Cylindrical secondary battery module, secondary battery pack including the same, and automobile

Abstract

According to an embodiment of the present invention, a cylindrical secondary battery module includes a plurality of cylindrical secondary battery cells each containing an electrode assembly and an electrolyte, a cell frame in which the cylindrical secondary battery cells are arranged, and a bus bar having a plurality of welds formed thereon, the bus bar being coupled to each of the cylindrical secondary battery cells, and the welds that are spaced apart from each other by a larger distance are welded to each other.

Description

[Technical field]

[0001] This application claims priority to Korean Patent Application No. 10-2021-0117933, filed on September 3, 2021, the entire contents of which are incorporated herein by reference in their entirety in the specification and drawings.

[0002] The present invention relates to a cylindrical secondary battery module, a secondary battery pack including the same, and an automobile, and more particularly, to a cylindrical secondary battery module capable of improving welding quality and ensuring durability even under high temperatures and vibration, and a secondary battery pack and an automobile including the same. [Background technology]

[0003] The recent technological development and increasing demand for mobile devices has been remarkable, and this has led to a rapid increase in the need for secondary batteries as energy sources. Conventionally, nickel-cadmium batteries or hydrogen-ion batteries have been used as secondary batteries, but recently lithium secondary batteries have been widely used because they have almost no memory effect compared to nickel-based batteries, can be charged and discharged freely, have a very low self-discharge rate, and have a high energy density.

[0004] This type of lithium secondary battery mainly uses a lithium-based oxide and a carbon material as the positive and negative active materials, respectively, and includes a secondary battery cell in which a separator is sandwiched between positive and negative plates coated with the positive and negative active materials, and an exterior material, such as a battery case, that encloses the secondary battery cell together with an electrolyte.

[0005] Lithium secondary batteries are composed of a positive electrode, a negative electrode, a separator sandwiched between them, and an electrolyte, and are classified as lithium ion batteries (LIBs), polymer lithium ion batteries (PLIBs), etc., depending on what materials are used as the positive and negative active materials. Generally, the electrodes of these lithium secondary batteries are formed by applying a positive or negative active material to a current collector such as an aluminum or copper sheet, mesh, film, or foil, and then drying it.

[0006] In general, secondary batteries can be classified into cylindrical, square, or pouch types depending on the shape of the exterior material in which the secondary battery cells are housed, and cylindrical secondary batteries can be used in the form of a secondary battery module by connecting multiple secondary battery cells in series or in parallel.

[0007] In cylindrical secondary batteries, the bus bars are joined to each of the secondary battery cells by welding, and resistance welding is usually used to minimize deformation of the electrode terminals of the secondary battery cells.

[0008] Resistance welding is a welding method in which a welding rod is used to press a bus bar and an electrode terminal against each other while passing an electric current through the bus bar, and the heat generated by the resistance is used to partially melt the bus bar and join the bus bar and the electrode terminal.

[0009] Here, examples of resistance welding include the two-spot welding method of FIG. 1 and the four-spot welding method of FIG. 4, as described in Korean Patent Publication No. 10-2021-0054790, which is a prior art document.

[0010] However, the two-spot welding method has a problem in that the welded portion of the busbar is prone to fracture under high temperature conditions, such as when a secondary battery is charged or discharged, or under vibration conditions, such as when a car is running.

[0011] Furthermore, the conventional four-spot welding method welds two points that are located close to each other, and compared to the two-spot welding method, this increases the reactive current, which not only causes surface splashing on the surface of the base material, but also causes problems such as uneven growth of the weld nugget, where the surface melts and hardens after welding.

[0012] Specifically, when the welding points of the busbars are close to each other, the current flows through the surfaces around the busbars, which have a relatively low resistance, and as a result, the current cannot contribute to the welding. This current that cannot contribute to the welding is called reactive current.

[0013] If the reactive current increases during resistance welding, the quality of the weld deteriorates and the weld is likely to break. Therefore, a method for reducing the reactive current is required. Summary of the Invention [Problem to be solved by the invention]

[0014] Therefore, a technical problem to be solved by the present invention is to provide a cylindrical secondary battery module capable of reducing reactive current, improving welding quality, and preventing a bus bar from being damaged by high temperature, vibration, or impact, and a secondary battery pack and automobile including the same. [Means for solving the problem]

[0015] According to one aspect of the present invention, there may be provided a cylindrical secondary battery module including: a plurality of cylindrical secondary battery cells that house an electrode assembly and an electrolyte; a cell frame in which the plurality of cylindrical secondary battery cells are arranged; and a bus bar coupled to each of the plurality of cylindrical secondary battery cells and having a plurality of welds formed thereon, wherein among the plurality of welds, welds that are spaced apart at a larger interval are welded to each other.

