Secondary batteries and battery packs

Abstract

The present invention relates to a secondary battery and a battery pack, and suppresses thermal degradation of a metal joint formed at a contact interface of structural components of an electrode terminal. The electrode terminal (20) of the secondary battery comprises: a first component (30) having a plate-shaped connecting portion (34); and a plate-shaped second component (40) connected to the connecting portion (34) of the first component (30) by surface contact. In the technology disclosed herein, a metal joint (70) and a heat insulating portion (80) are formed at the contact interface between the connecting portion (34) of the first component (30) and the second component (40), and the heat insulating portion (80) is formed at a position outside the metal joint (70) in a radial direction centered on the metal joint (70). Thus, even if a large amount of heat is applied to an area outside the heat insulating portion (80), the large amount of heat can be blocked by the heat insulating portion (80), thereby suppressing thermal degradation of the metal joint (70).

Description

Technical Field

[0001] The present invention relates to a secondary battery including an electrode terminal and a battery pack including a plurality of secondary batteries. Background Art

[0002] Currently, secondary batteries such as lithium-ion secondary batteries and nickel-metal hydride batteries are widely used in various fields, including vehicles and mobile terminals. The secondary battery generally includes an electrode body as a power generation element and a battery box for storing the electrode body. In addition, the secondary battery adopts a structure in which the electrode terminals connected to the electrode body inside the battery box are led out to the outside of the box. Moreover, the electrode terminals led out to the outside of the box are connected to external devices, other batteries, etc. via external connection components such as bus bars.

[0003] As an example of the prior art related to the above-mentioned electrode terminal, the structure described in Patent Document 1 can be cited. The electrode terminal described in Patent Document 1 includes an external terminal with good welding quality to the busbar, and a base portion connected to the external terminal at one end and the electrode body at the other end. Moreover, in the technology described in Patent Document 1, it is recommended to join the base portion and the external terminal by ultrasonic joining. By joining the structural components of the electrode terminal by metal-to-metal bonding such as such ultrasonic joining, it is possible to ensure appropriate joining strength and improve the conductivity at the interface of each component.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2011-124024

[0005] However, the inventors' research has revealed that there is room for improvement in the technology for joining the structural components of the electrode terminals through metal-to-metal bonding. Specifically, thermal welding, such as laser welding, is typically used to connect the electrode terminals, which are led outside the battery case, to the busbars. If the significant heat generated during this thermal welding is transferred to the joint (metallic joint) formed by the metal-to-metal bonding, this metal joint may thermally degrade, resulting in reduced joint strength and conductivity. Summary of the Invention

[0006] The present invention has been made to solve this problem, and an object of the present invention is to provide a technique for suppressing thermal degradation of a metal joint formed at a contact interface between components of an electrode terminal.

[0007] In order to achieve the above-mentioned object, the technology disclosed herein provides a secondary battery having the following structure.

[0008] The secondary battery disclosed herein comprises an electrode body, a battery case for housing the electrode body, and an electrode terminal connected to the electrode body inside the battery case and partially exposed to the outside of the battery case. The electrode terminal of the secondary battery comprises a first component having one end located inside the battery case and the other end located outside the battery case, and a plate-shaped second component connected to the first component outside the battery case. Furthermore, the first component comprises an axis extending through the battery case, and a plate-shaped connection portion formed at the upper end of the axis and in surface contact with the second component. Furthermore, in the secondary battery disclosed herein, a metal joint and a heat insulating portion are formed at the contact interface between the connection portion of the first component and the second component, and the heat insulating portion is formed at a position further outward than the metal joint in a radial direction centered on the metal joint.

[0009] In the secondary battery disclosed herein, a metal joint is formed at the contact interface between the first component and the second component, which are structural components of the electrode terminal. The metal joint is a joint based on metal bonding such as ultrasonic bonding, laser welding, and resistance welding. Moreover, in the secondary battery disclosed herein, a heat insulating portion is formed at a position further outward than the metal joint in a radial direction centered on the above-mentioned metal joint. Thus, even if a larger amount of heat (such as welding heat, etc.) is applied to an area further outward than the above-mentioned heat insulating portion, the larger amount of heat can be blocked by the heat insulating portion, thereby suppressing thermal degradation of the metal joint.

[0010] In a preferred embodiment of the secondary battery disclosed herein, the heat insulating portion is a cavity formed by separating a portion of the bottom surface of the second member from the upper surface of the connecting portion. This structure can suppress thermal degradation of the metal joint at low cost.

[0011] In a preferred embodiment of the secondary battery disclosed herein, the heat insulating portion is a heat insulating material that fills the space between the bottom surface of the connecting portion and the upper surface of the second member. This configuration can more appropriately suppress thermal degradation of the metal joint.

[0012] In a preferred embodiment of the secondary battery disclosed herein, the heat insulating portion is an annular heat insulating portion formed so as to surround the metal junction in a plan view, thereby more appropriately suppressing thermal degradation of the metal junction.

