Secondary batteries and battery packs

Abstract

To suppress thermal deterioration of a metal joint formed at a contact interface of members constituting an electrode terminal.SOLUTION: An electrode terminal 20 of a secondary battery disclosed herein includes a first member 30 having a plate-shaped connection portion 34, and a plate-shaped second member 40 connected to the connection portion 34 of the first member 30 in surface contact. In the technique disclosed herein, a metal joint 70 and a heat insulating portion 80 are formed at the contact interface between the connection portion 34 of the first member 30 and the second member 40, and the heat insulating portion 80 is formed outside the metal joint 70 in the radial direction in which the metal joint 70 is centered. As a result, even when 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, such that thermal deterioration of the metal joint 70 can be suppressed.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a secondary battery having electrode terminals and a battery pack including a plurality of secondary batteries. [Background technology]

[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. Such secondary batteries typically include an electrode assembly, which is a power-generating element, and a battery case that houses the electrode assembly. Furthermore, such secondary batteries employ a structure in which electrode terminals connected to the electrode assembly inside the battery case are extended to the outside of the case. The electrode terminals extended to the outside of the case are then connected to external devices, other batteries, or the like via external connection members such as bus bars.

[0003] An example of a conventional technique related to the electrode terminal is the structure described in Patent Document 1. The electrode terminal described in Patent Document 1 includes an external terminal with good welding quality to the bus bar, and a base portion having one end joined to the external terminal and the other end connected to the electrode body. The technique described in Patent Document 1 recommends joining the base portion and the external terminal by ultrasonic welding. By joining the constituent members of the electrode terminal by intermetallic bonding such as ultrasonic welding, it is possible to ensure suitable joint strength and improve the conductivity at the interface between each member. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-124024 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the inventors' investigations revealed that there is room for improvement in the technology for joining the constituent members of the electrode terminal by metal-to-metal bonding. Specifically, when connecting the electrode terminal that is extended to the outside of the battery case to the bus bar, thermal welding such as laser welding is usually used. If the large heat generated during such thermal welding is transmitted to the bond marks (metal joints) formed by the metal-to-metal bonding, the metal joints may thermally deteriorate, resulting in a decrease in the joint strength, conductivity, and the like.

[0006] The present invention has been made to solve such problems, and has an object to provide a technique for suppressing thermal deterioration of a metal joint formed at a contact interface between constituent members of an electrode terminal. [Means for solving the problem]

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

[0008] The secondary battery disclosed herein comprises an electrode assembly, a battery case that houses the electrode assembly, and an electrode terminal that is connected to the electrode assembly inside the battery case and has a portion exposed to the outside of the battery case. The electrode terminal of the secondary battery comprises a first member that has one end located inside the battery case and the other end located outside the battery case, and a plate-like second member that is connected to the first member outside the battery case. The first member further comprises a shaft that penetrates the battery case and a plate-like connecting portion that is formed at the upper end of the shaft and is in surface contact with the second member. In the secondary battery disclosed herein, a metal joint and a heat insulating portion are formed at the contact interface between the connecting portion of the first member and the second member, and the heat insulating portion is formed outside the metal joint in the radial direction centered on the metal joint.

[0009] In the secondary battery disclosed herein, a metal joint is formed at the contact interface between a first member and a second member, which are constituent members of an electrode terminal. The metal joint is a bonded mark formed by intermetallic bonding such as ultrasonic welding, laser welding, or resistance welding. In the secondary battery disclosed herein, a heat insulating portion is formed radially outward from the metal joint. As a result, even if a large amount of heat (e.g., welding heat) is applied to the region outside the heat insulating portion, the heat insulating portion can block the large amount of heat, 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 part of the bottom surface of the second member from the top surface of the connection portion. With this configuration, thermal degradation of the metal joint can be suppressed at low cost.

[0011] In a preferred embodiment of the secondary battery disclosed herein, the heat insulating portion is a heat insulating material filled in the space between the bottom surface of the connection portion and the top surface of the second member, which can more effectively 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 to surround the metal joint in a plan view, thereby more suitably suppressing thermal deterioration of the metal joint.

[0013] In a preferred embodiment of the secondary battery disclosed herein, the first and second members are made of different metal materials, and the technology disclosed herein can suppress thermal degradation of the metal junction, making it particularly suitable for use in joining dissimilar metals where metal joining is recommended.

