar shapes and sizes as is desired to accommodate the surfaces of the cathode tab56, the feedthrough pin74, the anode tab58, and the cover46. Electrode106may be coupled to a compressive member108.

The overall width of the electrode106including the compressive member108can be sized to approximately match the spacing between the feedthrough pin74and the cathode tab58. The dimension of the electrode106including the compressive member108ensures that the desired spacing is maintained, while also providing a compressive force to hold the battery components together until a robust weld joint is formed.

With the above described orientation, the weld joint is formed by current that flows in series from the top electrode102through the cathode tab56, the feedthrough pin74, the middle electrode106, the anode tab58, the cover46and the bottom electrode104. As such, both sets of welds can be produced simultaneously with this coupling technique.

In an alternate embodiment, the coupling techniques may utilize independent power supplies for formation of the weld joint between the cathode tab56and feedthrough pin74as well as the weld joint between the anode tab58and the cover46. The electrodes102,104, and106may be coupled to a power source such that a first current supply flows through electrodes102to106and a second current supply that is different from the first current supply flows through electrodes106to104. With this configuration, different levels of current can be delivered to form each of the cathode and anode weld joints. As stated above, the battery components may suitably be formed having dissimilar materials. As such, providing independent current supplies will enable the delivery of appropriate current supplies that are suitable for each set of materials.

The connection between the anode tab58and the cover46provides an electrical coupling for the power supply during operation of the battery38. Additionally, the connection of the tab58to the cover46also serves to mechanically couple the electrode assembly44to the cover46.

In accordance with some embodiments, the coupling tool100may include a securing mechanism122that is configured to retain the electrode assembly in a predefined configuration. The securing mechanism122may be embodied as a support frame to hold one or more of the components to be welded in a stationary position. For example, the securing mechanism122may be defined such that the electrode assembly is formed in a shape generally corresponding to that of the assembled electrode assembly once it is inserted in the case42. The securing mechanism122may include an enclosed body having a hollow region generally corresponding to the receptacle defined by the case42. In other embodiments, the securing mechanism122may include at least two rails that are spaced apart, to provide a width that generally corresponds to the width of the case and a third rail that is spaced apart from the bottom electrode104.

The coupling tool100may include a platform120onto which the bottom electrode104may be positioned. The platform120in conjunction with the bottom electrode104will inhibit movement of the cover46during a welding cycle. In alternative embodiments, the bottom electrode104may be integrated onto the platform120.

The securing mechanism122will hold the electrode assembly44and is moveable relative to the platform120so that the electrode assembly44can be positioned over the cover46to enable the tabs56,58to be aligned as discussed above. The securing mechanism122may compress the electrode assembly to a pre-determined thickness that substantially corresponds to the dimensions of the interior of the battery case42. As used in this disclosure, substantially may refer to the pre-determined thickness having a proportion of between 60% to 100%, and preferably about 90 to 99% of the internal volume of the battery case42. In doing so, the securing mechanism122ensures proper alignment of the electrode assembly44with the cover46in both lateral and transverse directions, while also compressing the electrode assembly44to the pre-determined dimensions during the welding process. The securing mechanism122also provides for the alignment of the tabs56,58in an overlapping orientation for the simultaneous coupling of the tabs to the feedthrough pin74and cover46.

FIG. 10is a schematic view of the coupling tool100ofFIG. 9that is utilized in one embodiment for fabrication of a battery for an IMD. The coupling tool100enables simultaneous welding of a first set of components and a second set of components. For example, the first set of components may include the feedthrough pin74and tab56and the second set of components may include the tab58and the cover46. As is known in the art, resistance spot welding may be utilized to create a bond between a pair of components.

By way of general explanation and described with reference toFIG. 10, resistance spot welding may be carried out via coupling tool100(partially shown) that may include a power supply (not shown) for electrical current supply and electrodes configured for clamping together each of the sets of components, as set forth in more detail below.

