JP7725822B2 - Energy storage element - Google Patents

Description

The present invention relates to an energy storage element comprising a container and an electrode assembly and a current collector housed in the container.

Patent Document 1 discloses a secondary battery having a rectangular exterior body as a container. In this secondary battery, a negative electrode terminal attached to the sealing plate of the container is connected to a first negative electrode current collector inside the container, and a negative electrode tab of the electrode assembly is connected to a second negative electrode current collector. The first negative electrode current collector and second negative electrode current collector are each arranged along the sealing plate. The second negative electrode current collector has a thin-walled portion with an opening formed therein, and the second negative electrode current collector is arranged on the first negative electrode current collector so that the opening faces the first negative electrode current collector. The second negative electrode current collector is welded to the first negative electrode current collector around the opening in the thin-walled portion.

Japanese Patent Application Laid-Open No. 2019-125492

In the above-mentioned conventional secondary battery (energy storage element), the electrode terminal fixed to the sealing plate (wall) of the container and the electrode body housed inside the container are connected by two current collectors, and the overlapping portion between the thin-walled portion of one of these two current collectors and the other current collector is welded. When two conductive members are overlapped and joined in this way, providing a thin-walled portion on at least one of the two members prevents an increase in the thickness of the overlapping portion. This increases the volume of the effective space inside the container, which is advantageous for improving energy density. However, in this case, a thin-walled portion is provided in part of the conductive path between the electrode terminal and the electrode body. This can cause a problem of reduced resistance to fusing in that portion, which hinders the reliability of the energy storage element.

The present invention was developed by the inventors with a new focus on the above-mentioned problems, and aims to provide an energy storage element with improved reliability and energy density.

An energy storage element according to one aspect of the present invention is an energy storage element comprising a container, an electrode body, and a current collector housed in the container, and comprising: a first joint where the current collector and a tab portion of the electrode body are joined; and a second joint formed at a position different from the first joint where the current collector is joined to a conductive member electrically connected to the tab portion; and the current collector has a thin-walled portion where a portion of the first joint is formed, and a thick-walled portion that is thicker than the thin-walled portion and where a portion of the second joint is formed.

With this configuration, the current collector is joined to the tab portion at the thin-walled portion, allowing the tab portion to be positioned close to the wall of the container in which the current collector is placed. This allows a larger proportion of the container's internal volume to be occupied by the electrode body main body (the portion of the electrode body other than the tab portion). As a result, the energy density of the energy storage element is improved. Furthermore, as conduction paths between the electrode body and the current collector, a direct conduction path via the first joint and a bypass conduction path via the conductive member and the second joint are provided. This reduces the current flowing through the thin-walled portion and suppresses a decrease in the current collector's meltdown resistance due to the thin-walled portion. Therefore, the energy density of the energy storage element can be improved while suppressing a decrease in the current collector's meltdown resistance.

The current collector may have a first side surface on the electrode body side that has a step that separates the thin portion from the thick portion, and a second side surface opposite the first side surface that is formed in a flat plate shape, and the conductive member may be a flat member located between the tab portion, the current collector, and the electrode body.

With this configuration, the thin-walled portion is positioned away from the electrode body in the thickness direction of the current collector. In other words, the thin thickness of the thin-walled portion has the effect of allowing the electrode body main body to be larger, which is more effective. Furthermore, because the conductive member is located between the current collector and the electrode body, the tab portion can be positioned closer to the wall of the container. This can further improve energy density.

The energy storage element may further include an electrode terminal fixed to the wall of the container, the current collector having a terminal connection portion that is an electrical connection portion with the electrode terminal and located on the opposite side of the wall from the electrode terminal, and the second joint portion may be located between the first joint portion and the terminal connection portion.

With this configuration, a second joint, which forms part of a bypass-like conductive path, is disposed between a first joint, which forms a direct conductive path between the tab portion of the electrode body and the current collector, and a terminal connection, which is the connection between the electrode terminal and the current collector. This shortens the length of the conductive path via the conductive member, further reducing the electrical resistance between the electrode body and the electrode terminal.

The width of the first joint portion in the overlapping direction between the current collector and the tab portion may be greater than the width of the second joint portion in the overlapping direction between the conductive member and the current collector.

With this configuration, the tab portion, which is a laminate of base material layers (metal foil), and the current collector are firmly joined by a relatively deep first joint. Furthermore, the second joint, which is the joint between the conductive member and the current collector, is formed relatively shallow, thereby suppressing the occurrence of spatter and other issues during joining. In other words, the reliability of the two joints is ensured while suppressing the occurrence of defects in the energy storage element caused by the joining process.

The first joint may be formed by welding at least the current collector and the tab portion.

With this configuration, while the tab portion is held down between the conductive member and the current collector, the tab portion and the current collector can be fused and joined together by laser welding, resistance welding, or the like. Holding down the tab portion between the conductive member and the current collector prevents gaps from forming between the base layers (metal foils) that make up the tab portion, allowing the current collector and tab portion to be efficiently welded together by laser welding, resistance welding, or the like.