[0014] Another aspect of the technology disclosed herein provides a battery pack in which multiple secondary batteries are electrically connected via a flat bus bar. In the battery pack disclosed herein, at least one of the multiple secondary batteries is a secondary battery having the above-described configuration. The bus bar is in surface contact with an upper surface of a second member, and the bus bar and the second member are connected by a thermal weld that penetrates the bus bar and reaches the second member. In the battery pack disclosed herein, the thermal weld is formed above the heat insulating portion or outside the heat insulating portion in the radial direction centered on the metal joint. This allows the heat generated during the formation of the thermal weld to be insulated by the heat insulating portion, thereby effectively suppressing thermal degradation of the metal joint when the bus bar is connected.

[0015] In a preferred embodiment of the battery pack disclosed herein, the heat insulating portion is a cavity formed by separating a part of the bottom surface of the second member from the top surface of the connection portion. This configuration makes it possible to suppress thermal degradation of the metal joint at low cost.

[0016] In an embodiment in which a cavity is provided as the heat insulating part, when the distance from the center of the metal joint to the outer edge of the metal joint in a plan view is L1, the distance from the center of the metal joint to the inner edge of the heat insulating part is L2, and the distance from the center of the metal joint to the center of the thermally welded part is L3, it is preferable that the following formula (1) be satisfied. This allows the heat insulating part to sufficiently insulate against the heat that is generated when the thermally welded part is formed, thereby more suitably suppressing thermal deterioration of the metal joint. L3-L2>L2-L1 (1) [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a perspective view schematically illustrating a secondary battery according to an embodiment. [Figure 2] FIG. 2 is a cross-sectional view schematically illustrating the vicinity of an electrode terminal of a secondary battery according to one embodiment. [Figure 3] FIG. 2 is a plan view illustrating the positional relationship between a metal joint and a heat insulating portion in a secondary battery according to one embodiment. [Figure 4] 1 is a perspective view schematically illustrating a battery pack according to an embodiment; [Figure 5] 3 is a cross-sectional view schematically illustrating the structure of a connection portion between an electrode terminal and a bus bar in a battery pack according to one embodiment. FIG. [Figure 6] FIG. 2 is a plan view illustrating the positional relationship between metal joints, heat insulating portions, and thermally welded portions in a battery pack according to one embodiment. [Figure 7] 10 is a plan view illustrating the positional relationship between metal joints, heat insulating portions, and thermally welded portions in a battery pack according to another embodiment. FIG. [Figure 8] 10 is a plan view illustrating the positional relationship between metal joints, heat insulating portions, and thermally welded portions in a battery pack according to another embodiment. FIG. [Figure 9] 10 is a plan view illustrating the positional relationship between metal joints, heat insulating portions, and thermally welded portions in a battery pack according to another embodiment. FIG. [Figure 10] 10 is a plan view illustrating the positional relationship between metal joints, heat insulating portions, and thermally welded portions in a battery pack according to another embodiment. FIG. [Figure 11] 10 is a plan view illustrating the positional relationship between metal joints, heat insulating portions, and thermally welded portions in a battery pack according to another embodiment. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0018] An embodiment of the technology disclosed herein will be described below. Note that the following embodiment is not intended to limit the technology disclosed herein. Furthermore, matters other than those specifically mentioned in this specification that are necessary for implementing the technology disclosed herein can be understood as design matters for a person skilled in the art based on prior art in the relevant field. In other words, the technology disclosed herein can be implemented based on the contents disclosed in this specification and common technical knowledge in the relevant field.

[0019] In the drawings referred to in the following description, the same reference numerals are used to designate components and parts that perform the same functions. Furthermore, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect the actual dimensional relationships. In each drawing, the symbol X indicates the "width direction," the symbol Y indicates the "depth direction," and the symbol Z indicates the "height direction." However, these directions are determined for the convenience of explanation and are not intended to limit the installation mode of the secondary battery or battery pack during use or manufacture.

[0020] Furthermore, in this specification, the term "secondary battery" refers generally to an electricity storage device in which charge carriers move between a pair of electrodes (positive and negative electrodes) via an electrolyte, resulting in a charge-discharge reaction. Such secondary batteries include so-called storage batteries such as lithium-ion secondary batteries, nickel-metal hydride batteries, and nickel-cadmium batteries, as well as capacitors such as electric double-layer capacitors. The technology disclosed herein is not limited to a specific type of secondary battery, but can be applied without particular limitation to all secondary batteries having electrode terminals and battery packs constructed using such secondary batteries.

