METHOD FOR BENDING AND IMPACT WELDING MULTIPLE CURVED METAL FILMS OF A BATTERY

Abstract

Procedures (500), comprising: Bending several metal foils (302) of a battery between a punch (204) and a die (202) to form bent metal foils (303), wherein the punch (204) and the die (202) are in a slidably connected relationship to each other, opposite surfaces of the punch (204) and the die (202) are knurled, and the opposite surfaces of the punch (204) and the die (202) are heated by inductive heating, resistance heating, or a combination thereof, and wherein the bent metal foils (303) are corrugated after forming and include a depression having a height of 0.1 to 2 millimeters; Arranging the several curved metal foils (303) in a foil holder; Arranging a battery lead (304) next to the multiple curved metal foils (303) such that a curved section of the multiple curved metal foils (303) is separated from the battery lead (304) by a distance of 0.1 to 2 millimeters, wherein the battery lead (304) has a knurled surface and wherein the knurled surface faces the multiple curved metal foils (303); and Impact welding of the multiple curved metal foils (303), wherein the impact welding is carried out by magnetic pulse welding and comprises activating one or more electrical coils (214, 218) placed near the multiple curved metal foils (303) to enable the multiple curved metal foils (303) to strike each other or the battery conductor (304) at a speed of 300 to 900 meters per second, thereby producing a weld between the metal foils (303) themselves as well as between the metal foils (303) and the battery conductor (304), wherein a Coil holder (206) comprising one or more electrical coils (214, 218), wherein either the coil holder (206) is opposite a first surface of the multiple curved metal foils and this first surface is opposite a second surface of the multiple curved metal foils which is opposite the battery conductor, or wherein the coil holder (206) is opposite a first surface of the battery conductor and this first surface is opposite a second surface of the battery conductor which is opposite a first surface of the multiple curved metal foils.

Description

INTRODUCTION

[0001] This document presents a method and a device for impact welding battery terminals. In particular, it discloses a method and a device for impact welding metals, including dissimilar metals, to improve weld quality.

[0002] Lithium-ion battery packs for vehicles and other high-performance applications can comprise multiple lithium-ion battery cells electrically connected to one another. Each cell includes multiple pairs of lithium-ion electrodes enclosed within a sealed pouch. Each electrode pair comprises a negative electrode, a positive electrode, and a separator that physically separates and electrically insulates the negative and positive electrodes. To facilitate lithium ion mobility, an electrolyte may be present, which conducts lithium ions. The electrolyte allows the lithium ions to flow through the separator between the positive and negative electrodes during the charge and discharge cycles of the lithium-ion battery cell.

[0003] Depending on their chemistry, each lithium-ion battery cell has a specific maximum or charging voltage (voltage at full charge) due to the different electrochemical potentials of the electrodes. For example, each lithium-ion battery cell can have a charging voltage in the range of 3 V to 5 V and a nominal open-circuit voltage in the range of 3.5 V to 4.5 V. Depending on the specific design of the battery pack, lithium-ion battery cells can be connected in series, parallel, or in both series and parallel.

[0004] The majority of electrode pairs are connected in parallel to electrochemically store and release electric current. Each electrode pair consists of an anode and a cathode with a separator between them. Each anode has an anode current collector with a negative foil, and each cathode has a cathode current collector with a positive foil. The negative foils of the anodes of the majority of electrode pairs are connected in parallel and electrically connected to a negative pole conductor that extends through the bag, and the positive foils of the cathodes of the majority of electrode pairs are connected in parallel and electrically connected to a positive pole conductor that extends through the bag.

[0005] Within each battery cell, the negative terminal is electrically connected to the negative contacts, which are in contact with the negative electrodes of the electrode pairs and thus exchange electrons. The positive terminal is electrically connected to the positive contacts, which are in contact with the positive electrodes of the electrode pairs and thus exchange electrons. Lithium-ion battery cells can be discharged and recharged many times.

