Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/348,665, filed Jan. 15, 2002. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates generally to electric storage batteries and more particularly to a battery construction, and method of manufacture thereof, suitable for use in implantable medical devices.  
         BACKGROUND OF THE INVENTION  
         [0003]    Rechargeable electric storage batteries are commercially available in a wide range of sizes for use in a variety of applications. As battery technology continues to improve, batteries find new applications which impose increasingly stringent specifications relating to physical size and performance. Thus, new technologies have yielded smaller and lighter weight batteries having longer storage lives and higher energy output capabilities enabling them to be used in an increasing range of applications, including medical applications, where, for example, the battery can be used in a medical device which is implanted in a patient&#39;s body. Such medical devices can be used to monitor and/or treat various medical conditions.  
           [0004]    Batteries for implantable medical devices are subject to very demanding requirements, including long useful life, high power output, low self-discharge rates, compact size, high reliability over a long time period, compatibility with the patient&#39;s internal body chemistry, etc. Although various battery chemistries have been tried, lithium ion technology is generally accepted as the preferred chemistry for medical implant applications.  
           [0005]    Such electric storage batteries are generally comprised of a tubular metal case enveloping an interior cavity which contains an electrode assembly surrounded by a suitable electrolyte. The electrode assembly generally comprises a plurality of positive electrode, negative electrode, and separator layers which are typically stacked and/or spirally wound to form a jellyroll. The positive electrode is generally formed of a metal substrate having positive active material coated on both faces of the substrate. Similarly, the negative electrode is formed of a metal substrate having negative active material coated on both faces of the substrate. In forming an electrode assembly, separator layers are interleaved between the positive and negative electrode layers to provide electrical isolation.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention is directed to an electric storage battery incorporating one or more aspects described herein for enhancing battery reliability while minimizing battery size. In addition, the invention is directed to a method for efficiently manufacturing the battery at a relatively low cost.  
           [0007]    In accordance with a first significant aspect of the invention, a feedthrough pin is provided which is directly physically and electrically connected to the inner end of an electrode substrate (e.g., positive), as by welding. The pin is used during the manufacturing process as an arbor to facilitate winding the layers to form an electrode assembly jellyroll. Additionally, in the fully manufactured battery, the pin extends through a battery case endcap and functions as one of the battery terminals. The battery case itself generally functions as the other battery terminal.  
           [0008]    More particularly, in accordance with an exemplary preferred embodiment, the inner end of the positive electrode substrate is spot welded to the feedthrough pin to form an electrical connection. The substrate, e.g., aluminum, can be very thin, e.g., 0.02 mm, making it difficult to form a strong mechanical connection to the pin, which is preferably constructed of a low electrical resistance, highly corrosion resistant material, e.g., platinum iridium, and can have a diameter on the order of 0.40 mm. In order to mechanically reinforce the pin and secure the pin/substrate connection, a slotted C-shaped mandrel is provided. The mandrel is formed of electrically conductive material, e.g., titanium-6AI-4V, and is fitted around the pin, overlaying the pin/substrate connection. The mandrel is then preferably welded to both the pin and substrate. The mandrel slot defines a keyway for accommodating a drive key which can be driven to rotate the mandrel and pin to wind the electrode assembly layers to form the spiral jellyroll.  
           [0009]    In accordance with a further significant aspect of the invention, the outer layer of the jellyroll is particularly configured to minimize the size, i.e., outer radius dimension, of the jellyroll. More particularly, in the exemplary preferred embodiment, the active material is removed from both faces of the negative electrode substrate adjacent its outer end. The thickness of each active material coat can be about 0.04 mm and the thickness of the negative substrate can be about 0.005 mm. By baring the outer end of the negative electrode substrate, it can be adhered directly, e.g., by an appropriate adhesive tape, to the next inner layer to close the jellyroll to while minimizing the roll outer radius dimension.  
