Energy storage element

Abstract

To provide a power storage element capable of improving the welding quality between an electrode body and a current collector.SOLUTION: A power storage element 10 comprises: an electrode body 600 that has a lamination part 620 in which electrode plates are laminated in a first direction; and a current collector 500 bonded with the lamination part 620. The power storage element 10 comprises a molten part 800 molten by laser welding in a state where the current collector 500 is overlapped with the lamination part 620 or in a state where the current collector 500 and a patch 700 sandwich the lamination part 620. The molten part 800 is formed in a state of penetrating through a junction member (a patch 700), which is the current collector 500 or the patch 700, in the first direction. A first width A1 in a second direction orthogonal to the first direction, of the molten part 800 on a surface 710 of the junction member is 1.24 times or more a second width B1 in the second direction, of the molten part 800 on a boundary surface 720 between the junction member and the lamination part 620.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a power storage element including an electrode body and a current collector.

Background Art

[0002] Conventionally, there is known a power storage element including an electrode body having a stacked portion in which electrode plates are stacked and a current collector, and the stacked portion and the current collector are joined by laser welding. For example, Patent Document 1 discloses a secondary battery (power storage element) including an electrode assembly (electrode body) having a tab group (stacked portion) in which tabs are stacked and a conductive member (current collector), and the tab group and the conductive member are laser welded.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above conventional power storage element, when laser welding the stacked portion of the electrode body and the current collector, the electrode plates in the stacked portion may float. In this case, when welding the stacked portion and the current collector, there is a risk of blow holes occurring or breakage occurring at the boundary between the portion melted by laser welding and the portion not melted. As a result, there is a risk that the welding quality between the stacked portion and the current collector deteriorates, such as a decrease in the bonding strength or an increase in resistance between the electrode body and the current collector.

[0005] The present invention has been made by the inventors of the present application newly focusing on the above problems, and an object thereof is to provide a power storage element capable of improving the welding quality between an electrode body and a current collector.

Means for Solving the Problems

[0006] An energy storage element according to one aspect of the present invention comprises an electrode body having a laminated portion in which electrode plates are stacked in a first direction, and a current collector joined to the laminated portion, wherein the current collector is superimposed on the laminated portion, or the current collector and a backing plate are melted by laser welding in a state in which the laminated portion is sandwiched between them, the molten portion is formed in a state in which the joining member, which is the current collector or the backing plate, penetrates in the first direction, and the first width of the molten portion in a second direction perpendicular to the first direction on the surface of the joining member is 1.24 times or more the second width of the molten portion in the second direction at the interface between the joining member and the laminated portion. [Effects of the Invention]

[0007] The energy storage element of the present invention can improve the welding quality between the electrode body and the current collector. [Brief explanation of the drawing]

[0008] [Figure 1] This is a perspective view showing the external appearance of the energy storage element according to the embodiment. [Figure 2] These are perspective and side views showing the individual components of a disassembled energy storage element according to an embodiment. [Figure 3] This is a perspective view showing the configuration of the electrode body according to the embodiment. [Figure 4] These are cross-sectional and plan views showing the configuration of the current collector, electrode body, laminated portion, and backing plate in a welded state according to the embodiment. [Figure 5] This graph shows the amount of floating of the electrode plates in the laminated electrode body from the current collector when the number of electrode plates and the thickness of the backing plate are changed in the laminated electrode body according to the embodiment. [Figure 6A] This graph shows the ratio of the first width to the second width when the number of electrode plates and the thickness of the backing plate in the laminated portion of the electrode body according to the embodiment are changed. [Figure 6B] This graph shows the relationship between the ratio of the first width to the second width and the amount of floating of the electrode plates in the laminated electrode body from the current collector, when the number of electrode plates and the thickness of the backing plate are changed in the laminated electrode body according to the embodiment. [Figure 7] This is a cross-sectional view showing the configuration of the current collector, the laminated portion of the electrode body, and the backing plate in a welded state according to Modification 1 of the Embodiment. [Figure 8] This is a cross-sectional view showing the configuration of the current collector and electrode body in a welded state, according to a modified example 2 of the embodiment. [Modes for carrying out the invention]

[0009] An energy storage element according to one aspect of the present invention comprises an electrode body having a laminated portion in which electrode plates are stacked in a first direction, and a current collector joined to the laminated portion, wherein the current collector is superimposed on the laminated portion, or the current collector and a backing plate are melted by laser welding in a state in which the laminated portion is sandwiched between them, the molten portion is formed in a state in which the joining member, which is the current collector or the backing plate, penetrates in the first direction, and the first width of the molten portion in a second direction perpendicular to the first direction on the surface of the joining member is 1.24 times or more the second width of the molten portion in the second direction at the interface between the joining member and the laminated portion.