[0021] 1. Secondary battery The structure of the secondary battery according to this embodiment will be described below with reference to Figs. 1 to 3. Fig. 1 is a perspective view that schematically shows the secondary battery according to this embodiment. Fig. 2 is a cross-sectional view that schematically shows the structure in the vicinity of the electrode terminal of the secondary battery according to this embodiment. Fig. 3 is a plan view that explains the positional relationship between the metal joint portion and the heat insulating portion in the electrode terminal of the secondary battery according to this embodiment.

[0022] (1) Overall structure 1, the secondary battery 1 according to this embodiment includes an electrode assembly (not shown), a battery case 10, and an electrode terminal 20. Each component will be described below.

[0023] (2) Electrode body The electrode assembly is a power-generating element housed inside the battery case 10. The structure of the electrode assembly is not particularly limited, and various structures that can be used in general secondary batteries can be used without particular limitation. For example, the electrode assembly can have a structure in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween. Specific examples of this type of electrode assembly structure include a wound electrode assembly in which a long strip-shaped positive electrode, a negative electrode, and a separator are wound together, and a laminated electrode assembly in which rectangular sheet-shaped positive electrodes, negative electrodes, and a separator are stacked together. Note that the detailed structure and materials of each component (positive electrode, negative electrode, and separator) that constitutes the electrode assembly can be those that can be used in general secondary batteries (e.g., lithium-ion secondary batteries) without particular limitation, and detailed description thereof will be omitted because they do not limit the technology disclosed herein.

[0024] Although not shown, in the secondary battery according to this embodiment, in addition to the electrode assembly, an electrolyte is also accommodated inside the battery case 10. As the electrolyte, a non-aqueous liquid electrolyte (nonaqueous electrolytic solution) containing a non-aqueous solvent and a supporting salt, or a solid electrolyte formed by molding a powdered electrolyte into a sheet shape, can be used. Note that the specific components of the electrolyte do not limit the technology disclosed herein, and therefore detailed description thereof will be omitted.

[0025] (3) Battery case The battery case 10 is a container that houses the electrode assembly and electrolyte. As shown in FIG. 1, the battery case 10 in this embodiment is a flat, rectangular container. The rectangular battery case 10 includes a flat, rectangular case body 12 with an open top and a plate-like lid 14 that closes the top opening of the case body 12. As will be described in detail later, as shown in FIGS. 1 and 2, terminal insertion holes 14a, which are openings through which electrode terminals 20 (first members 30) are inserted, are provided at both ends of the lid 14 in the width direction X. The outer shape of the battery case is not limited to the above-described shape and can be modified as appropriate depending on the specifications of the external device, the shape of the electrode assembly, and the like. For example, the battery case may be a cylindrical case with a bottom. The material of the battery case 10 is not particularly limited as long as it has the required strength. Suitable materials for the battery case 10 include lightweight, highly thermally conductive metal materials (e.g., aluminum, stainless steel, nickel-plated steel, etc.).

[0026] (3) Electrode terminal As shown in FIG. 1, the secondary battery 1 according to this embodiment includes a pair of electrode terminals 20. Parts of these electrode terminals 20 are exposed to the outside of the battery case 10. Although not shown, each electrode terminal 20 is connected to an electrode body (positive electrode or negative electrode) inside the battery case 10. In this specification, the electrode terminal connected to the positive electrode side of the electrode body is referred to as the "positive electrode terminal," and the electrode terminal connected to the negative electrode side is referred to as the "negative electrode terminal." As shown in FIG. 2, the electrode terminal 20 according to this embodiment includes a first member 30 and a second member 40. The components of the electrode terminal 20 according to this embodiment will be specifically described below. The structure of the electrode terminal 20 described below may be applied to either the positive electrode terminal or the negative electrode terminal, or to both.

[0027] (a) First member The first member 30 is a member having one end located inside the battery case 10 and the other end located outside the battery case 10. As shown in FIG. 2 , the first member 30 has a shaft 32 that penetrates the battery case 10. The shaft 32 is a columnar member extending in the height direction Z. The upper end of the shaft 32 is exposed outside the battery case 10 (above the lid 14), and the lower end is housed inside the battery case 10. The outer shape of the shaft 32 is not particularly limited and may be cylindrical or prismatic. However, considering the ease of closing the terminal insertion hole 14a of the lid 14 (sealing the battery case 10), the outer shape of the shaft 32 is preferably cylindrical. In addition, in this embodiment, a connecting portion 34 is formed at the upper end of the shaft 32. The connecting portion 34 is a plate-shaped member that comes into surface contact with the second member 40, which will be described later. The shape of the connection portion 34 in plan view is not particularly limited and may be circular or rectangular. In this embodiment, a rivet portion 36 is formed at the lower end of the shaft portion 32. The rivet portion 36 is formed by a crimping process in which the lower end of the cylindrically shaped shaft portion 32 is pressed radially outward to deform the shaft portion 32. The rivet portion 36 fixes a third member 50 (described later) to the battery case 10 (lid 14) and electrically connects the first member 30 and the third member 50.