[0016] In addition, the bus bar may be provided with four welds, and among the four welds, a first weld and a third weld located on a straight line in a first diagonal direction may be welded to each other, and among the four welds, a second weld and a fourth weld located on a straight line in a second diagonal direction may be welded to each other.

[0017] Furthermore, the first diagonal line, which is a line connecting the first welded portion and the third welded portion, and the second diagonal line, which is a line connecting the second welded portion and the fourth welded portion, may be arranged so as to be perpendicular to each other.

[0018] Furthermore, the welding of the welded portions may be performed by applying a first voltage in an arbitrary first direction to perform a primary welding, and then applying a second voltage in a second direction opposite to the first direction to perform a secondary welding.

[0019] Furthermore, the first voltage and the second voltage may be set to have different magnitudes.

[0020] Furthermore, the magnitude of the second voltage for the second welding may be set to be greater than the magnitude of the first voltage for the first welding.

[0021] Furthermore, the first voltage and the second voltage may be provided for different supply times.

[0022] Furthermore, a supply time of the second voltage for the second welding may be set to be longer than a supply time of the first voltage for the first welding.

[0023] Furthermore, the welds may be provided as protrusions formed on the busbars.

[0024] Meanwhile, according to another aspect of the present invention, a secondary battery pack including the above-mentioned cylindrical secondary battery module may be provided, and a vehicle including the cylindrical secondary battery module may be provided. Effect of the Invention

[0025] Embodiments of the present invention have the advantage that the spacing between welds can be increased to reduce reactive currents, thereby improving weld quality and protecting the busbar from damage caused by high temperatures, vibration, or impact. [Brief description of the drawings]

[0026] [Figure 1] 1 is a schematic perspective view of a cylindrical secondary battery module according to an embodiment of the present invention; [Diagram 2] FIG. 2 is an exploded perspective view of FIG. [Diagram 3] FIG. 2 is an enlarged view of part A in FIG. [Figure 4] 4 is a diagram illustrating a welding method between a secondary battery cell and a bus bar in a cylindrical secondary battery module according to an embodiment of the present invention; FIG. [Diagram 5] FIG. 5 is a diagram illustrating a graph according to the welding method of FIG. 4. [Figure 6] FIG. 5 is a graph showing an actual experiment using the welding method of FIG. 4. [Figure 7] FIG. 7 shows result data from the experiment of FIG. 6. [Figure 8] FIG. 7 is a graph showing a comparative experiment with FIG. 6. [Figure 9] FIG. 9 shows result data from the experiment of FIG. 8. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the attached drawings. Prior to this, the terms and words used in this specification and claims are not to be construed as being limited to their ordinary or dictionary meanings, but are to be construed as being in accordance with the meaning and concept of the technical idea of ​​the present invention, in accordance with the principle that the inventor himself can appropriately define the concept of the term in order to best describe the invention. Therefore, it should be understood that the embodiment described in this specification and the configuration shown in the drawings are merely the most preferred embodiment of the present invention, and do not represent the entire technical idea of ​​the present invention, and therefore there may be various equivalents and modifications that can be substituted therefor at the time of this application.

[0028] In the drawings, the size of each component or a specific part constituting each component is somewhat exaggerated, omitted, or illustrated in a schematic manner for ease of explanation and clarity. Therefore, the size of each component does not entirely reflect the actual size. If a detailed description of related publicly known functions or configurations is deemed to be likely to unnecessarily obscure the gist of the present invention, the detailed description will be omitted.

[0029] The term "coupled" or "connected" as used herein includes not only a case where one member is directly coupled or connected to another member, but also a case where one member is indirectly coupled or connected to another member via a joint member.

[0030] FIG. 1 is a schematic perspective view of a cylindrical secondary battery module according to one embodiment of the present invention, FIG. 2 is an exploded perspective view of FIG. 1, FIG. 3 is an enlarged view of portion A of FIG. 1, FIG. 4 is a diagram illustrating a welding method between a secondary battery cell and a bus bar in a cylindrical secondary battery module according to one embodiment of the present invention, and FIG. 5 is a diagram illustrating a graph based on the welding method of FIG. 4.