[0013] In a preferred embodiment of the secondary battery disclosed herein, the first and second components are made of different metal materials. Furthermore, the disclosed technology can suppress thermal degradation of the metal joint, making it particularly suitable for dissimilar metal-to-metal bonding, which is a preferred metal bonding method.

[0014] In addition, as another aspect of the technology disclosed herein, a battery pack is provided in which a plurality of secondary batteries are electrically connected via a flat bus bar. In the battery pack disclosed herein, at least one of the plurality of secondary batteries is a secondary battery of the above-mentioned structure. In addition, the bus bar is in surface contact with the upper surface of the second component, and the bus bar is connected to the second component by a heat welding portion that penetrates the bus bar and reaches the second component. Moreover, in the battery pack disclosed herein, the heat welding portion is formed above the heat insulating portion, or is formed at a position further outward than the heat insulating portion in the radial direction centered on the metal joint portion. Thus, the heat generated during the formation of the heat welding portion is insulated by the heat insulating portion, so that thermal degradation of the metal joint portion during bus bar connection can be properly suppressed.

[0015] In a preferred embodiment of the battery pack disclosed herein, the heat insulating portion is a cavity formed by separating a portion of the bottom surface of the second member from the upper surface of the connecting portion. This configuration can suppress thermal degradation of the metal joint at low cost.

[0016] Furthermore, preferably, in a configuration in which a cavity portion is provided as the heat insulating portion, the following formula (1) is satisfied when, in a plan view, the distance from the center of the metal joint to the outer edge of the metal joint is defined as L1, the distance from the center of the metal joint to the inner edge of the heat insulating portion is defined as L2, and the distance from the center of the metal joint to the center of the heat weld is defined as L3. This allows the heat insulating portion to sufficiently insulate the heat generated during the formation of the heat weld, thereby more appropriately suppressing thermal degradation of the metal joint.

[0017] L3-L2>L2-L1(1) BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a perspective view schematically showing a secondary battery according to one embodiment.

[0019] Figure 2 It is a cross-sectional view schematically showing the vicinity of an electrode terminal of a secondary battery according to one embodiment.

[0020] Figure 3 This is a plan view illustrating the positional relationship between a metal junction portion and a heat insulating portion in a secondary battery according to one embodiment.

[0021] Figure 4 It is a perspective view schematically showing a battery pack according to one embodiment.

[0022] Figure 5 This is a cross-sectional view schematically showing the structure of a connection portion between an electrode terminal and a bus bar in a battery pack according to one embodiment.

[0023] Figure 6This is a plan view illustrating the positional relationship among metal joints, heat insulating portions, and thermally welded portions in a battery pack according to one embodiment.

[0024] Figure 7 This is a plan view illustrating the positional relationship among metal joints, heat insulating portions, and thermally welded portions in a battery pack according to another embodiment.

[0025] Figure 8 This is a plan view illustrating the positional relationship among metal joints, heat insulating portions, and thermally welded portions in a battery pack according to another embodiment.

[0026] Figure 9 This is a plan view illustrating the positional relationship among metal joints, heat insulating portions, and thermally welded portions in a battery pack according to another embodiment.

[0027] Figure 10 This is a plan view illustrating the positional relationship among metal joints, heat insulating portions, and thermally welded portions in a battery pack according to another embodiment.

[0028] Figure 11 This is a plan view illustrating the positional relationship among metal joints, heat insulating portions, and thermally welded portions in a battery pack according to another embodiment.

[0029] Description of Reference Numerals

[0030] 1…secondary battery; 10…battery case; 12…case body; 14…cover; 20…electrode terminal; 30…first component; 32…shaft; 34…connecting portion; 36…nail; 40…second component; 42…recess; 46…groove; 50…third component; 62…washer; 64…insulator; 70…metal joint; 80, 80A to 80C…heat insulating portion; 90, 90A…thermal welding portion; 100…battery pack; 110…bus bar; 120…end plate; 130…restraining beam component; 140…spacer. DETAILED DESCRIPTION

[0031] The following describes one embodiment of the technology disclosed herein. The following embodiment is not intended to limit the technology disclosed herein. Furthermore, matters other than those specifically mentioned in this specification and necessary for implementing the technology disclosed herein can be understood as design matters by those skilled in the art based on the prior art in the relevant field. In other words, the technology disclosed herein can be implemented based on the content disclosed in this specification and common technical knowledge in the relevant field.

[0032] In addition, in the drawings referred to in the following description, the same reference numerals are used for components and parts that play the same role. In addition, the dimensional relationships (length, width, thickness, etc.) in the drawings do not reflect the actual dimensional relationships. In addition, the reference numeral X in the drawings represents the "width direction", the reference numeral Y represents the "depth direction", and the reference numeral Z represents the "height direction". These directions are specified for the convenience of explanation and are not intended to limit the setting form of the secondary battery or battery pack in use or manufacturing.

