Electricity storage device and electricity storage module including the same

Abstract

To provide a power storage device having a terminal of which a communication reliability is improved.SOLUTION: A power storage device disclosed here, comprises a first electrode terminal having a first conductive member 41, a second conductive member 42, and a metal bonding part 45. The metal bonding part 45 contains: a first region 451 in which a first metal occupies 70 mass% or more; and a second region 452 in which a second metal occupies 70 mass% or more. The first region 451 contains: a region A1 positioned to the first conductive member 41 side from a boundary surface B; and a first projection region P1 projected to a second conductive member 42 side from the boundary surface B. The second region 452 contains: a region A2 positioned to the second conductive member 42 side from the boundary surface B; and a second projection region P2 projected to the first conductive member 41 side from the boundary surface B.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The present invention relates to an electricity storage device and an electricity storage module including the same. [Background technology]

[0002] Patent Document 1 describes a dissimilar metal joint (laser joint) that includes a copper material, an aluminum material, and a molten mixed portion formed when a portion of the aluminum material melts and flows into the copper material, the molten mixed portion satisfying predetermined width and depth dimensions. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-211981 A Summary of the Invention [Problem to be solved by the invention]

[0004] According to the study by the present inventors, there is still room for improvement when applying the above technology to an electrode terminal of an electricity storage device used, for example, as a power source for driving a vehicle. That is, when using an electricity storage device for applications such as a power source for driving a vehicle, it is expected that external forces such as vibrations and impacts will be applied. However, in the technology of Patent Document 1, since the strength of the boundary portion between the molten part and the unmolten part is weak, there is a risk that the metal molten part will be destroyed when external forces are applied, causing the conductive connection of the terminal to become unstable or causing a connection failure. Therefore, it has been desired to improve the conductive reliability.

[0005] The present invention has been made in view of the above circumstances, and has an object to provide an electricity storage device including a terminal (dissimilar metal joint body) with improved conduction reliability. [Means for solving the problem]

[0006] The present invention provides an electricity storage device comprising: an electrode assembly having a first electrode and a second electrode; a battery case housing the electrode assembly and having a first surface with a through hole; and a first electrode terminal penetrating the through hole of the battery case and electrically connected to the first electrode. The first electrode terminal comprises a first conductive member having a first metal occupying the largest proportion by mass, a second conductive member having a second metal occupying the largest proportion by mass and having a shaft portion disposed in the through hole, and a metal joint portion at which the first conductive member and the second conductive member are joined. The metal joint includes a first region in which the first metal accounts for 70% by mass or more, and a second region in which the second metal accounts for 70% by mass or more, in a cross section perpendicular to the first surface, passing through the axis of the shaft portion, and extending radially of the shaft portion, where when a surface passing through the boundary portion where the first conductive member and the second conductive member abut around the metal joint is defined as a boundary surface, the first region includes a region located on the first conductive member side of the boundary surface and a first protruding region protruding toward the second conductive member side of the boundary surface, and the second region includes a region located on the second conductive member side of the boundary surface and a second protruding region protruding toward the first conductive member side of the boundary surface.

[0007] In the above metal joint, the first region includes the first protruding region, and the second region includes the second protruding region, so that the boundary between the first region and the second region has an uneven shape in cross section. This allows the first conductive member and the second conductive member to be mechanically fitted together, thereby improving the bonding strength of the boundary portion. In addition, by curving the boundary portion, the distance of the boundary can be increased, so that even if a crack occurs in the metal joint, the progress of the crack can be delayed. As a result, according to the technology disclosed herein, even if a force such as vibration or impact is applied from the outside during use, the first conductive member and the second conductive member can be easily maintained in a close contact state, and the conductive connection between the first conductive member and the second conductive member can be stably maintained. Therefore, it is possible to realize an electricity storage device having a terminal with improved conductive reliability of the metal joint. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view illustrating a power storage module according to an embodiment. [Diagram 2] FIG. 2 is a perspective view illustrating a schematic configuration of the electricity storage device. [Diagram 3] FIG. 3 is a schematic vertical cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 4 is a perspective view that typically shows the sealing plate assembly. [Diagram 5] FIG. 5 is a plan view that typically illustrates the vicinity of the negative electrode terminal in FIG. [Figure 6] FIG. 6 is a schematic vertical cross-sectional view taken along line VI-VI in FIGS. [Figure 7] FIG. 7 is a schematic vertical cross-sectional view showing only the negative electrode terminal of FIG. [Figure 8] FIG. 8 is an enlarged view that illustrates a schematic view of the vicinity of the metal joint in FIG. [Figure 9] FIG. 9(A) is an explanatory diagram illustrating a laser welding method, and FIG. 9(B) is a schematic vertical cross-sectional view of the vicinity of a metal joint taken along line IXB-IXB in FIG. 9(A). [Figure 10] FIG. 10(A) is a cross-sectional SEM image of the laser welding path and metal joint in the comparative example, and FIG. 10(B) is a cross-sectional SEM image of the laser welding path and metal joint in the example. [Figure 11] FIG. 11(A) is a plan view that shows a schematic diagram of a laser welding path according to Example 1, and FIG. 11(B) is a plan view that shows a schematic diagram of a laser welding path according to Example 2. As shown in FIG. [Figure 12] FIG. 12 is a comparison of the tensile strength of Examples 1 and 2. [Figure 13] 13(A) and (B) are views corresponding to FIGS. 9(A) and (B) according to the first modified example. [Figure 14] FIG. 14 is a view corresponding to FIG. 5 according to the second modified example. [Figure 15] FIG. 15 is a schematic vertical cross-sectional view of the vicinity of the metal joint taken along line XV-XV in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, some preferred embodiments of the technology disclosed herein will be described with reference to the drawings. Note that matters other than those specifically mentioned in this specification and necessary for carrying out the present invention (for example, the general configuration and manufacturing process of the power storage device and power storage module that do not characterize the present invention) can be understood as design matters of a person skilled in the art based on the conventional technology in the field. The present invention can be carried out based on the contents disclosed in this specification and the technical common sense in the field.

[0010] In the following drawings, the same reference numerals are used for components and parts having the same function, and duplicated explanations may be omitted or simplified. In addition, in this specification, the expression "X to Y" indicating a range includes the meaning of "greater than X" and "smaller than Y" as well as the meaning of "X to Y" and "smaller than Y".

[0011] FIG. 1 is a perspective view showing a schematic diagram of a power storage module 500 according to an embodiment. The power storage module 500 includes a plurality of power storage devices 100 arranged along an arrangement direction X, and a plurality of bus bars 200 electrically connecting the plurality of power storage devices 100 to each other. The power storage module 500 further includes a restraining mechanism 300. In the following description, the symbols L, R, F, Rr, U, and D in the drawings represent left, right, front, rear, top, and bottom, and the symbols X, Y, and Z in the drawings represent the thickness direction, long side direction perpendicular to the thickness direction, and up-down direction perpendicular to the thickness direction and long side direction, respectively, of the power storage device 100. The thickness direction X is also the arrangement direction of the power storage device 100. However, these are merely directions for convenience of description, and do not limit the installation form of the power storage module 500 in any way.

[0012] The restraining mechanism 300 is configured to apply a prescribed restraining pressure to the multiple electricity storage devices 100 in the arrangement direction X. Here, the restraining mechanism 300 is configured with a pair of end plates 310, a pair of side plates 320, and multiple screws 330. The pair of end plates 310 are arranged at both ends of the multiple electricity storage devices 100 in the arrangement direction X. The pair of end plates 310 sandwich the multiple electricity storage devices 100 in the arrangement direction X. The pair of end plates 310 are preferably made of metal.

[0013] The pair of side plates 320 bridge the pair of end plates 310. The pair of side plates 320 are preferably made of metal. The pair of side plates 320 are fixed to the end plates 310 by a plurality of screws 330 so that the binding load is, for example, approximately 10 to 15 kN. This applies a binding load to the plurality of power storage devices 100 from the arrangement direction X, and the power storage modules 500 are held integrally. However, the configuration of the binding mechanism is not limited to this. The binding mechanism 300 may include, for example, a plurality of binding bands, bind bars, or the like, instead of the side plates 320.