[0006] The negative foils of the anodes of multiple electrode pairs can be electrically connected in parallel and joined to the negative pole lead by laser welding, ultrasonic welding, or other methods. Similarly, the positive foils of the anodes of the majority of electrode pairs can be electrically connected in parallel and joined to the positive pole lead using laser welding.

[0007] Laser welding is a metal joining process in which a laser beam is directed onto a stack of metal workpieces to provide a concentrated energy source that creates a fusion weld between the overlapping metal pieces. The laser beam is directed onto or near a top surface of the workpiece stack. The heat generated by the absorption of the energy supplied by the laser beam initiates the melting of the metal workpieces, building up a molten weld pool within the workpiece stack. This molten weld pool solidifies to form a weld joint composed of resolidified material from all layers of the metal workpieces.

[0008] It is known that porosity and / or cracks can form along a laser welding fusion line of the films due to many factors, including surface properties. Ultrasonic pre-welding of the films serves to strengthen them. Subsequently, laser welding of conduits / films aligned at the pre-welded locations can be used as the final weld. Local material defects, which may manifest as gaps between layers in the workpiece stack and / or as voids in one or more workpieces, can impair the quality of the weld and thus the service life of the component enclosing the weld.If the stack of workpieces includes multiple sheets of foil welded to a battery lead, the occurrence of localized material voids can compromise the strength of the weld and impair the electrical conductivity between one or more of the sheets and the battery lead.

[0009] It is therefore desirable to develop new methods for bonding battery foils to a conductor or for bonding the foils to each other.

[0010] US 2018 / 0050496A1 discloses a method for assembling a part made of a metallic material and a part made of a composite material with an organic matrix. KR 101180910B1 discloses a method for manufacturing a cooking pot to bring folds in a shaped product into a pattern corresponding to a guide groove formed in a magnesium alloy sheet and to remove the folds through the guide groove. US 2013 / 0086961A1 describes the use of magnetic pulse welding for joining plates, such as battery plates, or magnetic pulse forming for shaping plates. CN 113020773A discloses a method for welding multilayer sheet metal joints based on magnetic pulses. CN 112975105A discloses a method for welding a battery terminal and connector.CN 1 13 422 166 A describes a connector, a battery cell and a battery pack, wherein the connector is used for electrically connecting multilayer pole tabs of a current collector. SUMMARY

[0011] A method comprises bending multiple metal foils of a battery between a punch and a die to form curved metal foils, wherein the punch and the die are slidably connected to each other, opposite surfaces of the punch and the die are knurled, and the opposite surfaces of the punch and the die are heated by inductive heating, resistance heating, or a combination thereof, and wherein the curved metal foils are corrugated after forming and include a depression having a height of 0.1 to 2 millimeters. The multiple curved metal foils are arranged in a foil holder, wherein a battery lead is positioned alongside the multiple curved metal foils such that a curved section of the multiple curved metal foils is separated from the battery lead by a distance of 0.1 to 2 millimeters.wherein the battery conductor has a knurled surface and wherein the knurled surface faces the multiple curved metal foils. The multiple curved metal foils are impact welded, wherein the impact welding is performed by magnetic pulse welding and comprises the activation of one or more electrical coils placed near the multiple curved metal foils to enable the multiple curved metal foils to impact each other or the battery conductor at a speed of 300 to 900 meters per second, thereby producing a weld between the metal foils themselves as well as between the metal foils and the battery conductor, wherein a coil holder comprises the one or more electrical coils, wherein either the coil holder faces a first surface of the multiple curved metal foils and this first surface faces a second surface of the multiple curved metal foils,which is opposite the battery lead, or wherein the coil holder is opposite a first surface of the battery lead and this first surface is opposite a second surface of the battery lead, which is opposite a first surface of the several curved metal foils.

[0012] In one embodiment, the several curved metal foils are supported on an anvil in the foil holder.

[0013] In another embodiment, the battery cable is placed over the several curved metal foils in the foil holder.