[0010] According to this, in an energy storage element, the molten portion formed by laser welding is formed in a state where it penetrates the joining member, which is a current collector or backing plate, and the first width of the molten portion on the surface of the joining member is 1.24 times or more the second width of the molten portion at the interface between the joining member and the laminated portion. In this way, because the molten portion penetrates the joining member, the laminated portion is laser-welded from the joining member side while being pressed down by the joining member, and the floating of the electrode plates within the laminated portion is suppressed during laser welding. However, if the joining member deforms when it melts, the pressure on the laminated portion by the joining member weakens, and there is a risk that the electrode plates will float up. In contrast, increasing the thickness of the joining member can suppress the deformation of the joining member. When the thickness of the joining member is increased, the ratio of the first width of the molten portion on the surface of the joining member to the second width of the molten portion at the interface between the joining member and the laminated portion becomes larger. The inventors of this application have found that the floating of the electrode plates within the laminated portion can be suppressed when the first width is 1.24 times or more the second width, as a means of solving the above problem. Therefore, by making the first width 1.24 times or more than the second width, the welding quality between the electrode body and the current collector can be improved.

[0011] The first width may be 1.41 times or more the second width.

[0012] The inventors of this application have found that if the first width is 1.41 times or more the second width, the floating of the electrode plates within the laminated section can be further suppressed. Therefore, by making the first width 1.41 times or more the second width, the welding quality between the electrode body and the current collector can be further improved.

[0013] The first width may be 1.54 times or more the second width.

[0014] The inventors of this application have found that if the first width is 1.54 times or more the second width, the floating of the electrode plates within the laminated section is almost eliminated. Therefore, by making the first width 1.54 times or more the second width, the welding quality between the electrode body and the current collector can be further improved.

[0015] The joining member may have a thickness of 0.2 mm or more in the first direction.

[0016] The inventor of the present application has found that by forming the joining member to have a thickness of 0.2 mm or more, deformation of the joining member can be suppressed during laser welding. If deformation of the joining member can be suppressed, the laminated portion can be more firmly held by the joining member, so that floating of the electrode plate in the laminated portion can be further suppressed.

[0017] The joining member may have a thickness in the first direction of 0.3 mm or more.

[0018] The inventor of the present application has found that by forming the joining member to have a thickness of 0.3 mm or more, deformation of the joining member can be further suppressed during laser welding. If deformation of the joining member can be further suppressed, the laminated portion can be further firmly held by the joining member, so that floating of the electrode plate in the laminated portion can be further suppressed.

[0019] Hereinafter, a power storage element according to an embodiment (including a modification thereof) of the present invention will be described with reference to the drawings. Each of the embodiments described below shows comprehensive or specific examples. The numerical values, shapes, materials, components, arrangement positions and connection forms of the components, manufacturing processes, order of manufacturing processes, etc. shown in the following embodiments are examples and are not intended to limit the present invention. In each drawing, dimensions and the like are not strictly illustrated. In each drawing, the same or similar components are denoted by the same reference numerals.

[0020] In the following description and drawings, the direction in which the pair of electrode terminals (positive and negative, hereinafter the same) of the energy storage element are aligned, the direction in which the pair of current collectors are aligned, the direction in which the pair of backing plates are aligned, or the direction in which the short sides of the container face each other is defined as the X-axis direction. The direction in which the long sides of the container face each other, or the thickness direction of the container or electrode body is defined as the Y-axis direction. The direction in which the electrode terminals and electrode body are aligned, the direction in which the current collectors and electrode body are aligned, the direction in which the electrode plates in the laminated portion of the electrode body are aligned, the direction in which the current collectors and backing plates are aligned, the thickness direction of the current collectors or backing plates, the direction in which the container body and lid of the energy storage element are aligned, or the vertical direction is defined as the Z-axis direction. These X-axis, Y-axis, and Z-axis directions intersect each other (orthogonal in this embodiment). Note that depending on the usage, the Z-axis direction may not be the vertical direction, but for the sake of explanation below, the Z-axis direction will be described as the vertical direction.