[0014] The bus bar 200 is a conductive member and electrically connects the plurality of power storage devices 100 to each other. The bus bar 200 is made of a conductive metal such as aluminum, an aluminum alloy, nickel, or stainless steel. The bus bar 200 is preferably made of aluminum or an aluminum alloy. In FIG. 1, the bus bar 200 is bridged between a positive electrode terminal 30 (see FIG. 2, specifically, a positive electrode first conductive member 31) and a negative electrode terminal 40 (see FIG. 2, specifically, a negative electrode first conductive member 41) of adjacent power storage devices 100 in the arrangement direction X, which will be described later. The bus bar 200 is attached to the positive electrode terminal 30 and the negative electrode terminal 40, respectively, by welding such as laser welding.

[0015] The power storage device 100 is a device that can store electric power and can be repeatedly charged and discharged. In this specification, the term "power storage device" is a concept that encompasses so-called secondary batteries such as lithium ion secondary batteries and nickel-metal hydride batteries, and capacitors such as lithium ion capacitors and electric double layer capacitors.

[0016] In FIG. 1, the multiple power storage devices 100 are arranged between a pair of end plates 310 along the arrangement direction X (in other words, the thickness direction X of the power storage devices 100). The shape, size, number, arrangement, and the like of the multiple power storage devices 100 constituting the power storage module 500 are not limited to the embodiment disclosed herein and can be changed as appropriate. In addition, other members such as spacers may be interposed between the power storage devices 100 adjacent to each other in the arrangement direction X. The multiple power storage devices 100 are connected in series here. However, the method of connecting the multiple power storage devices 100 is not limited to series and may be, for example, parallel, multi-series, multi-parallel, or the like.

[0017] FIG. 2 is a perspective view of the electricity storage device 100. FIG. 3 is a schematic longitudinal sectional view taken along line III-III in FIG. 2. As shown in FIG. 3, the electricity storage device 100 includes a battery case 10, an electrode body 20, a positive electrode terminal 30, a negative electrode terminal 40, a positive electrode current collector 50, and a negative electrode current collector 60. Although not shown, the electricity storage device 100 further includes a non-aqueous electrolyte (not shown). The non-aqueous electrolyte may be the same as a conventional one and is not particularly limited. The electricity storage device 100 is a lithium ion secondary battery. The electricity storage device 100 is characterized by including the positive electrode terminal 30 and / or the negative electrode terminal 40 disclosed herein, and other configurations may be the same as a conventional one.

[0018] The battery case 10 is a housing that contains the electrode assembly 20 and the nonaqueous electrolyte. As shown in FIG. 2, the battery case 10 has a flat, bottomed rectangular parallelepiped (rectangular) outer shape. The material of the battery case 10 may be the same as that used conventionally, and is not particularly limited. The battery case 10 is preferably made of a metal, more preferably made of aluminum, an aluminum alloy, iron, an iron alloy, or the like, and particularly preferably made of aluminum or an aluminum alloy. As shown in FIG. 3, the battery case 10 includes an exterior body 12 having an opening 12h, and a sealing plate (lid) 14 that closes the opening 12h. The battery case 10 preferably includes an exterior body 12 and a sealing plate 14.

[0019] As shown in Fig. 2, the exterior body 12 includes a substantially rectangular bottom wall 12a facing the opening 12h (see Fig. 3), a pair of long side walls 12b extending from the long sides of the bottom wall 12a and facing each other, and a pair of short side walls 12c extending from the short sides of the bottom wall 12a and facing each other. The area of ​​the long side walls 12b is larger than the area of ​​the short side walls 12c. In this specification, the term "substantially rectangular" includes not only a perfect rectangular shape (rectangular shape), but also a shape in which the corners connecting the long and short sides of the rectangle are rounded or a shape in which the corners have notches.

[0020] The sealing plate 14 is a plate-like member extending along the XY plane in FIG. 2. The sealing plate 14 is an example of a "first surface." As shown in FIG. 3, the sealing plate 14 is attached to the exterior body 12 so as to close the opening 12h. The sealing plate 14 faces the bottom wall 12a of the exterior body 12. The sealing plate 14 here has a substantially rectangular shape. It is preferable that the sealing plate 14 has a substantially rectangular shape. The battery case 10 is integrated by joining (preferably welding) the sealing plate 14 to the periphery of the opening 12h of the exterior body 12. The battery case 10 is hermetically sealed (sealed).

[0021] 3, the sealing plate 14 is provided with a liquid inlet 15, a drain valve 17, and two terminal outlet holes 18 and 19. The liquid inlet 15 is for injecting a non-aqueous electrolyte after the sealing plate 14 is assembled to the exterior body 12. The liquid inlet 15 is sealed with a sealing member 16. The drain valve 17 is configured to break when the pressure inside the battery case 10 reaches or exceeds a predetermined value, thereby discharging gas inside the battery case 10 to the outside.

[0022] As shown in FIG. 3, the terminal pull-out holes 18 and 19 penetrate the sealing plate 14 in the up-down direction Z. The terminal pull-out holes 18 and 19 are an example of a "through hole" provided in the sealing plate 14 (first surface). In a plan view, the terminal pull-out holes 18 and 19 are formed in an annular (e.g., annular) shape in a plan view. The terminal pull-out hole 18 has an inner diameter large enough to insert the shaft column portion 32s of the positive electrode terminal 30 (before being attached to the sealing plate 14) before being crimped, which will be described later. The terminal pull-out hole 19 has an inner diameter large enough to insert the shaft column portion 42s of the negative electrode terminal 40 (before being attached to the sealing plate 14) before being crimped, which will be described later.

[0023] As shown in FIG. 3, the electrode body 20 is accommodated inside the battery case 10 (specifically, the exterior body 12). Although not shown, the electrode body 20 has a positive electrode and a negative electrode. The positive electrode has a positive electrode current collector and a positive electrode mixture layer fixed on the positive electrode current collector and containing a positive electrode active material. The negative electrode has a negative electrode current collector and a negative electrode mixture layer fixed on the negative electrode current collector and containing a negative electrode active material. One of the positive electrode and the negative electrode is an example of a "first electrode", and the other is an example of a "second electrode". In this embodiment, the first electrode is a negative electrode, and the second electrode is a positive electrode. The first electrode is preferably a negative electrode, and the second electrode is preferably a positive electrode.

[0024] The configuration of the electrode body 20 may be the same as that of the conventional one, and is not particularly limited. The electrode body 20 is a flat wound electrode body in which a strip-shaped positive electrode and a strip-shaped negative electrode are stacked in an insulated state via a separator, and wound around a winding axis. However, in other embodiments, the electrode body 20 may be a laminated electrode body in which multiple rectangular positive electrodes and multiple rectangular negative electrodes are stacked in an insulated state. The number of electrode bodies 20 arranged inside one battery case 10 is not particularly limited, and may be one or more.

[0025] As shown in FIG. 3, a positive electrode current collector 23 is provided at one end (left end in FIG. 3) in the winding axis direction (long side direction Y in FIG. 3) of the electrode body 20. The positive electrode current collector 23 is an exposed part of the positive electrode current collector, and is made of a conductive metal such as aluminum, aluminum alloy, nickel, stainless steel, etc. A second part 52 of a positive electrode current collector 50, which will be described later, is attached to the positive electrode current collector 23. A negative electrode current collector 25 is provided at the other end (right end in FIG. 3) in the winding axis direction of the electrode body 20. The negative electrode current collector 25 is an exposed part of the negative electrode current collector, and is made of a conductive metal such as copper, copper alloy, nickel, stainless steel, etc. A second part 62 of a negative electrode current collector 60, which will be described later, is attached to the negative electrode current collector 25.

[0026] The positive electrode current collecting member 50 constitutes a conductive path that electrically connects the positive electrode (second electrode) of the electrode body 20 and the positive electrode terminal 30. The positive electrode current collecting member 50 is preferably made of the same metal type as the positive electrode current collecting part 23, for example, a conductive metal such as aluminum, an aluminum alloy, nickel, or stainless steel. As shown in FIG. 3, the positive electrode current collecting member 50 includes a substantially L-shaped first part 51 and a second part 52 that is electrically connected to the first part 51 and extends along the short side wall 12c of the exterior body 12. The first part 51 is attached to the inner surface of the sealing plate 14 by crimping in a state insulated via the internal insulating member 70. The first part 51 is electrically connected to the positive electrode terminal 30. The second part 52 is attached to the positive electrode current collecting part 23.

