Apparatus for impact welding of battery terminals

Abstract

Disclosed herein is an apparatus for magnetic welding of battery pots, the apparatus comprising a coil holder; wherein the coil holder comprises one or more electrical coils operable to be energized by an electrical current; a foil holding fixture; wherein the foil holding fixture comprises a plurality of arms; wherein each pair of adjacent arms is operable to move towards each other to crimp a plurality of battery foils; and an anvil; wherein the anvil is operable to support a battery tab and the battery foils.

Description

TECHNICAL FIELD

[0001] Disclosed herein is an apparatus for impact welding of battery terminals. More specifically, disclosed herein is an apparatus for welding dissimilar metals to reduce defects and be more tolerant of surface oxides / contaminants. BACKGROUND

[0002] Lithium ion battery packs for vehicles and other high power applications can include a plurality of lithium ion battery cells electrically connected together. Each battery cell includes a plurality of lithium ion electrode pairs enclosed within a sealed pouch housing. Each electrode pair includes a negative electrode, a positive electrode, and a separator physically separating and electrically isolating the negative electrode and the positive electrode. To facilitate lithium ion migration, an electrolyte that conducts lithium ions can be present within the separator. The electrolyte allows lithium ions to pass through the separator between the positive and negative electrodes to balance the flow of electrons that move between the electrodes by an external circuit around the separator during charging and discharging cycles of the lithium ion battery cell. Depending on their chemistry, each lithium ion battery cell has a maximum or charge voltage (voltage at full charge) due to the difference in electrochemical potential of the electrodes. For example, each lithium ion battery cell can have a charge voltage in the range of 3V to 5V and a nominal open circuit voltage in the range of 3.5V to 4V. The lithium ion battery cells can be connected in series, in parallel, or in series and parallel, depending on the specified battery pack design.

[0003] The plurality of electrode pairs are electrically connected in parallel to electrochemically store and release electrical power. Each electrode pair includes an anode and a cathode with a separator disposed between the anode and the cathode. Each anode has an anode current collector with a negative tab and each cathode has a cathode current collector with a positive tab. The negative tabs of the anodes of the plurality of electrode pairs are electrically connected in parallel and are electrically connected to a negative terminal tab that protrudes through the pouch and the positive tabs of the cathodes of the plurality of electrode pairs are electrically connected in parallel and are electrically connected to a positive terminal tab that protrudes through the pouch.

[0004] Within each battery cell, the negative terminal tab is in electrical communication with a negative current collector that is in contact with and exchanges electrons with the negative electrode of the electrode pair and the positive terminal tab is in electrical communication with a positive current collector that is in contact with and exchanges electrons with the positive electrode of the electrode pair. The lithium ion battery cell is capable of discharging and recharging over many cycles.

[0005] The negative tabs of the anodes of the plurality of electrode pairs can be electrically connected in parallel and electrically connected to the negative terminal tab using laser welding. Likewise, the positive tabs of the anodes of the plurality of electrode pairs can be electrically connected in parallel and electrically connected to the positive terminal tab using laser welding.

[0006] Laser welding is a metal joining process in which a laser beam is directed at a stack of metal workpieces to provide a concentrated energy source capable of creating a fusion weld joint between overlapping constituent metal workpieces. Layers of metal workpieces can be stacked and aligned relative to one another such that their joining surfaces overlap to establish a joining interface (or joining interfaces) within an intended weld site. A laser beam is then directed at or near the top surface of the workpiece stack. The heat generated by the absorption of energy supplied by the laser beam initiates melting of the metal workpieces and establishes a molten weld pool within the workpiece stack. The molten weld pool penetrates the metal workpiece struck by the laser beam and into the underlying metal workpiece(s) to a depth that intersects all established joining interfaces. The laser beam rapidly creates a molten weld pool as it strikes the top surface of the workpiece stack. The molten weld pool solidifies to form a welded joint composed of resolidified material from all layers of metal workpieces. This fusion of material from overlapping layers of metal workpieces forms the welded joint.

