Battery pack

Abstract

To bond between a terminal and a bus bar efficiently while suppressing a thermal influence on a gasket.SOLUTION: A battery pack includes: a plurality of cells including a container in which a charge-discharge body is accommodated, an electrode terminal provided on one surface of the container, and a sealing member that is provided between the container and the electrode terminal and seals between the container and the electrode terminal; and a bus bar to be bonded to the electrode terminal of the battery that is different. The bus bar includes a bus bar hole for exposing at least a part of an upper surface of the electrode terminal.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a battery pack.

Background Art

[0002] As the background art in this technical field, there is Japanese Patent No. 6392447 (Patent Document 1). This publication describes that "while using a battery bus bar with dimensional errors, the bus bar can be stably and reliably laser welded to the electrode terminal, and the battery cell can be electrically connected in a low-resistance state. That is, the above battery system is provided with a notch for guiding the protruding portion of the electrode terminal in the bus bar, and an exposure gap for exposing the welding surface of the electrode terminal is provided between this notch and the protruding portion. The bus bar is welded to the welding surface at the inner edge side of the notch by a fillet weld portion, and the opposing surface to the welding surface of the electrode terminal is welded to the welding surface at the penetration weld portion. It is welded to the electrode terminal with a predetermined welding width by both the fillet weld portion and the penetration weld portion."

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Patent Document 1 discloses a method for joining a terminal welding surface and a busbar notch using laser fillet welding and through welding. The method disclosed in Patent Document 1 uses the terminal's protrusion as a reference for laser irradiation to weld the widest possible area. However, with this method, a large area of ​​the terminal melts due to through welding, raising concerns about heat input to the gasket (sealing member) by the laser. The gasket is provided as a sealing material between the terminal and the cover material, maintaining its sealing properties and sealing through the repulsive force created by compression. Since the gasket is made of resin, if it is heated to a temperature exceeding its limit, it may deteriorate, reducing its repulsive force and potentially impairing its sealing properties. Laser welding generates heat above the melting point of the metal, so although the connection between the metal and the gasket does not melt, the temperature may rise to a level where the gasket deteriorates due to heat conduction from the metal to the gasket. Therefore, the present invention provides a structure that efficiently joins the terminal and the busbar while minimizing the thermal impact on the gasket. [Means for solving the problem]

[0005] To solve the above problems, for example, the configuration described in the claims may be adopted. The present invention includes several means for solving the above problems, but one example is "a battery pack comprising a container housing charge and discharge elements, electrode terminals provided on one surface of the container, a sealing member provided between the container and the electrode terminals to seal the space between the container and the electrode terminals, and busbars connected to the electrode terminals of different batteries, wherein the busbars are provided with busbar holes that expose at least a portion of the upper surface of the electrode terminals." [Effects of the Invention]

[0006] According to the present invention, the terminal and the busbar can be efficiently joined while minimizing the thermal impact on the gasket. [Brief explanation of the drawing]

[0007] [Figure 1] External perspective view of a rectangular rechargeable battery [Figure 2] Deconstructed perspective view of a rectangular rechargeable battery [Figure 3] Exploded perspective view showing a portion of the wound electrode group unfolded. [Figure 4] External perspective view of the battery module [Figure 5] Cross-sectional view of the mating portion between the terminal and busbar in Example 1 [Figure 6] Cross-sectional view of the mating portion after joining the terminal and busbar in Example 1. [Figure 7] Top view of the cell and busbar of Example 1 [Figure 8] Top view of the cell and busbar in Example 2 [Figure 9] Top view of the cell and busbar of Example 3 [Figure 10] Cross-sectional view of the mating portion between the terminal and busbar in Example 3 [Modes for carrying out the invention]

[0008] The following examples will be described with reference to the drawings. [Examples]

[0009] In this embodiment, an example of a flat wound secondary battery 100 is described. Figure 1 is a perspective view of the external appearance of a flat-wound secondary battery. The flat wound secondary battery 100 comprises a battery case 1 and a lid (battery lid) 6. The battery case 1 has sides and a bottom surface 1d, which have a pair of opposing wide sides 1b with a relatively large area and a pair of opposing narrow sides 1c with a relatively small area, and has an opening 1a above it.

