BATTERY WITH WELDED BUSBAR CONNECTIONS

Abstract

In a high-voltage vehicle electronics system, a battery comprises a multitude of battery cells, each with two electrode foils. The electrode foils are laser-welded to respective terminals using a fillet weld. The terminals can be connected to other electrical components, such as an inverter, via busbars or cables.

Description

AREA OF TECHNOLOGY

[0001] The present disclosure relates to laser welding. In particular, the present disclosure relates to the laser welding of foil electrode tongues of battery cells to a terminal tongue for an electric vehicle. GENERAL STATE OF THE ART

[0002] Laser welding works on the principle of using a focused beam of light, typically generated by a laser source, to heat and melt the materials to be joined. The laser beam is precisely directed at the joining area, where it rapidly heats the material to its melting point, creating a weld pool. Once the laser energy is removed from a specific region, the molten material solidifies, forming a strong bond between the parts.

[0003] Continuous-wave laser welding involves the continuous, uninterrupted delivery of laser energy to the workpiece. The focal region is continuously moved along the material. Pulsed laser welding involves the delivery of laser energy in short pulses, each lasting a fraction of a second. The focal region typically remains constant during a pulse and moves to a different position between pulses.

[0004] Laser welding is an extremely versatile joining process, but it presents particular challenges when working with materials like copper and aluminum due to their differing properties. Copper and aluminum have relatively high thermal conductivities. This high thermal conductivity makes it difficult to achieve sufficient heating at the weld joint. Furthermore, copper and aluminum strongly reflect infrared radiation, including the wavelength commonly used in many laser welding processes. This reflectivity can lead to poor absorption of the laser energy, resulting in insufficient heating. SUMMARY

[0005] One welding process involves stacking multiple metal foils to form a foil stack, placing an area of ​​the foil stack against a metal tongue, and focusing laser energy onto an edge of the foil stack. The edge of each metal foil is aligned along the edge of the foil stack. The tongue extends beyond the edge of the foil stack. The laser energy creates a fillet weld that bonds each of the metal foils to the tongue. The laser's focal point can be moved along the edge of the foil stack. The laser energy can be focused at an acute angle to the edge relative to the area of ​​the tongue. The laser wavelength can be in the blue or green spectrum. The metal foils can be made of copper. The tongue can be made of aluminum. The metal foils can be electrode tongues from battery cells.

[0006] A battery comprises a multitude of battery cells and a first terminal. Each battery cell has a first electrode foil, which is mechanically and electrically connected to the first terminal by a first fillet weld. Each battery cell may also have a second electrode foil, which is mechanically and electrically connected to a second terminal by a second fillet weld. The first terminal may be made of aluminum. The first electrode foils may be made of copper.

[0007] A battery comprises a plurality of battery cells and a first terminal. Each battery cell has a first electrode foil. The first electrode foils are stacked to form a first foil stack, with the edges of the first electrode foils aligned along an edge of the first foil stack. The first terminal is mechanically and electrically connected to the edges of each of the first electrode foils by a first fillet weld. Each battery cell may also have a second electrode foil. The second electrode foils may be stacked to form a second foil stack, with the edges of the second electrode foils aligned along an edge of the second foil stack. The battery may include a second terminal, which is mechanically and electrically connected to the edges of each of the second electrode foils by a second fillet weld.The first electrode foils and the second electrode foils can be made of copper. The first terminal and the second terminal can be made of aluminum. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 illustrates a block diagram of an electric vehicle. Fig. Figure 2 illustrates the structure of a battery designed for use in the electric vehicle. Fig. 1 is suitable. Fig. Figure 3 is a cross-sectional view of a stack of battery cell electrode foils joined to a terminal tongue using an overlap weld. Fig. Figure 4 is a cross-sectional view of a stack of battery cell electrode foils joined to a terminal tongue using a fillet weld. Fig. Figure 5 is a flowchart for a process for manufacturing a battery. DETAILED DESCRIPTION

[0008] Depending on the requirements, detailed embodiments of the present invention are disclosed in this document; however, it is understood that the disclosed embodiments are merely exemplary of the invention, which can be implemented in various and alternative forms. The figures are not necessarily to scale; some features may be greatly enlarged or reduced to show details of specific components. Therefore, specific structural and functional details disclosed in this document are not to be interpreted as limiting, but merely as a representative basis to teach those skilled in the art the diverse applications of the present invention.