[0031] Referring to the figure, a cylindrical secondary battery module 10 according to one embodiment of the present invention includes a plurality of cylindrical secondary battery cells 100, a cell frame 200, and a bus bar 300.

[0032] The cylindrical secondary battery cell 100 includes an electrode assembly, for example, a jelly-roll type electrode assembly, a cylindrical battery case in which an electrolyte is contained together with the electrode assembly, and electrode terminals 110 formed on the battery case, for example, a positive terminal formed on an upper portion of the battery case and a negative terminal formed on a lower portion of the battery case.

[0033] The electrode assembly may have a structure in which a positive electrode and a negative electrode are stacked with a separator sandwiched between them and wound up in a jelly roll shape. A positive electrode lead is attached to the positive electrode and connected to a positive electrode terminal, for example, at the upper part of the battery case, and a negative electrode lead is attached to the negative electrode and connected to a negative electrode terminal, for example, at the lower part of the battery case.

[0034] A cylindrical center pin may be inserted into the center of the electrode assembly. The center pin may serve to fix and support the electrode assembly and to function as a passage for releasing gas generated by an internal reaction during charging, discharging, and operation.

[0035] Here, a safety vent may be provided inside the battery case, for example, under the top cap, to rupture due to an increase in pressure inside the battery case to release gas.

[0036] A plurality of cylindrical secondary battery cells 100 may be connected in series or in parallel in various ways. For example, the cylindrical secondary battery cells 100 may be connected in series or in parallel by connecting the bus bars 300 to the positive and negative terminals of the cylindrical secondary battery cells 100, respectively.

[0037] The cell frame 200 is provided in various shapes and made of various materials so that the multiple cylindrical secondary battery cells 100 can be arranged therein. The cell frame 200 can be made of a metal material in order to maintain a certain level of rigidity, but the present invention is not limited to this material.

[0038] The bus bar 300 is coupled to each of the cylindrical secondary battery cells 100. The bus bar 300 can be made of various electrically conductive materials, for example, copper or various types of copper alloys. For example, the bus bar 300 can be made of a tin-plated copper alloy, but the material is not limited thereto.

[0039] 3, a plurality of welded portions 310 are formed on the bus bar 300. Here, the welded portions 310 may be provided as protrusions protruding from the bus bar 300. The plurality of welded portions 310 may be joined to the cylindrical secondary battery cells 100 by, for example, resistance welding. Here, among the plurality of welded portions 310, the welded portions 310 that are spaced apart at larger intervals are provided to be welded to each other.

[0040] 1 to 3 as an example, four welded portions 310 may be formed on bus bar 300. However, the number of welded portions 310 is not limited to four.

[0041] Then, among the four welds 310, the first weld 311 and the third weld 313 located on the first diagonal straight line 400 are welded to each other so that the welds 310 spaced apart at a greater distance are welded to each other.

[0042] Further, among the four welded parts 310, the second welded part 312 and the fourth welded part 314 located on the straight line 500 in the second diagonal direction are welded to each other. Here, the four welded parts 310 may be arranged so that connecting the four welded parts 310 in a straight line forms a square shape. Alternatively, the four welded parts 310 may be arranged so that connecting the four welded parts 310 in a straight line forms a rectangular parallelepiped shape or a diamond shape.

[0043] That is, referring to FIG. 3, the first weld 311 is welded to the third weld 313, which is located diagonally farthest from the first weld 311, and the second weld 312 is welded to the fourth weld 314, which is located diagonally farthest from the second weld 312.

[0044] In this manner, when the welds 310 that are spaced apart at a greater distance among the four welds 310, that is, the welds 310 that are furthest apart, are welded together, the reactive current decreases.

[0045] Of the current supplied for welding, the effective current contributing to welding increases relatively by the amount of the reduced reactive current, thereby improving the welding quality and preventing damage to the welded portion.

[0046] On the other hand, a first diagonal straight line 400 connecting the first welded portion 311 and the third welded portion 313 and a second diagonal straight line 500 connecting the second welded portion 312 and the fourth welded portion 314 can be arranged perpendicular to each other.

[0047] In this way, by arranging the straight line 400 in the first diagonal direction and the straight line 500 in the second diagonal direction so that they are perpendicular to each other, the distances between the four welds 310 are balanced, making it possible to perform uniform welding.

[0048] Referring to FIG. 4, welding between the weld portion 310 of the bus bar 300 and the electrode terminal 110 is performed while being pressed by a welding rod 800. At this time, the welding of the weld portion 310 is performed by applying a first voltage 610 in an arbitrary first direction to perform a primary welding, and then by applying a second voltage 710 in a second direction opposite to the first direction to perform a secondary welding.