[0010] Inside the battery can 1, a wound group 3 is housed, and the opening 1a of the battery can 1 is sealed by a battery lid 6. The battery lid 6 is in the shape of a substantially rectangular flat plate and is welded so as to close the upper opening 1a of the battery can 1, thereby sealing the battery can 1. The battery lid 6 is provided with a positive electrode external terminal 14 and a negative electrode external terminal 12. Charging is carried out on the wound group 3 via the positive electrode external terminal 14 and the negative electrode external terminal 12, and power is supplied to an external load. The battery lid 6 is integrally provided with a gas discharge valve 10. When the pressure inside the battery container rises, the gas discharge valve 10 opens and gas is discharged from the inside, reducing the pressure inside the battery container. Thereby, the safety of the flat wound secondary battery 100 is ensured.

[0011] FIG. 2 is an exploded perspective view of a rectangular secondary battery. The battery can 1 of the flat wound secondary battery 100 has a rectangular bottom surface 1d, side surfaces 1b and 1c that form a rectangular tube structure rising from the bottom surface 1d, and an opening 1a that is open upward at the upper ends of the side surfaces 1b and 1c. Inside the battery can 1, a wound group 3 is housed via an insulating protection film 2.

[0012] Since the wound group 3 is wound in a flat shape, it has a pair of semi-circular portions facing each other with a semi-circular cross-section and a flat portion continuously formed between the pair of semi-circular portions. The wound group 3 is inserted into the battery can 1 from one semi-circular portion so that the winding axis direction is along the lateral width direction of the battery can 1, and the other semi-circular portion side is arranged on the upper opening side.

[0013] The positive electrode foil exposed portion 34c of the wound group 3 is electrically connected to the positive electrode external terminal 14 provided on the battery lid 6 via a positive electrode current collector plate (current collecting terminal) 44. Also, the negative electrode foil exposed portion 32c of the wound group 3 is electrically connected to the negative electrode external terminal 12 provided on the battery lid 6 via a negative electrode current collector plate (current collecting terminal) 24. Thereby, power is supplied from the wound group 3 to an external load via the positive electrode current collector plate 44 and the negative electrode current collector plate 24, and external generated power is supplied to the wound group 3 via the positive electrode current collector plate 44 and the negative electrode current collector plate 24 for charging.

[0014] In order to electrically insulate the positive electrode external terminal 14 and the negative electrode external terminal 12, and the positive electrode current collector plate 44 and the negative electrode current collector plate 24 from the battery lid 6 respectively, a gasket 5 which is a sealing member and an insulating plate 7 are provided on the battery lid 6. Also, after injecting an electrolytic solution into the battery can 1 from the liquid injection port 9, a liquid injection plug 11 is joined to the battery lid 6 by laser welding to seal the liquid injection port 9, and the flat wound secondary battery 100 is sealed.

[0015] Here, as the forming materials of the positive electrode external terminal 14 and the positive electrode current collector plate 44, for example, an aluminum alloy can be mentioned, and as the forming materials of the negative electrode external terminal 12 and the negative electrode current collector plate 24, for example, a copper alloy can be mentioned. Also, as the forming materials of the insulating plate 7 and the gasket 5, for example, resin materials having insulating properties such as polybutylene terephthalate, polyphenylene sulfide, perfluoroalkoxy fluororesin, etc. can be mentioned.

[0016] Also, a liquid injection port 9 for injecting an electrolytic solution into the battery container is formed in the battery lid 6, and this liquid injection port 9 is sealed by a liquid injection plug 11 after injecting the electrolytic solution into the battery container. Here, as the electrolytic solution injected into the battery container, for example, a non-aqueous electrolytic solution in which a lithium salt such as lithium hexafluorophosphate (LiPF6) is dissolved in a carbonate-based organic solvent such as ethylene carbonate can be applied.

[0017] The positive electrode external terminal 14 and the negative electrode external terminal 12 have a welding joint portion which is welded and joined to a bus bar or the like. The welding joint portion has a rectangular parallelepiped block shape protruding upward from the battery lid 6, and the lower surface faces the surface of the battery lid 6, and the upper surface is parallel to the battery lid 6 at a predetermined height position.

