Battery module, method of manufacturing the same, and battery pack

Abstract

A battery module and a manufacturing method thereof are disclosed. The battery module according to one embodiment of the present application includes: a battery cell stack in which a plurality of battery cells are stacked; a busbar frame connected to the battery cell stack; an electrode lead connected to the battery cell stack and including a first metal; and a busbar overlapping the electrode lead and including a second metal, wherein the electrode lead and the busbar form a weld by welding, the weld includes a first region in which a center part is located in the electrode lead and a second region in which a center part is located in the busbar with respect to a boundary between the electrode lead and the busbar, and precipitates of the first metal and the second metal are distributed in both the first region and the second region.

Description

Technical Field

[0001] Cross-reference to related applications

[0002] This application claims the benefit of Korean Patent Application No. 10-2020-0044829, filed with the Korean Intellectual Property Office on April 13, 2020, the disclosure of which is incorporated herein by reference in its entirety.

[0003] This invention relates to a battery module and a method for manufacturing the battery module, and more specifically, to a battery module having improved physical properties of the welded portion and a method for manufacturing the battery module. Background Technology

[0004] Secondary batteries can be easily applied to various product groups and possess electrical characteristics such as high energy density. They are widely used not only in portable devices but also in electric vehicles or hybrid electric vehicles powered by electric motors, energy storage systems, and more. Because their main advantages are a significant reduction in fossil fuel use and the complete absence of byproducts in energy consumption, these secondary batteries are attracting attention as a new environmentally friendly energy source for improving energy efficiency.

[0005] Small mobile devices use one or more battery cells per device, while medium or large devices such as vehicles require high power and large capacity. Therefore, medium or large battery modules with multiple battery cells electrically connected to each other are used.

[0006] Meanwhile, with the continued increase in demand for high-capacity secondary battery structures (including their use as energy storage sources), the demand for multi-module battery packs is also growing. A multi-module structure is a component of multiple battery modules that are connected in series and / or in parallel.

[0007] Meanwhile, when multiple battery cells are connected in series or parallel to form a battery pack, it is common practice to first form a battery module composed of battery cells, and then use at least one of the battery modules and add other components to form a battery pack.

[0008] To enable electrical connection of battery cells within the battery module, electrode leads are interconnected, and the connections can be soldered to maintain this connection. Furthermore, the battery module can connect battery cells in parallel and / or in series. For this purpose, one end of the electrode leads can be fixed to a busbar using methods such as soldering to achieve electrical connection between battery cells.

[0009] In addition, electrical connections between battery cells are typically formed by joining electrode leads to busbars. To connect battery cells in parallel, electrode leads of the same polarity are connected and joined together; to connect battery cells in series, electrode leads of different polarities are connected and joined together.

[0010] As mentioned above, when the busbar and electrode leads are welded, the physical properties of the welded part deteriorate due to the precipitation of intermetallic compounds, and thus the tensile strength, fatigue life and conductivity may deteriorate. Summary of the Invention

[0011] Technical issues

[0012] The purpose of this invention is to provide a battery module with improved physical properties of the welded portion and a method for manufacturing the battery module.

[0013] However, the technical problems to be solved by the embodiments of the present invention are not limited to the above-described problems, and various extensions can be made within the scope of the technical ideas included in the present invention.

[0014] Technical solution

[0015] According to one embodiment of the present invention, a battery module is provided, comprising: a battery cell stack in which a plurality of battery cells are stacked; a busbar frame connected to the battery cell stack; an electrode lead connected to the battery cell stack and comprising a first metal; and a busbar overlapping the electrode lead and comprising a second metal, wherein the electrode lead and the busbar are welded to form a weld portion, wherein, based on the boundary surface between the electrode lead and the busbar, the weld portion includes a first region with a central portion located in the electrode lead and a second region with a central portion located in the busbar, and wherein precipitates of the first metal and the second metal are distributed in both the first region and the second region.

[0016] The battery module may further include cell platforms protruding from adjacent battery cells in a battery cell stack, wherein electrode leads may protrude from the cell platforms and include a plurality of electrode leads having the same polarity, and wherein the electrode leads may overlap with a busbar.

[0017] The battery module may further include a third metal plating between the electrode leads and the busbar, on which the busbar is plated.