[0007] It is known that laser weld fusion lines along the foil create porosity and / or cracks due to moisture absorbed by the oxide on the foil surface and tab surface. Ultrasonic pre-welding of the foil is used to consolidate the foil and remove some or all of the absorbed moisture and some of the oxide. Subsequently, laser welding of the tab / foil aligned to the pre-weld location will result in a weld with reduced porosity / cracking. Localized material porosity, which can manifest as gaps between layers in the workpiece stack and / or voids in one or more workpieces, can affect the service life of the welded joint, and thus the component comprising the welded joint. When the workpiece stack comprises multiple foils welded to a battery tab, the presence of localized material porosity can compromise the strength of the welded joint and affect the electrical conductivity between the one or more foils and the battery tab.

[0008] Accordingly, it is desirable to develop new methods for bonding battery foils to tabs or for bonding foils together. SUMMARY

[0009] Disclosed herein is an apparatus for magnetic welding of a battery boiler, the apparatus comprising a coil holder; wherein the coil holder comprises one or more electrical coils operable to be energized by an electrical current; a foil holding fixture; wherein the foil holding fixture comprises a plurality of arms; wherein each pair of adjacent arms is operable to move towards one another to crimp a plurality of battery foils; and an anvil; wherein the anvil is operable to support a battery tab and the battery foils.

[0010] In one embodiment, each pair of adjacent arms moves symmetrically about a vertical axis that passes through the coil.

[0011] In another embodiment, each pair of adjacent arms is positioned symmetrically about the one or more electrical coils.

[0012] In yet another embodiment, the coil holder further comprises a plurality of electrical coils; wherein each set of electrical coils is located at a different height from a surface of the coil holder.

[0013] In yet another embodiment, each electrical coil of the one or more electrical coils is energized by a different strength of electrical current.

[0014] In yet another embodiment, each set of electrical coils is energized by a different strength of electrical current.

[0015] In yet another embodiment, the coil holder comprises an electrically insulating material.

[0016] In yet another embodiment, the electrically insulating material comprises an organic polymer, a ceramic, or a combination thereof.

[0017] In yet another embodiment, the plurality of arms are transported along a guide rail; wherein the arms have a groove at a rear end that engages the guide rail.

[0018] In yet another embodiment, the coil holder is in communication with an electrical energy source.

[0019] In yet another embodiment, the plurality of arms comprise an electrically insulating material.

[0020] In yet another embodiment, each set of electrical coils energizes a bond in a different region of the electrical foil.

[0021] In yet another embodiment, different sets of electrical coils can be energized simultaneously.

[0022] In yet another embodiment, different sets of electrical coils can be energized sequentially.

[0023] Disclosed herein is a method comprising: placing a plurality of electrical foils of a battery in a foil holding fixture; crimping the plurality of electrical foils by moving at least one pair of adjacent arms of the foil holding fixture; energizing at least one electrical coil disposed on a crimped portion of the plurality of electrical foils; and bonding the electrical foils to one another.

[0024] In one embodiment, the plurality of electrical foils are supported on an anvil.

[0025] In another embodiment, a tab of the battery is placed under the electrical foils.

[0026] In yet another embodiment, the tab of the battery has a knurled surface, and wherein the knurled surface faces the electrical foils.

[0027] In yet another embodiment, the at least one pair of adjacent arms move symmetrically about a vertical axis that passes through the at least one electrical coil.

[0028] In yet another embodiment, different electrical foils of the plurality of electrical foils are energized sequentially to bond different portions of the foils.

[0029] The above features and advantages of the present disclosure, and other features and advantages, are readily apparent from the following detailed description when taken in connection with the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0030] Other features, aspects, and details are described below with reference to the drawings. The drawings are provided and are part of this specification and illustrate aspects and aspects of the present disclosure.