[0021] In the following explanation, the X-axis positive direction refers to the direction of the X-axis arrow, and the X-axis negative direction refers to the opposite direction. When simply referring to the X-axis direction, it refers to either the X-axis positive direction or the X-axis negative direction, or either direction. The same applies to the Y-axis and Z-axis directions. In the following, the Z-axis direction may also be referred to as the first direction, and the direction perpendicular to the Z-axis direction (such as the Y-axis direction or X-axis direction) may be referred to as the second direction. Expressions indicating relative directions or orientations, such as parallel and orthogonal, may include cases where they are not strictly those directions or orientations. When two directions are parallel, it means not only that the two directions are perfectly parallel, but also that they are substantially parallel, i.e., that they may have a difference of, for example, a few percent. In the following explanation, when the term "insulation" is used, it means "electrical insulation".

[0022] (Embodiment) [1. General description of the energy storage element 10] First, a general description of the energy storage element 10 in this embodiment will be given. Figure 1 is a perspective view showing the external appearance of the energy storage element 10 according to this embodiment. Figure 2 is a perspective view and a side view showing each component of the energy storage element 10 according to this embodiment when it is disassembled. Specifically, Figure 2(a) is an exploded perspective view of the energy storage element 10. Figure 2(b) is a side view showing the configuration when the laminated portion 620 of the electrode body 600 is sandwiched between the current collector 500 and the backing plate 700 and welded, as viewed from the X-axis positive direction.

[0023] The energy storage element 10 is a secondary battery (single cell) capable of charging and discharging electricity, and specifically, is a non-aqueous electrolyte secondary battery such as a lithium-ion secondary battery. The energy storage element 10 is used for power storage or power supply purposes. Specifically, the energy storage element 10 is used as a battery for driving or starting the engine of mobile vehicles such as automobiles, motorcycles, watercraft, ships, snowmobiles, agricultural machinery, construction machinery, or railway vehicles for electric railways. Examples of automobiles include electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and fossil fuel (gasoline, diesel, liquefied natural gas, etc.) vehicles. Examples of railway vehicles for electric railways include electric trains, monorails, maglev trains, and hybrid trains equipped with both diesel engines and electric motors. The energy storage element 10 can also be used as a stationary battery for household or commercial use.

[0024] 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 a capacitor. The energy storage element 10 may not be a secondary battery, but a primary battery that allows the user to use the stored electricity without charging. The energy storage element 10 may be a battery using a solid electrolyte. The energy storage element 10 may be a pouch-type energy storage element. In this embodiment, the energy storage element 10 is shown in a flat rectangular parallelepiped shape (square), but the shape of the energy storage element 10 is not limited to a rectangular parallelepiped shape, but may be cylindrical, oval cylindrical, or a polygonal prism shape other than a rectangular parallelepiped.

[0025] As shown in Figure 1, the energy storage element 10 comprises a container 100, a pair of electrode terminals 200 (positive and negative), and a pair of upper gaskets 300 (positive and negative). As shown in Figure 2, the container 100 houses a pair of lower gaskets 400 (positive and negative), a pair of current collectors 500 (positive and negative), an electrode body 600, and a pair of backing plates 700 (positive and negative). An electrolyte (non-aqueous electrolyte) is sealed inside the container 100, but this is not shown in the illustration. There are no particular restrictions on the type of electrolyte, as long as it does not impair the performance of the energy storage element 10, and various types can be selected. In addition to the above components, spacers placed to the side, above, or below the electrode body 600, an insulating film enclosing the electrode body 600, etc., may also be arranged.

[0026] The container 100 is a rectangular parallelepiped (square or box-shaped) case having a container body 110 with an opening and a lid 120 that closes the opening of the container body 110. The container body 110 is a rectangular cylindrical member with a bottom that constitutes the main body of the container 100. The container body 110 has a pair of short sides on both sides in the X-axis direction, a pair of long sides on both sides in the Y-axis direction, and a bottom surface on the Z-axis negative side. The lid 120 is a rectangular plate-shaped member that is long in the X-axis direction and constitutes the lid of the container 100, and is positioned in the Z-axis positive direction of the container body 110. The lid 120 is provided with a gas discharge valve 121 that releases pressure when the pressure inside the container 100 rises excessively, and an injection part 122 for injecting electrolyte into the container 100, etc.

