A high-capacity cylindrical multi-tab cell and a method of manufacturing the same

Abstract

The application discloses a high-capacity cylindrical multi-pole lug battery cell and a preparation method thereof, which comprises a shell, a winding core group arranged in the shell, a winding core, a positive pole lug and a negative pole lug, the winding core is wound by a positive pole sheet, a negative pole sheet and a separator, the positive pole lug is arranged at one axial end of the winding core and comprises a plurality of positive pole lugs drawn from the positive pole sheet, the negative pole lug is arranged at the axial end of the winding core and comprises a plurality of negative pole lugs drawn from the negative pole sheet, the positive pole lug and the negative pole lug are distributed in the circumferential direction of the same end surface of the winding core, and the two are staggered by 90-180 degrees in the circumferential direction. Compared with a traditional opposite-side pole lug scheme, the height occupation of one-side pole lug bending is reduced. Only one gasket is needed to meet the insulation protection requirement of two pole lugs on the same side, compared with the opposite-side pole lug scheme, one gasket is arranged at each end of the winding core, and the axial space is further released.

Description

Technical Field

[0001] This invention relates to the field of power battery technology, specifically to a high-capacity cylindrical multi-tab battery cell and its preparation method. Background Technology

[0002] Cylindrical lithium-ion batteries are widely used in consumer electronics, power tools, and new energy vehicles due to their high degree of standardization, mature manufacturing processes, and good consistency. As application scenarios increasingly demand higher battery energy density, maximizing cell capacity within the limited cylindrical space has become a key focus for the industry.

[0003] Currently, in multi-tab cylindrical battery cell designs, the positive and negative tabs are typically designed with opposite ends, meaning the positive tab extends from one end of the core and the negative tab from the other. After the core is assembled into the casing, the positive and negative tabs need to be bent in their respective directions. The bending of the positive tab requires space along the axial direction of one end of the core, while the bending of the negative tab requires space along the axial direction of the other end. This means that the height design of the electrode sheet needs to allow for the bending height of the tabs at both ends, resulting in a limitation on the effective height of the electrode sheet and thus restricting the cell capacity design.

[0004] To address these issues, some solutions attempt to place the positive and negative tabs on the same side. However, existing same-side tab designs typically require two connecting tabs to connect to the positive and negative tabs respectively. These two connecting tabs and their corresponding insulating pads still occupy a certain amount of axial space, limiting the capacity increase. Furthermore, the welding process for the connecting tabs in same-side tab designs is complex and prone to generating metal shavings, which can affect battery safety. Summary of the Invention

[0005] In view of the above, the object of the present invention is to provide a high-capacity cylindrical multipole battery cell.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a high-capacity cylindrical multi-tab battery cell, comprising: case; A core assembly, which is disposed within the housing, includes a core, a positive electrode tab, and a negative electrode tab. The core is formed by winding a positive electrode sheet, a negative electrode sheet, and a diaphragm. The positive electrode tab is disposed at one axial end of the winding core and includes a plurality of positive electrode tabs led out from the positive electrode sheet; the negative electrode tab is disposed at one axial end of the winding core and includes a plurality of negative electrode tabs led out from the negative electrode sheet. The positive electrode tab and the negative electrode tab are distributed circumferentially on the same end face of the winding core, and are offset from each other by 90° to 180° in the circumferential direction.

[0007] Ideally, the positive electrode tab and the negative electrode tab are distributed circumferentially on the same end face of the winding core, and are offset by 180° in the circumferential direction.

[0008] Ideally, it also includes: A positive electrode connector, which is connected to the positive electrode tab; A negative electrode connector is connected to the negative electrode tab.

[0009] Furthermore, the positive electrode connecting piece is used to electrically connect the positive electrode tab to the battery cap; The negative electrode connecting piece is used to electrically connect the negative electrode tab to the housing.

[0010] Furthermore, the negative electrode connecting piece has a bent portion, the shape of which matches the circumferential shape of the inner wall of the housing, so that the negative electrode connecting piece fits into the inner wall of the housing.

[0011] Furthermore, when the bent portion is bent to fit against the inner wall of the housing, the bent portion is welded to the housing by a through-laser welding process.

[0012] Furthermore, the positive electrode tab and the positive electrode connecting piece are connected by ultrasonic welding, and the negative electrode tab and the negative electrode connecting piece are connected by ultrasonic welding.