[0018] The positive electrode connection portion 14b and the negative electrode connection portion 12b each protrude from the lower surfaces of the positive electrode external terminal 14 and the negative electrode external terminal 12, respectively, and have a cylindrical shape at their tips that can be inserted into the positive electrode side through hole 46 and the negative electrode side through hole 26 of the battery cover 6. The positive electrode connection portion 14b and the negative electrode connection portion 12b penetrate the battery cover 6 and protrude inward from the positive electrode current collector plate base 41 and the negative electrode current collector plate base 21 of the positive electrode current collector plate 44 and the negative electrode current collector plate 24, and their tips are crimped to integrally fix the positive electrode external terminal 14 and the negative electrode external terminal 12, and the positive electrode current collector plate 44 and the negative electrode current collector plate 24 to the battery cover 6. A gasket 5 is interposed between the positive electrode external terminal 14 and the negative electrode external terminal 12 and the battery cover 6, and an insulating plate 7 is interposed between the positive electrode current collector plate 44 and the negative electrode current collector plate 24 and the battery cover 6.

[0019] The positive electrode current collector plate 44 and the negative electrode current collector plate 24 each have a rectangular plate-shaped positive electrode current collector plate base 41 and negative electrode current collector plate base 21 positioned opposite the lower surface of the battery cover 6, and a positive electrode side connection end 42 and a negative electrode side connection end 22 that are bent at the side ends of the positive electrode current collector plate base 41 and the negative electrode current collector plate base 21, extending toward the bottom surface along the wide surface of the battery can 1, and connected in a state where they are overlapped opposite the positive electrode foil exposed portion 34c and the negative electrode foil exposed portion 32c of the winding group 3. The positive electrode current collector plate base 41 and the negative electrode current collector plate base 21 each have a positive electrode side opening hole 43 and a negative electrode side opening hole 23, through which the positive electrode connection portion and the negative electrode connection portion are inserted.

[0020] An insulating protective film 2 is wound around the winding group 3, with the central axis being an axis perpendicular to the winding axis direction of the winding group 3, along the flattened surface of the winding group 3. The insulating protective film 2 consists of a single sheet or multiple film members made of synthetic resin such as polypropylene, and has a length that allows it to be wound around the winding group 3 with the winding center being a direction parallel to the flattened surface of the winding group 3 and perpendicular to the winding axis direction. Furthermore, the insulating protective film 2 covers the winding group 3 on the bottom surface 1d side of the battery can 1, thereby preventing contact between the winding group 3 and the battery can 1.

[0021] Figure 3 is an exploded perspective view showing a portion of the wound electrode assembly unfolded. The winding group 3 is constructed by winding a negative electrode 32 and a positive electrode 34 in a flattened shape with separators 33 and 35 in between. In the winding group 3, the outermost electrode is the negative electrode 32, and the separators 33 and 35 are wound further outside of it. The separators 33 and 35 serve to insulate the positive electrode 34 and the negative electrode 32.

[0022] The portion of the negative electrode 32 coated with the negative electrode mixture layer 32b is wider than the portion of the positive electrode 34 coated with the positive electrode mixture layer 34b, so that the portion coated with the positive electrode mixture layer 34b is always sandwiched between the portions coated with the negative electrode mixture layer 32b. The exposed positive foil portion 34c and the exposed negative foil portion 32c are bundled together at their flat surfaces and connected by welding or the like. The separators 33 and 35 are wider than the portion coated with the negative electrode mixture layer 32b in the width direction, but since they are wound around the exposed positive foil portion 34c and the exposed negative foil portion 32c so that the metal foil surface at the ends is exposed, they do not interfere with bundling and welding.

[0023] The positive electrode 34 has a positive electrode active material mixture on both sides of the positive electrode foil, which is the positive electrode current collector, and a positive electrode foil exposed portion 34c is provided at one end in the width direction of the positive electrode foil where the positive electrode active material mixture is not applied. The negative electrode 32 has a negative electrode active material mixture on both sides of the negative electrode foil, which is the negative electrode current collector, and a negative electrode foil exposed portion 32c is provided at the other end in the width direction of the positive electrode foil where the negative electrode active material mixture is not applied. The positive electrode foil exposed portion 34c and the negative electrode foil exposed portion 32c are regions where the metal surface of the electrode foil is exposed, and are wound so that they are positioned on one side and the other side in the winding axis direction.