           [0010]    A battery case in accordance with the invention is comprised of a tubular case body having open first and second ends. The feedthrough pin preferably carries a first endcap physically secured to, but electrically insulated from, the pin. This first endcap is preferably secured to the case body, as by laser welding, to close the open first end and form a leak free seal. With the jellyroll mounted in the case and the first endcap sealed, the interior cavity can thereafter be filled with electrolyte from the open second end.  
           [0011]    In accordance with a still further aspect of the invention, the jellyroll assembly is formed with a flexible electrically conductive tab extending from the negative electrode substrate for electrical connection to the battery case. In accordance with a preferred embodiment, the tab is welded to a second endcap which is in turn welded to the case. The tab is sufficiently flexible to enable the second endcap to close the case body second end after the interior cavity is filled with electrolyte via the open second end. In accordance with an exemplary preferred embodiment, the tab is welded to the inner face of the second endcap such that when the jellyroll is placed in the body, the tab locates the second endcap proximate to the body without obstructing the open second end. After electrolyte filling, the case body is sealed by bending the tab to position the second endcap across the body second end and then laser welding the endcap to the case body.  
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0012]    [0012]FIG. 1 is a side view of a feedthrough pin subassembly in accordance with the invention;  
         [0013]    [0013]FIG. 2 is a longitudinal sectional view through the subassembly of FIG. 1;  
         [0014]    [0014]FIG. 3 is a plan view of a positive electrode strip utilized in the exemplary preferred electrode assembly in accordance with the invention;  
         [0015]    [0015]FIG. 4 is a side view of the positive electrode strip of FIG. 3;  
         [0016]    [0016]FIG. 5 is an enlarged sectional view of the area A of FIG. 4 showing the inner end of the positive electrode strip of FIGS. 3 and 4;  
         [0017]    [0017]FIG. 6 is an isometric view showing the bared inner end of the positive electrode substrate spot welded to the feedthrough pin and configured to receive a C-shaped mandrel thereon;  
         [0018]    [0018]FIG. 7 is an end view showing the C-shaped mandrel being crimped to the pin and electrode;  
         [0019]    [0019]FIG. 8 is an end view showing the C-shaped mandrel mounted on the pin and capturing the positive electrode substrate therebetween;  
         [0020]    [0020]FIG. 9 is an isometric view depicting a drive key accommodated in the slot of the C-shaped mandrel;  
         [0021]    [0021]FIG. 10 is a plan view showing the drive key coupled to a drive motor for rotating the C-shaped mandrel;  
         [0022]    [0022]FIG. 11 is a schematic end view depicting how rotation of the C-shaped mandrel and pin can wind positive electrode, negative electrode, and separator strips to form a spiral jellyroll electrode assembly;  
         [0023]    [0023]FIG. 12 is a plan view of a negative electrode strip utilized in the exemplary preferred electrode assembly in accordance with the invention;  
         [0024]    [0024]FIG. 13 is a side view of the negative electrode strip of FIG. 12;  
         [0025]    [0025]FIG. 14 is an enlarged sectional view of the area A of FIG. 13 showing the inner end of the negative electrode strip of FIGS. 12 and 13;  
         [0026]    [0026]FIG. 15 is an enlarged sectional view of the area B of FIG. 13 showing the outer end of the negative electrode strip of FIGS. 11 and 12;  
         [0027]    [0027]FIG. 16 is an isometric view showing that the layers of a spirally wound electrode assembly, i.e., jellyroll;  
         [0028]    [0028]FIG. 17 is a plan view of the negative electrode strip showing the attachment of a flexible electrically conductive tab to the bared outer end of the negative electrode substrate;  
         [0029]    [0029]FIG. 18 is an enlarged sectional view showing how the outer turn of the negative electrode strip is taped to the next inner layer to close the jellyroll to minimize its outer radius dimension;  
         [0030]    [0030]FIG. 19 is an isometric view depicting the jellyroll electrode assembly being inserted into a cylindrical battery case body;  
         [0031]    [0031]FIG. 20 is an isometric view showing a battery case body with the negative electrode tab extending from the open case body;  
         [0032]    [0032]FIG. 21 is an isometric view showing how the negative electrode tab is mechanically and electrically connected to an endcap for sealing the case body second end;  
         [0033]    [0033]FIG. 22 is a side view showing how the negative electrode tab holds the second endcap proximate to the case body second end without obstructing the open second end;  
         [0034]    [0034]FIG. 23 is a front view showing the weld position and the relationship between the various components; and  
         [0035]    [0035]FIG. 24 is an enlarged sectional view of the second end of the battery case showing the endcap in sealed position. 