[0028] (b) Second member The second member 40 is a plate-like member connected to the first member 30 outside the battery case 10. As shown in FIG. 1, the second member 40 in this embodiment is a plate-like member that is substantially rectangular in plan view and is disposed outside the battery case 10 (above the lid 14). The shape of the second member in plan view is not particularly limited and may be circular. As shown in FIG. 2, the bottom surface 40a (the surface facing the battery case 10) of the second member 40 is in surface contact with the upper surface 34a of the connection portion 34 of the first member 30. As will be described in detail later, a metal joint 70 is formed at the contact interface between the upper surface 34a of the connection portion 34 and the bottom surface 40a of the second member 40, and the first member 30 and the second member 40 are connected by the metal joint 70. Furthermore, a recess 42 is formed on the bottom surface of the second member 40 in this embodiment, and the connection portion 34 of the first member 30 is fitted into the recess 42. This restricts movement of the second member 40 in the width direction X or the depth direction Y when vibration or an external force is applied to the electrode terminal 20, thereby preventing damage to the metal joint 70 due to movement of the second member 40. Furthermore, in this embodiment, a locking portion 44 that protrudes toward the shaft portion 32 of the first member 30 is formed at the lower end of the side wall of the recess 42. This restricts movement of the second member 40 in the height direction Z, thereby more reliably preventing damage to the metal joint 70 due to movement of the second member 40.

[0029] (c) Third member The electrode terminal 20 in this embodiment includes a third member 50. Although not shown, the third member 50 has a current collecting portion extending along the height direction Z. The current collecting portion of the third member 50 is connected at its lower end to the electrode body (positive electrode or negative electrode). As shown in FIG. 2 , an upper end 52 of the third member 50 is bent so as to fit along the inner surface of the battery case 10 (lid body 14). The upper end 52 of the third member 50 is fixed to the battery case 10 (lid body 14) by the rivet portion 36 of the first member 30 and is electrically connected to the first member 30. As a result, the electrode body inside the battery case 10 and the second member 40 outside the battery case 10 are electrically connected via the third member 50 and the first member 30. Note that the third member 50 is not an essential component of the electrode terminal in the technology disclosed herein. For example, when a part of the first member is extended along the height direction and connected to the electrode body, an electrode terminal can be constructed that does not have a third member.

[0030] (4) Insulating materials Next, the secondary battery 1 according to this embodiment includes an insulating member that prevents electrical conduction between the electrode terminals 20 and the battery case 10. As shown in Fig. 2, the insulating member according to this embodiment includes a gasket 62 and an insulator 64.

[0031] The gasket 62 is an insulating member disposed on the outer surface of the battery case 10 (the upper surface of the lid body 14). The gasket 62 is a box-shaped insulating member having a housing portion 62a on its upper surface. The connecting portion 34 of the first member 30 and the second member 40 are housed in the housing portion 62a of the gasket 62. This provides insulation between the lid body 14 and the first member 30, and between the lid body 14 and the second member 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 lid body 14. The protrusion 62b of the gasket 62 is disposed between the shaft portion 32 of the first member 30 and the lid body 14 inside the terminal insertion hole 14a, thereby insulating these members. Furthermore, the gasket 62 is pressurized during the crimping process when the rivet portion 36 of the first member 30 is formed, and is therefore compressed between the lid 14 and the second member 40 (or between the lid 14 and the connecting portion 34). This seals any gaps that may be formed when the various members are attached to the lid 14, preventing the flow of liquid (such as moisture intrusion or electrolyte leakage) between the inside and outside of the battery case 10. The gasket 62 is preferably made of an insulating resin that is easily elastically deformable. Examples of materials for the gasket 62 include fluorinated resins such as perfluoroalkoxy fluororesin (PFA), polyphenylene sulfide resin (PPS), and aliphatic polyamide.

[0032] The insulator 64 is a plate-shaped insulating member having an opening 64a and is disposed between the battery case 10 (lid 14) and the third member 50. This insulates the lid 14 from the third member 50. The opening 64a of the insulator 64 is disposed so as to overlap the terminal insertion hole 62c of the gasket 62 in a plan view, and the shaft 32 of the first member 30 is inserted through the opening 64a. This reliably prevents contact between the shaft 32 of the first member 30 and the lid 14. Furthermore, during the crimping process used to form the rivet 36 at the lower end of the first member 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 crimps the gasket 62 and the insulator 64 together, more reliably preventing the flow of liquid between the inside and outside of the battery case 10. Like the gasket 62, the insulator 64 is preferably formed from an insulating resin that is easily elastically deformable.