[0024] For the positive electrode 34, 100 parts by weight of lithium manganate (chemical formula LiMn2O4) was used as the positive electrode active material, to which 10 parts by weight of flake graphite as a conductive material and 10 parts by weight of polyvinylidene fluoride (hereinafter referred to as PVDF) as a binder were added. N-methylpyrrolidone (hereinafter referred to as NMP) was added as a dispersion solvent and kneaded to prepare a positive electrode mixture. This positive electrode mixture was applied to both sides of a 20 μm thick aluminum foil (positive electrode foil), leaving welded areas (uncoated positive electrode areas). Subsequently, after drying, pressing, and cutting processes, a positive electrode 34 with a positive electrode active material coating thickness of 90 μm, excluding the aluminum foil, was obtained.

[0025] Furthermore, although this embodiment illustrates the case in which lithium manganate is used as the positive electrode active material, other lithium manganates having a spinel crystal structure, lithium manganese composite oxides partially substituted or doped with a metal element, lithium cobaltate or lithium titanate having a layered crystal structure, or lithium-metal composite oxides partially substituted or doped with a metal element may also be used.

[0026] For the negative electrode 32, a negative electrode mixture was prepared by adding 10 parts by weight of PVDF as a binder to 100 parts by weight of amorphous carbon powder as the negative electrode active material, and then adding NMP as a dispersion solvent and kneading the mixture. This negative electrode mixture was applied to both sides of a 10 μm thick copper foil (negative electrode foil), leaving welded areas (uncoated negative electrode areas). Subsequently, after drying, pressing, and cutting processes, a negative electrode 32 with a negative electrode active material coating thickness of 70 μm, excluding the copper foil, was obtained.

[0027] In this embodiment, the example shows the use of amorphous carbon as the negative electrode active material, but it is not limited to this. Natural graphite capable of inserting and removing lithium ions, various artificial graphite materials, carbonaceous materials such as coke, compounds such as Si and Sn (e.g., SiO, TiSi2, etc.), or composite materials thereof may also be used. The particle shape is also not particularly limited, and can be flaky, spherical, fibrous, or lumpy.

[0028] Furthermore, although this embodiment illustrates the use of PVDF as a binder for the coated portion of the positive electrode and negative electrode, polymers such as polytetrafluoroethylene, polyethylene, polystyrene, polybutadiene, butyl rubber, nitrile rubber, styrene-butadiene rubber, polysulfide rubber, nitrocellulose, cyanoethylcellulose, various latexes, acrylonitrile, vinyl fluoride, vinylidene fluoride, propylene fluoride, chloroprene fluoride, acrylic resins, and mixtures thereof can be used.

[0029] Furthermore, as the core, for example, a resin sheet with higher bending rigidity than the positive electrode foil, negative electrode foil, or separator 33 can be wound up and used.

[0030] Figure 4 is an external perspective view of the battery module. The battery module 80 is made by connecting multiple flat wound secondary batteries 100 in series. Busbars 50 are used for electrical connection between cells, and the positive and negative terminals are joined by laser welding. Since the positive and negative terminals are made of different materials (aluminum and copper), laser welding requires joining the same metals. Therefore, to convert the materials on the busbar component, the busbar is made of clad aluminum and copper. Using the clad busbar, the aluminum and copper are joined by laser welding, with the same metals as the terminals.

[0031] Figure 5 is a cross-sectional view of the joint between the terminal and the busbar in Example 1, Figure 6 is a cross-sectional view after welding the joint between the terminal and the busbar, and Figure 7 is an external view of the joint between the terminal and the busbar from above. The terminal 14 is provided with an electrode terminal projection 14a on the upper side of the cell, and the busbar 50 is provided with a busbar hole 50a for fitting the electrode terminal projection 14a. In this example, the structure of the positive electrode is shown, but a similar structure can be used for the negative electrode. The electrode terminal projection 14a and the busbar hole 50a are round in shape, each with a diameter of approximately Φ2mm to 4mm. In this example, one electrode terminal projection 14a is provided in the center of the terminal, but multiple electrode terminal projections 14a may be provided. When multiple electrode terminal projections 14a are provided, the diameter of the electrode terminal projection 14a and the diameter of the busbar hole 50a need to be reduced. This is because a contact area is required for the cell charging probe. Furthermore, increasing the number of busbar holes 50a makes terminal processing more difficult, and the presence of multiple busbar holes 50a also necessitates consideration of the impact on strength. Considering these impacts on processing, it is desirable to limit the number of electrode terminal protrusions 14a to one or two.