     
    
     DETAILED DESCRIPTION  
       [0036]    Attention is initially directed to FIGS. 1 and 2 which illustrate a preferred feedthrough pin subassembly  10  utilized in accordance with the present invention. The subassembly  10  is comprised of an elongate pin  12 , preferably formed of a solid electrically conductive material, having low electrical resistance and high corrosion resistance such as platinum iridium, preferably 90Pt/10Ir. The pin  12  extends through, and is hermetically sealed to a header  14 . The header  14  is comprised of dielectric disks, e.g., ceramic,  16  and  18  which sandwich a glass hollow cylinder  20  therebetween. The glass hollow cylinder is hermetically sealed to the pin  12 . The outer surface of the glass hollow cylinder  20  is sealed to the inner surface of an electrically conductive hollow member  22 , e.g., titanium-6AI-4V. As will be seen hereinafter, the conductive hollow material  22  functions as a battery case endcap in the final product to be described hereinafter.  
         [0037]    Attention is now directed to FIGS. 3, 4, and  5  which illustrate a preferred positive electrode strip  30  which is utilized in the fabrication of a preferred spirally wound jellyroll electrode assembly in accordance with the present invention. The positive electrode strip  30  is comprised of a metal substrate  32  formed, for example, of aluminum. Positive electrode active material  34 ,  36  is deposited, respectively on the upper and lower faces  38  and  40  of the substrate  32 . Note in FIGS. 3, 4, and  5  that the right end of the substrate  32  is bare, i.e. devoid of positive active material on both the upper and lower faces  38 ,  40 .  
         [0038]    It is to be pointed out that exemplary dimensions are depicted in FIGS.  1 - 5  and other figures herein. These exemplary dimensions are provided primarily to convey an order of magnitude to the reader to facilitate an understanding of the text and drawings. Although the indicated dimensions accurately reflect one exemplary embodiment of the invention, it should be appreciated that the invention can be practiced utilizing components having significantly different dimensions.  
         [0039]    [0039]FIG. 6 depicts an early process step for manufacturing a battery in accordance with the invention utilizing the pin subassembly  10  (FIGS. 1, 2) and the positive electrode strip  30  (FIGS.  3 - 5 ). A topside electrode insulator (not shown), which may comprise a thin disk of DuPont Kapton® polyimide film, is slipped onto the pin  12  adjacent the header  14 . In accordance with the present invention, the bare end of the electrode strip substrate  32  is electrically connected to the pin  12  preferably by resistance spot welding, shown at  44 . Alternatively, substrate  32  may be ultrasonically welded to the pin  12 . The thinness, e.g. point 0.02 mm of the substrate  32 , makes it very difficult to form a strong mechanical connection between the substrate and the pin  12 . Accordingly, in accordance with a significant aspect of the present invention, an elongate C-shaped mandrel  48  is provided to mechanically reinforce the pin  12  and secure the substrate  32  thereto.  