Conventional spot welding tools utilize a pair of axially aligned and opposing electrodes that press upon opposite sides of the component pair to be bonded for formation of individual weld joints. Therefore, the need for the dual opposed pressing action from the axially aligned electrodes means that only one weld joint can be created for any given opposing electrode pair.

The coupling tool100is configured having a top electrode102, a bottom electrode104and an opposed electrode106. The coupling tool100is utilized in a bonding operation that forms two discrete weld joints simultaneously. In the illustrative embodiment, the weld joints are formed on two sets of components. The coupling tool100is configured such that the two sets of components are oriented in an overlapping relationship along a common lateral axis. As such, the welding current flows from the top electrode102through the opposed electrode106to the bottom electrode104. Thus, the coupling tool100is configured to create a first bond between the first set of components, such as the feedthrough pin74and tab56, and a second bond between the second set of components such as the tab58and the cover46.

As is described in more detail with reference to the electrodes in the embodiment ofFIG. 11, the electrodes102-106may be independently addressable. That is, the power supply includes independent current paths that are defined for each set of the electrodes102,106and106,104. In this configuration, the power supply may suitably generate different current amounts for each independent current path. This embodiment may be of particular application for coupling components having dissimilar materials.

The shape and size of the tips of the electrodes102,104,106will control the distribution of heat at the location of the weld joint. Moreover, these dimensions will control the geometry of the weld joint. As such, the tips of each of the electrodes102-106will be selected having a predetermined shape. Examples of the predetermined shapes for the tips include domed, conical, or flat. Therefore, a given tip shape will be selected as a function of the material of the components to be coupled and the desired weld joint geometry. Preferably, the electrodes102-106may be formed with a contact surface area in the range of 0.03 inches to 0.08 inches.

In accordance with embodiments of this disclosure, a compressive force is suitably applied between the electrodes102,106and electrodes106,104to place the components under compression. Electrode106may include compressive member108to place the components between electrode102and electrode106under compression and the components between electrode106and electrode104under compression. The compression force between any two electrodes may be selected to generate direct physical contact between any two components to be bound. For example, a force in the range of 5 to 12 lbs may be applied between any two electrodes.

In an illustrative welding sequence, the coupling tool100is utilized to create a weld joint by application of current through the electrodes102-106coupled with a compressive force that is generated between the top electrode102and the opposed electrode106, as well as the compressive force that is generated between the opposed electrode106and the bottom electrode104. Without intending to be bound by theory, the current flowing across the electrodes generates heat at the intersection of the component surfaces and the electrodes102-106. Coupled with the application of mechanical forces holding the components in place, the heat will cause the melting of the components with a subsequent re-solidification in the absence of current flow.

It is contemplated that the components in the first set of components may have dissimilar materials whereas the components in the second set of components may also have dissimilar materials, both of which are different from the materials of the first set of components.

FIG. 11depicts an alternate embodiment of a coupling tool200for performing a coupling operation. The coupling tool200may suitably be used for forming a plurality of weld joints220in a device such as the battery38. For example, coupling tool200may be suitable for coupling a battery having more than two overlapping tabs to externally accessible terminals.

Coupling tool200includes a top electrode202, a bottom electrode204, and a plurality of opposed electrodes206a,206b, and206n. Although only three opposed electrodes206a,206band206nare shown, it is contemplated that the tool200may include any number of electrodes. Similar to the electrodes of the coupling tool200, the shape and size of each of electrodes202-206can also be varied to control the heat balance to each weld joint.

A weld power supply208is provided for generating the weld current that is utilized during the welding operation. The weld power supply208may include multiple supply outlets for electrical connections to each of the electrodes. This enables the formation of independent current paths for each of the weld joints or for groupings of weld joints.

It will be appreciated the present invention can take many forms and embodiments. The true essence and spirit of this invention are defined in the appended claims, and it is not intended the embodiment of the invention presented herein should limit the scope thereof.

The foregoing discussion is presented to enable a person skilled in the art to make and use the present teachings. 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 present teachings. Thus, the present teachings are not intended to be limited to embodiments shown, but are to be accorded the widest scope consistent with the principles and features disclosed herein.