[0014] The aforementioned features and advantages, as well as other features and advantages of the disclosure, are readily apparent from the following detailed description in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Further features, advantages and details are listed only as examples in the following detailed description, which refers to the drawings, where: Fig. 1 is an exemplary representation of a battery; Fig. 2 shows an aspect of a stamp and die for shaping the foils of a battery (not shown) before welding the foils together and to the battery cell conductor; Fig. 3 shows another aspect of a stamp and die for shaping the foils of a battery (not shown) before welding the foils together and to the battery cell conductor; Fig. 4 shows another aspect of a stamp and die for shaping the foils of a battery using induction heating; Fig. 5 shows another aspect of a stamp and die for shaping the foils of a battery using resistance heating; and Fig. Figure 6 is a process flow diagram that illustrates the process of impact welding the bent metal foils. DETAILED DESCRIPTION

[0016] The following description is merely exemplary and is not intended to limit the present disclosure, its application, or its use. It is understood that in the drawings, corresponding reference numerals denote identical or corresponding parts and features.

[0017] This discloses a forming device comprising a punch and a die that can be used to deform one or more battery foils to create a gap between a battery foil and a battery conductor so that they can be impact welded together. The deformation is also referred to herein as bending. The gap can be used in impact welding to promote an increase in the velocity between the battery foils and the battery conductor when the battery foils are subjected to energy. This application of energy is sometimes referred to as the "driving force." The driving force increases the velocity of the foils in the direction of the conductor, which in turn promotes impact between the foils and the conductor, thereby producing a weld between the foils themselves as well as between the foils and the conductor.The gap provides the foils with the distance that is desirable for increasing their speed (while being subjected to energy) so that they can strike each other or a battery lead with sufficient force or dynamics to create a bond.

[0018] The foils can be referred to as flyers (because they move in the direction of the conductor after being subjected to energy), and the conductor is referred to as the target. Impact welding encompasses various welding processes, such as explosion welding (EXW), magnetic pulse welding (MPW), vaporizing foil actuator welding (VFAW), laser impact welding (LIW), or a combination thereof. According to the invention, impact welding is achieved by magnetic pulse welding.

[0019] During bending, the foils and the tab can be interlocked (sometimes called crimping) and bonded together using a punch and die with knurled, opposing surfaces. The interlocking primarily refers to the mechanical interlocking that occurs when the mating surfaces are roughened by contact with a knurled deformation force. In this case, the battery foils can be deformed with a punch and die featuring knurled surfaces. This deformation causes the surfaces of the battery foils to become roughened, and due to this surface roughness, they mechanically interlock.

[0020] Bonding refers to the contact between two surfaces where chemical diffusion can occur from one mating surface to the opposite contact surface. For example, if battery foils are bonded together, components from one foil can diffuse into an adjacent foil. Bonding typically occurs when there is an increase in temperature during contact between the two opposing contact surfaces. For instance, if the opposing surfaces are knurled at an elevated temperature (at or above the metal's softening point), the opposing surfaces can interlock and bond. If the temperature is not raised to approximately the metal's softening point during knurling, the opposing surfaces will most likely interlock but not bond.

[0021] This document also discloses a welding device and a method for performing impact welding to bond the metal foils of a battery to one another and / or to bond the metal foils to the battery conductor. In one embodiment, the battery can be a lithium-ion battery. The method consists of bringing the curved battery foils close to a battery conductor and applying energy to the curved foils via an electric current discharged through magnetic coils. This energy application causes the battery foils to be accelerated across the gap (created by the bending) and to strike the battery conductor with a force sufficient to weld the battery foils to one another or to the battery conductor. The battery foils and the battery conductor can be heated independently during this welding process to induce bonding.

[0022] Before describing the apparatus and method for magnetically welding the foils of a battery, a brief introduction to the relevant parts of a battery is given to improve the understanding of this disclosure.