[0032] The busbar 50 is fitted into the electrode terminal projection 14a after multiple cells have been arranged and fixed in place. For this reason, a loose tolerance is required for the fitting state in order to ensure good positioning and fit. Specifically, the dimensions of the electrode terminal projection 14a and the busbar 50 hole a are determined so that the gap between the electrode terminal projection 14a and the busbar 50 hole a is approximately 0.1 mm. Furthermore, the outer edge of the upper surface of the electrode terminal projection 14a is rounded or cornered. Similarly, the inner edge of the busbar hole 50a facing the electrode terminal projection 14a is rounded or cornered. The rounded or cornered edges of the electrode terminal projection 14a and the busbar hole 50a are both approximately 0.1 mm to 0.5 mm in size, which is sufficient for fitting.

[0033] The electrode terminal projection 14a and the busbar hole 50a are fitted together, and the outer surface of the electrode terminal projection 14a and the inner surface of the busbar hole 50a are butt-welded together with a laser. By setting the diameter of the laser welding to approximately 0.5 mm to 1.0 mm, sufficient penetration is possible even with a loose fitting tolerance.

[0034] Furthermore, by making the height of the electrode terminal projection 14a greater than the thickness of the busbar 50, the electrode terminal projection 14a protrudes beyond the busbar 50 when mated. For example, if the thickness of the busbar 50 is approximately 0.8 mm to 1.0 mm, the height of the electrode terminal projection 14a should be 1.0 mm or more. Considering the manufacturing tolerances of the terminals, a height of about 1.2 mm for the electrode terminal projection 14a is desirable. An inspection probe is brought into contact with the protruding portion of the electrode terminal projection 14a. To inspect the welding condition between the terminal and the busbar, the resistance between the terminals of the cell can is measured to confirm the electrical connection. Therefore, since the probe can be brought into direct contact with the protruding electrode terminal projection 14a, the probe can be easily positioned and the inspection can be performed more easily.

[0035] Furthermore, in this invention, the aforementioned fitting structure can be applied to both the positive and negative electrodes, or to only one side of the positive or negative electrode, while still achieving its intended effect. The positive electrode is made of aluminum, and since sufficient penetration is required to obtain strength, the presence of a protrusion allows for efficient penetration. The negative electrode is made of copper, and due to the influence of reflectivity, laser power is required. By creating a butt joint structure between the outer surface of the electrode terminal protrusion 14a and the inner surface of the busbar hole 50a, welding can be performed with less laser power. [Examples]

[0036] Figure 8 is a cross-sectional view of the joint between the terminal and the busbar in Example 2. Parts of the structure in Figure 8 that are the same as in Example 1 will not be explained. In Example 1, the electrode terminal projection 14a is round, but in Example 2, it is elongated. Also, in Example 2, the busbar hole 50a is elongated, and this elongated hole is positioned parallel to the short side of the terminal. By making the straight portion of the elongated hole longer, a larger welding area can be obtained. Furthermore, by making the busbar hole 50a longer than the shape of the electrode terminal projection 14a, it is easier to position the fitting. Because the butt joint between the outer surface of the electrode terminal projection 14a and the inner surface of the busbar hole 50a is longer, a larger welding area can be obtained, so partial welding is acceptable instead of full-circumference welding.

[0037] Before connecting the terminals and busbars, there is a step to charge the cells. At that time, the probes are brought into contact with the top surface of the terminals. Flat surfaces are required for the current and voltage detection probes to make contact. In Example 2, the area of ​​the electrode terminal projection 14a is increased, which reduces the contact area for the charging probes, so it is necessary to devise a way to adjust the diameter and position of the probes. [Examples]

[0038] Figure 9 is a top view of the cell and busbar of Example 3, and Figure 10 is a cross-sectional view of the joint between the terminal and busbar of Example 3. Parts similar to those of Examples 1 and 2 will not be explained. In Example 3, the upper surface of the electrode terminal projection 14a has a larger area than the upper surface of the terminals other than the electrode terminal projection 14a. The electrode terminal projection 14a has a similar shape to the positive electrode external terminal 14, with one side being about 1 to 2 mm shorter. For example, if the outer dimensions of the positive electrode external terminal 14 are 10.5 mm × 7.5 mm, the outer dimensions of the electrode terminal projection 14a should be 9 mm × 6 mm.