[0031] Figure 1 is an exemplary view of a battery;

[0032] Figure 2A is an exemplary view of a battery and a device to facilitate magnetic welding;

[0033] Figure 2B depicts an expanded view of a coil holder in an inverted position;

[0034] Figure 3 is an exemplary view of a coil holder holding multiple different coil sets;

[0035] Figure 4 is another exemplary view of a device to facilitate magnetic welding;

[0036] Figure 5A is another exemplary view of a device to facilitate magnetic welding;

[0037] Figure 5B is an exemplary view of a foil holding fixture having arms spaced as far apart as possible;

[0038] Figure 5C is another exemplary view of a foil holding fixture having opposing arms spaced closer to each other than in Figure 5B

[0039] Figure 6 is an exemplary view of foil before and after crimping. DETAILED DESCRIPTION

[0040] The following description is merely exemplary in nature and is not intended to limit the present disclosure, its application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

[0041] ​Disclosed herein is an apparatus and method of performing magnetic impulse welding (hereinafter magnetic welding) to join metal foils of a battery together and / or to join the metal foils to battery tabs. In one embodiment, the battery can be a lithium-ion battery. The apparatus advantageously includes a coil holder that holds a plurality of coils that generate a magnetic field, and a battery foil holding fixture on which metal tabs having knurled surfaces are disposed, and on which the foils are disposed during the welding process. In embodiments, the battery foil holding fixture includes a plurality of movable arms that can be moved back and forth with respect to each other to create a gap between the foils that allows the foils to contact each other and join to each other at a speed of 400 to 900 meters per second.

[0042] Before describing the apparatus and method for magnetic welding foils of a battery, a brief introduction to relevant parts of a battery is presented to enhance the understanding of the present disclosure.

[0043] Referring to the drawings, wherein like numerals refer to like or similar Figure 1 An embodiment of a prismatic lithium-ion battery cell 10 is schematically shown, which includes a plurality of electrode pairs 20 arranged in a stack and sealed in a flexible pouch 12 containing electrolytic material 13. A first positive battery cell tab 29 and a second negative battery cell tab 24 protrude from the flexible pouch 12. Each electrode pair 20 includes an anode 21 arranged on an anode (or negative) current collector 22 and a cathode 26 arranged on a cathode (or positive) current collector 27, and is separated by a separator 25. The cathode current collector 27 is made of aluminum or an aluminum alloy, and includes a positive foil (or cathode foil) 28. The anode current collector 22 is made of copper, a copper alloy, or another material, and includes a negative foil (or anode foil) 23.

[0044] The negative current collector 22 and the positive current collector 27 are thin metal plates that contact their respective negative electrode 21 and positive electrode 26 over a considerable interface surface area. The purpose of these metal current collectors 22, 27 is to exchange free electrons with their respective negative electrode 21 and positive electrode 26 during discharging and charging of the electrode pair 20. To facilitate the overall distribution and flow of electrons, each negative current collector 22 includes a negative foil 23, and each positive current collector 27 includes a positive foil 28.

[0045] The plurality of negative foils 23 protrude away from the electrode pairs 20 and are positioned in overlapping alignment with each other, and the plurality of positive foils 28 also protrude away from the electrode pairs 20 and are positioned in overlapping alignment with each other. The sets of negative foils 23 and positive foils 28 to which they are attached are either separated from each other on different sides of the electrode pairs 20 (as shown), or are located on the same side of the electrode pairs 20 (not shown). The plurality of positive foils 28 of the cathode current collector 27 are arranged in the first stack 14 and are electrically coupled and mechanically joined to the positive cell tabs 29 in the manner described herein. The plurality of negative foils 23 of the anode current collector 22 are arranged in the second stack 16 and are electrically coupled and mechanically joined to the second negative cell tabs 24.

[0046] Each electrode pair 20 includes a positive electrode (or cathode) 26, a negative electrode (or anode) 21, and a separator 25 disposed between the positive electrode 26 and the negative electrode 21 to physically separate and electrically insulate the positive electrode 26 and the negative electrode 21 from each other. An electrolytic material 13 that conducts lithium ions is contained within the separator 25 and is exposed to each of the positive electrode 26 and the negative electrode 21 to allow lithium ions to move between the positive electrode 26 and the negative electrode 21.