The present invention makes it possible to provide an energy storage element with improved reliability and energy density.

1 is a perspective view showing the appearance of an energy storage element according to an embodiment; FIG. 2 is an exploded perspective view of the energy storage element according to the embodiment. FIG. 2 is a first cross-sectional view showing the configuration of a current collector and its surroundings according to the embodiment. FIG. 4 is a second cross-sectional view corresponding to FIG. 3 . 4 is a cross-sectional view showing the difference in depth between a first bonding portion and a second bonding portion according to the embodiment. FIG. 10A to 10C are first diagrams showing another example of a procedure for joining a current collector and a tab portion according to an embodiment. FIG. 7 is a second view corresponding to FIG. 6; FIG. 10 is a cross-sectional view showing a connection structure between a tab portion and a current collector according to a first modified example of the embodiment. FIG. 10 is a cross-sectional view showing a connection structure between a tab portion and a current collector according to a second modified example of the embodiment. FIG. 11 is a bottom view showing a connection structure between a tab portion and a current collector according to a third modified example of the embodiment.

Hereinafter, with reference to the drawings, energy storage elements according to embodiments (and variations thereof) of the present invention will be described. Note that the embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, component placement and connection configurations, manufacturing processes, and the order of manufacturing processes shown in the following embodiments are merely examples and are not intended to limit the present invention. Furthermore, the dimensions and other information shown in the drawings are not strictly accurate.

In the following description and drawings, the X-axis direction is defined as the direction in which the pair of electrode terminals (positive and negative) of the energy storage element, the direction in which the pair of current collectors are aligned, the direction in which the pair of tabs of the electrode assembly are aligned, or the direction in which the short sides of the container face each other. The Y-axis direction is defined as the direction in which the long sides of the container face each other, the short side of the container, or the thickness direction of the container. The Z-axis direction is defined as the direction in which the electrode terminals, current collectors, and electrode assembly are aligned, the direction in which the container body and lid of the energy storage element are aligned, the longitudinal direction of the short side of the container, the winding axis direction of the electrode assembly, or the up-down direction. The X-axis, Y-axis, and Z-axis directions intersect (orthogonal in this embodiment). Note that depending on the usage mode, the Z-axis may not be the up-down direction; however, for convenience of explanation, the Z-axis will be described below as the up-down direction. In the following description, for example, the positive X-axis direction refers to the direction of the X-axis arrow, and the negative X-axis direction refers to the direction opposite to the positive X-axis direction. The same applies to the Y-axis and Z-axis directions.

(Embodiment)
[1. General Description of Energy Storage Element]
First, an energy storage device 10 according to the present embodiment will be generally described with reference to Figures 1 and 2. Figure 1 is a perspective view showing the appearance of the energy storage device 10 according to the embodiment. Figure 2 is an exploded perspective view of the energy storage device 10 according to the embodiment.

The energy storage element 10 is a secondary battery capable of charging and discharging electricity, specifically a non-aqueous electrolyte secondary battery such as a lithium-ion secondary battery. The energy storage element 10 is used, for example, as a battery for driving or starting the engine of a mobile object such as an automobile, motorcycle, personal watercraft, boat, snowmobile, agricultural machinery, construction machinery, or electric railway vehicle. Examples of such automobiles include electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and gasoline-powered automobiles. Examples of such electric railway vehicles include electric trains, monorails, linear motor cars, and hybrid electric trains equipped with both a diesel engine and an electric motor. The energy storage element 10 can also be used as a stationary battery for home or commercial use.

The energy storage element 10 is not limited to a non-aqueous electrolyte secondary battery, but may be a secondary battery other than a non-aqueous electrolyte secondary battery, or may be a capacitor. The energy storage element 10 may also be a primary battery that allows stored electricity to be used without the user having to charge it, rather than a secondary battery. The energy storage element 10 may also be a battery that uses a solid electrolyte. While the present embodiment illustrates the energy storage element 10 in a rectangular parallelepiped (cornered) shape, the shape of the energy storage element 10 is not limited to a rectangular parallelepiped, and may be a polygonal prism, an oval cylinder, or other shape besides a rectangular parallelepiped.

As shown in FIG. 1, the energy storage element 10 comprises a container 100, a pair of electrode terminals 200 (positive and negative, hereinafter the same), and a pair of upper gaskets 300. As shown in FIG. 2, the container 100 contains a pair of lower gaskets 400, a pair of current collectors 500, and an electrode assembly 700. An electrolyte solution (non-aqueous electrolyte) is sealed inside the container 100, but this is not shown. There are no particular restrictions on the type of electrolyte solution, and various types can be selected as long as it does not impair the performance of the energy storage element 10. In addition to the above components, spacers arranged above or to the sides of the electrode assembly 700, or insulating films encasing the electrode assembly 700, etc., may also be arranged.

