Patent Document

CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from U.S. provisional application Ser. No. 60/888,179, filed Feb. 5, 2007. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention pertains generally to an apparatus and method for manufacturing components for implantable medical devices such as batteries or capacitors. More particularly, the present invention relates in one embodiment to thermal encapsulation of a battery or capacitor electrode within a protective polymer film. 
         [0004]    2. Description of Related Art 
         [0005]    Devices for heat sealing a variety of objects within thermoplastic films are generally known. Additionally, the sealing of capacitor and battery electrodes within thermoplastic films is also known. The encapsulation of an electrode within a porous polymer film is also known. The film provides a physical separation between the electrode, and an associated opposite polarity electrode, thereby preventing a short circuit between the electrodes. 
         [0006]    Conventional thermal encapsulation systems generally are capable of cutting and sealing low melting point thermoplastic polymers such as polypropylene, but are not effective at processing polytetrafluoroethylene (PTFE) and similar high melting temperature fluoropolymers. However, subsequent capacitor or battery manufacturing processes after electrode encapsulation, such as case welding, occur at high temperatures. Low melting polymer separator films can be damaged during these processes, resulting in product that must be scrapped. Additionally, the hard materials and sharp edges of the components used in these systems may damage the separator film during the encapsulation process, or during removal of the encapsulated electrode from the encapsulation apparatus. 
         [0007]    There are also no provisions for applying tension to the film to take up slack immediately prior to contact by the heating element of the apparatus, or for accommodating variances in thickness between electrodes being processed. Conventional systems are set up to encapsulate an electrode having the upper limit of the thickness tolerance. This results in some electrodes having encapsulating films that are loosely fitted. 
         [0008]    What is needed, therefore, is a thermo-encapsulating apparatus and method that is capable of providing a tight fitting defect-free encapsulation of an electrode in a high melting point thermoplastic material. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention meets the above-described needs by providing an apparatus and method for cutting and heat sealing polytetrafluoroethylene film and other high melting separator sheet materials enveloping individually shaped cathodes, anodes or other active components, for use in batteries or capacitors and other implantable medical devices. 
         [0010]    The apparatus includes an electrode holding fixture and a heater assembly. The electrode holding fixture is comprised of a platen having an upper surface and a lower surface; an electrode holding die disposed on the upper surface of the platen and including an elastic body having an upper surface and a pocket formed in the elastic body. The pocket has an upper portion, a lower portion, and a wall surface shaped to correspond to the perimeter of the electrode. An electrode support is disposed in the lower portion of the pocket of the elastic body and comprises an upper surface and a lower surface. 
         [0011]    The heater assembly is comprised of a dielectric base having an upper plate portion and a lower plate portion, the lower plate portion providing a heater channel formed therein; and a heating element including an upper portion disposed in the heater channel of the dielectric base and a lower portion extending beyond the lower surface of the base and comprising a cutting edge and a shoulder. A portion of the heating element is shaped to match a corresponding portion of the wall surface of the pocket of the elastic body. The heater assembly is operatively associated with the electrode holding fixture such that when they are pressed together, the cutting edge and shoulder of the heater element cuts and seals the separator material between the upper surface of the elastic body and the heater element. The dielectric base is preferably formed from a machinable ceramic material. 
         [0012]    The electrode holding die may be further comprised of a base plate that is joined to the platen. The electrode support is preferably made of a dielectric material, and may be shaped to correspond to the perimeter of the electrode. The electrode support is also preferably movable within the pocket of the elastic body. When the electrode is wrapped or enveloped in the sheet of separator material and disposed in the pocket of the elastic body, the electrode support is forced against the sheet of separator material by at least one spring in contact with the lower surface of the electrode support. 
         [0013]    In another embodiment, the apparatus includes an ejection tool for ejecting an electrode disposed in the pocket of the elastic body. The ejection tool comprises a piston disposed in a cavity in the electrode support, a shaft having an upper portion connected to the piston and passing through a hole in the electrode support, and a lower portion passing through a hole in the platen. The ejection tool is preferably connected to an actuator, which may include a lever and fulcrum assembly. 
         [0014]    The elastic body of the electrode holding die may be made of a polysiloxane elastomer. The elastic body may further include a clearance notch extending from the wall surface of the pocket to the outer sidewall of the elastic body. The clearance notch is positioned to receive a wire contact extending from the electrode. The notch, in combination with an associated tab on the heating element, enables sealing of the separator sheet around the wire. 