[0009] With reference to Fig. Figure 1 shows a block diagram of an exemplary electric vehicle (“EV”) 12. In this example, the EV 12 is a plug-in hybrid electric vehicle (PHEV). The EV 12 includes one or more electric machines 14 (“e-machines”) mechanically connected to a transmission 16. The electric machine 14 is capable of operating as a motor and as a generator. The transmission 16 is mechanically connected to an internal combustion engine 18 and to a drive shaft 20, which is mechanically connected to wheels 22. The electric machine 14 can provide propulsion and deceleration capabilities while the internal combustion engine 18 is switched on or off. The electric machine 14 can reduce vehicle emissions by allowing the internal combustion engine 18 to operate at more efficient speeds and enables the EV 12 to operate in electric mode with the internal combustion engine 18 switched off under certain conditions..

[0010] A traction battery 24 (“battery”) stores energy that can be used by the electric machine 14 to propel the EV 12. The battery 24 typically provides a high-voltage (HV) direct current (DC) output. The battery 24 is electrically connected to a power electronics module 26. The power electronics module 26 is electrically connected to the electric machine 14 and provides the capability to transfer energy bidirectionally between the battery 24 and the electric machine. For example, the battery 24 may provide a DC voltage, while the electric machine 14 may require a three-phase alternating voltage (three-phase AC voltage) to operate. The power electronics module 26 can convert the DC voltage into a three-phase AC voltage to operate the electric machine 14.In a regeneration mode, the power electronics module 26 can convert the three-phase AC voltage from the electric machine 14, which acts as a generator, into DC voltage that is compatible with the battery 24.

[0011] The battery 24 is rechargeable by an external power source 36 (e.g., the mains). An electric vehicle supply equipment (EVSE) 38 is connected to the external power source 36. The EVSE 38 provides circuitry and controls for controlling and managing the transfer of energy between the external power source 36 and the EV 12. The external power source 36 can supply DC or AC electrical power to the EVSE 38. The EVSE 38 may have a charging plug 40 for insertion into a charging port 34 of the EV 12. The charging port 34 can be any type of connector configured to transfer power from the EVSE 38 to the EV 12. A power conversion module 32 of the EV 12 can condition the power supplied by the EVSE 38 to provide the correct voltage and current levels to the battery 24.The power conversion module 32 can interface with the EVSE 38 to coordinate the delivery of power to the battery 24. Alternatively, various components described as electrically connected can transfer power using wireless inductive coupling.

[0012] The various components discussed may have one or more associated controllers to manage and monitor their operation. These controllers may be microprocessor-based devices. They may communicate via a serial bus (e.g., a Controller Area Network (CAN)) or via separate wires. For example, a system controller 48 (i.e., a vehicle controller) is present to coordinate the operation of the various components.

[0013] As described, the EV 12 in this example is a PHEV, which includes an internal combustion engine 18 and a battery 24. In other embodiments, the EV 12 is a battery electric vehicle (BEV). In a BEV configuration, the EV 12 does not include an internal combustion engine.

[0014] Fig. Figure 2 illustrates a structure suitable for the traction battery 24. The battery can include a set of battery cells 60. Each battery cell 60 can include a positive electrode foil 62 and a negative electrode foil 64. The electrode foils can be made of copper, aluminum, or another electrically conductive material. Unlike rigid electrodes, the thickness of an electrode foil makes it flexible. Each positive electrode foil can be electrically connected to each other and to the positive terminal 66, while each negative electrode foil can be electrically connected to each other and to the negative terminal 68. A terminal is a rigid, electrically conductive element that extends to the outside of the battery housing 69 to allow connection with other electrical components, such as the power electronics module 26 and the power conversion module 32.The connecting tabs can be made of copper, aluminum, or another electrically conductive material, which may be the same material as the corresponding electrode foils or a different material. The electrical connections can be formed by welding, such as laser welding.

[0015] In laser welding, the two primary operating modes are conductive mode and keyhole mode. These modes differ in their approach to material interactions and heat transfer, resulting in different welding characteristics and applications.

[0016] In conductive laser welding, the laser beam's energy is primarily absorbed at the material surface, causing localized heating. The beam is focused over a relatively large area, resulting in a comparatively low energy density. The heat conducted through the material creates a shallow weld pool near the fusion area. As the weld pool cools, it resolidifies with a distinct grain pattern compared to the areas that never melted. This resolidified region bonds with each of the pieces being joined, creating both a mechanical and electrical connection.

[0017] Keyhole laser welding involves creating a vapor-filled cavity, or "keyhole," within the material thickness. The beam is focused on a relatively small area, resulting in a comparatively high energy density compared to conductive mode. The intense laser energy causes localized vaporization of the material, creating a cavity that extends deep into the material. This keyhole acts as a channel through which the laser beam can penetrate deeply, enabling significantly deeper penetration than in conductive mode. As with conductive mode, the weld pool solidifies upon cooling with a distinctly different grain pattern and forms a mechanical and electrical bond with the workpieces.