The container 100 is a rectangular parallelepiped (box-shaped) case having a container body 110 with an opening formed therein and a lid 120 that closes the opening of the container body 110. With this configuration, the container 100 is designed so that the interior can be sealed by, for example, welding the container body 110 and the lid 120 together after the electrode body 700 and other components are housed inside the container body 110. The materials for the container body 110 and the lid 120 are not particularly limited, but are preferably weldable metals such as stainless steel, aluminum, aluminum alloy, iron, and plated steel sheet.

The container body 110 is a rectangular cylindrical member with a bottom that forms the main body of the container 100, with an opening formed on the positive side of the Z axis. The lid body 120 is a rectangular plate-like member that is elongated in the X axis direction and forms the lid of the container 100, and is positioned to close the opening of the container body 110. The lid body 120 is equipped with a gas exhaust valve 122 that exhausts gas from inside the container 100 if the internal pressure of the container 100 rises excessively.

The electrode body 700 is an electricity storage element (power generation element) that includes a positive electrode plate, a negative electrode plate, and a separator and can store electricity. Specifically, the electrode body 700 is formed by winding layers of positive and negative electrode plates with the separator sandwiched between them. As a result, multiple tabs (plate ends) on the substrate layer (metal foil) of the positive electrode plate are stacked to form the positive electrode side tab portion 720, and tabs (plate ends) on the substrate layer (metal foil) of the negative electrode plate are stacked to form the negative electrode side tab portion 720. Note that, although the present embodiment employs an electrode body 700 with an oval cross-sectional shape, the cross-sectional shape of the electrode body 700 may also be elliptical, etc.

The electrode terminal 200 is electrically connected to the electrode body 700 via the current collector 500. The electrode terminal 200 is joined to the current collector 500 by crimping or other means and attached to the lid 120. Specifically, the electrode terminal 200 has a shaft portion 210 (rivet portion) extending downward (in the negative Z-axis direction). The shaft portion 210 is inserted into the through-hole 301 in the upper gasket 300, the through-hole 123 in the lid 120, the through-hole 401 in the lower gasket 400, and the through-hole 501 in the current collector 500, and is crimped. This secures the electrode terminal 200, along with the upper gasket 300, the lower gasket 400, and the current collector 500, to the lid 120. The electrode terminal 200 is formed of a conductive material such as a metal, such as aluminum, an aluminum alloy, copper, or a copper alloy. Furthermore, it is not essential that the shaft portion 210 be provided on the electrode terminal 200. For example, the shaft portion 210 may be integrally provided on the current collector 500, pass through the lower gasket 400, the cover 120, the upper gasket 300, and the electrode terminal 200, and be crimped to the outside of the electrode terminal 200.

The current collector 500 is a plate-like member that electrically connects the electrode body 700 and the electrode terminal 200. In this embodiment, the current collector 500 is substantially rectangular when viewed in the thickness direction (Z-axis direction) and has a first side surface 505 that is the side facing the electrode body 700 (the negative Z-axis direction) and a second side surface 506 that is the side surface opposite the first side surface 505. The positive electrode side current collector 500 is formed of a metal such as aluminum or an aluminum alloy, and the negative electrode side current collector 500 is formed of a metal such as copper or a copper alloy. In this embodiment, the tab portion 720 of the electrode body 700 is joined to the first side surface 505 of the current collector 500, and further, a conductive member 550 electrically connected to the tab portion 720 is also joined to the first side surface 505.

The method for joining the current collector 500 and the electrode terminal 200 is not limited to crimping, and may be ultrasonic welding, laser welding, resistance welding, or other welding, or mechanical joining other than crimping, such as screw fastening. The current collector 500 and the tab portion 720 may be joined by laser welding, resistance welding, ultrasonic welding, or other methods. In this embodiment, the current collector 500 and the tab portion 720 are welded by laser welding. The configuration of the current collector 500 and its surroundings in this embodiment will be described later using Figures 3 to 7.

The upper gasket 300 is a flat, insulating sealing member disposed between the lid 120 of the container 100 and the electrode terminal 200. The lower gasket 400 is a flat, insulating sealing member disposed between the lid 120 and the current collector 500. The upper gasket 300 and the lower gasket 400 are formed from an insulating material, such as a resin such as polypropylene (PP), polyethylene (PE), polyphenylene sulfide resin (PPS), polyethylene terephthalate (PET), polyether ether ketone (PEEK), tetrafluoroethylene perfluoroalkyl vinyl ether (PFA), polytetrafluoroethylene (PTFE), polybutylene terephthalate (PBT), or polyethersulfone (PES), or a composite material containing these resins.

[2. Configuration of current collector and its surroundings]
Next, the configuration of the current collector 500 and its periphery will be described with reference to FIGS. 3 to 7 , focusing particularly on the connection structure between the current collector 500 and the tab portion 720. In this embodiment, the two current collectors 500 arranged in the X-axis direction of the energy storage element 10 and their periphery configurations are substantially identical. Therefore, the following description will focus on the current collector 500 on the negative X-axis side. Various matters regarding the current collector 500 and tab portion 720 described below may be applied to the current collector 500 and tab portion 720 on both the positive and negative electrode sides.