[0027] With this configuration, the container 100 is sealed inside by welding or other means to the container body 110 and the lid 120 after the electrode body 600 and the lid 120 have been placed inside the container body 110. The material of the container 100 (container body 110 and lid 120) is not particularly limited and can be made of weldable metals such as stainless steel, aluminum, aluminum alloy, iron, or plated steel sheet, but resin can also be used.

[0028] The electrode body 600 is an energy storage element (power generation element) that comprises a positive electrode plate, a negative electrode plate, and a separator, and is capable of storing electricity. The electrode body 600 is formed by winding layers of material arranged so that a separator is sandwiched between the positive electrode plate and the negative electrode plate. As a result, the non-active material layer portion (uncoated active material portion) of the positive electrode plate is stacked to form the stacked portion 620 of the positive electrode. Similarly, the non-active material layer portion (uncoated active material portion) of the negative electrode plate is stacked to form the stacked portion 630 of the negative electrode. In other words, the electrode body 600 has an electrode body main body portion 610 and stacked portions 620 and 630 that protrude from a part of the electrode body main body portion 610 in the Z-axis positive direction and extend in the Y-axis positive direction. In this embodiment, the electrode body 600 is an oval-shaped wound electrode body when viewed from the Z-axis direction, but it may be elliptical, circular, or any other shape when viewed from the Z-axis direction. A detailed explanation of the configuration of the electrode body 600 will be given later.

[0029] The electrode terminals 200 are terminal members (positive and negative terminals) that are electrically connected to the electrode body 600 via the current collector 500. The electrode terminals 200 are metallic members that lead the electricity stored in the electrode body 600 to the external space of the energy storage element 10 and introduce electricity into the internal space of the energy storage element 10 in order to store electricity in the electrode body 600. The electrode terminals 200 are made of a conductive material such as aluminum, aluminum alloy, copper, or copper alloy. The electrode terminals 200 are connected (joined) to the current collector 500 by crimping or the like and are attached to the cover 120.

[0030] Specifically, the electrode terminal 200 has a shaft portion 201 (rivet portion) extending downward (in the negative Z-axis direction). The shaft portion 201 is then inserted into the through hole 301 of the upper gasket 300, the through hole 123 of the cover 120, the through hole 401 of the lower gasket 400, and the through hole 501 of the current collector 500, and crimped. In this way, the electrode terminal 200 is fixed to the cover 120 together with the upper gasket 300, the lower gasket 400, and the current collector 500. The method of connecting (joining) the electrode terminal 200 and the current collector 500 is not limited to crimping, and welding methods such as ultrasonic welding, laser welding or resistance welding, or mechanical joining other than crimping, such as screw joining, may also be used.

[0031] The current collector 500 is a current collecting member (positive electrode current collector and negative electrode current collector) that electrically connects the electrode body 600 and the electrode terminal 200. The positive electrode current collector 500 is connected (joined) to the laminated portion 620 of the positive electrode of the electrode body 600 by welding, and as described above, it is joined to the electrode terminal 200 of the positive electrode by crimping or the like. The negative electrode current collector 500 is connected (joined) to the laminated portion 630 of the negative electrode of the electrode body 600 by welding, and as described above, it is joined to the electrode terminal 200 of the negative electrode by crimping or the like. In this embodiment, the current collector 500 is a flat plate-shaped and rectangular member. The material of the current collector 500 is not particularly limited, but the positive electrode current collector 500 is made of a conductive material such as aluminum or an aluminum alloy, similar to the positive electrode base material of the electrode body 600 described later. The negative electrode current collector 500 is formed of a conductive material such as copper or a copper alloy, similar to the negative electrode substrate of the electrode body 600 described later.