[0023] With reference to the drawings, illustrated Fig. Figure 1 schematically shows an embodiment of a prismatically shaped lithium-ion battery cell 10, which includes a plurality of electrode pairs 20 arranged in a stack and sealed in a flexible pouch 12 containing an electrolyte material 13. A first, positive battery cell lead 29 and a second, negative battery cell lead 24 protrude from the flexible pouch 12. Each of the electrode pairs 20 includes an anode 21, which is arranged on an anode (or negative) current collector 22, and a cathode 26, which is arranged on a cathode (or positive) current collector 27, and they are 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 encloses a negative foil (or anode foil) 23.

[0024] The negative and positive current collectors 22, 27 are thin metal plates that are in contact with their respective negative and positive electrodes 21, 26 over a considerable interface area. The purpose of these metal current collectors 22, 27 is to exchange free electrons with their respective negative and positive electrodes 21, 26 during the discharge and charging of the electrode pairs 20. To facilitate the collective distribution and flow of the electrons, each of the negative current collectors 22 encloses the negative foil 23, and each of the positive current collectors 27 encloses the positive foil 28.

[0025] The majority of negative foils 23 project away from the electrode pairs 20 and are arranged in an overlapping orientation, and the majority of positive foils 28 also project away from the electrode pairs 20 and are arranged in an overlapping orientation. The aligned sets of negative and positive foils 23, 28 are either separated from each other on opposite sides of the electrode pairs 20 (as shown) or are located on the same side of the electrode pairs 20 (not shown). The majority of positive foils 28 of the cathode current collectors 27 are arranged in a first stack 14 and are electrically coupled and mechanically connected to the positive battery cell lead 29 as described herein. The majority of negative foils 23 of the anode current collectors 22 are arranged in a second stack 16 and are electrically coupled and mechanically connected to the second negative battery cell lead 24.

[0026] Each of the electrode pairs 20 includes a positive electrode (or cathode) 26, a negative electrode (or anode) 21, and a separator 25, which is positioned between the positive and negative electrodes 26, 21 to physically separate and electrically insulate them. The electrolytic material 13, which conducts lithium ions, is contained within the separator 25 and is exposed to both the positive and negative electrodes 26, 21, allowing lithium ions to move between them.

[0027] The apparatus and method disclosed herein are used to bond the plurality of positive foils 28 together to form a first stack 14, and to bond the plurality of negative foils 23 together to form a second stack 16. The use of impact welding has some significant advantages over other known methods—in particular, it can be used to bond dissimilar metals, including metals with oxide coatings and impurities, without adverse effects on the battery.

[0028] As mentioned previously, impact welding uses a driving force and a suitable gap (between the welder and the target) to create a solid-state weld at approximately room temperature. This weld is completed in microseconds and can be stronger than the joined base metals.

[0029] In magnetic pulse welding, the conductive workpiece is placed in or next to an electric coil, which accelerates it over a distance to strike the second workpiece at extremely high speed. 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 results from repulsive magnetic fields between the workpiece and the coil, which are generated by eddy currents in the workpiece. The reaction forces between the opposing magnetic fields force the workpieces toward each other at high speed, initiating welding. The impact velocity is typically 300–900 m / s. A preferred form of impact welding is magnetic impact welding.

[0030] Solid-state welding occurs when two metals are pressed together with such force that their atoms begin exchanging electrons, effectively bonding them together. The actual process takes no more than 100 microseconds. Because neither heat nor melting is required, dissimilar metals can be welded using this technique. In impact welding, this phenomenon is triggered by accelerating the metal into a viscoplastic phase and striking the other workpiece to create a bond. This bonding process does not use a protective atmosphere, fillers, or other auxiliary materials. Magnetic pulse welding is a "cold" or, at most, a "hot" welding process; the temperature is significantly lower than the melting point of the metals. For this reason, no fusion zone is created. The weld can be the strongest part of the assembly.Impact welding is highly repeatable, reproducible, and reliable, making it well-suited for high-volume production. Many welding combinations using different metals are possible. It is a weld without a heat-affected zone. The bond between the different metals is of high quality, aesthetically pleasing, and produces a cleaner interface. The bond retains mechanical strength (typical joints can be stronger than the base material). All these advantages result in significantly lower costs and much higher quality and productivity.