Figure 3 is a first cross-sectional view showing the current collector 500 and its surrounding structure according to an embodiment, and Figure 4 is a second cross-sectional view corresponding to Figure 3. Specifically, Figure 3 illustrates a partial cross-section of the energy storage element 10 in the XZ plane passing through line III-III in Figure 2, showing the state before the tab portion 720 is bonded to the current collector 500. Figure 4 is a partial cross-section of the energy storage element 10 at the same position as Figure 3, showing the partial cross-section after the tab portion 720 is bonded to the current collector 500. Figure 5 is a cross-sectional view showing the difference in depth (width in the Z-axis direction) of the first bonding portion 551 and the second bonding portion 552 according to an embodiment. Note that the position of the cross-section in Figure 5 and Figures 6 to 9 described below is the same as the position of the cross-section in Figure 3.

As shown in Figures 3 to 5, in this embodiment, the tab portion 720 of the electrode assembly 700 is electrically connected to the current collector 500 by two joints formed at different positions. Specifically, as shown in Figures 3 and 4, a first joint 551 is formed at the portion where the current collector 500, tab portion 720, and conductive member 550 are overlapped, and a second joint 552 is formed at the portion where the current collector 500 and conductive member 550 are overlapped. The first joint 551 is formed from the underside of the conductive member 550 (the surface on the negative Z-axis side; the same applies below), penetrating the conductive member 550 and tab portion 720, and partially reaching the current collector 500. As a result, the tab portion 720 and the conductive member 550 are both mechanically and electrically connected to the current collector 500. The second joint 552 is formed at a position different from the first joint 551, penetrating the conductive member 550, and partially reaching the current collector 500. This mechanically and electrically connects the conductive member 550 to the current collector 500. Thus, in this embodiment, from the perspective of electrical connection, the tab portion 720 of the electrode assembly 700 is directly connected to the current collector 500 at the first joint 551, and is further indirectly connected to the current collector 500 at the second joint 552 via the conductive member 550.

More specifically, the portion of the current collector 500 where the tab portion 720 overlaps is the thin portion 510, and the thin portion 510 and the tab portion 720 are joined at the first joint portion 551. Furthermore, the portion of the current collector 500 where the conductive member 550 directly overlaps is the thick portion 520, and the second joint portion 552 joins the thick portion 520 and the conductive member 550. The thin portion 510 is thinner than the thick portion 520, and a step portion 507 is formed at the boundary between the thin portion 510 and the thick portion 520 in the current collector 500.

That is, the energy storage element 10 according to this embodiment includes a container 100, an electrode assembly 700 and a current collector 500 housed in the container 100, a first joint 551, and a second joint 552. The first joint 551 is a portion where the current collector 500 and the tab portion 720 of the electrode assembly 700 are joined. The second joint 552 is formed at a position different from the first joint 551 and is a portion where the current collector 500 is joined to a conductive member 550 electrically connected to the tab portion 720. The current collector 500 has a thin portion 510 where a portion of the first joint 551 is formed, and a thick portion 520 that is thicker than the thin portion 510 and where a portion of the second joint 552 is formed.

As described above, in this embodiment, the current collector 500 is joined to the tab portion 720 at the thin-walled portion 510. Therefore, the tab portion 720 can be positioned closer to the wall of the container 100 (the lid 120 in this embodiment). This allows the electrode body main body 710 to account for a larger proportion of the internal volume of the container 100, thereby improving the energy density of the energy storage device 10. On the other hand, since the cross-sectional area of the current collector 500 is reduced at the thin-walled portion 510, forming the thin-walled portion 510 on the current collector 500 reduces the meltdown resistance of the current collector 500. In this embodiment, the energy storage device 10 has a second joint portion 552, which is the portion where the conductive member 550 electrically connected to the tab portion 720 and the current collector 500 are joined. Therefore, the conductive member 550 also functions as a conductive path between the electrode body 700 and the current collector 500. This reduces the current flowing through the thin-walled portion 510, and suppresses a decrease in the fusing resistance of the current collector 500 caused by the thin-walled portion 510. Therefore, with the energy storage element 10 according to this embodiment, it is possible to improve the energy density of the energy storage element 10 while suppressing a decrease in the fusing resistance of the current collector 500.

For example, "joining the current collector and the conductive member" does not simply mean bringing the current collector and the conductive member into contact, but rather means electrically and mechanically connecting the current collector and the conductive member by a specified method such as welding or crimping. In this embodiment, the current collector 500 and the conductive member 550 are electrically and mechanically connected at the second joint 552 by welding, which makes it easier to stabilize the resistance value of the bypass conduction path passing through the second joint 552 and also reduces variation in the resistance value between products. This supplementary note also applies to the joint between the tab portion and the current collector and the joint between the tab portion and the conductive member.

In addition, in this embodiment, as shown in Figures 3 and 4, a step portion 507 is formed on the first side surface 505 of the current collector 500 on the electrode body 700 side, separating the thin portion 510 and the thick portion 520. Furthermore, the second side surface 506 of the current collector 500 opposite the first side surface 505 is formed in a flat plate shape. The conductive member 550 is a flat plate-shaped member located between the current collector 500 and the electrode body 700.