         [0015]    The apparatus preferably further comprises a film tensioning block mounted on the lower surface of the insulative base. The film tensioning block is operatively associated with the elastic body. When the heater assembly and electrode holding fixture are pressed together, the elastic body and the film tensioning block pinch the portion of separator material engaged between them and apply tension to the sheet of separator material wrapped around the electrode. In order for the tension to be more strongly applied to the separator material, a friction-reducing film such as polyamide may be disposed on the upper surface of the elastic body. The apparatus may also include a tool for immobilizing the proximal and distal ends of the sheet of separator material prior to pressing of the heater assembly and the electrode holding fixture together. 
         [0016]    The heater assembly may be joined to a suspension plate, with standoffs disposed between them. In like manner, the electrode holding fixture may be joined to a mounting base, with standoffs separating them in order to limit heat conduction to the mounting base. The electrode holding fixture may also be mounted on a slide assembly so that it can be withdrawn from beneath the heater assembly to enable easy loading of an electrode and separator film into the pocket of the elastic body. 
         [0017]    The present method for cutting and heat sealing a separator film around individually shaped electrodes is performed with the above apparatus and comprises placing a sheet of separator material on the upper surface of the elastic body; placing an electrode having a perimeter corresponding to the shape of the pocket upon the sheet of separator material in alignment with the pocket; forcing the electrode downwardly into the pocket, thereby drawing the separator sheet down into the pocket into contact with the electrode support; folding a distal portion of the separator sheet over the electrode and into contact with a proximal portion of the separator sheet; energizing the heating element; and bringing the heater assembly into contact with the electrode holding fixture with sufficient pressure to cut and seal the separator material between the upper surface of the elastic body and the heating element. 
         [0018]    The apparatus and method of the present invention are advantageous over the prior art particularly because they are effective for processing high temperature separator materials requiring temperatures of from about 100° C. to about 500° C. for being thermally cut and sealed. That way, the present apparatus and method enables the manufacturing of electrodes enveloped in separator materials that have a relatively higher melting point, such as polytetrafluoroethylene, which is cut and sealed at a temperature of about 400° C. These separator materials are much more resistant to damage during subsequent high temperature manufacturing processes such as case welding. The present invention also results in the production of electrodes with more tightly fitting, defect-free separator films having a minimal flap or flashing at the electrode perimeter. 
         [0019]    Additional objects, advantages, and characterizing features of the present invention will become increasingly more apparent upon a reading of the following detailed description together with the included drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    The present invention will be described by reference to the following drawings, in which like numerals refer to like elements, and in which: 
           [0021]      FIG. 1  is a perspective view of one apparatus for cutting and heat sealing a separator film around an electrode; 
           [0022]      FIG. 2  is an upper perspective view of the electrode holding fixture of the assembly of  FIG. 1 , joined to a mounting base and mounted on a slide; 
           [0023]      FIG. 3  is a lower perspective view of a heater assembly and suspension plate of the apparatus of  FIG. 1 ; 
           [0024]      FIG. 4  is an exploded view of the electrode holding fixture of  FIG. 2 ; 
           [0025]      FIG. 5  is a perspective view of the electrode holding die of the electrode holding fixture of  FIG. 2 ; 
           [0026]      FIG. 5A  is a detailed view of a clearance notch in the electrode holding die positioned to receive a wire extending from an electrode; 
           [0027]      FIG. 5B  is a detailed view of the clearance notch of  FIG. 5A  being deformed by the wire when a tab of the heating element presses downwardly on the wire; 
           [0028]      FIG. 6  is an exploded view of the heater assembly of  FIG. 3 ; 
           [0029]      FIG. 7  is a perspective view of a heating element used in the heater assembly; 
           [0030]      FIG. 7A  is a detailed view of a terminal of the heating element of  FIG. 7 ; 
           [0031]      FIG. 7B  is a cross-sectional view of the cutting and sealing region of the heating element taken along line  7 B- 7 B of  FIG. 7 ; 
           [0032]      FIG. 8  is a perspective view of an apparatus for cutting and heat sealing a separator film around an electrode, shown with the electrode and separator film loaded in a pocket of the electrode holding die; 
           [0033]      FIG. 8A  is a side elevation view of a portion of the heater assembly and suspension plate of the apparatus of  FIG. 1 , with a partial cutaway view showing the contact between a thermocouple and the upper surface of the heating element; 
           [0034]      FIG. 9  is a cross-sectional view taken along the line  9 - 9  of  FIG. 8 ; 
           [0035]      FIG. 9A  is a detailed cross-sectional view of a first portion of the sealing region and a film tensioning block of the apparatus; 
           [0036]      FIG. 10  is a cross-sectional view of the apparatus taken along line  10 - 10  of  FIG. 8 , and depicting the piston of the electrode ejection tool and the electrode support forced against the separator film and the lower surface of the electrode; 
           [0037]      FIG. 10A  is a detailed cross-sectional view of a second portion of the sealing region of the apparatus; and 
           [0038]      FIG. 11  is a side elevation view of the ejection tool and actuator for ejecting an electrode disposed in the pocket of the elastic body. 