[0039] In Example 2, the busbar hole 50a was made into an elongated hole to increase the welding area, but this resulted in a reduced contact area for the cell charging probe. In Example 3, the upper surface area of ​​the electrode terminal projection 14a was made larger, allowing the charging probe contact area and the resistance measurement probe for joint confirmation to be in contact with the upper surface of the electrode terminal projection 14a. In Example 3, a U-shaped notch was provided at the end of the busbar 50, and the electrode terminal projection 14a was brought into contact with the inside of the U-shape and locked in place.

[0040] As described above, the flat wound secondary battery 100, which is a battery pack according to the embodiment, comprises a container in which charge and discharge elements are housed, electrode terminals provided on one surface of the container, and a sealing member provided between the container and the electrode terminals to seal the space between the container and the electrode terminals. Furthermore, the flat wound secondary battery 100 has busbars that are connected to the electrode terminals of different batteries, respectively. The electrode terminals have electrode terminal projections extending away from one surface, and the busbars have busbar holes into which the electrode terminal projections are fitted. The electrode terminals and the busbars are fitted together and in contact with each other, and the connection between the outer surface of the electrode terminal projection and the inner surface of the busbar hole is at least partially welded.

[0041] According to the structure of the present invention, by welding the outer surface of the terminal projection to the inner surface of the busbar hole, the welding position is moved further away from the gasket, thereby reducing the thermal impact on the busbar due to welding. Furthermore, the market demand for smaller cells necessitates lowering the height of the terminals. As the terminals become smaller, there is a greater concern about the thermal impact on the gasket from the laser, but as in the present invention, the thermal impact can be reduced by making the welding portion with the busbar a projection. One reason why the thermal effects can be reduced is that the laser is efficiently incident on the outer surface of the electrode terminal projection and the inner surface of the busbar hole through butt welding, allowing for efficient melting with less power. Furthermore, one reason why thermal effects can be reduced is that by fitting the terminal and busbar together, structural strength can be maintained against shear, reducing the strength required for the molten area, thus allowing for less penetration. This eliminates the need for through welding to obtain sufficient strength, as it is enough to ensure electrical conductivity. Furthermore, in this invention, the aforementioned fitting structure can be applied to both the positive and negative electrodes, or to only one side of the positive or negative electrode, while still achieving its intended effect. The positive electrode is made of aluminum, and since sufficient penetration is required to obtain strength, the presence of protrusions allows for efficient penetration. The negative electrode is made of copper, and due to the influence of reflectivity, laser power is required. By creating a butt joint structure between the outer surface of the electrode terminal protrusion and the inner surface of the busbar hole, welding can be performed with less laser power. Furthermore, according to the structure of the present invention, the electrode terminal protrusion is made higher than the busbar thickness, and the electrode terminal protrusion protrudes from the top surface, making post-joining inspection easier. The post-joining inspection is a resistance test to guarantee electrical connection, and is measured by contacting the electrode terminal protrusion protruding from the busbar with an inspection probe. By directly targeting the electrode terminal protrusion, contact failures can be reduced to compensate for errors in probe position.

[0042] As illustrated in Examples 1 and 2, the busbar can be provided with a busbar hole that penetrates the portion in contact with the electrode terminal, and the hole can be fitted with the electrode terminal projection to restrict movement in the shear direction. In this way, fitting the electrode terminal projection into the busbar hole facilitates the positioning of the busbar, and the inner surface of the busbar hole and the outer surface of the electrode terminal projection can be used for welding. Furthermore, since the movement of the busbar is restricted by the fitting, welding does not need to be aimed at obtaining structural strength, and low-power welding aimed at ensuring electrical conductivity is sufficient. Furthermore, the entire boundary where the busbar hole and the electrode terminal projection meet may be welded, or only a portion of it may be welded.

[0043] Furthermore, it is preferable that the electrode terminal has a beveled edge on the outer circumference of the electrode terminal projection. Similarly, it is preferable that the busbar hole has a beveled edge on the inner circumference facing the electrode terminal. These bevels may be flat or curved surfaces. These bevels make it even easier to fit and position the busbar hole and the electrode terminal projection.

[0044] As illustrated in Example 2, the busbar hole may be an elongated hole, and its movement in the short direction may be restricted by contact with the fitted electrode terminal projection. In this case, the electrode terminal projection may be oval or circular. If the shape of the electrode terminal projection is oval, the boundary between the busbar hole and the electrode terminal projection becomes longer, which is advantageous for welding. On the other hand, if the shape of the electrode terminal projection is circular, a tolerance in the longitudinal direction of the elongated hole can be increased.