[0031] Fig. Figure 2 shows an aspect of a forming device 200 for forming (also bending) the foils 302 of a battery (not shown) before welding the foils to each other and to the battery cell lead 304. The battery may have one or more metal foils. In this document, the foils are sometimes referred to as a plurality of foils, but it is understood that the battery may have a single foil or multiple foils. If the battery has a single foil, it is welded to the battery lead. If the battery comprises multiple foils, the foils may alternatively be welded to each other and to the battery lead. These foils are referred to herein as metal foils.

[0032] The battery cell conductor 304 (also referred to as battery conductor 304) generally comprises copper or aluminum. In one embodiment, the surface of the battery conductor 304 is knurled (or has a surface structure / projection) to further improve the weld quality between the conductor and the foils arranged on it. The knurling of the battery conductor produces a surface roughness that increases the distance between the conductor 304 and the nearest foil (from the majority of the curved foils 302), which allows the foils to accelerate when exposed to opposing magnetic fields. The gap provides the curved foils 302 with the necessary space to accelerate toward the conductor 304 and weld to it upon impact. This enables a good weld between the curved foils 302 and the battery conductor 304.

[0033] The forming device 200 comprises a punch 204 and a die 202, which are slidably connected to each other. In other words, the punch 204 can engage with the die 202 to bend the metal foils 302 of the battery when the metal foils are positioned between the punch and the die 202. The first surface 203 of the punch 204, which is in contact with the opposite first surface 205 of the die 202, is knurled. The knurled first surface 203 and the knurled opposite first surface 205 promote adhesion and create an interlocking action between the foils when they are compressed between the punch 204 and the die 202. The knurling improves the interlocking and the bond between the foils.

[0034] The metal foils 302 typically have a thickness of 6 to 16 micrometers. A stack generally comprises 6 to 240 metal foils. After the metal foils 302 have been placed between the punch 204 and the die 202, the punch 204 is moved toward the die 202. Compressive forces are exerted on the metal foils 302 via the punch 204. The metal foils 302 are deformed (e.g., bent) to assume a shape determined by the shape of the opposing surfaces of the punch 205 and the die 203. During bending, the knurled surfaces 205 and 203 of the punch and die promote interlocking and bonding of the metal foils, resulting in greater surface contact between the metal foils 302 of the battery. After bending the metal foils, the punch is removed from the die and a new set of metal foils can be placed in the space between the punch and the die.The process is repeated to produce another set of bent metal foils 303.

[0035] After the metal foils are bent, the bent metal foils 303 are subjected to impact welding in a welding device 400, which comprises an anvil 208 and a coil holder 206. The anvil 208 provides physical support to the battery lead 304 during the impact welding process. The coil holder 206 is made of an electrically insulating material and contains one or more magnetic coils 210, which cause the bent metal foils 303 to come into contact with the battery lead 304 at high speed.

[0036] In a method for operating the welding device 400, a battery lead 304 is arranged on the curved foils 303. The battery lead 304 has a thickness of 0.1 to 0.6 millimeters. An anvil 208 is arranged on the battery lead 304. The coil holder 206, which contains a magnetic coil 210, is then brought close to the curved metal foils 303 and the battery lead 304. The curved metal foils 303 are located on the side of the battery lead 304 opposite the anvil 208.

[0037] In other words, with reference to Fig. 2, the coil holder 206 faces a first surface 302A of the bent metal foils 303. The second surface 302B of the bent metal foils (opposite the first surface of the bent metal foils 303) faces a first surface 304A of the battery lead 304. The second surface 304B of the battery lead 304 (opposite the first surface 304A of the battery lead 304) faces the anvil 208. In another embodiment (not shown in Fig. 2) The battery lead 304 and the curved metal foils 303 can exchange their positions such that a first surface 304A of the battery lead 304 faces the coil holder 206, while the opposite second surface 304B faces a first surface 302A of the battery foils. The second surface 302B of the battery foils faces the anvil 208.