[0018] Fig. Figure 3 illustrates a method for laser welding a stack 70 of electrode foils to a terminal tongue 72. One face of the stack is held in contact with the terminal tongue while a laser beam 74 is focused onto a second face of the stack opposite the terminal tongue. The laser energy heats the material, forming a molten pool 76 that extends through the stack 70 of foils into the terminal tongue. After the laser beam is removed, the molten pool solidifies, mechanically and electrically bonding the foils to each other and to the terminal tongue. The laser can be controlled to operate in either conductive or keyhole mode during this process. Under certain circumstances, the laser beam can be moved continuously along a path on the top face of the stack.Under other circumstances, the laser can be pulsed on and off, remaining in one position while on and moving to another while off, thus creating an array of separate welds. This method requires a relatively high energy density to ensure that the weld pool penetrates the terminal. Weld quality problems are more likely when the energy density is high.

[0019] Fig. Figure 4 illustrates an alternative method for laser welding a stack 70 of electrode foils to a terminal 72. The terminal 72 can be the positive terminal 66 or the negative terminal 68 of the battery. Fig. 2. The electrode foils that make up the foil stack 70 can be the positive electrode foils 62 or the negative electrode foils 64 of the battery cells 60 of the battery. Fig. 2 be.

[0020] As in the first method, a surface of the stack is held in contact with the connecting tongue. However, instead of focusing the laser beam on a surface of the stack opposite the connecting tongue, the laser beam is focused 74' on the ends of the foils.

[0021] A surface formed by the edges of the separate foils can be referred to as the edge surface of the foil stack 70. The laser beam can be aligned at an acute angle relative to the surface of the connecting tongue and relative to the edge surface of the foil stack. Instead of creating a melt pool extending through the stack of foils, a melt pool 76' is formed at the edge surface and extends into the connecting tongue.

[0022] After the laser beam is removed (74'), the weld pool solidifies, mechanically and electrically bonding the foils to each other and to the connecting tongue. The solidified weld pool forms a fillet weld, meaning that the modified grain structure is formed along surfaces of the two parts that intersect at an angle. For example, the two surfaces can intersect at a right angle. Specifically, the fillet weld is formed along the edge surface of the foil stack and an end face of the connecting tongue. The laser beam can either be moved continuously along the edge surface of the stack or pulsed. Since the weld pool for this process does not need to be as deep as for the process described above, the laser beam can be moved continuously along the edge surface of the stack or pulsed. Fig. 3. A lower-energy laser beam can be used. Wavelengths in the green / blue spectrum can be effective in applications where they are not compatible with the method from Fig. 3 would not be effective.

[0023] Fig.Figure 5 illustrates a process for manufacturing a battery. At Figure 80, the battery cells are assembled into an array. This may involve installing the battery cells into a housing 69. Each battery cell includes a positive electrode foil and a negative electrode foil. At Figure 82, the positive electrode foils are brought together and clamped to form a positive foil stack. At Figure 84, the positive foil stack is clamped to a positive terminal such that a surface of the terminal in contact with the foil stack extends beyond an edge face of the foil stack. Alternatively, a single clamp may hold the positive electrode foils together and to the terminal. At Figure 86, a laser is focused onto an edge face of the positive foil stack to create a fillet weld between the positive foil stack and the positive terminal.The laser beam can be directed at an acute angle relative to a surface of the connection tongue that is in contact with the foil stack. A similar process is carried out to create a fillet weld between the negative electrode foils and the negative connection tongue at 88, 90, and 92.

[0024] Although exemplary embodiments have been described above, it is not intended that these embodiments describe all possible forms covered by the claims. The terms used in the description are descriptive and not limiting, and it is understood that various modifications may be made without altering the spirit and scope of protection of these disclosed subject matter.

[0025] As previously described, the features of different embodiments can be combined to form further embodiments of the invention, which may not be expressly described or illustrated. Although different embodiments may have been described in such a way that they offer advantages or are preferred over other embodiments or implementations according to the prior art with respect to one or more desired properties, the person skilled in the art understands that compromises may be made with respect to one or more features or properties in order to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes may include, among others: strength, service life, market capacity, appearance, packaging, size, maintenance capacity, weight, manufacturability, ease of assembly, etc.Thus, embodiments that are described as less desirable than other embodiments or implementations of the prior art with respect to one or more properties are not outside the scope of protection of the disclosure and may be desirable for certain applications.