[0018] The first metal may include aluminum, and the second metal may include copper.

[0019] The coating may include nickel.

[0020] The precipitates can be distributed inside the welded area.

[0021] A battery pack according to another embodiment of the present invention includes the battery module described above.

[0022] A method for manufacturing a battery module according to another embodiment of the present invention includes: a step of stacking a plurality of battery cells to form a battery cell stack; a step of overlapping the same busbar with at least one of electrode leads protruding from adjacent battery cells in the battery cells; and a step of welding the electrode leads to the busbar, wherein the step of welding the electrode leads to the busbar includes: a step of preheating the electrode leads using a laser having a first energy; and a step of welding the preheated electrode leads to the busbar using a laser having a second energy, wherein the first energy is lower than the second energy.

[0023] The step of welding electrode leads to busbars may include inducing a eutectic reaction between a first metal contained in the electrode leads and a second metal contained in the busbars.

[0024] In the step of welding the electrode leads to the busbar, the alloy concentration of the second metal mixed with the first metal can be from 22 wt% to 52 wt%.

[0025] The welding speed of the step of preheating the electrode leads can be higher than the welding speed of the preheated electrode leads and busbars.

[0026] The method for manufacturing a battery module may further include a step of forming a coating of a third metal on the busbar before the step of soldering the electrode leads to the busbar.

[0027] A laser can have a pattern of laser beams emanating from the center outwards.

[0028] Lasers can produce tornado-like welding beams.

[0029] According to another embodiment of the present invention, the welding method is a method for welding electrode leads to a busbar, comprising: preheating the electrode leads using a laser having a first energy; and welding the preheated electrode leads to the busbar using a laser having a second energy, wherein the first energy is lower than the second energy, and wherein the method includes a step of inducing a eutectic reaction between a first metal contained in the electrode leads and a second metal contained in the busbar.

[0030] Beneficial effects

[0031] According to an embodiment of the present invention, the steps of preheating the electrode leads with a relatively low laser energy input and welding the preheated electrode leads to the busbar can be performed to control the alloy concentration between dissimilar metals and thereby induce a eutectic reaction during the welding process of the busbar to the electrode leads.

[0032] Therefore, the melting point can be lowered, and the cooling time to suppress the precipitation of intermetallic compounds is longer, thus making the control of intermetallic compound precipitation very advantageous.

[0033] In addition, after welding through a preheating step, a slow cooling step allows the precipitates to spread throughout the weld with sufficient melt flow, thereby improving tensile strength. Attached Figure Description

[0034] Figure 1 This is a perspective view showing a portion of a battery module according to an embodiment of the present invention;

[0035] Figure 2 It is along Figure 1 A sectional view taken by cutting line A-A';

[0036] Figure 3 This is a schematic plan view illustrating the welding structure of the electrode leads and busbar according to an embodiment of the present invention;

[0037] Figure 4 This is a plan view schematically illustrating the welding method of electrode leads and busbars according to a comparative example;

[0038] Figure 5 and Figure 6 This is a schematic plan view illustrating a welding method according to an embodiment of the present invention;

[0039] Figure 7 This is a view showing a welded portion formed by a welding method according to an embodiment of the present invention;

[0040] Figure 8 It is a diagram showing the binary phase diagram of aluminum and copper;

[0041] Figure 9 This is a view showing the laser welding beam according to a comparative example;

[0042] Figure 10 This is a view showing a laser welding beam according to an embodiment of the present invention. Detailed Implementation

[0043] In the following description, various embodiments of the invention will be described in detail with reference to the accompanying drawings, enabling those skilled in the art to readily implement them. The invention can be modified in various different ways and is not limited to the embodiments set forth herein.

[0044] For clarity, descriptions of parts not related to the specification are omitted, and the same elements throughout the specification are indicated by the same reference numerals.

[0045] Furthermore, the dimensions and thicknesses of the various elements are arbitrarily shown in the accompanying drawings for ease of description, and the invention is not necessarily limited to the cases shown in the drawings. The thicknesses of layers, regions, etc., are exaggerated in the accompanying drawings for clarity. The thicknesses of certain layers and regions are exaggerated in the accompanying drawings for ease of description.