         [0040]    The mandrel  48  preferably comprises an elongate titanium or titanium alloy such as Ti-6AI-4V tube  50  having a longitudinal slot  52  extending along the length thereof. The arrow  54  in FIG. 6 depicts how the mandrel  48  is slid over the pin  12  and substrate  32 , preferably overlaying the line of spot welds  44 . The mandrel  48 , pin  12 , and substrate  32  are then preferably welded together, such as by resistance spot welding or by ultrasonic welding. Alternatively, the mandrel  48  may be crimped onto the pin  12  at least partially closing the “C” to create a strong mechanical connection. In the case of forming only a mechanical connection and not necessarily a gas-tight electrical connection between the mandrel  48  and the pin and substrate, the mandrel material is preferably made of a material that will not lead to electrolysis. When used with electrolytes that tend to contain hydrofluoric acid, the mandrel is preferably made of  304 ,  314 , or  316  stainless steels or aluminum or an alloy thereof chosen for its compatibility with the other materials. FIG. 7 is an end view showing the step of crimping the mandrel  48  to the pin  12  and substrate  32 . Supporting die  126  is used to support the mandrel  48  and crimping dies  124  and  125  are used to deform the edges of the mandrel  48  to bring them closer together and mechanically connect the mandrel  48  to the pin  12  and substrate  32 . By crimping in the direction of arrows  127  and  128 , a strong connection is formed without damaging the thin electrode or disturbing the electrical connection between the pin and the electrode.  
         [0041]    [0041]FIG. 8 is an end view showing the slotted mandrel  48  on the pin  12  with the substrate  32  extending tangentially to the pin  12  and terminating adjacent the interior surface of the mandrel tube  50 . The tube  50  is preferably sufficiently long so as to extend beyond the free end of the pin  12 . As depicted in FIG. 9, this enables a drive key  56  to extend into the mandrel slot  52 .  
         [0042]    [0042]FIG. 10 schematically depicts a drive motor  60  for driving the drive key  56  extending into mandrel slot  52 . With the pin subassembly header  14  supported for rotation (not shown), energization of the motor  60  will orbit the key drive  56  to rotate the mandrel  48  and subassembly  10  around their common longitudinal axes. The rotation of the mandrel  48  and subassembly  10  is employed to form a jellyroll electrode assembly in accordance with the present invention.  
         [0043]    More particularly, FIG. 11 depicts how a jellyroll electrode assembly is formed in accordance with the present invention. The bare end of the substrate  32  of the positive electrode strip  30  is electrically connected to the pin  12  as previously described. The conductive mandrel  48  contains the pin  12  and bare substrate end, being welded to both as previously described. A strip of insulating separator material  64  extending from opposite directions is introduced between the mandrel  48  and positive electrode substrate  32 , as shown. A negative electrode strip  70  is then introduced between the portions of the separator material extending outwardly from mandrel  48 .  
         [0044]    The preferred exemplary negative electrode strip  70  is depicted in FIGS.  12 - 15 . The negative electrode strip  70  is comprised of a substrate  72 , e.g. titanium, having negative active material formed on respective faces of the substrate. More particularly, note in FIG. 14 that negative active material  74  is deposited on the substrate upper surface  76  and negative active material  78  is deposited on the substrate lower surface  80 . FIG. 14 depicts the preferred configuration of the inner end  82  of the negative electrode strip  70  shown at the left of FIGS. 12 and 13. FIG. 15 depicts the configuration of the outer end  83  of the negative electrode strip  70  shown at the right side of FIGS. 12 and 13.  
         [0045]    Note in FIG. 14 that one face of the substrate inner end  82  is bared. This configuration can also be noted in FIG. 11 which shows how the negative substrate inner end  82  is inserted between turns of the separator strip  64 . After the strip  70  has been inserted as depicted in FIG. 11, the aforementioned drive motor  60  is energized to rotate pin  12  and mandrel  48 , via drive key  56 , in a counterclockwise direction, as viewed in FIG. 11. Rotation of pin  12  and mandrel  48  functions to wind positive electrode strip  30 , separator strip  64 , and negative electrode strip  70 , into the spiral jellyroll assembly  84 , depicted in FIG. 16. The assembly  84  is comprised of multiple layers of strip material so that a cross section through the assembly  84  would reveal a sequence of layers in the form pos/sep/neg/sep/pos/sep/neg/ . . . , etc.  