[0033] In addition, the "secondary battery" in this specification generally refers to an electrical storage device that generates a charge and discharge reaction by moving a charge carrier between a pair of electrodes (positive and negative electrodes) via an electrolyte. In addition to so-called storage batteries such as lithium-ion secondary batteries, nickel-metal hydride batteries, and nickel-cadmium batteries, the secondary battery also includes capacitors such as double-layer capacitors. The technology disclosed herein is not limited to a specific type of secondary battery and can be applied without particular limitation to all secondary batteries having electrode terminals and battery packs constructed using the secondary batteries.

[0034] 1. Secondary batteries

[0035] Below, refer to Figures 1 to 3 The structure of the secondary battery according to this embodiment will be described. Figure 1 It is a perspective view schematically showing the secondary battery according to this embodiment. Figure 2 : is a cross-sectional view schematically showing the structure of the secondary battery in the vicinity of the electrode terminal according to this embodiment. Figure 3 It is a plan view illustrating the positional relationship between the metal joining portion and the heat insulating portion in the electrode terminal of the secondary battery according to the present embodiment.

[0036] (1) Overall structure

[0037] like Figure 1 As shown, the secondary battery 1 according to this embodiment includes an electrode body (not shown), a battery case 10, and an electrode terminal 20. Each structure will be described below.

[0038] (2) Electrode body

[0039] The electrode body is a power generation element housed inside the battery case 10. The structure of the electrode body is not particularly limited, and various structures that can be used in general secondary batteries can be adopted without particular restrictions. For example, a structure in which a positive electrode and a negative electrode are overlapped with a separator can be adopted for the electrode body. As specific examples of the structure of such an electrode body, a wound electrode body formed by winding and overlapping long strips of positive electrodes, negative electrodes and separators, and a stacked electrode body formed by stacking rectangular sheets of positive electrodes, negative electrodes and separators can be cited. In addition, for the detailed structure and materials of the various components (positive electrodes, negative electrodes and separators) constituting the electrode body, structures and materials that can be used in general secondary batteries (such as lithium-ion secondary batteries) can be adopted without particular restrictions. That is, the structure and materials of the various components constituting the electrode body are not limited to the technology disclosed here, and therefore a detailed description is omitted.

[0040] In addition, although not shown in the figure, in the secondary battery involved in this embodiment, in addition to the above-mentioned electrode body, an electrolyte is also accommodated in the interior of the battery case 10. As the electrolyte, a non-aqueous liquid electrolyte (non-aqueous electrolyte) containing a non-aqueous solvent and a supporting electrolyte, a solid electrolyte formed by molding a powdered electrolyte into a sheet, etc. can be used. In addition, the specific composition of the electrolyte does not limit the technology disclosed here, so a detailed description is omitted.

[0041] (3)Battery box

[0042] The battery case 10 is a container for storing the above-mentioned electrode body and electrolyte. Figure 1 As shown in FIG. 1 , the battery case 10 in this embodiment is a flat square container. The square battery case 10 includes a flat square box body 12 with an open top surface, and a plate-shaped cover 14 that closes the top surface opening of the box body 12. Although described in detail later, Figure 1 and Figure 2 As shown, terminal insertion holes 14a serving as openings for inserting the electrode terminals 20 (first component 30) are provided at both ends of the cover body 14 in the width direction X. In addition, the outer shape of the battery case is not limited to the above-mentioned shape, and can be appropriately changed according to the specifications of the external device, the shape of the electrode body, etc. For example, the battery case can also be a cylindrical case with a bottom. In addition, the material of the battery case 10 is not particularly limited as long as it is a material with the required strength. As a preferred example of the material of the battery case 10, metal materials that are lightweight and have good thermal conductivity (such as aluminum, stainless steel, nickel-plated steel, etc.) can be cited.

[0043] (3) Electrode terminals

[0044] like Figure 1As shown, the secondary battery 1 involved in this embodiment has a pair of electrode terminals 20. A portion of these electrode terminals 20 is exposed to the outside of the battery box 10. In addition, although omitted from the figure, each electrode terminal 20 is connected to the electrode body (positive electrode or negative electrode) inside the battery box 10. In this specification, the electrode terminal connected to the positive side of the electrode body is referred to as a "positive terminal", and the electrode terminal connected to the negative side is referred to as a "negative terminal". Moreover, as Figure 2 As shown, the electrode terminal 20 in this embodiment includes a first component 30 and a second component 40. The structural components of the electrode terminal 20 in this embodiment are described in detail below. The structure of the electrode terminal 20 described below can be applied to either the positive terminal or the negative terminal, or to both.