[0046] Furthermore, it should be understood that when an element such as a layer, membrane, region, or plate is referred to as being "on" or "above" another element, it can be directly on the other element or there may be intermediate elements present. Conversely, when an element is referred to as being "directly on" another element, it indicates that there are no intermediate elements present. Additionally, the terms "on" or "above" refer to being positioned above or below a reference portion, and do not necessarily mean being positioned at the upper end of the reference portion in the direction opposite to gravity.

[0047] Furthermore, throughout the specification, when a section is referred to as "including" a certain component, unless otherwise stated, it means that the section may further include other components, without excluding other components.

[0048] Furthermore, throughout the instruction manual, when referred to as a "plane," it means the target portion as viewed from above, and when referred to as a "section," it means the target portion as viewed from the side of a vertically cut cross-section.

[0049] Figure 1 This is a perspective view showing a portion of a battery module according to an embodiment of the present invention. Figure 2 It is along Figure 1 The sectional view cut by the cutting line A-A'.

[0050] refer to Figure 1 and Figure 2 According to an embodiment of the present invention, a battery module 100 includes: a module frame 300; a battery cell stack 120 inserted into the module frame 300; and a busbar frame 130 located on an open side of the module frame 300 and connected to the battery cell stack 120. The battery cell stack 120 is formed by stacking a plurality of battery cells 110 in one direction.

[0051] The module frame 300 can be a single frame covering all four surfaces of the battery cell stack 120, excluding the front and rear surfaces. This means that a horizontally assembled type of frame is required to insert the battery cells into the single frame. However, the module frame 300 is not limited to a single frame and can have a shape that includes a U-shaped frame with openings on its upper, front, and rear surfaces, as well as an upper plate covering the upper part of the battery cell stack 120.

[0052] A cell platform 135 is formed extending from the pouch covering the battery cell 110. Electrode leads 160 protruding from the cell platform 135 can meet and pass through a lead groove (not shown). The distance between adjacent cell platforms 135 can gradually narrow as the distance from the battery cell 110 increases. At this time, the electrode leads 160 protruding from the cell platform 135 can have the same polarity. When adjacent electrode leads 160 have different polarities, the distance between the electrode leads 160 protruding from their cell platforms 135 can become wider as they move away from the battery cell 110.

[0053] According to an embodiment of the present invention, a compression pad 200 is formed between the outermost battery cell 110 and the side surface portion of the module frame 300. The compression pad 200 can be formed using a polyurethane-based material. The compression pad 200 can absorb deformation of the thickness of the battery cell 110 due to expansion and changes in the battery cell 110 due to external impact. At least one compression pad 200 can be formed not only between the outermost battery cell 110 and the side surface portion of the module frame 300, but also between adjacent battery cells 110.

[0054] A guide 260 is formed on the busbar frame 130. Before forming the cell platform 135 that extends the electrode leads 160 of each of the three adjacent battery cells 110, the electrode leads 160 are guided through lead slots, and the guide 260 may be formed on one side of the busbar frame 130. Specifically, the busbar frame 130 may include the guide 260 within its rear surface, which is positioned separate from the battery cells 110.

[0055] A predetermined guiding space can be formed on the rear surface of the busbar frame 130 by means of the guide 260, so that the three electrode leads 160 can be brought close to each other with respect to the cell platform 135 before passing through the lead slot. Multiple guides 260 can be provided. Here, multiple guides 260 can be provided to correspond to the number of lead slots. Therefore, the electrode leads 160 adjacent between the multiple battery cells 110 form three pairs, and then the electrode leads 160 can pass through the lead slot via each guide 260 to form a group of electrode leads 160.

[0056] The number of electrode leads 160 forming the group of electrode leads 160 is not limited to three, and can be changed according to the arrangement of the electrode leads of the positive and negative electrodes of the battery cell 110.

[0057] Figure 3 This is a plan view schematically showing the welding structure of electrode leads and busbars according to an embodiment of the present invention.

[0058] refer to Figure 3 Multiple electrode leads 160 protrude from a cell platform 135, which extends from a pouch covering the battery cell 110. The electrode leads 160 protruding from the cell platform 135 can be bent in the direction of the busbar 280. The bent electrode leads 160 can overlap with the same busbar 280, and multiple electrode leads 160 are simultaneously welded to the busbar 280 to form a welded section WP.