[0032] The backing plate 700 is positioned to sandwich the laminated portion 620 or 630 of the electrode body 600 between the current collector 500 and the backing plate 700, and is a member that is joined (welded) to the laminated portion 620 or 630 together with the current collector 500 while the laminated portion 620 or 630 is sandwiched between the current collector 500 and the backing plate 700. In this embodiment, the backing plate 700 is a flat and rectangular member, positioned in the negative Z-axis direction of the laminated portion 620 or 630, and sandwiches the laminated portion 620 or 630 between the current collector 500 and the backing plate 700 in the Z-axis direction (see Figure 2(b)). The material of the backing plate 700 is not particularly limited, but the backing plate 700 for the positive electrode is made of a metal such as aluminum or an aluminum alloy, similar to the positive electrode base material of the electrode body 600. The backing plate 700 for the negative electrode is made of a metal such as copper or a copper alloy, similar to the negative electrode base material of the electrode body 600.

[0033] In this configuration, the laminated portion 620 or 630 of the electrode body 600 is sandwiched between the current collector 500 and the backing plate 700, and the current collector 500, the laminated portion 620 or 630, and the backing plate 700 are welded together to form a molten portion 800 (see Figure 2(b)). In this embodiment, one molten portion 800 is formed for one current collector 500, but the number of molten portions 800 is not particularly limited. A detailed explanation of the configuration for welding the current collector 500, the laminated portion 620 or 630 of the electrode body 600, and the backing plate 700 will be given later.

[0034] The upper gasket 300 is a flat, insulating member (gasket) positioned between the lid 120 of the container 100 and the electrode terminal 200, providing insulation and sealing between the lid 120 and the electrode terminal 200. The lower gasket 400 is a flat, insulating member (gasket) positioned between the lid 120 and the current collector 500, providing insulation between the lid 120 and the current collector 500. The upper gasket 300 and lower gasket 400 are formed from insulating resins such as polypropylene (PP), polyethylene (PE), polystyrene (PS), polyphenylene sulfide resin (PPS), polyphenylene ether (PPE (including modified PPE)), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyether ether ketone (PEEK), tetrafluoroethylene perfluoroalkyl vinyl ether (PFA), polytetrafluoroethylene (PTFE), polyethersulfone (PES), ABS resin, or composite materials thereof.

[0035] [2. Description of the configuration of electrode body 600] Next, the configuration of the electrode body 600 will be described in detail. Figure 3 is a perspective view showing the configuration of the electrode body 600 according to this embodiment. Specifically, Figure 3(a) shows the configuration of the electrode body 600 shown in Figure 2 with a portion of the winding state unfolded, and Figure 3(b) shows the configuration of the electrode body 600 after winding.

[0036] As shown in Figure 3(a), the electrode body 600 is formed by alternately stacking and winding a positive electrode plate 640, a negative electrode plate 650, and separators 661 and 662. In other words, the electrode body 600 is formed by stacking and winding the positive electrode plate 640, separator 661, negative electrode plate 650, and separator 662 in this order.

[0037] The positive electrode plate 640 is an electrode plate in which a positive electrode active material layer is formed on the surface of a positive electrode substrate, which is a long, strip-shaped metal foil made of aluminum or an aluminum alloy. The negative electrode plate 650 is an electrode plate in which a negative electrode active material layer is formed on the surface of a negative electrode substrate, which is a long, strip-shaped metal foil made of copper or a copper alloy. As the positive electrode substrate and the negative electrode substrate, any known material that is stable against oxidation-reduction reactions during charging and discharging can be used, such as nickel, iron, stainless steel, titanium, calcined carbon, conductive polymer, conductive glass, and Al-Cd alloy. As the positive electrode active material used in the positive electrode active material layer and the negative electrode active material used in the negative electrode active material layer, any known material that is capable of intercalating and deintercalating lithium ions can be used.

[0038] As positive electrode active materials, polyanionic compounds such as LiMPO4, LiMSiO4, LiMBO3 (where M is one or more transition metal elements selected from Fe, Ni, Mn, Co, etc.), lithium titanate, LiMn2O4, and LiMn 1.5 Ni 0.5 Spinel-type lithium manganese oxides such as O4, lithium transition metal oxides such as LiMO2 (where M is one or more transition metal elements selected from Fe, Ni, Mn, Co, etc.) can be used. As negative electrode active materials, lithium metals, lithium alloys (lithium-silicon, lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, and lithium metal-containing alloys such as Wood's alloys), alloys capable of intercalating and deintercalating lithium, carbon materials (e.g., graphite, non-graphitizable carbon, easily graphitizable carbon, low-temperature calcined carbon, amorphous carbon, etc.), silicon oxides, metal oxides, lithium metal oxides (Li4Ti5O 12 Examples include polyphosphate compounds, or compounds of transition metals and group 14 to 16 elements, such as Co3O4 and Fe2P, which are generally called conversion negative electrodes.