[0045] (a) Part 1

[0046] The first component 30 is a component having one end located inside the battery case 10 and the other end located outside the battery case 10. Figure 2 As shown, the first component 30 has a shaft portion 32 that passes through the battery case 10. The shaft portion 32 is a columnar component extending in the height direction Z. The upper end of the shaft portion 32 is exposed to the outside of the battery case 10 (above the cover 14). In addition, the lower end of the shaft portion 32 is housed inside the battery case 10. In addition, the outer shape of the shaft portion 32 is not particularly limited and can be cylindrical or prismatic. Among them, if the ease of blocking the terminal insertion hole 14a of the cover 14 (sealing the battery case 10) is taken into consideration, the outer shape of the shaft portion 32 is preferably cylindrical. In addition, in this embodiment, a connecting portion 34 is formed at the upper end of the shaft portion 32. The connecting portion 34 is a plate-shaped component that is in surface contact with the second component 40 described later. In addition, the shape of the connecting portion 34 when viewed from above is not particularly limited and can be circular or rectangular. In addition, in this embodiment, a nail portion 36 is formed at the lower end of the shaft portion 32. The nail portion 36 is formed by caulking the lower end of the cylindrical shaft portion 32 to deform radially outward. The nail portion 36 fixes the third member 50 (described later) to the battery case 10 (lid 14) and electrically connects the first member 30 and the third member 50.

[0047] (b) Part 2

[0048] The second component 40 is a plate-shaped component connected to the first component 30 outside the battery case 10. Figure 1 As shown, the second component 40 in this embodiment is a plate-shaped component that is approximately rectangular in a top view. The plate-shaped second component 40 is arranged outside the battery box 10 (above the cover 14). In addition, the shape of the second component in a top view is not particularly limited and can be circular. Figure 2As shown, the bottom surface 40a of the second member 40 (the surface facing the battery case 10) is in surface contact with the upper surface 34a of the connecting portion 34 of the first member 30. Although described in detail later, a metal joint 70 is formed at the interface between the upper surface 34a of the connecting portion 34 and the bottom surface 40a of the second member 40. This metal joint 70 connects the first and second members 30 and 40. Furthermore, in this embodiment, a recess 42 is formed on the bottom surface of the second member 40, into which the connecting portion 34 of the first member 30 is inserted. This restricts movement of the second member 40 in the width direction X and depth direction Y when vibration or external force is applied to the electrode terminal 20, and prevents damage to the metal joint 70 caused by this movement of the second member 40. Furthermore, in this embodiment, a locking portion 44 is formed at the lower end of the side wall of the recess 42, protruding toward the shaft portion 32 of the first member 30. Thus, the movement of the second member 40 in the height direction Z can be restricted, and therefore, damage to the metal joint 70 caused by the movement of the second member 40 can be more reliably prevented.

[0049] (c) Part 3

[0050] The electrode terminal 20 in this embodiment includes a third component 50. Although not shown in the figure, the third component 50 has a current collecting portion extending along the height direction Z. The current collecting portion of the third component 50 is connected to the electrode body (positive electrode or negative electrode) at its lower end. Figure 2 As shown, the upper end portion 52 of the third component 50 is bent along the inner surface of the battery case 10 (cover 14). Moreover, the upper end portion 52 of the third component 50 is fixed to the battery case 10 (cover 14) by the nail portion 36 of the first component 30, and is electrically connected to the first component 30. Thus, the electrode body inside the battery case 10 is electrically connected to the second component 40 outside the battery case 10 via the third component 50 and the first component 30. In addition, the third component 50 is not an essential structural component of the electrode terminal in the technology disclosed here. For example, when a part of the first component is extended in the height direction to connect it to the electrode body, an electrode terminal without a third component can be constructed.

[0051] (4) Insulation components

[0052] Next, the secondary battery 1 according to this embodiment includes an insulating member for preventing electrical conduction between the electrode terminal 20 and the battery case 10. Figure 2 As shown, the insulating member in this embodiment includes a washer 62 and an insulator 64 .

[0053] The gasket 62 is an insulating component placed on the outer surface of the battery case 10 (the upper surface of the cover 14). The gasket 62 is a box-shaped insulating component with a housing 62a on its upper surface. The housing 62a of the gasket 62 houses the connecting portion 34 of the first component 30 and the second component 40. This provides insulation between the cover 14 and the first component 30, and between the cover 14 and the second component 40. Furthermore, the gasket 62 in this embodiment has a cylindrical protrusion 62b having a terminal insertion hole 62c. The protrusion 62b of the gasket 62 is inserted into the terminal insertion hole 14a of the cover 14. Furthermore, the protrusion 62b of the gasket 62 is sandwiched between the shaft 32 of the first component 30 and the cover 14 within the terminal insertion hole 14a. This ensures insulation between the first component 30 and the cover 14. In addition, the gasket 62 is pressurized during the riveting process when forming the nail portion 36 of the first component 30. Therefore, the gasket 62 is compressed between the cover body 14 and the second component 40 (or between the cover body 14 and the connecting portion 34). In this way, the gap when the components are assembled to the cover body 14 is sealed, thereby preventing the circulation of liquid inside and outside the battery box 10 (intrusion of water, leakage of electrolyte). In addition, it is preferred that the gasket 62 is formed of an insulating resin that is easily elastically deformed. As an example of the material of the gasket 62, fluororesins such as perfluoroalkoxy fluororesin (PFA), polyphenylene sulfide resin (PPS), aliphatic polyamide, etc. can be cited.