[0038] The coil 210 is electrically activated (a current flows through the coils), thereby generating a magnetic force that causes the foils 303 to come into contact with the conductor 304 at high speed. Electrically insulating materials can be polymers or ceramics. The distance between the curved metal foils 303 and the conductor 304 is denoted as d1 in Fig. 2. It is desirable that d1 be between 0.1 and 2.0 millimeters. In other words, the punch and die produce a depression in the metal foils with a height (d1) of 0.1 to 2 millimeters. This distance allows the curved metal foils 303 to strike the conductor 304 with sufficient speed, force, and momentum (when activated) to achieve a successful bond with the conductor 304.

[0039] In one embodiment, the welding device 400 can include a clamp (not shown) to press the curved foils downwards and bring them into contact with the battery lead or, alternatively, as close as possible to the battery lead 304. In another embodiment, a coil holder (containing a plurality of coils) (not shown) can be positioned such that each coil of the plurality of coils is located directly above the curved section of a battery foil (if the battery foil contains a plurality of curved sections) (not shown). The plurality of coils is then energized using an electric current. The opposing magnetic fields cause the foils to accelerate towards each other and strike against each other to bond. In one embodiment, the foils are accelerated in the direction of the lead to bond with the lead and form a weld 306.

[0040] It should be noted that the in Fig. Figure 2 shows a coil holder 206 containing a single coil 210. The coil holder can contain a plurality of coils (not shown), each of which can be arranged next to a curved section of the battery foils. The plurality of coils can all be activated simultaneously or sequentially to facilitate contact between the foils and the conductor, thus creating a weld. The coil(s) can be connected to a power source (not shown).

[0041] In one embodiment, the curved foils and the battery lead can be heated independently of each other in the device 400 before or during the impact welding process. Such independent heating can be achieved by infrared heating, convection heating, laser heating, or the like, or a combination thereof. This heating can facilitate the bonding of the curved foils to each other or to the battery lead.

[0042] Fig. Figure 3 shows another aspect of a forming device 200, which includes a punch 204 and a die 202 for bending the foils 302 of a battery (not shown) before welding the foils 302 to each other and to the battery cell conductor 304 (in the welding device 400). The punch 204 and the die 202 are again slidably connected to each other. In this case, the opposing surfaces 205 and 203 of the punch 204 and the die 202, respectively, are hemispherical or semicylindrical and arranged in a fit-outside-inside configuration. For example, surface 205 can project into surface 203 (or vice versa) and bend the majority of the metal foils, causing them to interlock and bond together. When area 205 is equipped with the interior configuration, it protrudes into area 203, which is equipped with the exterior configuration.Alternatively, if area 203 is equipped with the external configuration, it extends into area 205, which is equipped with the internal configuration.

[0043] The opposing surfaces 205 and 203 (which are immovably connected to each other) fit together and may be knurled. As in Fig. As discussed in section 2, the punch 204 can engage with the die 202 to bend the metal foils 302 of the battery when the metal foils are located between the punch and the die 202.

[0044] The knurled first surface 205 and the knurled opposite first surface 203 promote interlocking and bonding between the films when compressed between the punch 204 and the die 202.

[0045] Fig. Figure 3 also shows the welding device 400, which includes the anvil 208 that supports the battery lead 304 and the majority of battery foils 302 during impact welding. A coil holder 206, containing an electrical coil 210, can be positioned below or above the curved foils during the generation of a magnetic pulse that causes welding in the foils 302 and welding of the battery foils 302 to the lead 304. The function of the anvil and the coil holder has already been described and will not be explained again in detail here.