[0027] The negative electrode current collecting member 60 constitutes a conductive path that electrically connects the negative electrode (first electrode) of the electrode body 20 and the negative electrode terminal 40. The negative electrode current collecting member 60 is preferably made of the same metal type as the negative electrode current collecting part 25, for example, a conductive metal such as copper, a copper alloy, nickel, or stainless steel. As shown in FIG. 3, the negative electrode current collecting member 60 includes a substantially L-shaped first part 61 and a second part 62 that is electrically connected to the first part 61 and extends along the short side wall 12c of the exterior body 12. The first part 61 is attached to the inner surface of the sealing plate 14 by crimping in a state insulated via the internal insulating member 70. The first part 61 is electrically connected to the negative electrode terminal 40. The second part 62 is attached to the negative electrode current collecting part 25.

[0028] 4 is a perspective view that illustrates a schematic diagram of a sealing plate assembly, that is, an assembly in which a positive electrode terminal 30, a negative electrode terminal 40, a first portion 51 of a positive electrode current collecting member 50, and a first portion 61 of a negative electrode current collecting member 60 are attached to a sealing plate 14. The positive electrode terminal 30 and the negative electrode terminal 40 are preferably attached to the sealing plate 14.

[0029] The positive electrode terminal 30 is disposed at one end of the sealing plate 14 in the long side direction Y (the left end in Figs. 2 to 4). As shown in Fig. 3, the positive electrode terminal 30 is electrically connected to the positive electrode (second electrode) of the electrode body 20 via a positive electrode current collecting member 50. The positive electrode terminal 30 includes two types of conductive members, that is, a positive electrode first conductive member 31 and a positive electrode second conductive member 32. The positive electrode first conductive member 31 and the positive electrode second conductive member 32 are integrated and electrically connected to each other. The positive electrode first conductive member 31 is disposed outside the battery case 10. The positive electrode first conductive member 31 is plate-shaped here. The positive electrode first conductive member 31 is insulated from the outer surface of the sealing plate 14 (the upper surface in Fig. 3) by an external insulating member 90. When the power storage module 500 (see Fig. 1) is fabricated, a bus bar 200 is attached to the positive electrode first conductive member 31.

[0030] The positive electrode second conductive member 32 extends from the inside to the outside of the battery case 10 through the terminal pull-out hole 18. The positive electrode second conductive member 32 includes a shaft column portion 32s disposed in the terminal pull-out hole 18. The positive electrode second conductive member 32 is insulated from the sealing plate 14 by an internal insulating member 70 and a gasket 80. The gasket 80 has a function of insulating the sealing plate 14 from the positive electrode second conductive member 32 and closing the terminal pull-out hole 18. Here, the positive electrode second conductive member 32 is crimped and fixed to the peripheral portion surrounding the terminal pull-out hole 18 of the sealing plate 14 by crimping while being insulated from the sealing plate 14. A crimped portion 30c is formed at the end (lower end in FIG. 3) of the positive electrode second conductive member 32 on the side of the exterior body 12. The positive electrode second conductive member 32 is fixed to the sealing plate 14 and electrically connected to the first portion 51 by crimping.

[0031] The negative electrode terminal 40 is disposed at the end of the other side in the long side direction Y of the sealing plate 14 (the right end in Figs. 2 to 4). As shown in Fig. 3, the negative electrode terminal 40 is electrically connected to the negative electrode (first electrode) of the electrode body 20 via the negative electrode current collecting member 60. In this embodiment, the negative electrode terminal 40 is an example of a "first electrode terminal electrically connected to the negative electrode (first electrode)". The first electrode terminal is preferably the negative electrode terminal 40. Below, a detailed configuration will be described for the case where the first electrode terminal is the negative electrode terminal 40. However, in other embodiments, the first electrode terminal may be the positive electrode terminal 30. In that case, in the following description, the "negative electrode" can be appropriately read as the "positive electrode".

[0032] FIG. 5 is a plan view showing the vicinity of the negative electrode terminal 40 in FIG. 4. FIG. 6 is a schematic longitudinal sectional view taken along the line VI-VI in FIG. 4 and FIG. 5. FIG. 7 is a schematic longitudinal sectional view showing only the negative electrode terminal 40 in FIG. 6. As shown in FIG. 6, the negative electrode terminal 40 includes two types of conductive members, that is, a negative electrode first conductive member 41 and a negative electrode second conductive member 42. The negative electrode first conductive member 41 is an example of a "first conductive member". The negative electrode second conductive member 42 is an example of a "second conductive member". The negative electrode first conductive member 41 and the negative electrode second conductive member 42 are integrated and electrically connected to each other by a fastening portion 43 and a metal joint portion 45, which will be described later. However, the fastening portion 43 is not essential and may be omitted in other embodiments.

[0033] The negative electrode first conductive member 41 is made of a conductive metal such as aluminum, an aluminum alloy, nickel, or stainless steel. The negative electrode first conductive member 41 preferably contains aluminum or an aluminum alloy. At least the vicinity of the metal joint 45 of the negative electrode first conductive member 41 is preferably made of aluminum or an aluminum alloy. The negative electrode first conductive member 41 is preferably made of aluminum or an aluminum alloy. In the present embodiment, the negative electrode first conductive member 41 is mainly made of the first metal. In other words, the first metal occupies the largest proportion on a mass basis. The first metal preferably occupies 50 mass% or more of the entire negative electrode first conductive member 41 (excluding the portion where the metal joint 45 is formed), more preferably 70 mass% or more, and particularly preferably 90 mass% or more. The first metal is preferably aluminum. The first metal is preferably the same metal type as the bus bar 200.

[0034] The negative electrode first conductive member 41 is disposed outside the battery case 10. Here, the negative electrode first conductive member 41 is plate-shaped. As shown in Fig. 6, the negative electrode first conductive member 41 is insulated from the outer surface of the sealing plate 14 (the upper surface in Fig. 6) by an external insulating member 90. It is preferable that the external insulating member 90 is disposed between the negative electrode first conductive member 41 and the sealing plate 14. It is preferable that the external insulating member 90 is a resin member.

[0035] As shown in FIG. 5, the negative electrode first conductive member 41 is substantially rectangular here. The negative electrode first conductive member 41 is divided into two parts in the long side direction Y, and has a connection part 41a electrically connected to the negative electrode second conductive member 42, and an extension part 41b arranged on one side of the connection part 41a in the long side direction Y (left side in FIG. 5). The extension part 41b is a part to which the bus bar 200 is attached when the power storage module 500 (see FIG. 1) is fabricated. The extension part 41b is an example of a "bus bar connection region". By having the extension part 41b, it is possible to secure a sufficient ground contact area with the bus bar 200, and it is possible to improve the conduction reliability of the power storage module 500. In FIG. 5 and FIG. 7, the bus bar 200 and the weld part W between the bus bar 200 and the negative electrode first conductive member 41 are indicated by virtual lines (two-dot chain lines).

[0036] As shown in FIG. 7, the negative electrode first conductive member 41 is flat and has a lower surface 41d and an upper surface 41u. The lower surface 41d is in contact with the negative electrode second conductive member 42. As can be seen from FIG. 6, the lower surface 41d is a surface facing the battery case 10 (specifically, the sealing plate 14). The upper surface 41u is a surface away from the battery case 10 and the negative electrode second conductive member 42. As shown in FIG. 7, the negative electrode first conductive member 41 has a thin-walled portion 41t recessed from the upper surface 41u and formed to be thinner than the extending portion 41b, a through hole 41h penetrating in the vertical direction Z, and a recessed portion 41r recessed from the lower surface 41d.