[0054] The insulator 64 is a plate-shaped insulating component with an opening 64a. It is positioned between the battery case 10 (lid 14) and the third component 50. This insulates the lid 14 from the third component 50. Furthermore, the opening 64a of the insulator 64 is positioned so that it overlaps with the terminal insertion hole 62c of the gasket 62 in a plan view, allowing the shaft 32 of the first component 30 to be inserted therethrough. This reliably prevents contact between the shaft 32 of the first component 30 and the lid 14. Furthermore, during the riveting process when forming the nail 36 at the lower end of the first component 30, the lower surface of the protrusion 62b of the gasket 62 is pressed against the periphery of the opening 64a of the insulator 64. This pressurizes the gasket 62 and the insulator 64, further reliably preventing the flow of liquid inside and outside the battery case 10. Furthermore, the insulator 64, like the gasket 62, is preferably formed from an elastically deformable insulating resin.

[0055] (5) Connection between the first and second components

[0056] As described above, in the secondary battery 1 according to this embodiment, a metal joint 70 is formed at the contact interface between the connection portion 34 of the first component 30 and the second component 40. The metal joint 70 is a joint formed by joining the first component 30 and the second component 40 by metal-to-metal bonding such as ultrasonic welding, laser welding, or resistance welding. Figure 2As shown in FIG. 1 , the metal joint 70 in this embodiment is formed on the axis SC of the shaft portion 32 of the first component 30. As an example, when ultrasonic bonding is used to form the metal joint 70, the first component 30 and the second component 40 are clamped so that the horn and the anvil are arranged on the axis SC of the shaft portion 32 to perform ultrasonic bonding. In addition, although the technology disclosed herein is not limited, as Figure 3 As shown, the metal joint 70 can be roughly circular when viewed from above. According to the joining means and joining conditions, the metal joint 70 can also be roughly rectangular (roughly square, roughly rectangular) when viewed from above. In addition, from the perspective of properly connecting the first component 30 and the second component 40, it is preferred to appropriately adjust the joining conditions so that the diameter of the metal joint 70 is 0.3 mm or more. In addition, from the perspective of more properly connecting the first component 30 and the second component 40, it is more preferred that the diameter of the metal joint 70 is 0.5 mm or more, and particularly preferably 1.0 mm or more. On the other hand, the upper limit of the diameter of the metal joint 70 is not particularly limited, and can be 10.0 mm or less, 5.0 mm or less, or 2.0 mm or less.

[0057] As described above, by forming a metal joint 70 at the contact interface between the connection portion 34 of the first component 30 and the second component 40, the first component 30 and the second component 40 can be connected with low resistance and high strength. However, if a large amount of heat is applied during the connection of the busbar, etc. and the metal joint 70 is thermally degraded, the conductivity and the bonding strength may be greatly reduced. In order to suppress the thermal degradation of the metal joint 70, in the secondary battery 1 involved in this embodiment, a heat insulating portion 80 is formed at the contact interface between the connection portion 34 and the second component 40. Moreover, as Figure 3 As shown, the heat insulating portion 80 is formed outside the metal joint 70 in the radial direction centered on the metal joint 70. Thus, even if a large amount of heat is applied to the area above the heat insulating portion 80 and outside the heat insulating portion 80, the large amount of heat can be blocked by the heat insulating portion 80, thereby suppressing thermal degradation of the metal joint 70 during welding of the bus bar, etc.

[0058] In addition, the heat insulating portion 80 involved in this embodiment is a cavity formed between the connecting portion 34 and the second component 40. Specifically, the second component 40 in this embodiment is provided with a groove 46 separated from the upper surface 34a of the connecting portion 34 on a part of its bottom surface 40a. Thus, the heat insulating portion 80 consisting of a cavity can be formed at the contact interface between the connecting portion 34 and the second component 40. According to this structure, thermal degradation of the metal joint 70 can be suppressed at a low cost. In addition, the groove for forming the heat insulating portion can also be formed on the upper surface of the connecting portion of the first component instead of the bottom surface of the second component. In addition, if the heat conduction to the metal joint can be blocked, the form of the heat insulating portion is not particularly limited. For example, the heat insulating portion can also be formed by filling the space in the contact interface between the connecting portion of the first component and the second component with a heat insulating material. As the heat insulating material, an inorganic heat insulating material with excellent heat resistance (a coating layer including glass wool, aluminum oxide particles, a coating layer including silica particles, etc.) is preferred. By using such a heat insulating material, thermal degradation of the metal joint 70 can be more appropriately suppressed.