[0013] Ideally, it also includes: An insulating pad is disposed at one axial end of the winding core and is penetrated by the positive electrode tab and the negative electrode tab.

[0014] Another object of the present invention is to provide a method for preparing a high-capacity cylindrical multi-tab battery cell, comprising the following steps: A winding core is provided, which is formed by winding a positive electrode sheet, a negative electrode sheet and a diaphragm. During winding, the positive electrode tab and the negative electrode tab are led out from the same end of the winding core and are offset from each other by 90° to 180° in the circumferential direction. The positive electrode tab is welded to the positive electrode connecting piece, and the negative electrode tab is welded to the negative electrode connecting piece; Install the winding core into the housing; The negative electrode connecting piece is welded to the housing; Weld the cap to the positive electrode connecting piece; seal.

[0015] Optimally, before welding the positive electrode tab and the negative electrode tab to the positive electrode connecting piece and the negative electrode connecting piece respectively, the method further includes: placing an insulating pad on the axial end face of the core, so that the positive electrode tab and the negative electrode tab pass through the insulating pad; The negative electrode connecting piece has a bent portion, the shape of which matches the circumferential shape of the inner wall of the housing. After the core is inserted into the housing, the bent portion is bent to fit against the inner wall of the housing, and then the bent portion is welded to the housing by through laser welding.

[0016] This invention proposes a multi-tab battery cell assembly scheme with coiled same-side tabs, which changes the space occupied by the positive and negative tabs in terms of height from both tabs to both tabs occupying the same side. Compared with the existing opposite-side tab scheme, this has the following advantages: (1) Significantly increased cell capacity. By placing the positive and negative electrodes on the same end face of the winding core, the electrode bending only requires one height space along the axial direction of the winding core, reducing the height occupied by bending one electrode compared to the traditional opposite-side electrode outlet scheme. Simultaneously, the positive and negative electrodes pass through the same insulating gasket, requiring only one gasket to meet the insulation protection requirements of both electrodes on the same side. Compared to the opposite-side electrode outlet scheme, which requires a gasket at each end of the winding core, this further frees up axial space. The space freed up in these two aspects provides greater margin for electrode height design, enabling a higher cell capacity within the same external dimensions.

[0017] (2) High rate performance. The present invention adopts a multi-tab structure design, which can effectively reduce the internal resistance of the battery and reduce the heat generation during high current charging and discharging, so as to achieve high capacity while maintaining excellent high rate performance.

[0018] (3) High process safety. In the assembly process of this invention, the tabs and connecting pieces are ultrasonically welded, and the negative electrode connecting piece and the shell are externally penetrating laser welded. The welding process will not generate metal shavings inside the core, effectively avoiding the risk of internal short circuit caused by metal shavings and improving process safety. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the core assembly of the present invention; Figure 2 This is a partial structural schematic diagram of the high-capacity cylindrical multi-pole battery cell of the present invention; Figure 3 This is a schematic diagram of the high-capacity cylindrical multi-pole battery cell of the present invention; Figure 4 This is a schematic diagram of the structure of the high-capacity cylindrical multi-pole battery cell of the present invention (the core assembly is placed in the housing). Detailed Implementation

[0020] The preferred embodiments of the present invention will now be described in detail.

[0021] The foregoing descriptions and other technical contents, features, and effects of this invention will be clearly presented in the following detailed description of a preferred embodiment with reference to the accompanying drawings. The directional terms used in the following embodiments, such as up, down, left, right, front, or back, are merely for reference to the accompanying drawings. Therefore, the directional terms used are for illustrative purposes and not for limiting the invention.

[0022] The following detailed description of various embodiments of the present invention, with reference to the accompanying drawings. Besides these detailed descriptions, the present invention can be widely implemented in other embodiments, and any easy substitutions, modifications, or equivalent changes to the described embodiments are included within the scope of the present invention and are subject to the claims. In the description of the specification, many specific details are provided to give the reader a more complete understanding of the present invention; however, the present invention may still be implemented even if some or all of the specific details are omitted. Furthermore, well-known steps or components are not described in the details to avoid unnecessarily limiting the present invention. The same or similar components in the drawings will be represented by the same or similar symbols. It should be noted that the drawings are for illustrative purposes only and do not represent the actual size or quantity of components; some details may not be fully drawn for the sake of simplicity. Example 1

[0023] This embodiment provides a high-capacity cylindrical multi-tab battery cell, such as... Figures 1 to 4 As shown, it mainly includes a shell 1, a core assembly 2, an insulating pad 3, a positive electrode connecting piece 4, and a negative electrode connecting piece 5.