[0059] When electrode leads 160 and busbars 280 are welded, the physical properties of the weld joint deteriorate due to the precipitation of intermetallic compounds; therefore, tensile strength, fatigue life, and conductivity may deteriorate. Specifically, such as... Figure 3 As illustrated in the example, the following limitations arise when simultaneously welding multiple electrode leads 160. First, to weld electrode leads 160 that thicken due to overlap, the specifications of the welding machine must be increased. Second, as the number of overlapping electrode leads 160 increases, the specifications of the welding machine should also be increased. Third, as the number of overlapping electrode leads 160 increases, the welding deviation of each electrode lead 160 layer increases, which may lead to a decrease in weld quality. That is, the electrode lead 160 layer closest to the welding machine may be over-welded, while the electrode lead 160 layers farther from the welding machine may be weakly welded. Ultimately, in the case of non-electroplated busbars, the physical properties of the weld cannot be guaranteed. Intermetallic compounds precipitate at a high concentration at the molten interface of the weld, and the weld strength may be significantly reduced.

[0060] Reference Figure 4 The comparative examples describe the problem of intermetallic compounds precipitating at high concentrations and reducing weld strength.

[0061] Figure 4 This is a plan view schematically illustrating a method for welding electrode leads and busbars according to a comparative example.

[0062] refer to Figure 4 Electrode leads 16, containing aluminum, and busbars 28, containing copper, are laser welded. During laser welding, the material moves along the flow direction, and CuAl2 precipitates (PM) are precipitated at a high concentration as intermetallic compounds at the weld interface (FI). These precipitates (PM) significantly reduce the weld strength, so electrode leads 16 and busbars 28 may be separated even by small impacts.

[0063] Figure 5 and Figure 6 This is a schematic plan view illustrating a welding method according to an embodiment of the present invention.

[0064] refer to Figure 5According to an embodiment of the invention, at least one of the electrode leads 160 may overlap with the same busbar 280. The electrode leads 160 and the busbar 280 may then be soldered.

[0065] The step of welding the electrode lead 160 and the busbar 280 includes preheating the electrode lead 160 using a laser with a first energy. The magnitude of the first energy is relatively low compared to the welding steps described later. This preheating step allows for control of the alloy concentration in the welding steps, thereby improving the melt flowability of the metals to be welded. Preferably, the preheated portion formed in this step is formed only on the electrode lead 160. This is because precipitates begin to form when the laser energy used for preheating is transmitted to the busbar 280.

[0066] During laser welding, rapid cooling easily leads to the formation of precipitates. However, according to embodiments of the present invention, a preheating process can delay the cooling time to maximize the precipitate formation time. Furthermore, the preheating step of the electrode leads 160 can increase the surface cleanliness and absorption rate of the laser beam.

[0067] refer to Figure 6 A laser with a second energy can be used to weld preheated electrode leads 160 and busbars 280. In this case, the second energy is greater than the first energy. During this step, a eutectic reaction may occur between a first metal contained in the electrode leads 160 and a second metal contained in the busbars 280. The first metal contains aluminum, and the second metal contains copper.

[0068] When a eutectic reaction is induced between the first and second metals, welding can be performed at temperatures lower than the existing weldable temperatures. For example, the eutectic reaction of aluminum-copper occurs at approximately 548 degrees Celsius, and at this eutectic temperature, the viscosity of the weld joint (WP) is lowest, thus allowing for very high fluidity. At the aluminum-copper eutectic reaction concentration, the fluidity of the molten metal increases, thereby reducing the distribution of intermetallic compounds precipitated at the weld interface.

[0069] According to an embodiment of the present invention, the welding speed of the preheated electrode lead 160 can be higher than the welding speed of the preheated electrode lead 160 and the busbar 280.

[0070] In the following text, reference will be made to Figure 7 Describe the steps for dispersing precipitates generated in the weld.

[0071] Figure 7 This is a view showing a welded portion formed by a welding method according to an embodiment of the present invention.