[0046] Fig. Figure 3 shows two embodiments of how the anvil 208 and the coil holder 206 can be used. In one embodiment (bottom left in Figure 3) Fig. 3) The coil holder 206 is placed on one side of the curved foils 302, while the battery lead 304 lies on the opposite side of the curved foils 302. An anvil supporting the battery lead 304 lies on the side of the battery lead opposite the side facing the curved foils 302. In the other embodiment (bottom right in Fig. 3) The coil holder 206 rests on the top of the battery lead 304, while the curved battery foils 302 rest on the underside of the battery lead 304. An anvil 208 with a surface 209 that can accommodate the curved foils 302 serves to support the foils during the impact welding process.

[0047] In short, the anvil and the coil holder can be made of Fig. 3. Reverse the positions around the curved foils and the lead. If the anvil is next to the battery lead, the coil holder is next to the curved foils and vice versa, while the battery lead and the curved foils are always directly next to each other.

[0048] In these two embodiments (the one on the bottom left and the one on the bottom right in Fig. 3 are shown), the activation of the coil(s) in the coil holder promotes the movement of the curved foils towards the battery lead, resulting in welding.

[0049] Fig. Figure 4 is another exemplary representation of a forming device 200, in which the punch 204 and the die 202 (which are slidably connected to each other) are each equipped with induction coils 210 and 212 to heat the punch and the die. The induction coils 210 and 212 are located near the opposing counter surfaces 205 and 203 and heat the metal foils by induction heating. Induction heating is the heating of materials (e.g., metals) by electromagnetic induction. An induction heater consists of an electromagnet (not shown) and an electronic oscillator (not shown) that passes a high-frequency alternating current (AC) through the electromagnet. The rapidly changing magnetic field penetrates the object and generates electric currents inside the conductor, so-called eddy currents. The eddy currents flow through the resistance of the material and heat it by Joule heating.

[0050] Induction heating heats the opposing surfaces 205 and 203 to soften the metal foils 302 arranged between the punch and die and to produce the bent metal foils 303. The punch and die exert compressive forces to bond and interlock the metal foils during the induction heating process.

[0051] The opposing surfaces 205 and 203 of the punch 204 and the die 202 can be flat (as in Fig. 2 to be seen) or hemispherical or semi-cylindrical (as in Fig. 4) and are arranged in a pass-in-outside configuration, as shown above in Fig. 3 explained in detail. The opposing mating surfaces 205 and 203 may be knurled.

[0052] After forming the curved metal foils 303, these can be arranged in the welding device 400 next to a battery lead 304 and subjected to a magnetic force (via the coil holder 206, which contains the coil 210) to facilitate bonding of the metal foils to each other and to the lead. This method is described in Fig. 2 described in detail and will not be repeated for the sake of brevity.

[0053] As before in Fig. As can be seen in section 3, the anvil and the coil holder can be seen from Fig. 4. Reverse the positions around the curved foils and the lead. If the anvil is next to the battery lead, the coil holder is next to the curved foils, and vice versa.

[0054] Fig. Figure 5 is another exemplary method for forming battery metal foils 302 using a forming device 200 comprising the punch 204 and the die 202, both of which are heated by resistance heating. In this case, both the punch 204 and the die 202 are equipped with electrical coils (214 and 218, respectively) and cooling systems (216 and 220, respectively). The electrical coils 214 and 218 heat the surfaces of the punch and die, respectively, by conduction (the heat is dissipated by the resistance heating of the coils 214 and 218). The cooling system can use cooling water to control the heat generated at the surfaces of the punch and die and to maintain the punch and die at a desired temperature.

[0055] The heat generated by the electrical coils 214 and 218 is used to heat the opposing counter surfaces 205 and 203, softening the metal foils 302 arranged between the punch and the die and producing the bent metal foils 303. The punch and the die exert compressive forces on the metal foils to cause bonding and interlocking of the metal foils during the induction heating process.

[0056] The opposing surfaces 205 and 203 of the punch 204 and the die 202 can be flat (as in Fig. 2 to be seen), or hemispherical or semi-cylindrical (as in Fig. 5) and are arranged in a pass-in-outside configuration, as shown above in Fig. 3 described in detail. The opposing mating surfaces 205 and 203 may be knurled. After bending the metal foils 303, they can be arranged in the welding device 400 next to a battery lead 304 and subjected to a magnetic force via the coil 210 (which is contained in the coil holder 206) to facilitate bonding of the metal foils to each other and to the lead. This method is described in Fig. 2 described in detail and will not be repeated for the sake of brevity.