         [0046]    [0046]FIG. 15 depicts a preferred configuration of the outer end  83  of the negative electrode strip  70 . Note that the outer end  88  of the substrate  72  is bared on both its top and bottom faces. Additionally, as shown in FIG. 17, a flexible metal tab  90  is welded crosswise to the substrate  72  so as to extend beyond edge  92 . More particularly, note that portion  94  of tab  90  is cantilevered beyond edge  92  of negative electrode strip  70 . This tab portion, as will be described hereinafter, is utilized to mechanically and electrically connect to an endcap for closing a battery case.  
         [0047]    Attention is now called to FIG. 18, which illustrates a preferred technique for closing the jellyroll assembly  84 . That is, the bared end  88  of the negative electrode substrate  72  extending beyond the negative active material coat  78  is draped over the next inner layer of the jellyroll assembly  84 . The end  88  can then be secured to the next inner layer, e.g., by appropriate adhesive tape  96 . One such suitable adhesive tape is DuPont Kapton® polyimide tape. It is important to note that the outer end configuration  88  of the negative electrode strip  70  enables the outer radius dimension of the jellyroll assembly  84  to be minimized as shown in FIG. 18. More particularly, by baring the substrate  72  beyond the active material  78 , the tape  96  is able to secure the substrate end without adding any radial dimension to the jellyroll assembly. In other words, if the outer end of the substrate were not sufficiently bared, then the tape  96  would need to extend over the active material and thus add to the outer radius dimension of the jellyroll  84 . Furthermore, the bare substrate  72  is more flexible than the substrate coated with active material  78  and conforms more readily to the jellyroll assembly  84 , making it easier to adhere it to the surface of the jellyroll. These space savings, although seemingly small, can be clinically important in certain medical applications. It should be noted that the electrode need only be bared at an end portion long enough to accommodate the tape  96 , as shown in FIG. 18. Because the uncoated substrate does not function as an electrode, it would waste space in the battery to bare any more than necessary to accommodate the tape. In a preferred embodiment, the length of uncoated substrate is between 1 and 8 mm, and more preferably about 2 mm.  
         [0048]    [0048]FIG. 19 depicts the completed jellyroll assembly  84  and shows the cantilevered tab portion  94  prior to insertion into a battery case body  100 . The case body  100  is depicted as comprising a cylindrical metal tube  101  having an open first end  104  and open second end  106 . Arrow  107  represents how the jellyroll assembly  84  is inserted into the cylindrical tube  101 . FIG. 20 depicts the jellyroll assembly  84  within the tube  101  with the cantilevered negative electrode tab  94  extending from the case open second end  106 . The case open first end  104  is closed by the aforementioned header  14  of the pin subassembly  10  shown in FIGS. 1 and 2. More particularly, note that the metal hollow member  22  is configured to define a reduced diameter portion  108  and shoulder  110 . The reduced diameter portion  108  is dimensioned to fit into the open end  104  of the cylindrical tube  101  essentially contiguous with the tube&#39;s inner wall surface. The shoulder  110  of the hollow member  22  engages the end of the case tube  101 . This enables the surfaces of the reduced diameter portion  108  and shoulder  110  to be laser welded to the end of the case  100  to achieve a hermetic seal.  