[0047] The apparatus and methods disclosed herein are used to join the plurality of positive foils 28 together to form the first stack 14 and the plurality of negative foils 23 together to form the second stack 16. The use of magnetic welding has some significant advantages over other known methods - notably, it can be used to join dissimilar metals, to join metals with oxide coatings and contaminants, without any adverse effects on the battery.

[0048] Magnetic pulse welding (MPW) uses electromagnetically generated forces to create a solid-state cold weld at room temperature. The weld is completed in a few microseconds and is stronger than the base metals being joined. No heat, filler material, or gas is used. A conductive workpiece (also known as a flyer workpiece because it is displaced by the exciting current) is placed inside or near an electric coil, which accelerates it a distance to impact a second workpiece (which is a stationary workpiece) at extremely high speeds. A large amount of energy in the form of an electric current is discharged through the coil in an extremely short period of time. Some systems can discharge up to 2 million amperes in less than or equal to 100 microseconds. The acceleration is the result of the repulsive magnetic field (pressure) between the workpiece and the coil that is generated by the incoming current in the coil (causing eddy currents in the workpiece). This magnetic pressure forces the conductive flyer workpiece to weld at high speed towards the second stationary workpiece. The impact speed is greater than 1000 kilometers / hour (km / h).

[0049] When two metals are forced together with the strength of their atoms sharing electrons, solid-state cold welding occurs, effectively fusing the two metals together. The actual process lasts no more than 100 microseconds. Since no heating or melting is involved, this technique can be used to weld dissimilar metals. MPW triggers this phenomenon by accelerating a metal to a viscous plastic phase and impacting another workpiece at a precise speed and angle. No shielding atmosphere, filler material, or other auxiliary materials are used in this joining process. The magnetic pulse welding process is a "cold" welding process; the material does not get above 30°C. Therefore, no heat-affected zone is created, and the metal does not degrade. The weld becomes the strongest part of the assembly.

[0050] Other advantages of magnetic pulse welding are that it can be used to join features that were not possible in previous designs. It is a high-speed process - typical pulses last 10 to 100 microseconds (ps), so the only time constraints are loading and unloading. It is highly repeatable, reproducible, and reliable, making it ideal for high-volume production. Many welding combinations using dissimilar metals are possible. It is a cold weld with no heat-affected zone. It is a green process that produces no heat, sparks, smoke, or radiation. It is also a clean process with no pre- or post-welding. The bond between different metals is of high quality, very aesthetic, and creates a cleaner interface. The bond retains mechanical strength (typical joints are stronger than the base material). The bond is a high-precision bond with no distortion. Corrosion is typically not formed in the weld area. All of these advantages translate into significantly lower costs and much higher quality and productivity.

[0051] Figure 2A An apparatus 200 for welding a foil 104 of a battery 100 is depicted. The battery 100 includes a pouch 102 from which the foil 104 protrudes. The structure of the battery 100 and its foil 104 has been described in detail above in Figure 1 and will not be described in detail again.

[0052] The apparatus 200 includes a coil holder 202, a foil holding fixture 208, and an anvil 206 on which the foil 104 is disposed during magnetic welding. Figure 2A and Figure 2BThe coil holder 202 shown in FIG. 1 comprises an electrically insulating material containing an electrical coil 204. The electrical coil 204 can be positioned anywhere within the thickness "t" of the coil holder 202, but is preferably located on the surface closest to the battery foil. In one embodiment, the electrical coil 204 is located near the lower surface 203 of the coil holder 202 and near the front end of the coil holder 202. When the apparatus 200 is used to solder the foil, the front end of the coil holder 202 is the end closest to the foil 104. The rear end 201, opposite the front end of the coil holder 202, can be connected to a power source that supplies electrical energy to the plurality of electrical coils 204. In one embodiment, the rear end 201 includes contacts (not shown) for connecting the coil holder 202 to a capacitor bank (not shown).