With this configuration, as shown in Figures 3 and 4, the thin-walled portion 510 is positioned away from the electrode body 700 in the thickness direction of the current collector 500. In other words, the thin thickness of the thin-walled portion 510 further enhances the effect of making the electrode body main body 710 larger. Furthermore, because the conductive member 550 is positioned between the current collector 500 and the electrode body 700, the tab portion 720 can be positioned closer to the wall of the container 100 (the lid 120 in this embodiment) compared to when the conductive member 550 is positioned between the current collector 500 and the wall of the container 100 (the lid 120 in this embodiment). For these reasons, the energy density can be further improved.

The energy storage element 10 according to this embodiment also includes an electrode terminal 200 fixed to the wall (lid 120) of the container 100. The current collector 500 has a terminal connection portion 508, which is an electrical connection portion with the electrode terminal 200, located on the opposite side of the lid 120 from the electrode terminal 200. As shown in FIG. 4, the second joint portion 552 is located between the first joint portion 551 and the terminal connection portion 508. In this embodiment, the shaft portion 210 of the electrode terminal 200 is inserted into the through-hole 501 of the current collector 500 and crimped, thereby forming a crimped portion 211 at the tip of the shaft portion 210 (the portion protruding from the through-hole 501). In other words, the peripheral portion of the through-hole 501 (see FIG. 2) in the current collector 500 is the terminal connection portion 508.

With this configuration, a second joint 552 that forms part of a bypass-like conductive path is disposed between a first joint 551 that forms a direct conductive path between the tab portion 720 of the electrode body 700 and the current collector 500, and a terminal connection 508 that connects the electrode terminal 200, which is the external terminal of the energy storage element 10, and the current collector 500. In other words, the second joint 552 is disposed in the conductive path between the first joint 551 and the terminal connection 508. This shortens the length of the conductive path via the conductive member 550, thereby further reducing the electrical resistance between the electrode body 700 and the electrode terminal 200.

In addition, in this embodiment, the width of the first joint 551 in the overlapping direction between the current collector 500 and the tab portion 720 is greater than the width of the second joint 552 in the overlapping direction between the conductive member 550 and the current collector 500. Specifically, as shown in FIG. 5 , if the width of the first joint 551 in the Z-axis direction is Da and the width of the second joint 552 in the Z-axis direction is Db, Da > Db.

With this configuration, the tab portion 720, which is a laminate of base material layers (metal foil), and the current collector 500 are firmly joined by the relatively deep first joint 551. Furthermore, the second joint 552, which is the joint between the conductive member 550 and the current collector 500, is formed relatively shallow. Typically, increasing the depth of the joint requires more energy to form the joint, which makes spatter and small pieces of metal foil more likely to occur during joining. In this embodiment, by making the first joint relatively deep, the tab portion 720 and the current collector 500 are firmly joined, while the second joint is relatively shallow, reducing the occurrence of spatter and small pieces of metal foil during formation of the second joint. In other words, the reliability of the two joints is ensured while reducing the occurrence of defects caused by the joining process.

In addition, in this embodiment, welding is used as a method for forming the first joint 551. That is, the first joint 551 is formed by welding at least the current collector 500 and the tab portion 720 together. In this embodiment, as described above, the tab portion 720 and the current collector 500 are melted and joined together by laser welding, thereby forming the first joint 551. Resistance welding, for example, can also be used as an alternative to laser welding. In this embodiment, as shown in FIGS. 3 and 4 , when joining the tab portion 720 and the current collector 500, the tab portion 720 and the current collector 500 can be joined while pressing the conductive member 550 against the current collector 500. That is, by pressing the multiple base layers (metal foils) stacked in the tab portion 720 in the stacking direction with the conductive member 550, the tab portion 720 and the current collector 500 can be joined while preventing gaps from forming between the base layers. Gaps between base material layers can cause welding defects when welding by laser welding or resistance welding, but in this embodiment, the first joint 551 can be formed with gaps between the base material layers suppressed. For this reason, adopting the configuration of this embodiment is particularly significant when forming the first joint 551 by laser welding or resistance welding.

The joining of the current collector 500 and the tab portion 720 and the joining of the current collector 500 and the conductive member 550 are carried out by overlapping the tab portion 720 and the conductive member 550 on the current collector 500, as shown in Figures 3 and 4. This procedure is one example, and it is also possible, for example, to join the current collector 500 and the conductive member 550, and then overlap the tab portion 720 and the conductive member 550 on the current collector 500 to join the current collector 500 and the tab portion 720. This will be explained with reference to Figures 6 and 7.