[0024] The housing 1 is a cylindrical structure with one end open and the other closed, made of alloy material, which has good structural strength and corrosion resistance (such as stainless steel, aluminum alloy, etc.). A groove 11 can be provided on the housing 1, located near the open end of the housing 1, to axially limit and fix the core assembly 2 after it is installed in the housing 1, preventing the core assembly 2 from moving inside the housing 1.

[0025] The core assembly 2 is disposed within the housing 1 and includes a core 21, a positive electrode tab 22, and a negative electrode tab 23. The core 21 is manufactured by a winding process from a positive electrode sheet, a negative electrode sheet, and a separator. The positive electrode sheet includes a positive current collector (such as aluminum foil) and a layer of positive active material coated on the surface of the positive current collector; the negative electrode sheet includes a negative current collector (such as copper foil) and a layer of negative active material coated on the surface of the negative current collector; the separator is disposed between the positive and negative electrode sheets to prevent direct contact between the positive and negative electrode sheets from causing a short circuit. The positive electrode sheet, separator, and negative electrode sheet are sequentially stacked and wound into a cylindrical core 21.

[0026] A positive electrode tab 22 is disposed at one axial end of the winding core 21 and includes multiple positive electrode tabs extending from the positive electrode sheet. The multiple positive electrode tabs converge and coalesce at one axial end of the winding core 21 to form a positive electrode tab group (i.e., positive electrode tab 22). The number of positive electrode tabs is preferably 3 to 10. A negative electrode tab 23 is disposed at the same axial end of the winding core 21 and includes multiple negative electrode tabs extending from the negative electrode sheet. The multiple negative electrode tabs converge and coalesce at one axial end of the winding core 21 to form a negative electrode tab group (i.e., negative electrode tab 23). The number of negative electrode tabs 23 is preferably 3 to 10. In this embodiment, the positive electrode tab 22 and the negative electrode tab 23 are distributed circumferentially on the same end face of the winding core 21, and are offset 180° circumferentially (of course, in other embodiments, they can also be offset by any angle between 90° and 180°). By placing the positive electrode tab 22 and the negative electrode tab 23 on the same end face of the core 21, the tab bending only requires one height space in the axial direction of the core 21. Compared with the opposite side tab solution, it reduces the height occupied by the tab bending on one side, providing more margin for the electrode height design.

[0027] An insulating gasket 3 is disposed at one axial end of the core 21 and is penetrated by the positive electrode tab 22 and the negative electrode tab 23. The insulating gasket 3 is made of insulating materials, such as polypropylene (PP), polyethylene terephthalate (PET), polyimide (PI), PVDF, PTFE, and other plastic materials. When the positive electrode tab 22 and the negative electrode tab 23 are bent, it can prevent the positive electrode tab 22 and the negative electrode tab 23 from directly contacting the end face of the core 21 and causing a short circuit. In this embodiment, since the positive electrode tab 22 and the negative electrode tab 23 are both led out from the same end face of the core 21, only one insulating gasket 3 is needed to simultaneously meet the insulation protection requirements of both tabs, reducing the gasket material by one compared to the opposite-side tab solution. In this embodiment, the insulating gasket 3 is approximately an integral circular structure, with the positive electrode tab 22 and the negative electrode tab 23 extending through the corresponding positions of the insulating gasket 3.

[0028] The positive electrode connecting piece 4 is connected to the positive electrode tab 22, used to electrically connect the positive electrode tab 22 to the cap (battery cap). The negative electrode connecting piece 5 is connected to the negative electrode tab 23, used to electrically connect the negative electrode tab 23 to the casing 1. The positive electrode tab 22 and the positive electrode connecting piece 4 are connected by ultrasonic welding, and the negative electrode tab 23 and the negative electrode connecting piece 5 are connected by ultrasonic welding. Ultrasonic welding has the advantages of strong welding and no metal shavings, which can effectively ensure welding quality and process safety.