[0053] Suitable electrically insulating materials for the coil holder 202 include thermoplastic organic polymers, thermosetting organic polymers, or combinations thereof Suitable organic polymers include polyolefins, polystyrenes, poly(meth)acrylates, polyesters, polyimides, polyetheretherketones, polysiloxanes, polyvinyl fluoride, or combinations thereof.

[0054] Another class of suitable electrically insulating materials includes ceramics. Examples of ceramics include silicon dioxide, aluminum oxide, titanium dioxide, zirconium oxide, ceria, or combinations thereof. Combinations of ceramics with organic polymers may also be used.

[0055] Figure 2B An expanded view of coil holder 202 is depicted in an inverted position. The lower surface 203 of coil holder 202 contains multiple electrical coils 204, while the upper surface 205 does not contain any coils. The number of electrical coils is proportional to the number of crimp spaces in foil retaining fixture 208. The crimp spaces are the areas between the arms of foil retaining fixture 208, as will be described later. In one embodiment, the arms of foil retaining fixture 208 move symmetrically around a vertical axis through the coils.

[0056] The spacing "D1" between the electrical coils is also proportional to the spacing "D2" between the crimp spaces in the foil clamping fixture. The coil holder 202 may contain 2 or more coils, preferably 4 or more coils, and preferably 5 or more coils.

[0057] exist Figure 3 In the embodiment depicted in FIG, the coil holder 202 may include a plurality of electrical coils 204A, 204B, and 204C, wherein each of the plurality of coils is located at a different distance (t1, t2, and t3, respectively) from a lower surface 205 of the coil holder 202. The coil holder has a thickness "t" encompassed between the upper surface 203 and the lower surface 205 of the coil holder.

[0058] Different distances (t1, t2 and t3, respectively) allow the battery foils (not shown) to be subjected to different intensities or configurations (depending on the coil set 204A, 204B or 204C used) of the electric field (and thus the magnetic field) in order to improve the joining between the battery foils. Figure 3 A front view, a top view and a side view of the coil holder 202 are depicted, the coil holder 202 containing a plurality of coil sets 204A, 204B and 204C located at distances t1, t2 and t3, respectively, from the lower surface 205 of the coil holder 202. During the welding operation, the front end 207 of the coil holder is positioned close to the battery pocket and foils (not shown), while the back end 201 of the coil holder contacts the capacitor bank (not shown). Each coil set 204A, 204B and 204C is located at a distance L1 from the front end 207. It is also reasonable that each coil set 204A, 204B or 204C is located at a different distance (not shown) from the front end 207. Different distances from the front end can also be used to subject the battery foils to different intensities or configurations of the electric field (and thus the magnetic field). In another embodiment (not shown), each coil set can be located at a different height from the surface of the coil holder 202.

[0059] Although Figure 3 While the coil holder 202 is depicted as having 3 coil sets (first set 204A, second set 204B and third set 204C), it is indeed reasonable that the coil holder contains less than 3 coil sets or, alternatively, more than 3 coil sets. Switches (not shown) can be used to direct the energy to any one of the coil sets, or alternatively, to any combination of the coil sets. In another embodiment, the switches can be used to direct the energy to any combination of the coils in the coil sets.

[0060] It should be noted that different amounts of electrical energy can be supplied to the coils. Alternatively, the energy supplied to a single set of coils can vary over time. By using different coils, using different amounts of energy in each coil set, using different amounts of energy in a single coil over different time periods, or a combination thereof, the amount of joining energy and the location of the binding energy can be varied, thereby improving the quality of the joining between the foils and the quality of the joining between the foils and the respective tabs.