       
    
    
       [0039]    The present invention will be described in connection with preferred embodiments, however, it will be understood that there is no intent to limit the invention to the embodiments described. On the contrary, the intent is to cover all alternatives, modifications, and equivalents as may be included within the scope of the invention as defined by the appended claims. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0040]    In the following description, the terms “separator film,” “separator sheet,” and “sheet of separator material” are used interchangeably, and are meant to indicate a relatively thin material that provides physical separation between a first electrode and an associated opposite polarity electrode, thereby preventing a short circuit between the electrodes. Exemplary power sources comprising opposite polarity electrodes include a capacitor or a battery. 
         [0041]    Referring now to the drawings,  FIGS. 1 to 3  illustrate the present thermo-encapsulation apparatus  10  comprised of an electrode holding fixture  100  and a heater assembly  200 . The electrode holding fixture  100  may be joined to a mounting base  20  comprised of one or more rigid plates  22 ,  24  and  26 . Electrode holding fixture  100  is preferably separated from mounting base  20  by standoffs  28 ,  30 ,  32  and  34  in order to thermally isolate the fixture  100  and to provide clearance for an electrode ejection tool  190 , which will be subsequently described herein. 
         [0042]    Electrode holding fixture  100  and mounting base  20  may also be mounted on a slide assembly  40  comprised of a plate  42 , outer guide rails  44  and  46 , and a center rail  48 . Electrode holding fixture  100  is horizontally movable along plate  42 , as indicated by bidirectional arrow  99 . This is done by manipluating handle  50 . In that manner, the electrode assembly  100  is withdrawn from beneath the heater assembly  200  to enable easy loading of an electrode and separator film therein. A proximity sensor  21  is provided to detect the correct positioning of the electrode holding fixture  100  beneath the heater assembly  200  prior to heat sealing. 
         [0043]    The heater assembly  200  is preferably joined to a suspension plate  60  with standoffs  62 ,  64 ,  66  and  68  disposed there between. The standoffs thermally isolate heater assembly  200  from suspension plate  60 . 
         [0044]    The thermo-encapsulating apparatus  10  also comprises a main block  80  upon which the slide assembly  40  is mounted. The main block  80  further includes posts  82  and  84 . A linear actuator (not shown) such as a pneumatic or hydraulic cylinder, or a linear stepper motor may be mounted on posts  82  and  84  and operatively connected to the heater assembly  200 . The linear actuator is used to lower the heater assembly  200  and bring it into contact with the electrode holding fixture  100  during the heat sealing process. 
         [0045]    The electrode holding fixture  100  will now be described with particular reference to  FIGS. 2 ,  4  and  5 . Electrode holding fixture  100  is comprised of a platen  102 , an electrode holding die  110  and an electrode support  140 . Platen  102  has an upper surface  104  and a lower surface  106 . Electrode holding die  110  is disposed on the upper surface  104  of the platen  102  and includes a deformable body  112 , preferably of an elastomeric material, having an upper surface  114  with a pocket  116  formed therein. The pocket  116  has an upper portion  118 , a lower portion  119  and a wall surface  120  shaped to correspond to the perimeter  4  of an electrode  2 . 
         [0046]    Electrode holding fixture  100  is further comprised of the electrode support  140  disposed in the lower portion  119  of the pocket  116  of the elastic body  112 . The electrode support  140  includes an upper surface  142  and a lower surface  144  and is preferably made of a dielectric material that is both electrically and thermally insulative. The electrode support  140  is preferably shaped to correspond to the perimeter  4  of the electrode  2  which it supports. That is to provide uniform support and thermal contact with electrode  2  during heat sealing. The dielectric material may be a machinable glass ceramic such as mica or MACOR®, which is manufactured and sold by Corning Inc. of Corning N.Y. Other structurally strong, heat-resistant ceramics that can be cast and fired to near net shape may also be used. 