[0037] As shown in FIG. 5, the thin-walled portion 41t is formed in an annular (e.g., circular) shape so as to surround the through-hole 41h in a plan view. The metal joint portion 45 is provided in the thin-walled portion 41t. The through-hole 41h is formed in the center of the thin-walled portion 41t in a plan view. The through-hole 41h can function as an escape route for distortion caused by gas and heat generated during welding. The through-hole 41h is formed in a circular shape in a plan view. The through-hole 41h is provided on the inner periphery side of the fastening portion 43 and the metal joint portion 45. The negative electrode second conductive member 42 (specifically, a flange portion 42f described later) is exposed from the through-hole 41h.

[0038] As shown in Fig. 7, the recess 41r is provided on the outer periphery side of the metal joint portion 45. Although not shown, the recess 41r is formed in an annular (e.g., circular) shape in a plan view. Here, the recess 41r is formed in a tapered shape that decreases in diameter toward the lower surface 41d of the negative electrode first conductive member 41 (in other words, as it approaches the negative electrode second conductive member 42). A fastening portion 43 is provided in the recess 41r. A narrowed portion 42n of the negative electrode second conductive member 42, which will be described later, is inserted into the recess 41r.

[0039] The negative electrode second conductive member 42 is composed of a conductive metal such as copper, a copper alloy, nickel, or stainless steel. The negative electrode second conductive member 42 preferably contains copper or a copper alloy. At least the vicinity of the metal joint 45 of the negative electrode second conductive member 42 is preferably composed of copper or a copper alloy. The negative electrode second conductive member 42 is preferably made of copper or a copper alloy. In the present embodiment, the negative electrode second conductive member 42 is mainly composed of the second metal. In other words, the second metal accounts for the largest proportion on a mass basis. The second metal preferably accounts for 50 mass% or more of the entire negative electrode second conductive member 42 (excluding the portion where the metal joint 45 is formed), more preferably accounts for 70 mass% or more, and particularly preferably accounts for 90 mass% or more. The second metal is particularly preferably copper. The second metal is preferably a metal having a higher hardness (e.g., Vickers hardness (HV)) than the first metal. The second metal is preferably the same metal type as the negative electrode current collecting part 25 and / or the negative electrode current collecting member 60. The negative electrode second conductive member 42 may be mainly made of copper or a copper alloy and may have a metal coating part in which a part or all of the surface is coated with a metal such as Ni. This can increase resistance to electrolytes and improve corrosion resistance.

[0040] As shown in FIG. 6, the negative electrode second conductive member 42 extends from the inside to the outside of the battery case 10 through the terminal pull-out hole 19. The negative electrode second conductive member 42 is insulated from the sealing plate 14 by an internal insulating member 70 and a gasket 80. The gasket 80 has a function of insulating the sealing plate 14 and the negative electrode second conductive member 42, and closing the terminal pull-out hole 19. The negative electrode second conductive member 42 is crimped and fixed to the peripheral portion surrounding the terminal pull-out hole 19 of the sealing plate 14 in a state insulated from the sealing plate 14 by crimping. A crimped portion 40c is formed at the end (lower end in FIG. 6) of the negative electrode second conductive member 42 on the side of the exterior body 12. The negative electrode second conductive member 42 is fixed to the sealing plate 14 by crimping, and is electrically connected to the first portion 61.

[0041] Here, the negative electrode second conductive member 42 is substantially cylindrical. The negative electrode second conductive member 42 is preferably columnar. As shown in FIG. 7, the negative electrode second conductive member 42 has an axis C. The negative electrode second conductive member 42 has a flange portion 42f electrically connected to the negative electrode first conductive member 41, and an axial column portion 42s connected to the lower end portion of the flange portion 42f. The negative electrode second conductive member 42 preferably has the flange portion 42f at its upper portion, and includes the axial column portion 42s below the flange portion 42f.

[0042] As shown in FIG. 6, the flange portion 42f is a portion that protrudes from the terminal pull-out hole 19 of the sealing plate 14 to the outside of the battery case 10. The flange portion 42f has a larger outer shape than the axial column portion 42s. Although not shown, the flange portion 42f has a substantially cylindrical outer shape. The flange portion 42f has a larger outer shape than the terminal pull-out hole 19 of the sealing plate 14. As shown in FIG. 7, the axis of the flange portion 42f coincides with the axis C of the negative electrode second conductive member 42. The flange portion 42f has a lower surface 42d, a side surface (outer peripheral surface) 42o extending upward from the lower surface 42d, a constricted portion 42n in which a part of the side surface 42o is constricted, and an upper surface 42u. The upper surface 42u is in contact with the recess 41r of the negative electrode first conductive member 41. A metal joint portion 45 is provided on the upper surface 42u.

[0043] As shown in FIG. 7, the constricted portion 42n is provided continuously or intermittently on a part of the side surface 42o of the flange portion 42f. Although not shown, the constricted portion 42n is formed in an annular shape (for example, a circular ring) in a plan view. When the constricted portion 42n is formed in an annular shape, a high-strength fastening portion 43 can be formed. The constricted portion 42n is formed symmetrically with respect to the axis C of the flange portion 42f. The constricted portion 42n is formed in an inverted tapered shape that expands in diameter toward the upper surface 41u (in other words, the further away from the shaft column portion 42s). The fastening portion 43 is provided in the constricted portion 42n. The constricted portion 42n is inserted into the recess 41r of the negative electrode first conductive member 41. Here, the constricted portion 42n is fitted into the recess 41r of the negative electrode first conductive member 41 and is fitted into the recess 41r.

[0044] As shown in FIG. 7, the shaft column portion 42s extends downward from the lower end of the flange portion 42f. The shaft column portion 42s is an example of a "shaft portion". Although not shown, the shaft column portion 42s is cylindrical here. The axis of the shaft column portion 42s coincides with the axis C of the flange portion 42f. Before the crimping process, the lower end of the shaft column portion 42s, i.e., the end opposite to the side where the flange portion 42f is located, is hollow. As shown in FIG. 6, the shaft column portion 42s is disposed in the terminal drawing hole 19 of the sealing plate 14. The lower end of the shaft column portion 42s is expanded by the crimping process to form the crimped portion 40c. The shaft column portion 42s is electrically connected to the first portion 61 of the negative electrode current collecting member 60 by the crimping process.

[0045] The fastening portion 43 is a mechanical fixing portion between the negative electrode first conductive member 41 and the negative electrode second conductive member 42. Here, it is a mechanical fixing portion between the recess 41r and the flange portion 42f (more specifically, the constricted portion 42n). By providing the fastening portion 43 in addition to the metal joint portion 45, the electrical conductivity reliability of the negative electrode terminal 40 can be further improved. The method of forming the fastening portion 43 is not particularly limited as long as it is a mechanical joint using mechanical energy, and may be, for example, press fitting, crimping, shrink fitting, riveting, folding, bolt joining, or the like.

[0046] As shown in FIG. 6, in this embodiment, the fastening portion 43 is provided on the lower surface 41d of the negative electrode first conductive member 41. Here, the fastening portion 43 is a fitting portion in which the recess 41r of the negative electrode first conductive member 41 and the narrowed portion 42n of the negative electrode second conductive member 42 are fitted together. Specifically, the fastening portion 43 is a press-fit fitting portion in which the narrowed portion 42n of the negative electrode second conductive member 42 is fitted into the recess 41r of the negative electrode first conductive member 41 by press-fitting. The fastening portion 43 is configured by fixing (for example, pressing and fixing) the inner wall of the recess 41r of the negative electrode first conductive member 41 to the narrowed portion 42n of the negative electrode second conductive member 42. Thereby, for example, even if the negative electrode first conductive member 41 and the negative electrode second conductive member 42 are made of different metals, they can be suitably fixed together.

[0047] The fastening portion 43 is provided on the outer circumferential side of the flange portion 42f relative to the metal joint portion 45. Although not shown, the fastening portion 43 is formed in an annular (e.g., circular) shape in a plan view. The fastening portion 43 is formed continuously here. This increases the strength of the fastening portion 43, and further improves the conduction reliability of the negative electrode terminal 40.