[0061] Figure 4 , Figure 5A , Figure 5B and Figure 5C An exemplary embodiment of the apparatus 200 without the coil holder 202 is depicted. Figure 4 An enlarged view of the foil holding fixture 208 and the anvil 206 is depicted, the foils 104 being disposed on the anvil 206 during magnetic welding. Figure 4 A plurality of coils 204 as well as parts of the apparatus 200 are depicted. Figure 5A isFigure 4 A further enlarged view of the device 200, and showing portions of the device 200 without the coil retainer 202. The foil retention fixture 208 includes a rear rail 210 for supporting a plurality of arms 208(1), 208(2), 208(3), 208(4), 208(5), 208(6), etc. The arms can move toward and away from each other along the rear rail 210. The rear rail 210 includes rails 210a and 210b along which the respective arms can travel back and forth relative to each other to facilitate crimping of the foil 104. Each arm has a groove (e.g., dovetail slot, spline, etc.) at its rear end that engages with the rails 210a and 210b and allows the arms to travel back and forth. The arms and rear rail are made of an electrically insulating material, such as those detailed above.

[0062] Figure 5B and 5C is a schematic view of an exemplary rear rail 210 having a plurality of arms 208(1), 208(2), 208(3), 208(4), 208(5), 208(6), 208(7), 208(8), 208(9), 208(10), etc. In one embodiment, the odd numbered arms 208(1), 208(3), 208(5), and 208(7) move synchronously in one direction, while the even numbered arms 208(2), 208(4), 208(6), and 208(8) move synchronously in the opposite direction of the odd numbered arms. Figure 5B is shown in a rear rail in which the opposing pairs of arms (e.g., 208(1) and 208(2)) are further apart than in Figure 5C is shown in a rear rail in which the opposing pairs of arms (e.g., 208(1) and 208(2)) are further apart than in Figure 5C is shown in a rear rail in which the opposing pairs of arms (e.g., 208(1) and 208(2)) are further apart than in Figure 4 ). Each pair of opposing arms moves toward and away from each other along the rails 210a and 210b. In other words, for each coil in the coil retainer 202, there is a pair of arms on the foil retention fixture 208. When the opposing pair of arms are clamping the foil and moving toward each other, these arms crimp the plurality of foils directly below each coil.

[0063] This synchronous movement of the even and odd arms allows each pair of adjacent arms to move toward each other to crimp the foil, and then move away from each other after the welding operation has occurred (thereby releasing the foil). In one embodiment, the synchronous movement of the arms can be facilitated and controlled by stepper motors (not shown) in communication with a microprocessor (not shown).

[0064] is depicted in Figure 6 is depicted in Figure 6The plurality of foils 104A, 104B, 104C, 104D, and 104E are depicted before and after being crimped by arms 208(2) and 208(1) (indicated by arrows). Crimping occurs when the foils are secured downward by an adjacent pair of arms (of the foil holding fixture) that are moving toward each other. As the foils move toward each other, the radius of curvature of each foil decreases and the average distance between adjacent foils increases. Crimping decreases the length of the foils from ml to m2 and decreases the radius of curvature of each foil (and thus the average distance between foils) to facilitate movement of the foils to promote welding. The radius of curvature of the foils after crimping is less than the radius of curvature before crimping.

[0065] Before crimping, the plurality of foils are separated by an average distance al. After crimping, the plurality of foils are separated by an average distance a2 that is greater than al. The increase in the average distance between the foils facilitates an increase in the speed of the foils toward each other when subjected to the opposing magnetic field. The opposing magnetic field forces the workpieces toward each other at high speed to promote welding. The increase in speed promotes greater impact between the foils, which facilitates stronger welding between the foils.

[0066] Now referring again to Figure 4 and 5A It can be seen that during the magnetic welding operation, the plurality of foils 104 are located on an anvil 206. The anvil 206 is preferably manufactured from one of the electrically insulating materials detailed above. The anvil 206 is supported from a battery support tab 108 (either a positive battery cell tab or a negative battery cell tab). As noted above, the tab typically comprises copper or aluminum. In one embodiment, the surface of the tab 108 is knurled (or has surface texture / protrusions) to further enhance the quality of the weld between the tab and the foils disposed thereon (by introducing a gap). The knurling creates a surface roughness that increases the gap between the tab 108 and the nearest foil (of the plurality of foils), which allows the foils to accelerate when subjected to the opposing magnetic field. This gap provides space for the foils 104 to accelerate toward the tab 108 and join with the tab 108 upon impact with the tab 108. This allows for a good join between the foils 104 and the tab 108.