[0033] (5) Connection between the first member and the second member 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 member 30 and the second member 40. This metal joint 70 is a joining mark formed when the first member 30 and the second member 40 are joined together by a metal-to-metal bond such as ultrasonic welding, laser welding, or resistance welding. As shown in FIG. 2 , the metal joint 70 according to this embodiment is formed on the axis SC of the stem 32 of the first member 30. As an example, when forming the metal joint 70 using ultrasonic welding, the first member 30 and the second member 40 may be sandwiched between a horn and anvil so that they are positioned on the axis SC of the stem 32. While not limiting the technology disclosed herein, as shown in FIG. 3 , the metal joint 70 may be substantially circular in plan view. However, depending on the joining method and joining conditions, the metal joint 70 may also be substantially rectangular (e.g., substantially square or rectangular) in plan view. From the viewpoint of suitably connecting the first member 30 and the second member 40, it is preferable to adjust the joining conditions appropriately so that the diameter of the metal joint 70 is 0.3 mm or more. From the viewpoint of more suitably connecting the first member 30 and the second member 40, it is more preferable 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, there is no particular upper limit to the diameter of the metal joint 70, and it may be 10.0 mm or less, 5.0 mm or less, or 2.0 mm or less.

[0034] As described above, forming the metal joint 70 at the contact interface between the connection portion 34 of the first member 30 and the second member 40 allows the first member 30 and the second member 40 to be connected with low resistance and high strength. However, if the metal joint 70 is subjected to high heat during, for example, a bus bar connection, and thermal degradation occurs, the conductivity and bonding strength of the metal joint 70 may be significantly reduced. To suppress such thermal degradation of the metal joint 70, the secondary battery 1 according to this embodiment has a heat insulating portion 80 formed at the contact interface between the connection portion 34 and the second member 40. As shown in FIG. 3 , the heat insulating portion 80 is formed radially outward from the metal joint 70. As a result, even if high heat is applied to an area above the heat insulating portion 80 or outside the heat insulating portion 80, the heat insulating portion 80 can block the high heat, thereby suppressing thermal degradation of the metal joint 70 during, for example, welding of a bus bar.

[0035] The heat insulating portion 80 according to this embodiment is a cavity formed between the connecting portion 34 and the second member 40. Specifically, the second member 40 according to this embodiment has a groove 46 formed in a portion of its bottom surface 40a, spaced from the upper surface 34a of the connecting portion 34. This allows the heat insulating portion 80, which is a cavity, to be formed at the contact interface between the connecting portion 34 and the second member 40. This configuration reduces thermal degradation of the metal joint 70 at low cost. The groove for forming the heat insulating portion may be formed on the upper surface of the connecting portion of the first member, rather than on the bottom surface of the second member. Furthermore, the shape of the heat insulating portion is not particularly limited as long as it can block heat conduction to the metal joint. For example, the heat insulating portion may be formed by filling the space at the contact interface between the connecting portion of the first member and the second member with a heat insulating material. Suitable heat insulating materials include inorganic heat insulating materials with excellent heat resistance (such as glass wool, a coating layer containing alumina particles, or a coating layer containing silica particles). By using such a heat insulating material, thermal deterioration of the metal joint 70 can be more suitably suppressed.

[0036] As shown in FIG. 3 , the heat insulating portion 80 in this embodiment is an annular heat insulating portion 80 formed to surround the metal joint 70 in a plan view. Forming such an annular heat insulating portion 80 prevents excessive heat from reaching the metal joint 70 by circumventing the heat insulating portion 80, thereby more reliably suppressing thermal degradation of the metal joint 70. The dimension L4 (see FIG. 3 ) from the inner edge 82 to the outer edge 84 of the annular heat insulating portion 80 is preferably 3 mm or more, more preferably 5 mm or more, and particularly preferably 10 mm or more. This more effectively prevents excessive heat from reaching the metal joint 70. Considering the strength of a member (e.g., a second member) in which the groove for forming the heat insulating portion is provided, the dimension L4 in FIG. 3 is preferably 50 mm or less, more preferably 30 mm or less, and particularly preferably 20 mm or less.