[0059] In addition, if Figure 3 As shown, the heat insulating portion 80 in this embodiment is an annular heat insulating portion 80 formed so as to surround the metal joint 70 in a plan view. By forming such an annular heat insulating portion 80, it is possible to prevent heat from bypassing the heat insulating portion 80 and reaching the metal joint 70, thereby more reliably suppressing thermal degradation of the metal joint 70. In addition, the dimension L4 (see FIG. 1 ) from the inner edge 82 to the outer edge 84 of the annular heat insulating portion 80 is Figure 3 ) is preferably 3 mm or more, more preferably 5 mm or more, and particularly preferably 10 mm or more. This can more appropriately prevent a large amount of heat from reaching the metal joint 70. In addition, if the strength of the component (such as the second component) provided with the groove for forming the heat insulating portion is considered, the above Figure 3 The dimension L4 in the middle is preferably 50 mm or less, more preferably 30 mm or less, and particularly preferably 20 mm or less.

[0060] In addition, the technology disclosed herein is particularly suitable for the case where the first component and the second component are made of different metal materials. Moreover, in the connection between such different types of metals, ultrasonic bonding is also recommended from the perspective of forming a high-strength and low-resistance joint. However, the metal joint formed by ultrasonic bonding tends to have a greater degree of strength reduction and conductivity reduction after thermal degradation. In contrast, the technology disclosed herein can suppress thermal degradation of the metal joint and is therefore particularly suitable for the construction of electrode terminals having different types of metal joints, for which ultrasonic bonding is recommended.

[0061] As an example of an electrode terminal that is recommended for joining dissimilar metals using ultrasonic welding, an electrode terminal 20 can be cited in which the first component 30 is made of copper and the second component 40 is made of aluminum. Aluminum and copper tend to have higher resistance when joined by heat welding, so ultrasonic welding is recommended. For example, in a lithium-ion secondary battery, the negative terminal is recommended to be connected to the negative electrode (negative current collector) of the electrode body using copper materials, while the negative terminal is recommended to be connected to the bus bar using aluminum materials. In such a case, dissimilar metal bonding between copper and aluminum materials is required in the structural components of the negative terminal. In contrast, it is preferable to form a metal joint 70 using ultrasonic welding between the copper first component 30 and the aluminum second component 40. This allows the first component 30 and the second component 40 to be joined with relatively low resistance. Moreover, as described above, in the technology disclosed herein, thermal degradation of the metal joint 70 can be suppressed by the heat insulating portion 80, thereby maintaining the joint interface between the first component 30 and the second component 40, which are dissimilar metals, in a low resistance state. As described above, the technology disclosed herein is particularly applicable to the construction of negative terminals for lithium-ion secondary batteries that require intermetallic bonding between copper and aluminum materials. Furthermore, in this specification, the term "aluminum material" encompasses aluminum and alloys primarily composed of the aluminum. Here, an "alloy primarily composed of aluminum" refers to an alloy composed of at least 70% aluminum. Other elements that the aluminum material may contain are not particularly limited, but examples include silicon, iron, copper, manganese, magnesium, zinc, chromium, titanium, lead, and zirconium. On the other hand, the term "copper material" encompasses copper and alloys primarily composed of the copper. Furthermore, an "alloy primarily composed of copper" refers to an alloy composed of at least 50% copper. Other elements that the material may contain are not particularly limited, but examples include silicon, iron, manganese, magnesium, zinc, chromium, titanium, lead, tin, phosphorus, aluminum, nickel, cobalt, beryllium, and zirconium.

[0062] 2. Battery pack

[0063] Next, as another aspect of the technology disclosed herein, an embodiment of a battery pack constructed from a plurality of secondary batteries will be described. In the following description of the battery pack involved in this embodiment, reference is mainly made to Figures 4 to 6 . Figure 4 It is a perspective view schematically showing a battery pack according to this embodiment. Figure 5 : is a cross-sectional view schematically showing the structure of the connection portion between the electrode terminal and the bus bar in the battery pack according to this embodiment. Figure 6 This is a top view illustrating the positional relationship between the metal joint, the heat insulating portion, and the heat welding portion in the battery pack according to this embodiment. Figure 6In the figure, for the sake of convenience, the busbar 110 is omitted and the formation positions of the metal joint 70 and the heat insulating portion 80 are indicated by dotted lines. Figures 7 to 11 The same is true in Chinese.

[0064] like Figure 4 As shown, the battery pack 100 according to this embodiment includes a plurality of secondary batteries 1. Specifically, in the battery pack 100, a plurality of secondary batteries 1 having a flat, square battery case 10 are arranged along the depth direction Y with their flat surfaces facing each other. Furthermore, a pair of end plates 120 are arranged on both outer sides of the arrangement direction (depth direction Y) of the battery pack 100. By bridging the pair of end plates 120 with a restraining beam member 130, the plurality of secondary batteries 1 are restrained along the arrangement direction. Furthermore, in this embodiment, spacers 140 are arranged between adjacent secondary batteries 1 to uniformize the restraining pressure on the flat surfaces. Furthermore, the number of secondary batteries 1 constituting the battery pack 100 is not particularly limited and can be appropriately changed according to the purpose of the battery pack 100 (such as the required power and specifications of the external device). Furthermore, in the technology disclosed herein, not all of the plurality of secondary batteries constituting the battery pack need have the above-described structure. That is, the battery pack 100 according to this embodiment may also include a portion of secondary batteries having a structure different from that of the secondary batteries 1 according to the above-described embodiment.