[0048] The metal joint 45 is a metallurgical joint between the negative electrode first conductive member 41 and the negative electrode second conductive member 42. Here, it is a joint between the thin-walled portion 41t and the flange portion 42f. The metal joint 45 includes a molten solidified portion formed by melting the negative electrode first conductive member 41 and the negative electrode second conductive member 42 by irradiation with energy rays, melting, and solidifying. The molten solidified portion can be formed using, for example, light energy, electron energy, heat energy, or the like. Among them, welding is preferable. By welding, a high-strength metal joint 45 can be realized relatively easily and stably. The welding method is not particularly limited, and examples thereof include laser welding, electron beam welding, ultrasonic welding, resistance welding, and TIG (Tungsten Inert Gas) welding. The metal joint 45 is preferably a laser welded portion formed by laser welding. In addition, suitable conditions for laser welding will be shown in the manufacturing method described later.

[0049] As shown in FIG. 6, in this embodiment, the metal joint 45 is provided on the upper surface 41u of the negative electrode first conductive member 41. The metal joint 45 is provided at a position away from the through hole 41h. The metal joint 45 is provided on the outer periphery of the through hole 41h. The metal joint 45 is provided at a position away from the fastening portion 43. This can reduce the influence of heat on the fastening portion 43 and the like. The metal joint 45 can be a joint having a relatively higher rigidity than, for example, the fastening portion 43.

[0050] Here, the metal joint 45 is provided on the inner circumferential side (toward the center of the flange portion 42f) of the fastening portion 43 in a plan view. In other words, it is provided on the side closer to the center 42c of the negative electrode second conductive member 42. The metal joint 45 can be a joint having a relatively low strength (fragile) compared to the fastening portion 43. By disposing such a metal joint 45 on the inner circumferential side of the fastening portion 43, the metal joint 45 can be stably maintained and the electrical conductivity reliability of the negative electrode terminal 40 can be improved over a long period of time.

[0051] Here, the metal joint 45 is provided on the thin-walled portion 41t. This allows for less energy to be used during joining, and improves weldability. The metal joint 45 is formed continuously or intermittently. The metal joint 45 is formed symmetrically with respect to the axis C of the flange portion 42f. This increases the strength of the metal joint 45, and further improves the electrical reliability of the negative electrode terminal 40.

[0052] As shown in FIG. 5, the metal joint 45 is formed in an annular shape (for example, a circular ring) in a plan view. This increases the strength (for example, tensile strength) of the metal joint 45, and further improves the conduction reliability of the negative electrode terminal 40. Here, the metal joint 45 is provided so as to surround the center 42c of the flange portion 42f over the entire circumference. As shown in FIG. 7, the metal joint 45 is provided so as to surround the outer edge of the through hole 41h with the axis C of the flange portion 42f as the center. By providing the metal joint 45 on the periphery of the through hole 41h, it is possible to release distortion and deformation caused by heat during welding, and to reduce the influence on the fastening portion 43 and the like. In the cross-sectional view of FIG. 7, the side close to the extension portion 41b (left side of FIG. 7) is distinguished as the metal joint 45A, and the side away from the extension portion 41b (right side of FIG. 7) is distinguished as the metal joint 45B.

[0053] FIG. 8 is an enlarged view showing a schematic view of the vicinity of the metal joint 45A on the side close to the extension 41b in FIG. 7 (the left side in FIG. 7). As shown in FIG. 8, in a cross section perpendicular to the sealing plate 14 (first surface), passing through the axis C of the axial column portion 42s, and extending in the radial direction of the axial column portion 42s, the metal joint 45 includes a first region 451 and a second region 452. As shown by a dashed line in FIG. 8, the negative terminal 40 has a boundary surface B passing through the boundary portion where the negative electrode first conductive member 41 and the negative electrode second conductive member 42 abut on each other around the metal joint 45. The boundary surface B extends in a direction parallel to the sealing plate 14 (more specifically, the outer surface of the sealing plate 14 or the inner surface of the sealing plate 14). In FIG. 8, the boundary surface B passes through the metal joint 45. The boundary surface B roughly divides the metal joint portion 45 into the negative electrode first conductive member 41 side (upper part in FIG. 8) and the negative electrode second conductive member 42 side (lower part in FIG. 8).

[0054] In this embodiment, the cross section is a first cross section (cross section taken along line VI-VI in FIGS. 4 and 5) that passes through the axis C of the negative electrode second conductive member 42 and extends along the long side direction Y of the sealing plate 14 (first surface). However, in a case where the metal joint portion 45 has a shape other than annular and the metal joint portion 45 is not formed in the first cross section, the cross section may be a second cross section that passes through the axis C of the negative electrode second conductive member 42 and forms the smallest angle with the first cross section among cross sections that extend in the radial direction of the negative electrode second conductive member 42.

[0055] The first region 451 is a region in which the first metal (here, Al) occupies 70 mass% or more. The first region 451 may be a region in which the metal (mainly the second metal) constituting the negative electrode second conductive member 42 is melted into the negative electrode first conductive member 41. The first region 451 can suppress the generation of brittle intermetallic compounds by suppressing the melting of metals other than the first metal to less than 30 mass%, and can increase the strength (for example, tensile strength). The first region 451 is mostly located on the negative electrode first conductive member 41 side (upper side in FIG. 8) from the boundary surface B, and a part of it protrudes toward the negative electrode second conductive member 42 side (lower side in FIG. 8). The first region 451 includes a region A1 located on the negative electrode first conductive member 41 side (upper side in FIG. 8) from the boundary surface B, and a first protruding region P1 protruding toward the negative electrode second conductive member 42 side (lower side in FIG. 8) from the boundary surface B.

[0056] The second region 452 is a region in which the second metal (here, Cu) occupies 70 mass% or more. The second region 452 may be a region in which the metal (mainly the first metal) constituting the negative electrode first conductive member 41 is melted into the negative electrode second conductive member 42. The second region 452 can suppress the generation of brittle intermetallic compounds by suppressing the melting of metals other than the second metal to less than 30 mass%, and can increase the strength (for example, tensile strength). Contrary to the first region 451, the second region 452 is mostly located on the negative electrode second conductive member 42 side (lower in FIG. 8) than the boundary surface B, and a part of it protrudes toward the negative electrode first conductive member 41 side (upper in FIG. 8). The second region 452 includes a region A2 located on the negative electrode second conductive member 42 side (lower in FIG. 8) than the boundary surface B, and a second protruding region P2 protruding toward the negative electrode first conductive member 41 side (upper in FIG. 8) than the boundary surface B.

[0057] Thus, in this embodiment, the first region 451 includes the first protruding region P1, the second region 452 includes the second protruding region P2, and the boundary between the first region 451 and the second region 452 has an uneven shape. Usually, the boundary between the first region 451 and the second region 452 is slippery and tends to be weak in strength, but by making the boundary uneven in this way and mechanically fitting the negative electrode first conductive member 41 and the negative electrode second conductive member 42, the boundary becomes less slippery and the joint strength (e.g., tensile strength) can be improved. In addition, by curving the boundary, the distance of the boundary can be increased, so that even if a crack occurs in the metal joint 45, the progress of the crack can be delayed. As a result, according to the technology disclosed herein, even if external forces such as vibration or impact are applied during use, it becomes easier to maintain the negative electrode first conductive member 41 and the negative electrode second conductive member 42 in close contact with each other, and the conductive connection between the negative electrode first conductive member 41 and the negative electrode second conductive member 42 can be stably maintained.

[0058] As will be described in more detail later, the metal joint 45 in which the first region 451 includes the first protruding region P1 and the second region 452 includes the second protruding region P2 as shown in FIG. 8 can be realized, for example, by performing circumferential welding (wobbling) during welding.