[0067] In one embodiment, in one method of using the apparatus 200, a plurality of foils 104 (to be joined together) and knurled tabs 108 (to be joined to the plurality of foils) are installed on the anvil 206. The foil holding fixture 208 is then moved into position and pressed down on the plurality of foils. The arms of the foil holding fixture press down on the foils 104, bringing them into contact with the knurled tabs. Then, the pairs of adjacent arms of the foil holding fixture are moved toward each other in order to crimp the foils. The coil holders are then moved into position so that each coil in the plurality of coils is positioned directly above a crimped set of foils. A first set of coils is energized using electrical current. The opposing magnetic fields cause the foils to accelerate toward each other and impact each other to bond together. In one embodiment, the foils accelerate toward the knurled tabs to bond with the tabs. A second set of coils and / or a third set of coils can then be energized to promote improved joining in the bonded area, and also to promote joining of the foils in areas where joining has not previously occurred. Since the second set of coils and / or the third set of coils are located in a different position than the first set of coils, the foils are subjected to different opposing magnetic fields, which promote joining of the foils in areas where joining can not have previously occurred.

[0068] In other words, the first set of coils creates joining of the foils in a first area, while the second set of coils creates joining in a second area, which can be different from the first area. In this way, different areas of the plurality of foils can be joined together by using different sets of coils or by using different amounts of electrical energy in a single set of coils. The different sets of coils can be energized simultaneously or sequentially as desired.

[0069] The process of using magnetic welding to join foils together or to join foils to tabs is advantageous because dissimilar metals can be joined together. Contaminants do not destroy or weaken the join.

[0070] While the foregoing disclosure has been described in reference to illustrative embodiments, those skilled in the art will understand that various changes can be made and equivalents can be substituted without departing from the scope of the disclosure. In addition, many modifications can be made to adapt a particular situation or material to the teachings of the disclosure without departing from the central scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiments disclosed, but that the disclosure will include all embodiments falling within the scope of the disclosure.

Claims

1. An apparatus for magnetic welding of battery foils, comprising: a coil holder; wherein the coil holder comprises one or more electrical coils operable to be energized by an electrical current; a foil holding fixture; wherein the foil holding fixture comprises a plurality of arms; wherein each pair of adjacent arms is operable to move toward each other to crimp a plurality of battery foils, the crimping operable to increase an average distance between adjacent foils in the plurality of battery foils between the adjacent arms after crimping; and an anvil; wherein the anvil is operable to support a battery tab and the battery foils.

2. The apparatus of claim 1, wherein, Each pair of adjacent arms moves symmetrically about a vertical axis that passes through the coil.

3. The apparatus of claim 1, wherein each pair of adjacent arms is positioned symmetrically about the one or more electrical coils.

4. The apparatus of claim 1, wherein the coil holder further comprises a plurality of sets of electrical coils; wherein, Each set of electrical coils is located at a different height from a surface of the coil holder.

5. The apparatus of claim 1, wherein each electrical coil of the one or more electrical coils is energized by a different strength of electrical current.

6. The apparatus of claim 4, wherein each set of electrical coils is energized by a different strength of electrical current.

7. The apparatus of claim 1, wherein, The plurality of arms move along a guide rail; wherein the plurality of arms have a groove at a rear end that engages the guide rail.

8. The apparatus of claim 1, wherein the coil holder is in communication with an electrical energy source.

9. A method for magnetic welding of battery foils, comprising: placing a plurality of foils of a battery in a foil holding fixture; crimping the plurality of foils by moving at least one pair of adjacent arms of the foil holding fixture, the crimping operable to increase an average distance between adjacent foils in the plurality of foils between the adjacent arms after crimping; energizing at least one electrical coil disposed above a crimped portion of the plurality of foils; and joining the foils to each other; wherein the method further comprises supporting the plurality of foils on an anvil.

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