[0072] refer to Figure 7Electrode leads 160 and busbars 280 overlap and are welded to form a weld portion WP. Based on the boundary surface BS between electrode leads 160 and busbars 280, the weld portion WP includes: a first region WP1, in which the central portion is located within the electrode lead 160; and a second region WP2, in which the central portion is located within the busbar 280. During the welding process, the first metal forming the electrode lead 160 and the second metal forming the busbar 280 can react to form precipitates PM. According to an embodiment of the invention, the precipitates PM are distributed in the first region WP1 and the second region WP2. Conventionally, due to the low material flowability in the weld portion WP, most precipitates are formed at a high concentration at the weld interface FI. However, according to an embodiment of the invention, the alloy of the first metal and the second metal is widely dispersed in the flow direction in the weld portion WP, so precipitates PM may form in small amounts or almost none at all. In particular, the concentration of precipitates (PM) formed at the weld interface (FI) is very low, and the precipitates (PM) are minimized. Even if precipitates (PM) are formed, the weld strength can be improved by dispersing them throughout the weld area (WP).

[0073] Figure 8 This is a diagram showing the binary phase diagram of aluminum and copper.

[0074] refer to Figure 8 In the welding process according to an embodiment of the present invention, the alloy concentration of the second metal mixed with the first metal can be approximately 22 wt% to 52 wt%, preferably 30 wt% to 40 wt%, and more preferably 32 wt% to 35 wt%. The above ranges represent the temperature ranges within which the eutectic reaction occurs. As the temperature range narrows, more eutectic reactions occur, thus increasing the fluidity of the molten metal and reducing the distribution of intermetallic compounds precipitated at the weld interface.

[0075] When the alloy concentration is below the minimum of 22 wt%, weld penetration is unlikely to occur during welding. When the alloy concentration exceeds the maximum of 52 wt%, the metals do not alloy with each other but combine to form compounds. At an alloy concentration of around 54 wt%, which exceeds the maximum of 52 wt%, welding is a rapid cooling process, unlike the typical slow cooling solidification process, and therefore it is possible for the theta phase to form during solidification.

[0076] In the above embodiment, the first metal contained in the electrode lead 160 and the second metal contained in the busbar 280 are in contact with each other. As described above, according to embodiments of the present invention, even if a plating layer such as nickel is not formed between the electrode lead 160 and the busbar 280, the welding strength can be improved.

[0077] In a variant embodiment, a third metal can be plated as a coating on the busbar between the electrode leads and the busbar. The third metal includes nickel, which forms a complete solid solution with the copper forming the busbar. In a complete solid solution, no heterogeneous phases appear in the liquid and solid phases, and the solution is completely dissolved across all compositional ranges, thus preventing the formation of intermetallic compounds. Therefore, nickel can completely dissolve copper at the weld interface, thereby suppressing the precipitation reaction of intermetallic compounds caused by the aluminum-copper bond. While a nickel plating is not always necessary, adding a nickel plating layer in addition to the above welding method offers the advantage of achieving better weld strength.

[0078] Figure 9 This is a view showing the laser welding beam according to a comparative example. Figure 10 This is a view showing a laser welding beam according to an embodiment of the present invention.

[0079] refer to Figure 9 This is a pattern where the laser beam is concentrated from the outside to the center. In this case, the energy is concentrated in the central part, and a deep and narrow weld penetration may be formed in the central part. When this laser welding beam is applied to this embodiment, when a deep and narrow molten portion is formed in the center of the busbar, the laser plasma is emitted through the pinhole, thus interfering with the alloying reaction between the electrode leads and the second metal, and the concentration of the first metal in the busbar may increase at the lower end of the weld. As the concentration of the first metal increases at the interface of the weld, intermetallic compounds of the first and second metals may precipitate, and the weld strength may decrease sharply.

[0080] refer to Figure 10 According to an embodiment of the present invention, the laser welding beam increases the radius of the central part of the tornado, and the laser beam can irradiate from the center outward to reduce the energy density in the central part. Therefore, the weld penetration depth of the laser-welded portion becomes flat. Energy is uniformly transferred to the weld, making it easier to induce a eutectic reaction between the first and second metals. After the preheating step, the welding step using the laser welding beam according to an embodiment of the present invention is performed, followed by a slow cooling process, allowing the first and second metals to mix well due to sufficient melt flowability.

[0081] Meanwhile, one or more battery modules according to embodiments of the present invention can be encapsulated in a battery pack housing to form a battery pack.