         [0047]    The electrode holding die  110  may be comprised of a base plate  122  that is joined to the platen  102  with suitable fasteners (not shown). The elastic body  112  is molded to the base plate  122 . A recess or step  304  provided in the upper surface  104  of the platen  102  has a depth sufficient to receive the electrode holding die  110  therein. That sub-assembly has the spaced apart outer upper surfaces  306  of the platen  102  being substantially coplanar with the upper surface  124  of the holding die base plate  122 . 
         [0048]    The elastic body  112  is made of a heat-resistant elastomer having a relatively low thermal conductivity that is capable of recovering relatively quickly to its former shape from a deformation force. One preferred elastomer is a polysiloxane elastomer, commonly known as silicone rubber, having a Shore A durometer of between about 40 to about 90. Urethane is another suitable elastomer for this purpose. 
         [0049]    Turning now to  FIGS. 3 and 6 , the heater assembly  200  is comprised of an upper platform  202  to which a base plate  204  of a dielectric material is secured by fasteners (not shown). Inner and outer hold-down plates  206  and  208  are, in turn, secured to the base plate  204  to hold a heating element  230  in place. The dielectric base plate  204  and the inner and outer hold-down plates  206 ,  208  are preferably formed from a machinable ceramic material, such as MACOR® or mica. Details of the heating element  230  are shown in  FIGS. 6 ,  7 ,  7 A and  7 B. It is noted that in these drawings, the heating element  230  has been inverted from its installed position on the base plate  204  of the heater assembly  200 . This was done to more clearly show key features thereby. As shown, the T-shaped heating element  230  is comprised of a cutting and sealing portion  232  that extends from terminal  234  to terminal  236 . The cutting and sealing portion  232  includes a proximal head  238 , a cutting edge  240  and a sealing shoulder  242 . The cutting edge  240  and sealing shoulder  242  provide for cutting and sealing the separator film around the electrode, as will be explained subsequently. The head portion  238  includes relatively small flanges  238 A,  238 B that provide the heating element its T-shaped structure. The head portion  238  supported on the base plate  204  is held in position thereon by the edges  206 A,  208 A of the outer and inner hold-down plates  206 ,  208  capturing the respective flanges  238 A,  238 B. 
         [0050]    Heating element  230  is formed approximately in an omega (Ω) shape. Its cutting and sealing portion  232  is shaped to match a corresponding portion of the wall surface  120  of the pocket  116  of the elastic body ( FIG. 5 ) which, in turn, corresponds to the shape of the electrode perimeter  4  being sealed in a separator film. In this manner, heating element  230  cuts and seals the separator film around the perimeter of the electrode except for the portion that is wrapped around the straight edge of the electrode, i.e., the “open” portion of the omega shape between the terminals  233  and  235 . 
         [0051]    Heating element  230  may also include an additional central terminal  244  for a more secure attachment to the base plate  204 . Fasteners, which are partially shown in  FIG. 3 , engage with through holes in the terminals  234 ,  236  and  244  to secure the heating element  230  to the dielectric base  204 . The relatively large terminals  234 ,  236  and  244  also provide for easy connection to power supply wires (not shown). Additionally, the terminals  234 ,  236  and  244  prevent hot spots in the heating element at the terminals, thereby providing better control of the heat sealing process. 
         [0052]    The base plate  204  and the inner and outer hold-down plates  206 ,  208  are joined to the upper platform  202  by fasteners  222  (only shown for plates  204  and  208  in  FIG. 3 ) that are preferably countersunk therein. Then, when there is a need in manufacturing to process electrodes with a different shape, only heating element  230  and the hold-down plates  206 ,  208  need to be changed. The platform  202  and the base plate  204  are provided with a sufficient number of threaded openings to accommodate such changeovers. In a like manner and with regard to the electrode holding fixture, only the electrode holding die  110  and the electrode support  140  need to be changed. That way, the manufacturing changeover to process a different electrode batch is made faster, simpler, and lower in cost compared to prior heat sealing systems. 
         [0053]    The upper platform  202  of the heater assembly  200  is further provided with notches  214  and  216  ( FIG. 6 ) and a large through hole  218  for receiving polymeric plugs  223 ,  225  and  227 , respectively. The polymeric plugs  223 ,  225  and  227  provide stress relief to reduce the likelihood of cracking the dielectric base plate  204  at the fasteners. 
         [0054]    Certain additional preferred features of the thermo-encapsulating apparatus  10  will now be described along with the method for using the apparatus, and the advantages thereof.  FIG. 8  is a perspective view of the apparatus shown with an electrode and separator sheet loaded in a pocket of the electrode holding die. 