[0059] Although not particularly limited, as shown in FIG. 8, in a cross section perpendicular to the sealing plate 14 (first surface), passing through the axis C of the axial column portion 42s, and extending in the radial direction of the axial column portion 42s, the ratio C1 of the area of ​​the first projecting region P1 to the total area of ​​the first region 451 is preferably 0.01 to 0.4 (1 to 40%), more preferably 0.03 to 0.2 (3 to 20%). The ratio C2 of the area of ​​the second projecting region P2 to the total area of ​​the second region 452 is preferably 0.03 to 0.5 (3 to 50%), more preferably 0.05 to 0.3 (5 to 30%). By setting the ratio within the above range, the negative electrode first conductive member 41 and the negative electrode second conductive member 42 can be mechanically fitted together more firmly. In addition, the progress of cracks can be effectively delayed. Therefore, the effect of the technology disclosed herein can be exhibited at a higher level. The area ratio C2 of the second protruding region P2 is preferably larger than the area ratio C1 of the first protruding region P1. The area ratios C1 and C2 can be achieved by adjusting the welding conditions (e.g., laser output, wobbling frequency and width, etc.) described later.

[0060] 8, in a cross section (here, the cross section taken along line VI-VI in FIGS. 4 and 5) that is perpendicular to the sealing plate 14 (first surface), passes through the axis C of the axial column portion 42s, and extends in the radial direction of the axial column portion 42s, a portion of the boundary surface B that passes through the metal joint portion 45 is defined as a line segment LB. In this case, it is preferable that more than half (50%) of the line segment LB crosses the second region 452. By having the line segment LB cross the second region 452 containing a large amount of the second metal (here, Cu) having high hardness with a probability of more than half, the strength (e.g., tensile strength) and durability of the metal joint portion 45 can be improved.

[0061] When the negative electrode terminal 40 has a fastening portion 43, in at least one (preferably both) of the two metal joints 45 (metal joints 45A and 45B) included in the cross section of Fig. 7, it is preferable that the second protruding region P2 is disposed closer to the fastening portion 43 than the first protruding region P1 in a cross section (here, the cross section taken along line VI-VI in Figs. 4 and 5) that is perpendicular to the sealing plate 14 (first surface) and passes through the axis C of the axial column portion 42s and extends in the radial direction of the axial column portion 42s, as shown in Fig. 8. According to the study by the present inventors, when vibration, impact, or the like is applied to the fastening portion 43, destruction of the metal joint 45 begins from the fastening portion 43 side. Therefore, by arranging the second protruding region P2, which contains a large amount of the second metal (here, Cu) having a relatively high hardness, closer to the fastening portion 43 than the first protruding region P1, which contains a large amount of the first metal (here, Al) having a relatively low hardness, it is possible to improve the strength (e.g., tensile strength) and durability of the metal joint 45. The positional relationship between the first protruding region P1 and the second protruding region P2 can be adjusted by the welding conditions (specifically, the rotation direction of the wobbling) described later.

[0062] When the negative electrode terminal 40 has an extension portion 41b and the bus bar 200 is connected to the extension portion 41b, in at least one (preferably both) of the metal joint portion 45A and the metal joint portion 45B, the second protruding region P2 is preferably disposed closer to the extension portion 41b (bus bar connection region) than the first protruding region P1 in a cross section perpendicular to the sealing plate 14 (first surface) and extending along the long side direction Y of the sealing plate 14 (first surface) as shown in Fig. 8. In particular, in the metal joint portion 45A on the side closer to the extension portion 41b (left side in Fig. 7), the second protruding region P2 is preferably disposed closer to the extension portion 41b than the first protruding region P1.

[0063] The extension portion 41b is susceptible to forces such as vibrations and impacts through the busbar 200. When a force is applied to the extension portion 41b, the metal joint 45 starts to break from the extension portion 41b side. Therefore, by disposing the second protruding region P2, which contains a large amount of the second metal (here, Cu) having a relatively high hardness, closer to the extension portion 41b side than the first protruding region P1, which contains a large amount of the first metal (here, Al) having a relatively low hardness, the strength (e.g., tensile strength) and durability of the metal joint 45 can be improved. The positional relationship between the first protruding region P1 and the second protruding region P2 can be adjusted by the welding conditions (specifically, the rotation direction of the wobbling) described later.

[0064] 8, the metal joint 45 of this embodiment further includes a third region 453 at the boundary between the first region 451 and the second region 452. The third region 453 is a region in which the content of the first metal is 30 mass% or more and less than 70 mass% and the content of the second metal is 30 mass% or more and less than 70 mass%. However, the third region 453 is not essential and may be omitted in other embodiments.

[0065] Although not particularly limited, the negative electrode terminal 40 as described above can be manufactured, for example, by preparing the negative electrode first conductive member 41 and the negative electrode second conductive member 42 as described above, and by a manufacturing method including a fastening step and a welding step. The order of the fastening step and the welding step is not particularly limited, but from the viewpoint of suppressing damage to the metal joint 45 when forming the fastening part 43, it is preferable to perform the welding step after the fastening step. However, the fastening step may be performed after the welding step, or both steps may be performed approximately simultaneously. In addition, the manufacturing method disclosed herein may further include other steps at any stage.

[0066] In the fastening step, the negative electrode first conductive member 41 and the flange portion 42f of the negative electrode second conductive member 42 are mechanically fixed to form the fastening portion 43. The fastening portion 43 can be formed, for example, by inserting the narrowed portion 42n of the negative electrode second conductive member 42 into the recess 41r of the negative electrode first conductive member 41, and deforming the recess 41r of the negative electrode first conductive member 41 along the outer shape of the narrowed portion 42n of the negative electrode second conductive member 42, thereby fixing the inner wall of the recess 41r with the negative electrode second conductive member 42. This can improve the strength of the fastening portion 43. In some preferred embodiments, the fastening portion 43 is formed by fitting the recess 41r of the negative electrode first conductive member 41 and the narrowed portion 42n of the negative electrode second conductive member 42. For example, the fastening portion 43 can be formed by horizontally press-fitting the narrowed portion 42n of the negative electrode second conductive member 42 into the recess 41r of the negative electrode first conductive member 41. This can improve the workability of the fastening process.

[0067] In the welding and joining step, the thin portion 41t of the negative electrode first conductive member 41 and the flange portion 42f of the negative electrode second conductive member 42 are joined by welding to form the metal joint 45. By performing the welding and joining step after the fastening step, the metal joint 45 having a stable shape can be formed with high accuracy. The metal joint 45 can be formed, for example, by stacking the thin portion 41t of the negative electrode first conductive member 41 and the flange portion 42f of the negative electrode second conductive member 42, irradiating an energy beam from the side of the negative electrode first conductive member 41 (thin portion 41t), and welding so that the energy penetrates the thin portion 41t and reaches at least the upper surface 42u of the flange portion 42f. The welding is preferably performed by the method described above, for example, laser welding.

[0068] Although not particularly limited, in a preferred embodiment, a single-mode fiber laser is used to perform circumferential welding (wobbling). FIG. 9(A) is an explanatory diagram for explaining a method of laser welding when forming an annular metal joint 45 as shown in FIG. 5. FIG. 9(A) shows only the thin-walled portion 41t to be welded in a plan view. Although not particularly limited, when forming an annular metal joint 45, as shown in FIG. 9(A), welding is started from the welding start point (1), the overall laser advance direction is clockwise, the wobbling rotation direction is counterclockwise, and the laser light is irradiated to draw a circular trajectory to the welding end point (2) so as to surround the outer edge of the through hole 41h.

[0069] The welding conditions (e.g., laser output, welding speed, wobbling conditions (frequency and width), etc.) are design matters that can be appropriately adjusted depending on, for example, the materials of the negative electrode first conductive member 41 and the negative electrode second conductive member 42, the thickness of the negative electrode first conductive member 41, etc. In one example, the laser output is preferably about 500 to 1500 W, more preferably 1300 W or less, and even more preferably 600 to 1000 W. The welding speed is preferably about 10 to 1000 mm / s, and more preferably 50 to 100 mm / s. The wobbling frequency is preferably about 1000 Hz or less, for example, 100 to 600 Hz. The wobbling width is preferably 0.1 to 10 mm, and more preferably 0.2 to 1 mm. Under such conditions, the negative electrode second conductive member 42 (Cu), which is relatively difficult to melt, can be stably melted. Moreover, by preventing the melting depth from becoming too deep, the melting of Cu constituting the negative electrode second conductive member 42 can be suppressed.