         [0049]    Attention is now directed to FIGS.  21 - 24 , which depict the tab  94  extending from the second open end  106  of the case tube  101 . Note that the tab  94  extends longitudinally from the body close to the case tube adjacent to tube&#39;s inner wall surface. In accordance with a preferred embodiment of the invention, the tab  94  is welded at  110  to the inner face  112  of a circular second endcap  114 . In accordance with a preferred embodiment, the tab  94  is sufficiently long to locate the weld  110  beyond the center point of the circular endcap  114 . More particularly, note in FIGS.  21 - 24  that by locating the weld  110  displaced from the center of the cap  114 , the tab  94  can conveniently support the endcap  114  in a vertical orientation as depicted in FIG. 22 misaligned with respect to the open end  106 . This end cap position approximately perpendicular to the end  122  of the case  100  is a first bias position wherein the end cap advantageously tends to remain in that orientation with the case end open prior to filling. To further describe the relationship between the weld location and the various components, FIG. 23 shows a front view with various dimensions. L represents the length from the weld  110  to the top of the case  100  as measured parallel to the edge of the case. R is the radius of the end cap  114 . For the preferred geometry, L≦2R. Weld  110  is preferably made above the center point  111  of the end cap  114 . Preferably, the end cap  114  overlaps the case  100  by approximately R/2. By configuring the tab  94  and weld  110  as indicated, the endcap  114  can be supported so that it does not obstruct the open end  106 , thereby facilitating electrolyte filling of the case interior cavity via open end  106 . A filling needle or nozzle can be placed through open end  106  to fill the case. This obviates the need for a separate electrolyte fill port, thereby reducing the number of components and number of seals to be made, thus reducing cost and improving reliability. Furthermore, for small medical batteries, the end caps would be very small to have fill ports therein. In a preferred embodiment in which the case wall is very thin, for example, 0.002 inches, providing a fill port in the side wall of the case would be impractical. Even in the case of larger devices where space is less critical and the wall is more substantial, providing a fill port in the side of the case would mean the electrolyte would have a very long path length to wet the jellyroll. Note that while the case could be filled with electrolyte prior to welding tab  94  to endcap  114 , it would be difficult and messy to do so. Therefore, it is advantageous to configure the tab  94  and weld  110  as described to allow the weld to be made prior to filling.  
         [0050]    Preferably before filling, a bottomside electrode insulator (not shown), which may comprise a thin disk of DuPont Kapton® polyimide film, is installed into the case between the rolled electrode assembly and the still open end of the battery case.  
         [0051]    In a preferred filing method, there is a channel of air between the pin and the crimped or welded C-shaped mandrel, which is used as a conduit for quickly delivering the electrolyte to the far end of the battery and to the inside edges of the electrodes within the jellyroll. Filling from the far end of the battery prevents pockets of air from being trapped, which could form a barrier to further filling. This facilitates and speeds the filling process, ensuring that electrolyte wets the entire battery.  
         [0052]    Thereafter, the flexible tab  94  can be bent to the configuration depicted in FIG. 24. Note that the endcap  114  is configured similarly to header hollow member  22  and includes a reduced diameter portion  118  and a shoulder  120 . The reduced diameter portion snugly fits against the inner surface of the wall of tube  101  with the endcap shoulder  120  bearing against the end  122  of the cylindrical case  100 . The relatively long length of the tab  94  extending beyond the center point of the endcap surface  112  minimizes any axial force which might be exerted by the tab portion  94  tending to longitudinally displace the endcap  114 . The end cap position covering the end  122  of the case  100  is a second bias position wherein the end cap advantageously tends to remain in that orientation prior to welding. With the endcap in place, it can then be readily welded to the case wall  101  to hermetically seal the battery. With tab  90  welded to negative substrate  72  and with the negative electrode strip  70  as the outermost layer of the jellyroll, the endcap  114  becomes negative. In turn, welding the endcap  114  to the case  100  renders the case negative.  
         [0053]    From the foregoing, it should now be appreciated that an electric storage battery construction and method of manufacture have been described herein particularly suited for manufacturing very small, highly reliable batteries suitable for use in implantable medical devices. Although a particular preferred embodiment has been described herein and exemplary dimensions have been mentioned, it should be understood that many variations and modifications may occur to those skilled in the art falling within the spirit of the invention and the intended scope of the appended claims.

Technology Category: 5