[0049] For example, the first welding is performed by applying a first voltage 610 with the left side set as a positive pole and the right side set as a negative pole with reference to FIG. 4, and a first current 620 flowing in a first direction, i.e., from the left side to the right side in FIG. 4.

[0050] Then, after the primary welding, secondary welding is performed. The secondary welding is performed by applying a second voltage 710 with the right side set as a positive pole and the left side set as a negative pole with reference to FIG. 4, and by causing a second current 720 to flow in a second direction, i.e., from the right side to the left side in FIG. 4.

[0051] In this manner, in the cylindrical secondary battery module 10 according to an embodiment of the present invention, after the first welding, the voltage polarity is switched to be opposite and the second welding is performed. By welding in this polarity switching manner, it is possible to perform a balanced joint throughout the entire welded portion 310.

[0052] Meanwhile, in the above-described polarity switching type welding, the first voltage 610 for the first welding and the second voltage 710 for the second welding, which is switched to have the opposite polarity from the first voltage 610, may be set to have different magnitudes. For example, the magnitude of the second voltage 710 for the second welding may be set to be greater than the magnitude of the first voltage 610 for the first welding.

[0053] As one embodiment relating to voltages, and referring to Figure 5, the absolute magnitude of the first voltage 610 for the primary weld is 5.0 volts, while the absolute magnitude of the second voltage 710 for the secondary weld is 5.4 volts. Volts are indicated in Figure 5 as V.

[0054] If welding is performed at a high voltage from primary weld 310 when bus bar 300 and electrode terminal 110 are not yet welded, there is a risk that the weld will become unstable as splashes occur on the weld surface.

[0055] To solve this problem, the primary welding is performed at a voltage relatively smaller than that of the secondary welding. Then, once the bus bar 300 and the electrode terminal 110 are joined to a certain extent by the primary welding, the secondary welding can be performed stably without expulsion of the welded surface, even if a voltage higher than that of the primary welding is used.

[0056] In other words, as described above, if the magnitude of the second voltage 710 for the second welding is set to be greater than the magnitude of the first voltage 610 for the first welding, it is possible to prevent the occurrence of surface splashing on the welding surface and perform stable welding.

[0057] However, the magnitude of the voltage in Fig. 5 is merely one embodiment and is not limited to the magnitude of the voltage. Also, the fact that the second welding is shown at -5.4 volts in Fig. 5 means that the voltage is applied in the opposite direction to the first welding.

[0058] FIG. 6 is a graph showing an actual experiment using the welding method of FIG. 4, FIG. 7 is a graph showing result data from the experiment of FIG. 6, FIG. 8 is a graph showing a comparative experiment with FIG. 6, and FIG. 9 is a graph showing result data from the experiment of FIG. 8.

[0059] 6, in an actual experiment, the absolute magnitude of the first voltage 610 for the first welding is 4.4 volts, and the absolute magnitude of the second voltage 710 for the second welding is 4.8 volts, so that the absolute magnitudes of the first voltage 610 and the second voltage 710 are different from each other. In FIG. 6, volts are indicated by V, as in FIG. 5.

[0060] Referring to FIG. 7 showing the result data of the actual experiment of FIG. 6, when the pressing force is 3.8 kgf, the maximum value of the tensile force is 22.42 kgf, the minimum value is 16.38 kgf, and the average value is 19.55 kgf. Here, the pressing force is the force applied to the welded part during welding, and the tensile force is the force required when pulling the welded part to remove it after welding is completed. A high tensile force means that the bonding strength of the welded part is high, and the mechanical properties of the welded part are improved. Here, the tensile force is a value measured using a mechanical test, for example, a test to mechanically remove the welded part after welding is completed.

[0061] 8, in an actual experiment, the absolute magnitude of the first voltage 610 for the first welding and the absolute magnitude of the second voltage 710 for the second welding are the same, 4.8 volts. In FIG. 8, volts are indicated as V, as in FIG. 5.

[0062] Referring to FIG. 9 showing the result data of the actual experiment of FIG. 8, when the pressing force is 3.8 kgf, the maximum value of the pulling force is 18.20 kgf, the minimum value is 12 kgf, and the average value is 16.1 kgf.