[0045] Furthermore, in the battery pack manufacturing method according to the embodiment, a first step is performed in which a busbar is assembled to electrically connect the electrode terminals of different batteries, followed by a second step in which the electrode terminals and the busbar are welded together. In this first step, the electrode terminal projections are fitted into the busbar holes for assembly, and in the second step, at least partially welds the area along the boundary between the outer surface of the electrode terminal projections and the inner surface of the busbar holes. Therefore, the terminal and busbar can be efficiently joined while minimizing the thermal impact on the gasket.

[0046] Furthermore, in the battery pack manufacturing method according to the embodiment, a third step can be performed in which an inspection instrument is brought into contact with the electrode terminal protrusion to inspect the welding condition between the electrode terminal and the busbar. This is because, as disclosed in the embodiment, the electrode terminal protrusion remains exposed even after the busbar is welded.

[0047] Furthermore, in the battery pack manufacturing method according to the embodiment, in the second step, by irradiating the boundary between the electrode terminal projection and the busbar hole with laser light focused to a diameter larger than the gap at the boundary between the electrode terminal projection and the busbar hole, and welding them together, the thermal effect on the gasket can be further reduced.

[0048] The above embodiments do not limit the present invention, and the present invention can be implemented by appropriately modifying the illustrated structures. For example, in the above embodiments, a structure was illustrated in which a hole or notch is provided in the busbar and the electrode terminal projection of the electrode terminal is passed through or locked into it, but the shape of the busbar and the electrode terminal projection can be arbitrarily changed. As an example, the electrode terminal may be provided with two electrode terminal protrusions, and the end of the busbar may be assembled between the two electrode terminal protrusions. As another example, the electrode terminal may be provided with a U-shaped electrode terminal projection, and the end of the busbar may be housed inside the U-shape. Thus, any structure can be adopted as long as the busbar's movement in the shear direction is restricted by contact with the electrode terminal's projection while it is in contact with the electrode terminal. In any structure, restricting the busbar's movement eliminates the need to ensure structural strength in the welding. As a result, laser power can be suppressed, and the terminal and busbar can be joined efficiently while minimizing the thermal impact on the gasket. [Explanation of symbols]

[0049] 1: Battery can, 1a: Opening, 1b: Wide side, 1c: Narrow side, 1d: Bottom, 2: Insulating protective film, 3: Winding group, 5: Gasket, 6: Battery cover, 7: Insulating plate, 9: Liquid injection port, 10: Gas discharge valve, 11: Liquid injection plug, 12: Negative electrode external terminal, 12b: Negative electrode connection part, 14: Positive electrode external terminal, 14a: Electrode terminal projection, 14b: Positive electrode connection part, 21: Negative electrode current collector plate base, 22: Negative electrode side connection end, 23: Negative electrode side opening hole, 24: Negative electrode current collector plate 26: Negative electrode through hole, 32: Negative electrode, 32b: Negative electrode mixture layer, 32c: Negative electrode foil exposed portion, 33: Separator, 34: Positive electrode, 34b: Positive electrode mixture layer, 34c: Positive electrode foil exposed portion, 35: Separator, 41: Positive electrode current collector base, 42: Positive electrode connection end, 43: Positive electrode opening hole, 44: Positive electrode current collector, 46: Positive electrode through hole, 50: Busbar, 50a: Busbar hole, 51: Melting portion, 80: Battery module, 100: Flat wound secondary battery

Claims

1. A plurality of batteries comprising a container containing a charge / discharge element, electrode terminals provided on one side of the container, and a sealing member provided between the container and the electrode terminals to seal the space between the container and the electrode terminals, It has busbars that are connected to the electrode terminals of different batteries, The busbar is provided with a busbar hole that exposes at least a portion of the upper surface of the electrode terminal, The busbar hole is an elongated hole, and the upper surface of the electrode terminal has an oval electrode terminal projection. A battery pack in which the electrode terminal and the busbar are fitted together and in contact with each other such that the longitudinal direction of the electrode terminal projection and the busbar hole coincide.

2. The battery pack according to claim 1, characterized in that the upper surface of the electrode terminals exposed by the busbar hole is flat.

3. The battery pack according to claim 1, characterized in that the upper surface of the electrode terminal exposed by the busbar hole is a probe contact surface.

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