[0070] 9(B) is a schematic vertical cross-sectional view of the vicinity of the metal joints 45A and 45B along the line IXB-IXB in FIG. 9(A). As shown in FIG. 9(A), when the laser light is irradiated around the outer edge of the through hole 41h while the direction of rotation of the wobbling is the same, in a cross section (cross section of line IXB-IXB in FIG. 9(A)) perpendicular to the sealing plate 14 (first surface), passing through the axis C of the axial column portion 42s, and extending in the radial direction of the axial column portion 42s, in the metal joint 45A close to the extension portion 41b, the second protruding region P2 is disposed closer to the extension portion 41b than the first protruding region P1. On the other hand, in the metal joint 45B away from the extension portion 41b, the first protruding region P1 is disposed closer to the extension portion 41b than the second protruding region P2.

[0071] Here, the metal joint 45 is formed on the inner periphery side of the fastening portion 43. This makes the joint less likely to shift, improving the workability of the welding process. Also, when forming the metal joint 45, the welded portion is less likely to wobble, improving the weldability. Furthermore, since the thin-walled portion 41t is welded here, less energy is required, improving the weldability.

[0072] The power storage device 100 and the power storage module 500 can be used for various purposes, but are preferably used in purposes where external forces such as vibrations and impacts may be applied during use, typically as a power source (driving power source) for motors mounted on various vehicles, such as passenger cars, trucks, etc. The type of passenger car is not particularly limited, and examples include plug-in hybrid electric vehicles (PHEVs), hybrid electric vehicles (HEVs), battery electric vehicles (BEVs), etc.

[0073] Several examples of the present invention will be described below, but it is not intended that the present invention be limited to these examples.

[0074] <Test Example I - Formation of Metal Joint> First, a plate-shaped first conductive member (material: aluminum (A1050)) and a cylindrical second conductive member (material: copper (C1100)) were prepared. Next, for each of the examples and comparative examples, the first conductive member and the second conductive member were overlapped, and a single-mode fiber laser was applied from the side of the first conductive member to perform welding under the conditions shown in Table 1. This formed a metal joint.

[0075] [Table 1]

[0076] First, for each of the examples and comparative examples, the portion where the metal joint was formed was cut along the cross section along the center of the metal joint of the second conductive member, and each was embedded and polished to prepare an observation sample. Next, the prepared observation sample was etched with an etching solution (a 1:1 mixture of ammonia water diluted to 14% and hydrogen peroxide water diluted to 0.35%) to discolor the metal joint and make its boundary identifiable. Next, the observation sample was photographed using a scanning electron microscope (SEM) in a Hitachi electron microscope system SU1000 to obtain a cross-sectional image. The measurement conditions were as follows. The SEM observation images are shown in FIG. 10(A) and FIG. 10(B). Although not shown, the obtained SEM observation images were analyzed by energy dispersive X-ray spectroscopy (EDX) to analyze the distribution of metal elements (Al, Cu). <Measurement conditions> Acceleration voltage: 15kV Spot Intensity: 90 Focus distance: 10mm

[0077] 10(A) shows a trajectory of laser welding according to a comparative example and a cross-sectional SEM image of a metal joint, and FIG. 10(B) shows a trajectory of laser welding according to an embodiment and a cross-sectional SEM image of a metal joint. As shown in FIG. 10(A), the metal joint of the comparative example in which linear welding was performed was formed to become thinner as it moved away from the welded surface (in other words, the melting depth became deeper). In contrast, as shown in FIG. 10(B), the metal joint of the embodiment in which circumferential welding (wobbling) was performed included a first region in which Al (first metal) accounted for 70 mass% or more and had a first protruding region, and a second region in which Cu (second metal) accounted for 70 mass% or more and had a second protruding region, as shown in FIG. 8, and the boundary between the first region and the second region was curved in an uneven shape. Therefore, it was confirmed that the metal joint disclosed herein can be suitably formed, for example, by circumferential welding (wobbling).

[0078] <Test Example II - Positional relationship of protruding areas> In this test example, a plurality of negative electrode terminals were produced in which the positional relationship between the first protruding region P1 and the second protruding region P2 of the metal joint was changed by changing the direction of wobbling rotation (clockwise, counterclockwise) in the embodiment of test example I. Fig. 11(A) is a plan view of a negative electrode terminal that typically shows the trajectory of laser welding according to example 1, and Fig. 11(B) is a plan view of a negative electrode terminal that typically shows the trajectory of laser welding according to example 2.

[0079] That is, in Example 1, as shown in Fig. 11(A), in laser welding, welding was started from the welding start point (1), the overall laser travel direction was set from bottom to top (clockwise) in Fig. 11(A), the wobbling rotation direction was set to clockwise, and the laser light was irradiated to draw a linear trajectory to the welding end point (2). On the other hand, in Example 2, as shown in Fig. 11(B), in laser welding, welding was started from the welding start point (1), the overall laser travel direction was set from bottom to top (clockwise) in Fig. 11(B), the wobbling rotation direction was set to counterclockwise (reverse rotation of Example 1), and the laser light was irradiated to draw a linear trajectory to the welding end point (2). Note that the laser output was changed to 800 W for Examples 1 and 2.

[0080] When the metal joint thus produced was observed with an SEM, as shown in Fig. 12, in Example 1, the first protruding region P1 was located closer to the bus bar connection region than the second protruding region P2 (on the left side of Fig. 12). On the other hand, in Example 2, the second protruding region P2 was located closer to the bus bar connection region than the first protruding region P1. Example 2 is an example in which the positional relationship between the first protruding region P1 and the second protruding region P2 is the same as that of the metal joint 45 in Fig. 8 of the above-mentioned embodiment. Example 1 is an example of a metal joint having a shape that is a mirror image of the metal joint of Example 2, which is symmetrical.

[0081] Next, a bus bar was welded to the extension (bus bar connection area) of the negative electrode terminal of each example. Next, a commercially available tensile tester was prepared, and the second conductive member was held by the clamp of the tensile tester. Then, based on JIS K 6854-1 (Test method for peel adhesion strength Part 1: 90° peeling), the bus bar was pulled in a vertical direction (90° direction) so as to be peeled off from the first conductive member by the tensile tester, and the strength at which the metal joint broke was measured as the tensile strength (N). The results are shown in FIG. 12. Note that the higher the tensile strength value, the higher the joint strength.

[0082] 12, Example 2 in which the second protruding region P2 is disposed near the busbar connection region has a relatively higher tensile strength than Example 1 in which the first protruding region P1 is disposed near the busbar connection region. Therefore, it was found that by disposing the second protruding region P2 on the busbar connection region side, the strength and durability of the metal joint can be improved.

[0083] Although several embodiments of the present invention have been described above, the above embodiments are merely examples. The present invention can be implemented in various other forms. The present invention can be implemented based on the contents disclosed in this specification and the technical common sense in the field. The technology described in the claims includes various modifications and changes to the above-exemplified embodiments. For example, it is possible to replace a part of the above-mentioned embodiment with another modified form, and it is also possible to add another modified form to the above-mentioned embodiment. Furthermore, if a technical feature is not described as essential, it is also possible to delete it as appropriate.

[0084] <First Modification> For example, in the above embodiment, as shown in Fig. 5, the metal joint 45 is formed in an annular (e.g., circular) shape in plan view. Then, as shown in Fig. 9(A), the metal joint 45 is formed by irradiating the laser so as to trace a circular trajectory. However, the present invention is not limited to this. In a modification, the metal joint 45 may be formed in a shape such as a C-shape, a semicircular arc shape, a double or more circular shape, a spiral shape, a straight line shape, a broken line shape, or the like in plan view. The metal joint 45 may also be formed by laser welding in two or more separate steps.

[0085] Fig. 13(A) is a view corresponding to Fig. 9(A) according to the first modified example. For example, when forming a substantially annular metal joint 145 consisting of two semicircular arc-shaped parts, as shown in Fig. 13(A), for example, first, welding is started from the welding start point (1), the overall laser advance direction is clockwise, the wobbling rotation direction is clockwise, and the laser light is irradiated so as to draw a semicircular trajectory along the outer edge of the through hole 41h to the welding end point (2). Next, welding is started from the welding start point (3), the overall laser advance direction is clockwise, the wobbling rotation direction is counterclockwise (the rotation direction is changed), and the laser light is irradiated so as to draw a semicircular trajectory along the outer edge of the through hole 41h to the welding end point (4).