         [0055]    To begin the process, the electrode holding fixture  100  is withdrawn from beneath the heater assembly  200  using slide assembly  40  ( FIG. 1 ). A piece of separator sheet  3  is placed over the pocket  116  in the elastic body  112  of the electrode holding die  110 . An electrode  2  having a perimeter  4  corresponding to the shape of the pocket  116  is placed upon the sheet  3  in alignment with the pocket. The electrode  2  is then forced downwardly into the pocket  116 . This draws the separator sheet  3  down into pocket. The separator sheet  3  is now in contact with the electrode support  140  and is contiguous with the wall surface  120  of the pocket  116  in the elastic body  112 . 
         [0056]    Referring also to  FIG. 9A , a distal portion  5  of the separator sheet  3  is folded over the top surface  6  of the electrode  2 , thereby fully enveloping electrode  2  in the separator sheet. Apparatus  10  preferably also includes a tool  160  ( FIG. 8 ) for immobilizing the ends of the respective distal and proximal portions  5 ,  7  of the sheet  3  prior to pressing the heater assembly  200  and the electrode holding fixture  100  together. Holding tool  160  is comprised of an elongated rod  162  that is operatively connected to a handle  163 . Handle  163  is joined to the fulcrum  164  by a pin  165 . The fulcrum  164  is joined to the base  161 , which in turn is joined to the platen  102 . Tool  160  further comprises a spring loaded plunger  166  embedded in the handle  163 . 
         [0057]    To immobilize and hold the ends of the distal and proximal separator sheet portions  5 ,  7 , handle  163  is pressed downwardly, thereby raising the elongated rod  162  above the upper surface  124  of the base plate  122 . The ends of the distal and proximal portions  5 ,  7  of the sheet  3  are placed beneath rod  162 , and the handle  163  is released. The plunger  166  then forces handle  163  upwardly, as indicated by arrow  98 . By the action of fulcrum  164 , the rod  162  is forced downwardly, as indicated by arrow  97 , thereby pinching and immobilizing the ends of sheet  3  against the base plate  122 . 
         [0058]    It is noted that electrodes for electrochemical capacitors and batteries used to power implantable medical devices typically have a perimeter with at least one relatively straight portion. Referring also to  FIGS. 4 and 5 , pocket  116  in the elastic body  112  is provided with a corresponding straight portion  117  of wall  120 , which is distally positioned with respect to the rod  162  of the holding tool  160 . Thus, the fold of the separator sheet to form the wrap around electrode  2  is preferably made along the straight portion  117  and around the corresponding straight edge of electrode  2 . In that manner, puckers and wrinkles in the separator sheet prior to sealing are minimized. 
         [0059]    In the preferred embodiment, the electrode support  140  is also movable within the pocket  116  of the elastic body  112  and is continually forced upwardly. That way, when the electrode  2  is wrapped in the separator sheet  3  and disposed in the pocket  116  of the elastic body  112 , the electrode support  140  is forced against the separator material. In that manner, electrodes having a substantial variation in their thickness can be processed in the apparatus  10  and tightly sealed in the separator film. 
         [0060]    Referring in particular to  FIGS. 4 and 10 , springs  141  and  143  are provided for applying an upward force on the electrode support  140 . The respective outer ends  145  and  146  of the springs  141  and  143  abut against the bottoms of respective upper counterbores  101  and  103  in the platen  102 . The respective inner ends  147  and  148  of the springs  141  and  143  are in contact with the lower surface  144  of the electrode support  140  to thereby apply an upward bias thereto, as indicated by arrows  96 . Shoulder bolts  151  and  152  pass through holes that continue in platen  102  from the upper counter bores  101  and  103  to the lower counterbores  105  and  107 . The shoulder bolts  151  and  152  are engaged with threaded holes in the electrode support  140  and serve as locators for maintaining the springs  141  and  143  in position. 