[0065] In this embodiment, the electrode terminals 20 are connected to each other by bus bars 110 between two adjacent secondary batteries 1. A metal material having excellent electrical conductivity and strength is used for the bus bars 110. Figure 5 As shown, the bus bar 110 is in surface contact with the upper surface 40b of the second part 40 of the electrode terminal 20 and is thermally welded. Furthermore, the thermally welded portion 90, which serves as a connection mark for the thermal welding, is formed so as to penetrate the bus bar 110 and reach the second part 40. Furthermore, preferred examples of materials for the bus bar 110 in this embodiment include aluminum materials. Furthermore, from the perspective of preventing a decrease in electrical conductivity caused by thermal welding of dissimilar metal parts, it is preferred that the bus bar 110 be made of the same type of metal material as the second part 40 of the electrode terminal 20.

[0066] Here, as Figure 5 and Figure 6As shown, in this embodiment, the bus bar 110 and the electrode terminal 20 are thermally welded by forming a thermal weld portion 90 above the thermal insulation portion 80 formed at the contact interface between the connection portion 34 of the first member 30 and the second member 40. Specifically, a laser is irradiated above the thermal insulation portion 80 to form a pair of linear thermal weld portions 90 that oppose each other with the metal joint 70 sandwiched therebetween. This allows the thermal weld portions 90 to be formed while the thermal insulation portion 80 insulates the heat from the thermal welding, thereby suppressing thermal degradation of the metal joint 70.

[0067] In addition, in the technology disclosed here, the formation position of the heat welding part 90 (the laser irradiation position in the heat welding) is not limited to the upper part of the heat insulating part 80. For example, Figure 7 As shown, heat welding can also be performed by forming the heat weld portion 90 at a position further outward from the heat insulating portion 80 in the radial direction centered on the metal joint portion 70. Even in this case, the heat during heat welding can be insulated by the heat insulating portion 80, thereby suppressing thermal degradation of the metal joint portion 70.

[0068] Furthermore, from the perspective of more appropriately suppressing thermal degradation of the metal joint 70, the formation position of the heat welded portion 90 is preferably adjusted. Specifically, when the distance from the center C of the metal joint 70 to the outer edge 72 is set to L1, the distance from the center C of the metal joint 70 to the inner edge 82 of the heat insulating portion 80 is set to L2, and the distance from the center C of the metal joint 70 to the center of the heat welded portion 90 is set to L3, it is preferable to adjust the formation position of the heat welded portion 90 so as to satisfy the following equation (1). This can more appropriately prevent the large amount of heat during heat welding from reaching the metal joint 70. Furthermore, from the perspective of more reliably preventing thermal degradation of the metal joint 70, it is preferable to adjust the formation position of the heat welded portion 90 so as to satisfy the following equation (2). Furthermore, the following equations (1) and (2) are conditions that can be applied when the heat insulating portion 80 is a cavity. For example, when the heat insulating portion 80 is filled with a heat insulating material, it is preferable to adjust the formation position of the thermally welded portion 90 in consideration of the heat insulating property (thermal conductivity) of the heat insulating material.

[0069] L3-L2>L2-L1 (1)

[0070] L3-L2>(L2-L1)×1.5 (2)

[0071] In order to more reliably prevent thermal degradation of the metal joint 70 , it is preferable to adjust the thermal welding conditions (welding temperature, scanning speed, etc.) so that the width w of the linear thermal weld portion 90 satisfies the following formula (3).

[0072] L3-L2>w (3)

[0073] 3. Other Implementation Methods

[0074] An embodiment of the technology disclosed herein has been described above. However, the above embodiment is an example of a secondary battery (or battery pack) to which the technology disclosed herein is applied, and is not intended to limit the technology disclosed herein.

[0075] For example, in the above embodiment, a circular heat insulating portion 80 is formed to surround the metal joint 70 in a plan view. However, the heat insulating portion may be formed at a position outside the metal joint in a radial direction centered on the metal joint, and is not particularly limited to a specific planar shape. Figure 8 As shown in FIG. 1 , the heat insulating portion may be a four-sided ring-shaped heat insulating portion 80A surrounding the metal joint 70 in a top view. Even when the four-sided ring-shaped heat insulating portion 80A is formed, the heat generated during the formation of the heat welding portion 90 (during heat welding) can be appropriately insulated to suppress the thermal degradation of the metal joint 70. Furthermore, the planar shape of the heat insulating portion may not be Figures 6 to 8 For example, Figure 9 As shown, a pair of planar rectangular heat insulating portions 80B may be formed to oppose each other, sandwiching the metal joint 70. Furthermore, when these pair of heat insulating portions 80B are formed, the thermally welded portion 90 is formed above each heat insulating portion 80B (or radially outward of each heat insulating portion 80B). Thus, the heat insulating portions 80B can appropriately insulate the heat during thermal welding, thereby suppressing thermal degradation of the metal joint 70.