[0026] According to the present invention, a welding method comprises: stacking a plurality of metal foils to form a foil stack, wherein an edge of each metal foil is aligned along an edge of the foil stack; placing a face of the foil stack against a face of a metal tongue such that the face of the tongue extends beyond the edge of the foil stack; and focusing energy from a laser onto the edge of the foil stack to produce a fillet weld that attaches each of the metal foils to the tongue.

[0027] In one aspect of the invention, the method involves moving a focus of the laser along the edge of the foil stack.

[0028] In one aspect of the invention, the energy from the laser is focused at an acute angle relative to the surface of the tongue onto the edge.

[0029] In one aspect of the invention, the metal foils are made of copper.

[0030] In one aspect of the invention, the tongue is made of aluminum.

[0031] In one aspect of the invention, each of the metal foils is an electrode of a battery cell.

[0032] In one aspect of the invention, the wavelength of the laser lies in a blue or green spectrum.

[0033] According to the present invention, a battery is provided comprising: a plurality of battery cells, each comprising a first electrode foil; and a first terminal tongue; wherein the first electrode foil of each battery cell of the plurality of battery cells is mechanically and electrically connected to the first terminal tongue by a first throat weld.

[0034] According to one embodiment, the invention is further characterized by the following: a second connecting tongue; wherein each battery cell of the plurality of battery cells has a second electrode foil which is mechanically and electrically connected to the second connecting tongue by a second throat weld.

[0035] According to one embodiment, the first connecting tongue is made of aluminum.

[0036] According to one embodiment, the first electrode foils are made of copper.

[0037] According to the present invention, a battery is provided comprising: a plurality of battery cells, each of the battery cells having a first electrode foil, the first electrode foils being stacked to form a first foil stack, the edges of the first electrode foils being aligned along an edge of the first foil stack; and a first terminal tongue being mechanically and electrically connected to the edges of each of the first electrode foils by a first fillet weld.

[0038] According to one embodiment, each of the battery cells has a second electrode foil, wherein the second electrode foils are stacked to form a second foil stack, the edges of the second electrode foils being aligned along an edge of the second foil stack.

[0039] According to one embodiment, the first electrode foils and the second electrode foils are made of copper.

[0040] According to one embodiment, the invention is further characterized by a second connecting tongue which is mechanically and electrically connected to the edges of each of the second electrode foils by means of a second fillet weld.

[0041] According to one embodiment, the first connecting tongue and the second connecting tongue are made of aluminum.

Claims

[1] Welding methods comprising the following: Stacking a variety of metal foils to form a foil stack, with one edge of each metal foil aligned along an edge of the foil stack; Placing one face of the foil stack against a face of a metal tongue, such that the face of the tongue extends beyond the edge of the foil stack; and Focusing the energy from a laser onto the edge of the foil stack to create a throat weld that attaches each of the metal foils to the tongue. [2] Method according to claim 1, further comprising moving a focus of the laser along the edge of the foil stack. [3] Method according to claim 1, wherein the energy from the laser is focused at an acute angle relative to the surface of the tongue onto the edge. [4] Method according to claim 1, wherein the metal foils are made of copper. [5] Method according to claim 1, wherein the tongue is made of aluminium. [6] Method according to claim 1, wherein each of the metal foils is an electrode of a battery cell. [7] Method according to claim 1, wherein the wavelength of the laser lies in a blue or green spectrum. [8] Battery, comprising the following: a plurality of battery cells, each comprising a first electrode foil; and a first connecting tongue; wherein The first electrode foil of each battery cell of the multitude of battery cells is mechanically and electrically connected to the first terminal tongue by a first throat weld. [9] Battery according to claim 8, further comprising: a second connecting tongue; wherein Each battery cell of the multitude of battery cells has a second electrode foil which is mechanically and electrically connected to the second terminal tongue by a second throat weld. [10] Battery according to claim 8, wherein the first terminal tongue is made of aluminium. [11] Battery according to claim 8, wherein the first electrode foils are made of copper. [12] Battery, comprising the following: a plurality of battery cells, each of the battery cells having a first electrode foil, the first electrode foils being stacked to form a first foil stack, the edges of the first electrode foils being aligned along an edge of the first foil stack; and a first connecting tongue which is mechanically and electrically connected to the edges of each of the first electrode foils by a first fillet weld. [13] Battery according to claim 12, wherein each of the battery cells has a second electrode foil, wherein the second electrode foils are stacked to form a second foil stack, wherein the edges of the second electrode foils are aligned along an edge of the second foil stack. [14] Battery according to claim 13, wherein the first electrode foils and the second electrode foils are made of copper. [15] Battery according to claim 13, further comprising a second connecting tongue which is mechanically and electrically connected to the edges of each of the second electrode foils by a second fillet weld.

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