         [0061]    As indicated by bidirectional arrows  95 , electrode support  140  thus “floats” within the lower portion  119  of the pocket  116 . Its upward travel is stopped when the heads of bolts  151  and  152  bottom out in the lower counterbores  105  and  107 , and its downward travel is stopped when surface  144  contacts surface  104  of the platen  102 . When electrode  2  and separator sheet  3  are first loaded into pocket  116 , the upper surface  6  of the electrode  2  is above the upper surface  114  of the elastic body  112 , and the bolt heads  151  and  152  bottom out in the lower counterbores  105  and  107 . However, during the heat sealing step, when the heater assembly  200  is pressed against the electrode holding fixture  100 , the lower surface  206  of the housing plate  220  pushes down on the separator sheet  3  and electrode  2  until the upper electrode surface  6  is substantially coplanar with the upper surface  114  of the elastic body  112 . This occurs regardless whether there is a substantial thickness variation between individual electrodes being sealed, with springs  141  and  143  compressing as needed to adjust the position of electrode support  140 . (However, the maximum electrode thickness is ultimately limited to the depth of the pocket minus the sum of the electrode support and twice the separator sheet thickness.) 
         [0062]    It is also noted that the fit of the electrode  2  and separator film  3  in pocket  116  is snug, thereby providing a very tight fit of the separator film around the electrode as compared to prior art sealing apparatus. However, the silicone rubber material of the elastic body  112  is sufficiently soft so that in spite of the tight fit, damage to the separator sheet  3  by the relatively hard electrode  2  is minimized. 
         [0063]    It will be apparent that other spring arrangements can be used to achieve the same result of a floating electrode support. For example, the electrode support  140  and the platen  102  can be configured to have a single spring disposed in a counterbore around the shaft  184  of the ejection tool  180 . Alternatively, other springs such as leaf springs could be used. 
         [0064]    With the electrode  2  and separator sheet  3  loaded into the pocket  116  of the elastic body  112 , and with the ends of the separator sheet held down, the heat sealing step is now performed. The electrode holding fixture  100  is replaced beneath the heater assembly  200  using slide assembly  40 . The heating element  230  is energized by an electrical power supply (not shown) and heated to the desired temperature. Referring now to  FIG. 8 , heater assembly  200  is lowered, as indicated, by a suitable linear actuator (not shown), until the heating element  230  contacts the separator material on the upper surface  114  of the elastic body  112 . Heater assembly  200  is preferably provided with a pair of guide pins  224  and  226  ( FIG. 3 ). Guide pin has a “key” shape while guide pin  226  has a cylindrical shape and they engage with respectively shaped holes  109  and  309  in the platen  102 . In this manner, the heating element  230  is precisely brought into contact with the upper surface  114  of the elastic body  112  in the required position with respect to the perimeter  4  of electrode  2 . 
         [0065]    Referring also to  FIG. 8A , the thermo-encapsulating apparatus  10  may also include a temperature sensing device, such as thermocouple probe  270 , that is provided for measuring and controlling the temperature of the heating element  230 . This is important because the present thermo-encapsulating apparatus  10  is useful for enveloping an electrode structure in a variety of separator materials having a wide range of melting temperatures. Typical separators are of a polymeric material requiring temperatures of from about 100° C. to about 500° C. for being thermally sealed. One preferred material is polytetrafluoroethylene, which is sealed at a relatively high temperature range of about 200° C. to about 500° C., preferably about 400° C. Polyethylene is another preferred separator material that is sealed at a temperature range of about 130° C. to about 250° C. However, those skilled in the art will be able to readily determine at what temperature a particular polymeric material melts. That way, the present apparatus  10  makes it possible to regulate the temperature at which the separator sheet portions  5 ,  7  are fused to each other during the sealing step of the process. 
         [0066]    Thermocouple probe  270  is comprised of a female connector  272 , a male connector  274 , and a protective sheath  276  extending from the distal end  278  of connector  274 . The male connector  244  may be secured to a mounting block  275 , which in turn is secured to upper dielectric plate  203  by suitable fasteners (not shown). 
         [0067]    A pair of thermocouple wires (not shown) is connected to spades  280 ,  281  that extend from the proximal end  282  of the male connector  274 . These thermocouple wires are insulated, and extend through the protective sheath  276 , which is typically a thin-walled metallic tube. Within the distal tip  284  of sheath  276 , the thermocouple wires are joined to form the thermocouple junction, which is the point at which the temperature measurement is made by probe  270 . The thermocouple wires may be made of chromel and alumel alloys, thereby providing a K-type thermocouple. 
         [0068]    Spades  280  and  281  are insertable into corresponding receptacles that are connected to a pair of terminals (not shown) in female connector  276 . Additional thermocouple wires (not shown) are connected to these respective terminals, and extend out through a strain relief bushing  286 . These thermocouple wires in turn are connected to a thermocouple circuit board (not shown) that detects the voltage potential produced at the thermocouple junction and converts the potential into temperature data. This type of thermocouple instrument is well known and is manufactured and sold commercially by various companies such as Omega Engineering of Stamford, Conn. 