[0086] Fig. 13(B) is a view corresponding to Fig. 9(B) according to the first modified example. As shown in Fig. 13(A), when the direction of rotation of the wobbling is changed midway and laser light is irradiated, the second protruding region P2 is disposed closer to the extension portion 41b than the first protruding region P1 in both of the two metal joints 145 (metal joints 145A and 145B) in the cross section along line XIIIB-XIIIB in Fig. 13(A). This allows the strength and durability of the metal joints 145 to be further improved than in the above-mentioned embodiment.

[0087] <Second Modification> For example, in the above embodiment, the negative electrode first conductive member 41 is divided into a connection portion 41a and an extension portion 41b in the long side direction Y, and the extension portion 41b is disposed on one side in the long side direction Y. The bus bar 200 is attached to the extension portion 41b, avoiding the connection portion 41a. However, this is not limited to this. In the modification, the negative electrode first conductive member 41 does not need to be divided into the connection portion 41a and the extension portion 41b in the long side direction Y. In that case, the bus bar 200 may be attached to, for example, a central portion of the negative electrode first conductive member 41 in the long side direction Y, or an outer edge portion of the negative electrode first conductive member 41.

[0088] Fig. 14 is a view corresponding to Fig. 5 according to the second modified example. As shown in Fig. 14, in the negative terminal 240 of this modified example, the connection portion 241a is disposed at the center of the long side direction Y of the negative first conductive member 241. The bus bar 210 is attached to the center of the long side direction Y so as to cover the entire thin portion 241t from above. In this case, the welded portion W between the bus bar 210 and the negative first conductive member 241 is provided at the outer periphery of the metal joint portion 245. The negative second conductive member 242 may be the same as the negative second conductive member 42 of the above-mentioned embodiment.

[0089] Fig. 15 is a schematic vertical cross-sectional view of the vicinity of metal joints 245A, 245B taken along line XV-XV in Fig. 14. In the cross-section taken along line XV-XV in Fig. 14, in both metal joints 245A, 245B, the second protruding region P2 is disposed closer to the welded portion W with bus bar 200 than the first protruding region P1. This can further improve the strength and durability of metal joint 245, as in the case of the first modified example. Such metal joint 245 can be fabricated in the same manner as in the above-described embodiment.

[0090] As described above, specific aspects of the technology disclosed herein include those described in the following sections. Item 1: An electric storage device comprising: an electrode assembly having a first electrode and a second electrode; a battery case housing the electrode assembly and having a first surface with a through hole; and a first electrode terminal penetrating the through hole of the battery case and electrically connected to the first electrode, wherein the first electrode terminal comprises a first conductive member having a first metal occupying the largest proportion by mass; a second conductive member having a second metal occupying the largest proportion by mass and having a shaft portion disposed within the through hole; and a metal joint portion at which the first conductive member and the second conductive member are joined; the metal joint portion includes a first region in which the first metal accounts for 70% by mass or more and a second region in which the second metal accounts for 70% by mass or more in a cross section perpendicular to the first surface, passing through an axis of the shaft portion, and extending in a radial direction of the shaft portion, wherein when a surface passing through a boundary portion where the first conductive member and the second conductive member abut around the metal joint portion is defined as a boundary surface, the first region includes a region located on the first conductive member side of the boundary surface and a first protruding region protruding toward the second conductive member side from the boundary surface, and the second region includes a region located on the second conductive member side of the boundary surface and a second protruding region protruding toward the first conductive member side from the boundary surface. Item 2: The electricity storage device according to item 1, wherein in the cross section, a ratio of an area of ​​the second projected region to a total area of ​​the second region is 0.03 or more and 0.5 or less. Item 3: The electricity storage device according to item 1 or 2, wherein the first conductive member is made of aluminum or an aluminum alloy, and the second conductive member is made of copper or a copper alloy. Item 4: The energy storage device according to any one of items 1 to 3, wherein the second metal has a harderness than the first metal, the first electrode terminal further includes a fastening portion at which the first conductive member and the second conductive member are mechanically fastened, and in the cross section, the second protruding region is positioned closer to the fastening portion than the first protruding region. Item 5: The energy storage device according to any one of items 1 to 4, wherein the metal joint further includes a third region at the boundary between the first region and the second region, the third region having a content of the first metal of 30% by mass or more and less than 70% by mass and a content of the second metal of 30% by mass or more and less than 70% by mass. Item 6: A power storage module including: a plurality of the power storage devices according to any one of items 1 to 5; and a bus bar electrically connecting the plurality of power storage devices to each other. Item 7: The energy storage module described in item 6, wherein the first conductive member is approximately rectangular, and a busbar connection region to which the busbar is connected is provided on one side of a long side of the first conductive member, the second metal has a harderness than the first metal, and in a cross section perpendicular to the first surface and extending along the long side of the first surface, the second protruding region is positioned closer to the busbar connection region than the first protruding region. [Explanation of symbols]

[0091] 10 Battery case 14 Sealing plate (first side) 20 Electrode body 40 Negative electrode terminal (1st electrode terminal) 41, 241 Negative electrode first conductive member (first conductive member) 41b Extension portion (busbar connection area) 42, 242 Negative electrode second conductive member (second conductive member) 42s Shaft part (shaft part) 43 Fastening Part 45, 45A, 45B, 145, 245 Metal joints 451 First area P1 1st protrusion area 452 Second area P2 2nd protruding area 453 Third area 100 Energy storage device 200, 210 busbar 500 Energy Storage Module

Claims

1. an electrode assembly having a first electrode and a second electrode; a battery case that houses the electrode assembly and has a first surface that is provided with a through hole; a first electrode terminal that passes through the through hole of the battery case and is electrically connected to the first electrode; A power storage device comprising: The first electrode terminal is a first conductive member in which a first metal occupies the largest proportion by mass; a second conductive member having a second metal occupying a largest proportion by mass and having a shaft portion disposed within the through hole; a metal joint portion at which the first conductive member and the second conductive member are joined; Equipped with The metal joint is In a cross section perpendicular to the first surface, passing through the axis of the shaft portion, and extending in the radial direction of the shaft portion, A first region in which the first metal occupies 70 mass% or more; A second region in which the second metal accounts for 70 mass% or more, Here, when a surface passing through a boundary portion where the first conductive member and the second conductive member abut on each other around the metal joint is defined as a boundary surface, the first region includes a region located closer to the first conductive member than the boundary surface and a first protruding region protruding closer to the second conductive member than the boundary surface, the second region includes a region located closer to the second conductive member than the boundary surface, and a second protruding region protruding closer to the first conductive member than the boundary surface. Energy storage device.

2. In the cross section, a ratio of an area of ​​the second projected region to a total area of ​​the second region is 0.03 or more and 0.5 or less. The power storage device according to claim 1 .

3. the first conductive member is made of aluminum or an aluminum alloy; The second conductive member is made of copper or a copper alloy. The electricity storage device according to claim 1 or 2.

4. The second metal has a higher hardness than the first metal, the first electrode terminal further includes a fastening portion at which the first conductive member and the second conductive member are mechanically fastened to each other, In the cross section, the second protruding region is disposed closer to the fastening portion than the first protruding region. The electricity storage device according to claim 1 or 2.

5. The metal joint further includes a third region at a boundary between the first region and the second region, the third region having a content of the first metal of 30% by mass or more and less than 70% by mass and a content of the second metal of 30% by mass or more and less than 70% by mass. The electricity storage device according to claim 1 or 2.

6. A plurality of the electricity storage devices according to claim 1 or 2; A bus bar electrically connecting the plurality of power storage devices to each other; A storage module equipped with

7. the first conductive member has a substantially rectangular shape, and a bus bar connection region to which the bus bar is connected is provided on one side in a long side direction of the first conductive member, The second metal has a higher hardness than the first metal, In a cross section perpendicular to the first surface and extending along the long side direction of the first surface, the second protruding region is disposed closer to the bus bar connection region than the first protruding region. The power storage module according to claim 6 .

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