6 and 7 are first and second diagrams illustrating another example of the procedure for joining the current collector 500 and the tab portion 720 according to the embodiment. As shown in FIG. 6, first, a conductive member 550 formed in a generally L-shape is prepared. Specifically, for example, the end of the flat conductive member 550 where the second joint portion 552 is formed is bent relative to the remaining portion, thereby forming the conductive member 550 into a generally L-shape bent midway along its length. This end of the conductive member 550 is then joined to the current collector 500 before it is joined to the electrode terminal 200. As a result, the current collector 500 is joined to the conductive member 550 at the second joint portion 552. Thereafter, as shown in FIG. 7, the current collector 500 is joined to the electrode terminal 200. As a result, the current collector 500 is fixed to the lid 120. Furthermore, the tab portion 720 is positioned along the thin portion 510 of the current collector 500, and the end of the conductive member 550 opposite the end including the second joint portion 552 is bent toward the tab portion 720. In other words, the generally L-shaped conductive member 550 is deformed into a flat plate, and the conductive member 550 presses the tab portion 720 toward the thin portion 510 of the current collector 500. In this state, laser light is irradiated from the underside of the conductive member 550, bonding the conductive member 550 and the tab portion 720 to the thin portion 510 of the current collector 500. This forms the first joint portion 551, resulting in the connection structure between the current collector 500 and the tab portion 720 shown in FIG. 4 .

The above procedure allows for the removal of foreign matter generated during the formation of the second joint 552 after forming the joint portion (second joint 552) between the current collector 500 and the conductive member 550, but before joining the current collector 500 and the tab portion 720. This prevents problems such as micro-short circuits caused by conductive foreign matter remaining in the container 100. Furthermore, at the time of the joining operation to form the first joint 551, the conductive member 550 is fixed to the current collector 500 at the second joint 552. Therefore, it is easy or unnecessary to restrict the position of the conductive member 550 during the joining operation to form the first joint 551.

The above describes the energy storage element 10 according to the embodiment, focusing on the connection structure between the tab portion 720 of the electrode body 700 and the current collector 500. This connection structure may differ from the connection structure shown in Figures 2 to 7. Therefore, below, we will explain modified examples of the connection structure between the tab portion 720 and the current collector 500, focusing on the differences from the above embodiment.

(Variation 1)
FIG. 8 is a cross-sectional view showing a connection structure between a tab portion 720 and a current collector 500a according to a first modification of the embodiment. The energy storage element 10a according to this modification includes a first joint portion 551a where the current collector 500a and the tab portion 720 of the electrode body 700 are joined, and a second joint portion 552a formed at a position different from the first joint portion 551. The second joint portion 552a is where the conductive member 550 and the current collector 500 are joined. The current collector 500a has a thin portion 510a where a part of the first joint portion 551a is formed, and a thick portion 520a that is thicker than the thin portion 510a and where a part of the second joint portion 552a is formed. The energy storage element 10a according to this modification and the energy storage element 10 according to the embodiment have the same configuration.

However, in the embodiment, as shown in FIG. 4, the second joint 552 is formed when the conductive member 550 and the current collector 500 are stacked in their thickness direction (Z-axis direction). On the other hand, in this modified example, the conductive member 550a and the current collector 500a are butted together in a direction (X-axis direction in FIG. 8) perpendicular to the thickness direction (Z-axis direction), and the second joint 552a is formed at the butted portion.

Even in this case, the conductive paths between the electrode body 700 and the current collector 500a are a direct conductive path passing through the first joint 551a and a bypass conductive path passing through the second joint 552a and the conductive member 550a. This has the effect of suppressing a decrease in the meltdown resistance of the current collector 500.

When comparing the connection structures between the tab portion 720 and the current collector 500 (500a) in the embodiment and Variation 1, as can be seen from Figures 4 and 8, the connection structure of the embodiment allows for a smaller thickness for the thick portion 520 of the current collector 500. Therefore, for example, the cost of manufacturing the current collector 500 can be kept lower than the cost of manufacturing the current collector 500a. Furthermore, in the connection structure of Variation 1, forming the second joint 552a requires that the end face of the conductive member 550a and the end face of the stepped portion 507a of the current collector 500a be butted together without any gaps, a condition that is not easy to meet. In this regard, in the connection structure of the embodiment, the second joint 552 can be formed by overlapping the conductive member 550 and the current collector 500 in the thickness direction (see Figure 4). Therefore, it is relatively easy to form a second joint 552 with high joint reliability. Thus, from the standpoint of reducing the manufacturing costs of the current collector and ease of joining, for example, the connection structure according to the embodiment is preferable to the connection structure according to Modification 1.

(Variation 2)
FIG. 9 is a cross-sectional view showing a connection structure between a tab portion 720 and a current collector 500 according to Modification 2 of the embodiment. The energy storage element 10b according to this modification includes a first joint portion 551b where the current collector 500 and the tab portion 720 of the electrode body 700 are joined, and a second joint portion 552 formed at a position different from the first joint portion 551. The second joint portion 552 is where the conductive member 550 and the current collector 500 are joined. The current collector 500 has a thin portion 510 where a part of the first joint portion 551b is formed, and a thick portion 520 that is thicker than the thin portion 510 and where a part of the second joint portion 552 is formed. The energy storage element 10b according to this modification and the energy storage element 10 according to the embodiment share the above configuration.