[0057] As in Fig. 3 and Fig. 4. The anvil 208 and the coil holder 206 can exchange their positions around the curved metal foils and the battery lead. If the anvil is next to the battery lead, the coil holder is next to the curved foils, and vice versa.

[0058] Fig.Figure 6 shows a process 500 for impact welding the battery foils to the battery lead. In step 502, the battery foils are positioned between the punch and die and deformed to form the curved metal foils. The battery foils can optionally be heated before or during (step 503) the foil deformation process (step 501). The curved metal foils are then positioned next to a battery lead (step 504). The battery lead, along with the adjacent battery foils, is then positioned between the coil holder and the anvil (step 506). The coils in the coil holder are activated (step 508) to promote an impact between the foils themselves or between the foils and the lead, thus producing a weld.

[0059] The process of bonding foils to each other or to the conductor using magnetic welding has the advantage that dissimilar metals can be bonded together. Impurities do not interrupt or weaken the bond. This method can be a viable alternative welding process, replacing the two-stage ultrasonic / ultrasonic or ultrasonic / laser welding for batteries, which sometimes leads to battery failures. The process also allows for the bonding of dissimilar metals in a way that reduces defects (intermetallic compounds, porosity, and thermal cracking) and increases tolerance to surface oxides / impurities.

[0060] Although the foregoing disclosure has been described with reference to exemplary embodiments, it is known among those skilled in the art that various modifications can be made and equivalent elements substituted without altering the scope. Furthermore, many changes can be made to adapt a particular situation or material to the teachings of the disclosure without deviating from its essential scope. Therefore, the present disclosure is not intended to be limited to the specific embodiments disclosed, but rather to encompass all embodiments that fall within its scope.

Claims

[1] Procedure (500), comprising: Bending several metal foils (302) of a battery between a punch (204) and a die (202) to form bent metal foils (303), wherein the punch (204) and the die (202) are in a slidably connected relationship to each other, opposite surfaces of the punch (204) and the die (202) are knurled, and the opposite surfaces of the punch (204) and the die (202) are heated by inductive heating, resistance heating, or a combination thereof, and wherein the bent metal foils (303) are corrugated after forming and include a depression having a height of 0.1 to 2 millimeters; Arranging the several curved metal foils (303) in a foil holder; Arranging a battery lead (304) next to the multiple curved metal foils (303) such that a curved section of the multiple curved metal foils (303) is separated from the battery lead (304) by a distance of 0.1 to 2 millimeters, wherein the battery lead (304) has a knurled surface and wherein the knurled surface faces the multiple curved metal foils (303); and Impact welding of the multiple curved metal foils (303), wherein the impact welding is carried out by magnetic pulse welding and comprises activating one or more electrical coils (214, 218) placed near the multiple curved metal foils (303) to enable the multiple curved metal foils (303) to strike each other or the battery conductor (304) at a speed of 300 to 900 meters per second, thereby producing a weld between the metal foils (303) themselves as well as between the metal foils (303) and the battery conductor (304), wherein a Coil holder (206) comprising one or more electrical coils (214, 218), wherein either the coil holder (206) is opposite a first surface of the multiple curved metal foils and this first surface is opposite a second surface of the multiple curved metal foils which is opposite the battery conductor, or wherein the coil holder (206) is opposite a first surface of the battery conductor and this first surface is opposite a second surface of the battery conductor which is opposite a first surface of the multiple curved metal foils. [2] Method (500) according to claim 1, wherein the multiple curved metal foils (303) are supported on an anvil (208) in the foil holder. [3] Method (500) according to claim 1, further comprising placing the battery lead (304) over the several curved metal foils (303) in the foil holder.

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