[0076] In addition, in the technology disclosed herein, the area where heat welding is performed (i.e., the heat welding portion 90) is not particularly limited as long as it is above the heat insulating portion (or radially outward of the heat insulating portion), and can be changed as appropriate. Figure 6 、 Figure 10 As shown, heat welding can also be performed in a manner such that a portion of the heat welding portion 90 extends from the heat insulating portion 80, 80C. Even in such a case, as long as the heat welding portion 90 extending from the heat insulating portion 80, 80C is formed at a position further outward than the heat insulating portion 80, 80C in the radial direction centered on the metal joint 70, thermal degradation of the metal joint 70 can be sufficiently suppressed. For example, in Figure 10In the embodiment, heat welding is performed in such a manner that the upper end 92 of the heat welding portion 90 extends from the rectangular heat insulating portion 80C. However, when viewed from the straight line A connecting the upper end 92 of the heat welding portion 90 and the metal joint 70, the upper end 92 of the heat welding portion 90 is formed outside the heat insulating portion 80C. In this case, the heat generated when the upper end 92 of the heat welding portion 90 is formed can be insulated by the heat insulating portion 80C, thereby sufficiently suppressing thermal degradation of the metal joint 70. However, considering the possibility of heat bypassing the heat insulating portion and being conducted to the metal joint, it is preferable to form Figures 6 to 8 The annular heat insulating portion 80, 80A is shown.

[0077] Furthermore, in each of the above-mentioned embodiments, a pair of linear heat welding portions 90 are formed, which are opposed to each other with the metal joint portion 70 interposed therebetween. However, the planar shape of the heat welding portion is not limited to a linear shape, and various shapes can be adopted. For example, Figure 11 As shown, a ring-shaped heat welding portion 90A can also be formed to surround the heat insulating portion 80. Even in this case, the heat during heat welding can be properly insulated by the heat insulating portion 80, so that the thermal degradation of the metal joint 70 can be properly suppressed. Figure 11 In the embodiment, an annular heat-welded portion 90A having a larger radius than the outer edge 84 of the heat-insulating portion 80 is formed, and the heat-welded portion 90A is formed outside the heat-insulating portion 80 in the radial direction centered on the metal joint 70. However, the radius of the heat-welded portion 90A may be smaller than the outer edge 84 of the heat-insulating portion 80 and larger than the inner edge 82, and the annular heat-welded portion 90A may be formed above the heat-insulating portion 80. Even in this case, the heat-insulating portion 80 can appropriately insulate the heat during heat welding, thereby suppressing thermal degradation of the metal joint 70.

[0078] While specific examples of the present invention have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The invention disclosed herein includes various modifications and variations of the specific examples described above.

Claims

1. A battery pack comprising a plurality of secondary batteries electrically connected via a flat bus bar, characterized in that: At least one of the plurality of secondary batteries includes an electrode body, a battery case housing the electrode body, and an electrode terminal connected to the electrode body in the battery case and partially exposed to the outside of the battery case. The electrode terminal includes a first member having one end located inside the battery case and the other end located outside the battery case, and a plate-shaped second member connected to the first member outside the battery case. The first member includes a shaft portion penetrating the battery case and a plate-shaped connecting portion formed at an upper end of the shaft portion and in surface contact with the second member. A metal joint portion and a heat insulating portion are formed at a contact interface between the connection portion of the first component and the second component, and the heat insulating portion is formed at an outer side of the metal joint portion in a radial direction centered on the metal joint portion. The bus bar is brought into surface contact with the upper surface of the second member and is thermally welded to the second member, penetrating the bus bar and reaching the thermally welded portion of the second member to connect the bus bar to the second member. The thermally welded portion is formed above the heat insulating portion, or is formed outside the heat insulating portion in a radial direction centered on the metal joint portion.

2. The battery pack according to claim 1, wherein: The heat insulating portion is a cavity formed by separating a portion of the bottom surface of the second member from the upper surface of the connecting portion.

3. The battery pack according to claim 2, wherein: The metal joint portion is circular in a plan view, and when the distance from the center of the metal joint portion to the outer edge of the metal joint portion is set to L1, the distance from the center of the metal joint portion to the inner edge of the heat insulating portion is set to L2, and the distance from the center of the metal joint portion to the center of the heat welding portion is set to L3, the following formula (1) is satisfied: L3-L2>L2-L1 (1).

4. The battery pack according to claim 1, wherein: The heat insulating portion is a heat insulating material that fills a space between the bottom surface of the connecting portion and the upper surface of the second member.

5. The battery pack according to claim 1, wherein: The heat insulating portion is an annular heat insulating portion formed so as to surround the metal joint portion in a plan view.

6. The battery pack according to any one of claims 1 to 5, characterized in that: The first member and the second member are made of different metal materials.

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