However, in the embodiment, as shown in FIG. 4, the first joint 551 joins the conductive member 550 and the tab portion 720 together to the current collector 500, whereas in this modified example, the first joint 551b joins only the tab portion 720 to the current collector 500. Furthermore, the energy storage element 10b according to this modified example is provided with a third joint 553 that joins the conductive member 550 and the tab portion 720. In other words, it is not necessary to join both the conductive member 550 and the tab portion 720 to the current collector 500 with a single joint, and the joint that joins the tab portion 720 to the current collector 500 and the joint that joins the conductive member 550 to the tab portion 720 may be arranged separately from each other. Even in this case, the conductive paths between the electrode body 700 and the current collector 500 include a direct conductive path that passes through the first joint 551b and a bypass conductive path that passes through the third joint 553, the conductive member 550, and the second joint 552. This can prevent malfunctions such as melting of the current collector 500, and can also provide benefits such as improved charge/discharge efficiency.

9, the first joint 551b, the third joint 553, the second joint 552, and the terminal connection 508 of the current collector 500 are arranged in this order in the X-axis direction, but the order of these is not limited to that shown in FIG. 9. For example, the first joint 551b may be located on the negative X-axis side of the third joint 553, or may be located in the same position as the third joint 553 in the X-axis direction and arranged side by side in the Y-axis direction. Furthermore, the first joint 551b and the third joint 553 do not need to be completely separated from each other and may be arranged so that they partially overlap. In either case, a direct conductive path via the first joint 551b and a bypass conductive path via the third joint 553 are provided as conductive paths between the electrode body 700 and the current collector 500. This has the effect of suppressing a decrease in the fusing resistance of the current collector 500.

(Variation 3)
Fig. 10 is a bottom view showing the connection structure between the tab portion 720 and the current collector 500c according to Modification 3 of the embodiment. Specifically, Fig. 10 shows the connection structure as viewed from the electrode body main body 710 side (the negative Z-axis direction side).

The energy storage element 10c according to this modification includes a first joint 551c, where the current collector 500c and the tab portion 720 of the electrode assembly 700 are joined, and a second joint 552c formed at a different position from the first joint 551c. Although not shown in FIG. 10, in this modification, the first joint 551c is where the conductive member 550c and the tab portion 720 are collectively joined to the current collector 500. The second joint 552c is where the conductive member 550c and the current collector 500c are joined. The current collector 500c has a thin portion 510c where a portion of the first joint 551c is formed, and a thick portion 520c that is thicker than the thin portion 510c and where a portion of the second joint 552c is formed. The electrode terminal 200 is joined to the terminal connection portion 508c of the current collector 500c. The above configuration is common between the energy storage element 10c of this modified example and the energy storage element 10 of the embodiment.

However, in the embodiment, as shown in FIG. 4, the first joint 551 and the second joint 552 are aligned in the X-axis direction, whereas in this modification, the first joint 551c and the second joint 552c are aligned in the Y-axis direction. Even in this case, a direct conductive path via the first joint 551c and a bypass conductive path via the second joint 552c and the conductive member 550 are provided as conductive paths between the electrode body 700 and the current collector 500. This has the effect of suppressing a decrease in the meltdown resistance of the current collector 500. Furthermore, a structure in which the first joint 551c and the second joint 552c are aligned in the Y-axis direction is useful, for example, when the length of the current collector 500c in the X-axis direction is short.

The first and second bonding portions 551c and 552c do not need to be positioned in the same position in the X-axis direction, and may be offset in the X-axis direction. The shapes and sizes of the first and second bonding portions 551c and 552c do not need to be the same, and these shapes and sizes may be determined appropriately for each of the first and second bonding portions 551c and 552c.

(Other Modifications)
Although the energy storage device according to the embodiment and its modifications of the present invention has been described above, the present invention is not limited to the above-described embodiment and its modifications. In other words, the embodiment and its modifications disclosed herein are examples in all respects, and include all modifications within the meaning and scope of the claims.

For example, the connection structure between the current collector 500 and the tab portion 720 shown in FIG. 4 does not have to be provided on both the positive electrode side and the negative electrode side of the energy storage element 10. For example, when the positive electrode of the electrode assembly 700 is electrically connected to the container 100, the connection structure between the current collector 500 and the tab portion 720 shown in FIG. 4 may be provided only on the negative electrode side.

In addition, methods other than welding may be used to form the first and second joints 551 and 552. For example, the first and second joints 551 and 552 may be formed by ultrasonic bonding, or by mechanical methods such as crimping or fastening. Furthermore, the first and second joints 551 and 552 may be formed by different methods. In other words, the method for forming the first and second joints 551 and 552 may be appropriately selected depending on the required bonding strength, the state of the components to be joined during bonding (whether they are single components or combined with other components, etc.), and the bonding conditions (temperature, tool size, etc.).