[0063] 7 and 9, it can be seen that the tensile force is higher when the absolute magnitudes of the first voltage 610 and the second voltage 710 are different from each other than when the absolute magnitudes of the first voltage 610 and the second voltage 710 are the same. In other words, it can be seen that when the absolute magnitudes of the first voltage 610 and the second voltage 710 are different from each other, particularly when the absolute magnitude of the second voltage 710 is greater than the absolute magnitude of the first voltage 610, the mechanical properties of the weld are improved.

[0064] In addition, in the above-described polarity switching type welding, the supply time of the first voltage 610 for the first welding and the supply time of the second voltage 710 for the second welding, which is switched to have the opposite polarity to the first voltage 610, may be set to be different from each other. For example, the supply time of the second voltage 710 for the second welding may be set to be longer than the supply time of the first voltage 610 for the first welding. This is for the same reason as described in the section on the difference in magnitude between the first voltage 610 and the second voltage 710 above.

[0065] As an example of the application time, referring to Figure 5, the application time of the first voltage 610 for the first welding is 3.9 milliseconds, while the application time of the second voltage 710 for the second welding is 4.3 milliseconds, where milliseconds are shown in ms.

[0066] If welding is performed for a long time at a preset voltage from the primary weld 310 when the bus bar 300 and the electrode terminal 110 are not yet welded, there is a risk that the welding will become unstable as splashes occur on the weld surface.

[0067] To solve this problem, the first welding is performed for a relatively shorter time than the second welding. Once a certain degree of joining has been achieved by the first welding, the second welding can be performed stably without expulsion of the weld surface, even if a voltage is applied for a longer time than the first welding.

[0068] In other words, as described above, if the supply time of the second voltage 710 for the second welding is set to be longer than the supply time of the first voltage 610 for the first welding, it is possible to prevent the occurrence of surface expulsion on the welding surface and perform stable welding.

[0069] However, the voltage supply time shown in FIG. 5 is merely one embodiment, and the voltage supply time is not limited to this.

[0070] Meanwhile, referring to Fig. 6, in an actual experiment, the supply time of the first voltage 610 for the first welding is 2.5 ms, while the supply time of the second voltage 710 for the second welding is 2.9 ms. In Fig. 6, milliseconds are indicated in ms, as in Fig. 5.

[0071] 8, in an actual experiment, the supply time of the first voltage 610 for the first welding and the supply time of the second voltage 710 for the second welding are the same, 3.3 milliseconds. In FIG. 8, milliseconds are indicated as ms, as in FIG. 5.

[0072] 7 and 9, it can be seen that the tensile force is higher when the supply times of the first voltage 610 and the second voltage 710 are different than when the supply times of the first voltage 610 and the second voltage 710 are the same. In other words, it can be seen that when the supply times of the first voltage 610 and the second voltage 710 are different, especially when the supply time of the second voltage 710 is longer than the supply time of the first voltage 610, the mechanical properties of the weld are improved.

[0073] Hereinafter, the operation and effects of the cylindrical secondary battery module 10 according to one embodiment of the present invention will be described with reference to the accompanying drawings.

[0074] Referring to the figure, bus bar 300 is formed with welded portions 310 provided as protrusions. Four welded portions 310 may be formed on bus bar 300, and the welded portions 310 located on diagonal straight lines may be welded to each other. For example, first welded portion 311 and third welded portion 313 may be welded, and second welded portion 312 and fourth welded portion 314 may be welded.

[0075] In this way, by welding the welds 310 that are the furthest apart, the reactive current is reduced, the welding quality is improved, and damage to the welded portion can be prevented.

[0076] Then, when welding two welded portions 310 together, the first welding can be performed so that the current flows in a given direction, and then the voltage polarity can be switched to the opposite side so that the current flows in the opposite direction to the given direction, and a second welding can be performed.

[0077] Such switching of polarity welding allows for a balanced joint to be produced throughout the entire weld 310.

[0078] Meanwhile, in the polarity switching type welding, the first voltage 610 for the first welding and the second voltage 710 for the second welding, which is switched to have the opposite polarity from the first voltage 610, may be set to have different magnitudes, for example, the magnitude of the second voltage 710 for the second welding may be set to be greater than the magnitude of the first voltage 610 for the first welding.

[0079] In addition, in polarity switching type welding, the supply time of the first voltage 610 for the first welding and the supply time of the second voltage 710 for the second welding, which is switched to have the opposite polarity from the first voltage 610, may be set to be different from each other, for example, the supply time of the second voltage 710 for the second welding may be set to be longer than the supply time of the first voltage 610 for the first welding.

[0080] This has the effect of preventing the occurrence of surface splashing on the welded surface when welding the busbar 300 to the cylindrical secondary battery cell 100, making it possible to perform welding stably.