[0082] The aforementioned battery module and battery pack including the battery module can be applied to various devices. These devices can be applied to vehicle devices such as electric bicycles, electric vehicles, and hybrid vehicles, but the present invention is not limited thereto, and can be applied to various devices capable of using the battery module and battery pack including the battery module, which are also within the scope of the present invention.

[0083] Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concepts of the present invention as defined in the following claims are also within the scope of the claims.

[0084] Explanation of reference numerals in the attached figures

[0085] 160: Electrode leads

[0086] 280: Busbar

[0087] FI: Welding Interface

[0088] WP: Welding Department

Claims

1. A battery module, comprising: A battery cell stack, in which multiple battery cells are stacked; A busbar frame, the busbar frame being connected to the battery cell stack; Electrode leads, which are connected to the battery cell stack and contain a first metal; as well as A busbar that overlaps with the electrode leads and contains a second metal. The electrode leads and the busbar are welded together to form a welded section. Specifically, based on the boundary surface between the electrode lead and the busbar, the weld portion includes a first region with a central portion located in the electrode lead and a second region with a central portion located in the busbar, and The precipitates of the first metal and the second metal are distributed in both the first region and the second region. Specifically, a preheating section is formed only on the electrode lead, preheated by a low-energy laser, and the preheated electrode lead and the busbar are welded by a high-energy laser to control the alloy concentration between dissimilar metals and induce a eutectic reaction between the first metal contained in the electrode lead and the second metal contained in the busbar. The precipitates are distributed throughout the welded portion. The alloy concentration of the second metal mixed with the first metal is 22 wt% to 52 wt%.

2. The battery module of claim 1, further comprising cell platforms protruding from adjacent battery cells in the battery cell stack. in, The electrode leads protrude from the unit platform respectively, and include multiple electrode leads with the same polarity. The electrode lead overlaps with a busbar.

3. The battery module according to claim 1, wherein the battery module further comprises a coating of a third metal plated on the busbar between the electrode lead and the busbar.

4. The battery module according to claim 3, wherein, The first metal comprises aluminum, and the second metal comprises copper.

5. The battery module according to claim 4, wherein, The coating includes nickel.

6. A method for manufacturing a battery module according to claim 1, the method comprising: The step of stacking multiple battery cells to form a battery cell stack; The step of overlapping the same busbar with at least one of the electrode leads protruding from adjacent battery cells in the battery cell; as well as The step of welding the electrode leads to the busbar. The step of welding the electrode leads to the busbar includes: The step of preheating only the electrode leads using a laser with a first energy; and The step of welding the preheated electrode leads to the busbar using a laser with a second energy, and Wherein, the first energy is lower than the second energy. The step of welding the electrode lead to the busbar includes: inducing a eutectic reaction between the first metal contained in the electrode lead and the second metal contained in the busbar; and forming a weld between the electrode lead and the busbar. The precipitates of the first metal and the second metal are distributed throughout the welded portion. In the step of welding the electrode leads to the busbar, the alloy concentration of the second metal mixed with the first metal is 22 wt% to 52 wt%.

7. The method according to claim 6, wherein, The welding speed of the step in which the electrode leads are preheated is higher than the welding speed of the preheated electrode leads and the busbar.

8. The method of claim 6, further comprising, prior to the step of soldering the electrode leads to the busbar, forming a coating of a third metal on the busbar.

9. The method according to claim 6, wherein, The laser has a pattern of laser beams irradiated from the center outwards.

10. The method according to claim 9, wherein, The laser has a tornado welding beam.

11. A method for welding electrode leads to a busbar, comprising: The step of using a laser with a first energy to preheat only the electrode leads to control the alloy concentration between dissimilar metals; as well as The step of welding the preheated electrode leads to the busbar using a laser with a second energy. Wherein, the first energy is lower than the second energy, and The method includes the step of inducing a eutectic reaction between a first metal contained in the electrode lead and a second metal contained in the busbar. The step of welding the preheated electrode leads to the busbar using a laser with a second energy includes the step of forming a weld between the electrode leads and the busbar. The precipitates of the first metal and the second metal are distributed throughout the welded portion. In the step of welding the electrode leads to the busbar, the alloy concentration of the second metal mixed with the first metal is 22 wt% to 52 wt%.

12. A battery pack comprising the battery module according to claim 1.

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