[0037] The technology disclosed herein is particularly suitable for use when the first and second components are made of different metal materials. Furthermore, for this type of connection between dissimilar metals, ultrasonic bonding is recommended among the intermetallic bonding methods mentioned above, from the perspective of forming a high-strength, low-resistance joint. However, metal joints formed by ultrasonic bonding tend to experience a significant decrease in strength and conductivity when thermally deteriorated. In contrast, the technology disclosed herein can suppress thermal deterioration of the metal joint, making it particularly suitable for use in constructing electrode terminals with dissimilar metal joints, for which ultrasonic bonding is recommended.

[0038] An example of an electrode terminal for which ultrasonic welding is recommended for dissimilar metal joining is an electrode terminal 20 in which the first member 30 is made of copper and the second member 40 is made of aluminum. Ultrasonic welding is recommended for aluminum and copper materials because they tend to have high electrical resistance when joined by thermal welding. For example, for the negative electrode terminal of a lithium-ion secondary battery, a copper-to-copper connection is recommended between the negative electrode (negative electrode current collector) of the electrode body, while an aluminum-to-aluminum connection is recommended between the negative electrode and the bus bar. In such cases, dissimilar metal joining between copper and aluminum is required for the components of the negative electrode terminal. For this purpose, it is preferable to form a metal joint 70 using ultrasonic welding between the copper first member 30 and the aluminum second member 40. This allows the first member 30 and the second member 40 to be joined with relatively low resistance. As described above, the technology disclosed herein can suppress thermal degradation of the metal joint 70 by using the heat insulating member 80, thereby maintaining a low-resistance joint interface between the first member 30 and the second member 40, which are made of dissimilar metals. As described above, the technology disclosed herein is particularly suitable for use in constructing negative electrode terminals for lithium-ion secondary batteries, which require dissimilar metal joints between copper and aluminum materials. In this specification, the term "aluminum material" encompasses aluminum and alloys primarily containing aluminum. Here, "aluminum-based alloys" refers to alloys composed of at least 70% aluminum. Other elements that may be contained in the aluminum material include, but are not limited to, silicon, iron, copper, manganese, magnesium, zinc, chromium, titanium, lead, and zirconium. Meanwhile, the term "copper material" encompasses copper and alloys primarily containing copper. Here, "copper-based alloys" refers to alloys composed of at least 50% copper. Other elements that may be contained in the material include, but are not limited to, silicon, iron, manganese, magnesium, zinc, chromium, titanium, lead, tin, phosphorus, aluminum, nickel, cobalt, beryllium, zirconium, etc.

[0039] 2. Battery pack 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. The following description of the battery pack according to this embodiment will mainly refer to FIGS. 4 to 6. FIG. 4 is a perspective view that schematically shows the battery pack according to this embodiment. FIG. 5 is a cross-sectional view that schematically shows the structure of the connection portion between the electrode terminal and the bus bar in the battery pack according to this embodiment. FIG. 6 is a plan view that explains the positional relationship between the metal joints, the heat insulating portion, and the thermally welded portion in the battery pack according to this embodiment. For ease of explanation, FIG. 6 omits the bus bar 110, and indicates the positions where the metal joints 70 and the heat insulating portion 80 are formed by dotted lines. This also applies to FIGS. 7 to 11, which will be described later.

[0040] As shown in FIG. 4 , the battery pack 100 according to this embodiment includes a plurality of secondary batteries 1. Specifically, in this battery pack 100, the plurality of secondary batteries 1, each having a flat, rectangular battery case 10, are arranged along the depth direction Y with their flat surfaces facing each other. A pair of end plates 120 is disposed on both outer sides of the battery pack 100 in the arrangement direction (depth direction Y). The pair of end plates 120 are bridged by restraining beams 130, thereby restraining each of the plurality of secondary batteries 1 along the arrangement direction. In this embodiment, a spacer 140 is disposed between adjacent secondary batteries 1 to equalize the restraining pressure on the flat surfaces. The number of secondary batteries 1 constituting the battery pack 100 is not particularly specified and can be changed as appropriate depending on the purpose of the battery pack 100 (e.g., the power requirements and specifications of external devices). Furthermore, the technology disclosed herein does not require all of the secondary batteries constituting the battery pack to have the above-described configuration. That is, the battery pack 100 according to this embodiment may include some secondary batteries having a configuration different from that of the secondary batteries 1 according to the above-described embodiment.