[0029] The negative electrode connecting piece 5 has a bent portion 51, the shape of which matches the circumferential shape of the inner wall of the housing 1. When the negative electrode connecting piece 5 is bent outward, it can fit against the inner wall of the housing 1. Specifically, the negative electrode connecting piece 5 includes an integrally formed welding plane portion and an arc-shaped fitting portion (i.e., the bent portion 51). The welding plane portion is ultrasonically welded to the negative electrode tab 23, and the arc-shaped fitting portion fits against the inner wall of the housing 1. When the bent portion 51 is bent to fit against the inner wall of the housing 1, the bent portion 51 and the housing 1 can be welded by external laser welding. External laser welding is performed from the outside of the housing 1, which does not generate metal shavings inside the core 21, thus ensuring high safety.

[0030] A cap (not shown in the figure) is located at the open end of the housing 1. The cap is connected to the positive electrode connecting piece by laser welding to enable the positive electrode to output to the outside. A sealing ring (not shown in the figure) is provided between the cap 6 and the housing 1 to ensure the airtightness of the cell. Example 2

[0031] This embodiment provides a method for preparing a high-capacity cylindrical multi-tab battery cell, used to prepare the high-capacity cylindrical multi-tab battery cell described in Example 1, mainly including the following steps: S1: Winding to form a core.

[0032] A positive electrode sheet, a negative electrode sheet, and a separator are provided. The positive electrode sheet, separator, and negative electrode sheet are sequentially stacked and wound into a cylindrical core 21. During winding, the positive electrode tab 22 and the negative electrode tab 23 are drawn out from the same end of the core 21, and they are offset by 180° in the circumferential direction (of course, in other embodiments, they can be offset by any angle between 90° and 180°). The positive electrode tab 22 includes multiple positive tabs drawn from the positive electrode sheet, and the negative electrode tab 23 includes multiple negative tabs drawn from the negative electrode sheet. The multiple positive tabs are gathered and aggregated at one axial end of the core 21 to form a positive tab group (i.e., positive electrode tab 22), and the multiple negative tabs are gathered and aggregated at one axial end of the core 21 to form a negative tab group (i.e., negative electrode tab 23). The number of positive and negative tabs is preferably 3 to 10, respectively.

[0033] S2: Place an insulating pad.

[0034] An insulating pad 3 is placed on the axial end face of the core 21, allowing the positive electrode tab 22 and the negative electrode tab 23 to pass through it. The insulating pad 3 is made of insulating materials such as polypropylene (PP), polyethylene terephthalate (PET), polyimide (PI), PVDF, PTFE, etc. The insulating pad 3 is roughly a one-piece circular structure, covering the area between the positive electrode tab 22 and the negative electrode tab 23 and the end face of the core 21. When the positive electrode tab 22 and the negative electrode tab 23 are subsequently bent, the insulating pad 3 can prevent the positive electrode tab 22 and the negative electrode tab 23 from directly contacting the end face of the core 21 and causing a short circuit. Since the positive electrode tab 22 and the negative electrode tab 23 both extend from the same end face of the core 21, only one insulating pad 3 is needed to meet the insulation protection requirements of both tabs simultaneously. Compared with the opposite-side tab design, this reduces the material required for one pad and simplifies the assembly process.

[0035] S3: Pre-welded electrode tabs.

[0036] The multiple positive tabs of the positive electrode tab 22 are gathered, aggregated, and pre-welded to fix them; the multiple negative electrode tabs of the negative electrode tab 23 are gathered, aggregated, and pre-welded to fix them. Pre-welding can be performed using hot pressing or ultrasonic pre-welding methods, aggregating the multiple tabs into one piece, facilitating subsequent welding to the connecting piece. No metal shavings are generated during the pre-welding process, ensuring process safety.

[0037] S4: Welding of the electrode tab to the connecting piece.

[0038] The positive electrode tab 22 (positive electrode tab group) is connected to the positive electrode connecting piece 4 by ultrasonic welding, and the negative electrode tab 23 (negative electrode tab group) is connected to the negative electrode connecting piece 5 by ultrasonic welding. The positive electrode connecting piece 4 is used to electrically connect the positive electrode tab 22 to the cap (battery cap), and the negative electrode connecting piece 5 is used to electrically connect the negative electrode tab 23 to the housing 1. Ultrasonic welding has the advantages of strong welding and no metal shavings, which can effectively ensure welding quality and process safety. The negative electrode connecting piece 5 has a bent part 51, the shape of which matches the circumferential shape of the inner sidewall of the housing 1, which facilitates subsequent fitting and welding with the inner sidewall of the housing 1 after insertion into the housing. The ultrasonic welding parameters are adjusted according to the material and thickness of the tab and connecting piece to ensure welding strength.