Furthermore, while various examples of the arrangement and layout of the first joint portion, second joint portion, and terminal connection portion are shown using Figures 4, 8, 9, and 10, the arrangement and layout of these joint portions and terminal connection portions are not limited to these illustrated examples. For example, a terminal connection portion, which is the joint portion of the electrode terminal on the current collector, may be arranged between the first joint portion that joins the tab portion 720 to the current collector and the second joint portion that joins the conductive member to the current collector. For example, by arranging the conductive member so that it extends beyond the terminal connection portion in the X-axis direction, the first joint portion can be arranged on one side of the terminal connection portion in the X-axis direction, and the second joint portion can be arranged on the other side. Furthermore, in this description, the X-axis direction may be interpreted as the Y-axis direction. In other words, the terminal connection portion may be arranged between the first joint portion and the second joint portion in the Y-axis direction.

For example, from the perspective of further reducing the electrical resistance between the electrode body 700 and the electrode terminal 200, a structure in which the second joint portion is disposed between the first joint portion and the terminal connection portion (see Figures 4, 8, and 9) is said to be most preferable.

Furthermore, multiple tab portions may be joined to one current collector. For example, multiple tab portions 720 may be joined to one current collector 500, and a conductive member 550 electrically connected to these multiple tab portions 720 may be joined to the current collector 500. In this case, multiple first joint portions 551 and one second joint portion 552 are formed. Even in this case, a direct conductive path passing through the first joint portion 551 and a bypass conductive path passing through the second joint portion 552 and the conductive member 550 are provided as conductive paths between the electrode body 700 and the current collector 500. This can achieve the effect of suppressing a decrease in the fusing resistance of the current collector 500.

Furthermore, for example, in the energy storage element 10 according to the embodiment, there is no particular limitation on the order in which the first bonding portion 551, the second bonding portion 552, and the terminal connection portion 508 are formed. For example, the terminal connection portion 508 may be formed after the first bonding portion 551 and the second bonding portion 552 are formed. In other words, as long as the structure shown in FIG. 4 is realized, for example, the order in which these bonding portions and connection portions are formed may be determined as appropriate depending on the convenience of the manufacturing process, etc.

Furthermore, the type of electrode body provided in the energy storage element 10 is not limited to a wound type. For example, the energy storage element 10 may be provided with a laminated electrode body in which flat electrode plates are stacked, or an electrode body having a structure in which long strip-shaped electrode plates are stacked in an accordion-like manner by repeatedly folding in peaks and valleys. Furthermore, the energy storage element 10 may be provided with multiple electrode bodies.

Furthermore, the various supplementary points regarding the energy storage device 10 according to the embodiment described above may also be applied to any of the energy storage devices 10a to 10c according to Modifications 1 to 3. Furthermore, configurations constructed by arbitrarily combining the multiple components described above are also included within the scope of the present invention.

The present invention can be applied to energy storage elements such as lithium-ion secondary batteries.

10, 10a, 10b, 10c Energy storage element 100 Container 110 Container body 200 Electrode terminal 210 Shaft portion 211 Crimping portion 500, 500a, 500c Current collector 505 First side surface 506 Second side surface 507, 507a Step portion 508, 508c Terminal connection portion 510, 510a, 510c Thin portion 520, 520a, 520c Thick portion 550, 550a, 550c Conductive member 551, 551a, 551b, 551c First bonding portion 552, 552a, 552c Second bonding portion 553 Third bonding portion 700 Electrode body 710 Electrode body main body portion 720 Tab portion

Claims (5)

An energy storage element comprising a container, and an electrode assembly and a current collector housed in the container,
a first joint portion where the current collector and the tab portion of the electrode body are joined;
a second joint portion formed at a position different from the first joint portion, the second joint portion being a portion where the conductive member electrically connected to the tab portion and the current collector are joined,
the current collector has a thin portion in which a part of the first joint portion is formed, and a thick portion that is thicker than the thin portion and in which a part of the second joint portion is formed,
the current collector is disposed between the electrode body and the wall of the container;
the thinned portion is disposed between the tab portion and the wall portion,
The battery further includes an electrode terminal fixed to the wall portion and electrically connected to the current collector.
Energy storage element. In the current collector, a step portion that separates the thin portion and the thick portion is formed on a first side surface on the electrode body side, and a second side surface opposite to the first side surface is formed in a flat plate shape,
the conductive member is a flat plate-shaped member located between the tab portion and the current collector and the electrode body;
The energy storage element according to claim 1. the current collector has a terminal connection portion that is an electrical connection portion with the electrode terminal and is located on the opposite side of the wall portion from the electrode terminal,
the second joint portion is located between the first joint portion and the terminal connection portion;
The energy storage element according to claim 1 or 2. a width of the first joint portion in the overlapping direction between the current collector and the tab portion is larger than a width of the second joint portion in the overlapping direction between the conductive member and the current collector;
The energy storage element according to any one of claims 1 to 3. the first joint portion is formed by welding at least the current collector and the tab portion together,
The energy storage element according to any one of claims 1 to 4.