[0041] In this embodiment, the electrode terminals 20 of two adjacent secondary batteries 1 are connected to each other by a bus bar 110. The bus bar 110 is made of a metal material with excellent conductivity and strength. As shown in FIG. 5 , the bus bar 110 is in surface contact with the upper surface 40b of the second member 40 of the electrode terminal 20 and is thermally welded to the upper surface 40b. A thermal weld 90, which is a connection mark of this thermal welding, is formed so as to penetrate the bus bar 110 and reach the second member 40. Note that an aluminum material is a suitable example of a material for the bus bar 110 in this embodiment. Furthermore, from the viewpoint of preventing a decrease in conductivity due to thermal welding of dissimilar metal members, it is preferable that the bus bar 110 be made of the same metal material as the second member 40 of the electrode terminal 20.

[0042] 5 and 6, in this embodiment, the bus bar 110 and the electrode terminal 20 are thermally welded together so that a thermal weld 90 is formed above a heat insulating 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 beam is irradiated above the heat insulating portion 80 so that a pair of linear heat welds 90 are formed facing each other across the metal joint 70. This allows the heat weld 90 to be formed while the heat insulating portion 80 insulates against heat during thermal welding, thereby suppressing thermal deterioration of the metal joint 70.

[0043] In the technology disclosed herein, the position where the thermally welded portion 90 is formed (the position where the laser is irradiated during thermal welding) is not limited to above the insulating portion 80. For example, as shown in Fig. 7, thermal welding may be performed so that the thermally welded portion 90 is formed outside the insulating portion 80 in the radial direction from the metal joint 70 as the center. Even in this case, the insulating portion 80 can insulate the metal joint 70 from heat during thermal welding, thereby suppressing thermal deterioration of the metal joint 70.

[0044] The positions of the thermally welded joints 90 are preferably adjusted to more effectively suppress thermal degradation of the metal joints 70. Specifically, assuming that the distance from the center C of the metal joints 70 to the outer edge 72 is L1, the distance from the center C of the metal joints 70 to the inner edge 82 of the thermal insulation section 80 is L2, and the distance from the center C of the metal joints 70 to the center of the thermally welded joints 90 is L3, the positions of the thermally welded joints 90 are preferably adjusted to satisfy the following formula (1). This more effectively prevents the large heat generated during thermal welding from reaching the metal joints 70. Furthermore, to more reliably prevent thermal degradation of the metal joints 70, the positions of the thermally welded joints 90 are preferably adjusted to satisfy the following formula (2). The following formulas (1) and (2) are conditions that can be applied when the thermal insulation section 80 is hollow. For example, when the thermal insulation section 80 is filled with a thermal insulation material, the positions of the thermally welded joints 90 are preferably adjusted taking into account the thermal insulation properties (thermal conductivity) of the thermal insulation material. L3-L2>L2-L1 (1) L3-L2>(L2-L1)×1.5 (2)

[0045] Furthermore, from the viewpoint of more reliably preventing 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 90 satisfies the following formula (3). L3-L2>w (3)

[0046] 3. Other Embodiments The above describes one embodiment of the technology disclosed herein. Note that the above embodiment shows an example of a secondary battery (or a battery pack) to which the technology disclosed herein is applied, and is not intended to limit the technology disclosed herein.

[0047] For example, in the above-described embodiment, the insulating portion 80 is formed in a circular ring shape surrounding the metal joint 70 in a plan view. However, the insulating portion may be formed radially outward from the metal joint 70, and the specific planar shape is not particularly limited. For example, as shown in FIG. 8 , the insulating portion may be a square-ring-shaped insulating portion 80A surrounding the metal joint 70 in a plan view. Even when such a square-ring-shaped insulating portion 80A is formed, it is possible to appropriately insulate the heat generated during the formation of the thermally welded joint 90 (during thermal welding) and suppress thermal deterioration of the metal joint 70. Furthermore, the planar shape of the insulating portion does not have to be a ring shape as shown in FIGS. 6 to 8 . For example, as shown in FIG. 9 , a pair of insulating portions 80B having rectangular shapes in plan view may be formed facing each other across the metal joint 70. When such a pair of insulating portions 80B is formed, the thermally welded joint 90 is formed above each insulating portion 80B (or radially outward from each insulating portion 80B). This allows the heat generated during thermal welding to be appropriately insulated by the heat insulating portion 80B, and thermal deterioration of the metal joint 70 can be suppressed.