[0039] S5: Core inserted into shell.

[0040] The core 21, with the positive electrode connecting piece 4 and the negative electrode connecting piece 5 welded together, is inserted into the housing 1. The housing 1 is a cylindrical structure with one end open and the other closed, made of alloy material, possessing good structural strength and corrosion resistance (such as stainless steel, aluminum alloy, and other conventional alloy materials). When inserting, attention must be paid to the orientation, ensuring that the end containing the positive electrode tab 22 and the negative electrode tab 23 (i.e., the tab lead-out end) faces the open end of the housing 1. Since both the positive electrode tab 22 and the negative electrode tab 23 are led out from the same end face of the core 21, only the orientation of one end face needs to be controlled during insertion, simplifying the assembly operation.

[0041] S6: Bending and welding of negative electrode connecting piece.

[0042] After the core 21 is inserted into the housing 1, the bent portion 51 of the negative electrode connecting piece 5 is bent outward to fit against the inner wall of the housing 1. Then, the bent portion 51 is welded to the housing 1 by through-laser welding. Specifically, the bent portion 51 is bent towards the inner wall of the housing 1, so that the outer arc surface of the arc-shaped fitting portion (i.e., the bent portion 51) of the bent portion 51 fits against the inner wall of the housing 1. Then, through-laser welding is performed from the outside of the housing 1 to fix the bent portion 51 to the housing 1. This step achieves the electrical connection between the negative electrode tab 23 and the housing 1, making the entire housing 1 a negative electrode outlet channel. External through-laser welding is performed from the outside of the housing 1, which will not generate metal shavings inside the core 21, ensuring high safety. The bent portion 51 of the negative electrode connecting piece 5 is pre-formed into an arc shape that matches the circumferential shape of the inner wall of the housing 1 during the incoming material process, which facilitates a tight fit with the inner wall of the housing 1 after bending and ensures the welding effect.

[0043] S7: Grooving.

[0044] A groove 11 is formed on the housing 1, located near the open end of the housing 1. The groove 11 is used to axially limit and fix the core 21, preventing the core 21 from moving within the housing 1. The groove can be formed by rolling with a hob. The groove 11 further ensures the positional stability of the core 21 within the housing 1, improving the structural reliability of the battery cell.

[0045] S8: The cap is welded to the positive electrode connecting piece.

[0046] The cap (not shown in the figure) is laser-welded to the positive electrode connecting piece 4 to achieve electrical connection between the positive electrode tab 22 and the cap. The cap is located at the open end of the housing 1, and a sealing ring (not shown in the figure) is provided between the cap and the housing 1 to ensure the sealing of the cell. The positive electrode connecting piece 4 extends upward and is laser-welded to the cap to achieve the external output of the positive electrode.

[0047] S9: Seal.

[0048] The cap is sealed to the open end of the casing 1 to complete the battery encapsulation. Sealing methods include edge sealing or laser sealing. After sealing, a sealed space is formed inside the cell, and the cell can be activated after electrolyte injection.

[0049] The beneficial effects of the preparation method in this embodiment: The manufacturing method of this embodiment draws the positive electrode tab 22 and the negative electrode tab 23 from the same end of the core 21. The tab bending only needs to be performed at one axial end of the core 21, reducing the bending operation step by one end compared to the opposite-side tab drawing method. Simultaneously, only one insulating pad 3 is needed to meet the insulation protection requirements of the two tabs on the same side, reducing the pad placement step by one compared to the opposite-side tab drawing method. These two simplified processes effectively improve assembly efficiency and reduce production costs.

[0050] Furthermore, the ultrasonic welding and external penetrating laser welding involved in this embodiment are both mature processes that do not generate metal shavings inside the core 21, ensuring high process safety. The bent portion 51 of the negative electrode connecting piece 5 is pre-formed into an arc shape upon arrival, matching the circumferential shape of the inner wall of the shell 1, ensuring a good fit with the inner wall of the shell 1 after bending, facilitating the penetrating laser welding operation, and possessing good mass production feasibility. This preparation method is applicable not only to steel-shell cylindrical cells but also to aluminum-shell cylindrical cells, demonstrating good versatility.