[0081] Meanwhile, a secondary battery pack (not shown) according to an embodiment of the present invention may include one or more cylindrical secondary battery modules 10 according to an embodiment of the present invention as described above. In addition to the secondary battery module, the secondary battery pack (not shown) may further include a housing for accommodating the secondary battery module, and various devices for controlling charging and discharging of the secondary battery module, such as a battery management system (BMS), a current sensor, a fuse, etc.

[0082] Meanwhile, an automobile (not shown) according to one embodiment of the present invention may include the above-mentioned cylindrical secondary battery module 10 or a secondary battery pack (not shown), and the secondary battery pack (not shown) may include the cylindrical secondary battery module 10.

[0083] The cylindrical secondary battery module 10 or the secondary battery pack (not shown) according to an embodiment of the present invention may be applied to a specific automobile (not shown) that is configured to use electricity, such as an electric automobile or a hybrid automobile.

[0084] Although the present invention has been described above using limited embodiments and drawings, the technical concept of the present invention is in no way limited thereto, and it goes without saying that a person having ordinary knowledge in the technical field to which the present invention pertains can make various modifications and variations within the scope of the technical concept of the present invention and the equivalent scope of the claims. [Industrial Applicability]

[0085] INDUSTRIAL APPLICABILITY The present invention relates to a cylindrical secondary battery module, a secondary battery pack including the same, and an automobile, and is particularly applicable to industries related to secondary batteries. [Explanation of symbols]

[0086] 10. Cylindrical secondary battery module 100 Cylindrical secondary battery cell 110 Electrode terminal 200 Cell Frame 300 Busbar 310 Primary welding, welding 311 First Welding Section 312 Second Welding Section 313 No. 3 Welding Section 314 No. 4 Welding Section 400 First diagonal straight line 500 Second diagonal line 610 First Voltage 620 1st current 710 Second Voltage 720 2nd current 800 Welding Rod

Claims

1. a plurality of cylindrical secondary battery cells each containing an electrode assembly and an electrolyte; a cell frame in which the plurality of cylindrical secondary battery cells are arranged; a bus bar coupled to each of the plurality of cylindrical secondary battery cells and having a plurality of welds formed thereon; A method for manufacturing a cylindrical secondary battery module, comprising: Among the plurality of welds, two welds spaced apart at a larger interval are welded to the electrode terminal of the cylindrical secondary battery cell while being pressed against the electrode terminal by a welding rod; The welding of the welded portion is performed by applying a first voltage in a first direction to perform a primary welding, and then applying a second voltage in a second direction opposite to the first direction to perform a secondary welding, The bus bar has four welds formed therein; Among the four welds, a first weld and a third weld located on a straight line in a first diagonal direction are welded to the electrode terminal by the welding rod; Among the four welds, a second weld and a fourth weld located on a straight line in a second diagonal direction are welded to the electrode terminal by the welding rod; a magnitude of the second voltage for the second welding being greater than a magnitude of the first voltage for the first welding.

2. a plurality of cylindrical secondary battery cells each containing an electrode assembly and an electrolyte; a cell frame in which the plurality of cylindrical secondary battery cells are arranged; a bus bar coupled to each of the plurality of cylindrical secondary battery cells and having a plurality of welds formed thereon; A method for manufacturing a cylindrical secondary battery module, comprising: Among the plurality of welds, two welds spaced apart at a larger interval are welded to the electrode terminal of the cylindrical secondary battery cell while being pressed against the electrode terminal by a welding rod; The welding of the welded portion is performed by applying a first voltage in a first direction to perform a primary welding, and then applying a second voltage in a second direction opposite to the first direction to perform a secondary welding, The bus bar has four welds formed therein; Among the four welds, a first weld and a third weld located on a straight line in a first diagonal direction are welded to the electrode terminal by the welding rod; Among the four welds, a second weld and a fourth weld located on a straight line in a second diagonal direction are welded to the electrode terminal by the welding rod; a supply time of the second voltage for the second welding being longer than a supply time of the first voltage for the first welding.

3. 3. The method for manufacturing a cylindrical secondary battery module according to claim 1, wherein the first diagonal line connecting the first welded portion and the third welded portion and the second diagonal line connecting the second welded portion and the fourth welded portion are arranged perpendicular to each other.

4. The method for manufacturing a cylindrical secondary battery module according to claim 1 , wherein the welded portion is provided as a protrusion formed on the bus bar.

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