[0048] Furthermore, in the technology disclosed herein, the region where thermal welding is performed (i.e., thermal weld 90) is not particularly limited as long as it is above the thermal insulation (or radially outward of the thermal insulation), and can be modified as appropriate. For example, as shown in FIGS. 6 and 10 , thermal welding may be performed so that a portion of the thermal weld 90 protrudes from the thermal insulation 80, 80C. Even in such cases, thermal deterioration of the metal joint 70 can be sufficiently suppressed as long as the thermal weld 90 protruding from the thermal insulation 80, 80C is formed radially outward of the thermal insulation 80, 80C from the center of the metal joint 70. For example, in FIG. 10 , thermal welding is performed so that the upper end 92 of the thermal weld 90 protrudes from the rectangular thermal insulation 80C. However, when viewed along a line A connecting the upper end 92 of the thermal weld 90 and the metal joint 70, the upper end 92 of the thermal weld 90 is formed outside the thermal insulation 80C. In this case, the heat generated when forming the upper end 92 of the thermally welded portion 90 can be insulated by the heat insulating portion 80C, thereby sufficiently suppressing thermal deterioration of the metal joint 70. However, considering the possibility that heat that has traveled around the heat insulating portion may be transmitted to the metal joint, it is preferable to form annular heat insulating portions 80, 80A as shown in Figures 6 to 8.

[0049] Furthermore, in each of the above-described embodiments, a pair of linear thermal welds 90 are formed facing each other across the metal joint 70. However, the planar shape of the thermal welds is not limited to linear, and various shapes can be employed. For example, as shown in FIG. 11 , an annular thermal weld 90A may be formed surrounding the insulating portion 80. Even in this case, the insulating portion 80 can adequately insulate against heat during thermal welding, thereby appropriately suppressing thermal deterioration of the metal joint 70. Note that in FIG. 11 , an annular thermal weld 90A having a radius larger than the outer edge 84 of the insulating portion 80 is formed, and the thermal weld 90A is formed outside the insulating portion 80 in the radial direction centered on the metal joint 70. However, the radius of the thermal weld 90A may be smaller than the outer edge 84 of the insulating portion 80 and larger than the inner edge 82, and the annular thermal weld 90A may be formed above the insulating portion 80. Even in this case, the insulating portion 80 can adequately insulate against heat during thermal welding, thereby suppressing thermal deterioration of the metal joint 70.

[0050] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The invention disclosed herein includes various modifications and variations of the above specific examples. [Explanation of symbols]

[0051] 1 Secondary battery 10 Battery case 12 Case body 14 Lid 20 electrode terminal 30 First member 32 Shaft 34 Connection 36 Tack part 40 Second member 42 recess 46 Groove 50 Third member 62 Gasket 64 Insulator 70 Metal joints 80, 80A~80C Insulation section 90, 90A heat welded parts 100 battery packs 110 Busbar 120 End Plate 130 Restraining beam material 140 spacer

Claims

1. A secondary battery comprising: an electrode body; a battery case that houses the electrode body; and an electrode terminal that is connected to the electrode body inside the battery case and is 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-like second member connected to the first member outside the battery case, the first member includes a shaft portion that penetrates the battery case, and a plate-shaped connecting portion that is formed at an upper end of the shaft portion and that is in surface contact with the second member, A secondary battery characterized in that a metal joint and a heat insulating portion are formed at the contact interface between the connection portion of the first member and the second member, and the heat insulating portion is formed outside the metal joint in a radial direction centered on the metal joint.

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

3. The secondary battery according to claim 1 , wherein the heat insulating portion is a heat insulating material filled in a space between a bottom surface of the connection portion and an upper surface of the second member.

4. 4. The secondary battery 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.

5. 5. The secondary battery according to claim 1, wherein the first member and the second member are made of different metal materials.

6. A battery pack in which a plurality of secondary batteries are electrically connected via a flat bus bar, At least one of the plurality of secondary batteries is the secondary battery according to claim 1, the bus bar is in surface contact with an upper surface of the second member and is heat-welded to the upper surface of the second member, and the bus bar and the second member are connected by a heat-welded portion that penetrates the bus bar and reaches the second member, The battery pack, wherein the thermally welded portion is formed above the heat insulating portion or outside the heat insulating portion in a radial direction centered on the metal joint portion.

7. 7. The battery pack according to claim 6, wherein the heat insulating portion is a cavity formed by separating a part of a bottom surface of the second member from an upper surface of the connecting portion.

8. 8. The battery pack according to claim 7, wherein, in a plan view, when a distance from a center of the metal joint portion to an outer edge of the metal joint portion is L1, a distance from the center of the metal joint portion to an inner edge of the heat insulating portion is L2, and a distance from the center of the metal joint portion to a center of the thermally welded portion is L3, the following formula (1) is satisfied: L3-L2>L2-L1 (1)

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