[0051] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A high-capacity cylindrical multi-tab battery cell, characterized in that it include: Shell (1); The core assembly (2) is disposed inside the housing (1) and includes a core (21), a positive electrode tab (22) and a negative electrode tab (23). The core (21) is formed by winding a positive electrode sheet, a negative electrode sheet and a diaphragm. The positive electrode tab (22) is disposed at one axial end of the winding core and includes a plurality of positive electrode tabs led out from the positive electrode sheet; the negative electrode tab (23) is disposed at one axial end of the winding core and includes a plurality of negative electrode tabs led out from the negative electrode sheet. The positive electrode tab (22) and the negative electrode tab (23) are distributed circumferentially on the same end face of the core (21), and are offset from each other by 90° to 180° in the circumferential direction.

2. The high-capacity cylindrical multi-tab battery cell according to claim 1, characterized in that: The positive electrode tab (22) and the negative electrode tab (23) are distributed circumferentially on the same end face of the core (21), and are offset by 180° in the circumferential direction.

3. The high-capacity cylindrical multi-tab battery cell according to claim 1, characterized in that, It also includes: Positive electrode connecting piece (4), the positive electrode connecting piece (4) is connected to the positive electrode tab (22), The negative electrode connecting piece (5) is connected to the negative electrode tab (23).

4. The high-capacity cylindrical multi-tab battery cell according to claim 3, characterized in that: The positive electrode connecting piece (4) is used to electrically connect the positive electrode tab (22) to the battery cap; The negative electrode connecting piece (5) is used to electrically connect the negative electrode tab (23) to the housing (1).

5. The high-capacity cylindrical multi-tab battery cell according to claim 3 or 4, characterized in that: The negative electrode connecting piece (5) has a bent portion (51), the shape of which matches the circumferential shape of the inner wall of the housing (1) so that the negative electrode connecting piece (5) fits against the inner wall of the housing (1).

6. The high-capacity cylindrical multi-tab battery cell according to claim 5, characterized in that: When the bent portion (51) is bent to fit against the inner wall of the housing (1), the bent portion (51) and the housing (1) are welded by through laser welding.

7. The high-capacity cylindrical multi-tab battery cell according to claim 3, characterized in that: The positive electrode tab (22) and the positive electrode connecting piece (4) are connected by ultrasonic welding, and the negative electrode tab (23) and the negative electrode connecting piece (5) are connected by ultrasonic welding.

8. The high-capacity cylindrical multi-tab battery cell according to claim 1, characterized in that, It also includes: An insulating pad (3) is disposed at one axial end of the core (21) and is penetrated by the positive electrode tab (22) and the negative electrode tab (23).

9. A method for preparing a high-capacity cylindrical multi-tab battery cell, characterized in that, Includes the following steps: Provide a core (21), which is formed by winding a positive electrode plate, a negative electrode plate and a diaphragm. During winding, the positive electrode tab (22) and the negative electrode tab (23) are drawn out from the same end of the core (21) and are offset from each other by 90° to 180° in the circumferential direction. The positive electrode tab (22) is welded to the positive electrode connecting piece (4), and the negative electrode tab (23) is welded to the negative electrode connecting piece (5); Install the winding core (21) into the housing (1); The negative electrode connecting piece (5) is welded to the housing (1); The cap (6) is welded to the positive electrode connecting piece (4); seal.

10. The method for preparing a high-capacity cylindrical multi-tab battery cell according to claim 9, characterized in that: Before welding the positive electrode tab (22) and the negative electrode tab (23) to the positive electrode connecting piece (4) and the negative electrode connecting piece (5) respectively, the method further includes: placing an insulating pad (3) on the axial end face of the core (21) so that the positive electrode tab (22) and the negative electrode tab (23) pass through the insulating pad (3). The negative electrode connecting piece (5) has a bent portion (51). The shape of the bent portion (51) matches the circumferential shape of the inner wall of the housing (1). After the core (21) is inserted into the housing (1), the bent portion (51) is bent to fit against the inner wall of the housing (1). Then, the bent portion (51) is welded to the housing (1) by laser welding.

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