         [0069]    Small bores (not shown) are provided through the upper platform  202  and the base plate  204  for receiving the distal portion  288  of sheath  276 . The distal portion  288  extends downwardly through the bores so that its distal tip  284  is in direct contact with the proximal head  238  of the heating element  230 . In that manner, an accurate and responsive measurement of the temperature of the heating element  230  can be made by the thermocouple probe  270 . In one preferred embodiment, the proximal head  238  of heating element  230  and at least the distal portion  288  of the sheath  276  are coated with a thin film of electrically insulative and thermally conductive material that is unaffected by high temperatures. One suitable thin film coating is diamond-like carbon (DLC). 
         [0070]    It will be apparent to those skilled in the art that other known temperature measurement probes may be used instead of probe  270  to measure the temperature of heating element  230 . For example, a platinum resistance thermometer (PRT) may be used in a similar configuration. 
         [0071]      FIG. 10A  is a detailed cross-sectional view of the pressing of the sealing portion of the heating element against the separator sheet and the elastic body  112  near the perimeter of the electrode. As the cutting edge  240  of the heating element  230  cuts the overlapping layers  5  and  7  of separator sheet, the sealing shoulder  242  faces the electrode  2  and firmly presses a narrow band of the separator layers together. Then, the layers  5  and  7  are fused together under high pressure and heat at the shoulder  242 , thereby enveloping the electrode  2  within the separator sheet  3 . It can be seen that the upper surface  114  of the elastic body  112  near heating element  230  is elastically deformed during cutting and sealing. This deformation is reversed when the heating element  230  is removed. 
         [0072]    The apparatus preferably further comprises a film tensioning block  170  mounted on the outer hold-down plate  208 . The tensioning block is operatively associated with the elastic body  112 . When the heater assembly and the electrode holding fixture are pressed together, the elastic body  112  and the film tensioning block  170  pinch the separator portions  5 ,  7  together and apply tension to the separator material wrapped around the electrode  2 . 
         [0073]    Referring to  FIGS. 3 ,  9  and  9 A, film tensioning block  170  is joined to the outer hold-down plate  208 . The inner sidewall  172  of the tensioning block  170  is positioned with respect to the outer sidewall  121  of the elastic body  112  so that when the heater assembly  200  and electrode holding fixture  100  are pressed together, a gap is formed between them. The gap width is slightly less than two times the thickness of the separator film, so that the distal and proximal separator sheet portions  5 ,  7  are pinched between the sidewalls  121  and  172  during downward motion of the tensioning block  170 , as shown in  FIG. 9A . This downward motion results in a downward pulling of the distal and the proximal portions  5 ,  7  of the separator sheet  3 , as indicated by arrow  94 . This, in turn, results in tensioning of the distal and proximal separator portions  5 ,  7  around the electrode  2 , as indicated by arrow  93 . It is to be understood that the tensioning of the separator portions  5 ,  7  occurs immediately prior to contact of the heating element  230  with them, while they are still free to be displaced horizontally. Then, the cutting and sealing portion  232  of heating element  230  “bites” into the separator portions  5 ,  7 , cuts and seals them together as described previously. In this manner, a superior fit of the sealed separator sheet  3  to the electrode  2  is achieved. 
         [0074]    As shown in  FIG. 10A , in order for the tension to be more strongly applied to the separator material, a friction-reducing film  126  is provided on the upper surface  114  of the elastic body  112 . The friction reducing film has a lower coefficient of friction than the relatively “tacky” silicone rubber material of the elastic body  112 . This enables the proximal portion  7  of the separator material  3  to more easily slip along upper surface  114  during tensioning. In one embodiment, the friction reducing film is a polyimide. 
         [0075]    In a preferred embodiment, the elastic body of the electrode holding die includes a clearance notch positioned to receive a wire contact extending from the electrode. The notch, in combination with an associated tab on the heating element, enables sealing of the separator sheet around the wire. Referring to  FIGS. 5 ,  5 A and  5 B, clearance notch  130  is located in elastic body  112  in a position corresponding with the contact wire  9  extending laterally from the electrode  2 . This is typically in the “corner” of the electrode, i.e. where the straight edge of the electrode intersects the curved portion. Clearance notch  130  extends from pocket wall surface  123  to the outer sidewall  125  of the elastic body  112  and includes a recessed portion  128 , a wire sealing portion  132  and a barrier portion  134 . 
         [0076]    The bottom surfaces of wire sealing portion  132  and barrier portion  134  form a contiguous surface  133 . The wire  9  rests upon the separator sheet when the electrode  2  and the separator sheet  3  are first placed in the pocket  116  of the elastic body  112 . The separator sheet, in turn, rests upon notch surface  133 . (For the sake of simplicity of illustration, and in order to depict the interaction of wire  9  with notch  130 , the separator sheet is not shown in  FIG. 5B .) 
         [0077]    Referring also to  FIGS. 3 and 7 , heating element  230  is provided with a wire sealing tab  231  that is shaped to match the surfaces of the wire sealing portion  132  of clearance notch  130 . When heater assembly  200  is lowered and heating element  230  contacts the separator portions  5 ,  7  and the upper surface  114  of the elastic body  112 , sealing tab  231  contacts electrode wire  9  and pushes downwardly on it. The surface  133  of notch  130  deforms elastically as shown in  FIG. 5B , and the separator portions  5 ,  7  (not shown) disposed above and below wire  9  correspondingly deform as well. The heat from sealing tab  231  fuses the portions  5 ,  7  together proximate to the wire  9 . This provides a superior seal of the separator material around the wire  9 . The barrier portion  134  of notch  130  is made sufficiently narrow to prevent unwanted heat transfer inwardly from sealing tab  231  to the electrode  2 . 
         [0078]    The electrode  2  may include a J-bend  11 , a glass-to-metal-seal  12  and contact wire  14  joined to electrode wire  9  prior to the separator heat sealing process. These contacts are disposed in recessed portion  128  of the clearance notch  130  during sealing. If the glass-to-metal seal  12  is larger than the depth of the recessed portion  128 , the elastic body  112  will temporarily deform as needed where the seal contacts the recessed portion  128 . 
         [0079]    With the separator sheet  3  having been cut and sealed around the electrode  2  as described, the heater assembly  200  is now withdrawn upwardly from the electrode holding fixture  100 . The electrode holding fixture  100  with the electrode  2  sealed in the separator sheet  3  is withdrawn from beneath the heater assembly  200  using slide assembly  40  ( FIG. 1 ). The sealed electrode  2  is then removed from the pocket  116  of the elastic body  112 . 
         [0080]    Because of the tight fit of the electrode  2  and enveloping separator sheet  3  in the pocket  116  of the elastic body  112 , the thermo-encapsulating apparatus  10  preferably includes an ejection tool  180  for ejecting the sealed electrode from the pocket. Referring to  FIGS. 4 ,  9  and  11 , the ejection tool  180  is comprised of a piston  182  disposed in a cavity  154  in the electrode support, a shaft  184  having an upper portion  183  connected to the piston  182  and passing through a hole  156  in the electrode support, and a lower portion  185  passing through a hole  307  in the platen  102  of the electrode holding fixture  102 . The upper surface  187  of piston  182  is made large with respect to the size of electrode support  140 , and is provided with a radiused edge. These features prevent damage to the separator sheet  3  during ejection of the sealed electrode  2 . 
         [0081]    Although the ejection tool  180  may be operated by contact with an operator&#39;s finger, it is preferably connected to an actuator for easier operation. Referring to  FIGS. 9 and 11 , actuator  190  is comprised of a lever  191  that is connected to the ejection tool  180  by a pin  192 . The lever  191  is also connected to the platen  102  by a fulcrum block  193  and a pin  194 . When an operator pushes down on the handle  195  of lever  191  as indicated by arrow  92 , the ejection tool  180  moves upwardly as indicated by arrow  91 . This results in ejection of the sealed electrode  2 , as indicated by arrow  90 . A spring loaded plunger  196 , which is joined to the lever  191  and in contact with the bottom surface  106  of the platen  102 , provides a force on the lever  191  to return it to its home position. 
         [0082]    It is to be understood that while the present invention has been described in terms of “upper” and “lower” surfaces, and with the heater assembly located “above” the electrode holding fixture, there is no requirement that the apparatus be oriented and operated as shown with respect to gravity. These terms are simply used to indicate locations of certain elements with respect to each other and the appended drawings, and are not intended to be limiting with regard to the overall construction of the apparatus and its use. 
         [0083]    It is, therefore, apparent that there has been provided, in accordance with the present invention, an apparatus and method for thermal encapsulation of a battery or capacitor electrode within a protective polymer film. While this invention has been described in conjunction with preferred embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variations that fall within the broad scope of the appended claims.

Technology Category: 7