[0039] Separators 661 and 662 are microporous sheets made of resin. Any known material can be used for separators 661 and 662, as long as it does not impair the performance of the energy storage element 10. For example, separators 661 and 662 can be woven fabrics, nonwoven fabrics, or synthetic resin microporous membranes made of polyolefin resins such as polyethylene, which are insoluble in organic solvents.

[0040] The positive electrode plate 640 has a plurality of rectangular tabs 641 protruding in the positive Z-axis direction at its end in the positive Z-axis direction, and the plurality of tabs 641 are arranged in a stacked state in the Y-axis direction. Similarly, the negative electrode plate 650 has a plurality of rectangular tabs 651 protruding in the positive Z-axis direction at its end in the positive Z-axis direction, and the plurality of tabs 651 are arranged in a stacked state in the Y-axis direction. Tabs 641 and 651 are portions where the active material layer is not formed and the substrate is exposed. The shape of tabs 641 and 651 is not particularly limited.

[0041] As shown in Figure 3(b), multiple stacked tabs 641 are bundled together to form a stacked portion 620 that extends in the positive Z-axis direction. Similarly, multiple stacked tabs 651 are bundled together to form a stacked portion 630 that extends in the positive Z-axis direction. These stacked portions 620 and 630 are welded together with the current collector 500 and the backing plate 700 in the Y-axis direction, sandwiched between them, and then bent together with the current collector 500 and the backing plate 700 in the positive Y-axis direction. As a result, as shown in Figure 2(b), the stacked portion 620 has electrode plates (positive electrode plates 640) stacked in the Z-axis direction (first direction) and is sandwiched between the current collector 500 and the backing plate 700 in the Z-axis direction. Similarly, the laminated portion 630 has electrode plates (negative electrode plates 650) stacked in the Z-axis direction (first direction), and is sandwiched between the current collector 500 and the backing plate 700 in the Z-axis direction.

[0042] The electrode body portion 610 is the part that constitutes the main body of the electrode body 600, and specifically, it is the part of the electrode body 600 other than the laminated portions 620 and 630. The electrode body portion 610 is an elongated cylindrical or oval-shaped portion formed by winding the portions on which the active material layer of the positive electrode plate 640 and the negative electrode plate 650 is formed with the separators 661 and 662. If the electrode body 600 has an active material non-formed portion (uncoated active material portion) at the end of the electrode plate (positive electrode plate 640 or negative electrode plate 650) where the active material layer is not formed, and tabs (tabs 641 or 651) extend from the active material non-formed portion, then the electrode body portion 610 does not include the active material non-formed portion. In other words, in this configuration, the laminated portion 620 (or 630) is the portion in which multiple tabs 641 (or multiple tabs 651) and the active material non-formed portion are laminated. As a result, the electrode body portion 610 has a pair of curved electrode body curved portions 611 on both sides in the X-axis direction, and a pair of flat electrode body flat portions 612 connecting the pair of curved electrode body portions 611 on both sides in the Y-axis direction.

[0043] [3. Explanation of the welding configuration of the current collector 500, the laminated section 620, and the backing plate 700] Next, the configuration in which the current collector 500, the laminated portion 620 or 630 of the electrode body 600, and the backing plate 700 are welded together will be described in detail. The configuration in which the current collector 500, the laminated portion 620, and the backing plate 700 are welded together is the same as the configuration in which the current collector 500, the laminated portion 630, and the backing plate 700 are welded together. For this reason, the configuration in which the current collector 500, the laminated portion 620, and the backing plate 700 are welded together will be described below, and the configuration in which the current collector 500, the laminated portion 630, and the backing plate 700 are welded together will be omitted.

[0044] Figure 4 is a cross-sectional and plan view showing the configuration of the current collector 500, the laminated portion 620 of the electrode body 600, and the backing plate 700 in a welded state according to this embodiment. Specifically, Figure 4(a) is a cross-sectional view showing the configuration when the current collector 500, the laminated portion 620 of the electrode body 600, and the backing plate 700 are welded together and cut by a plane that includes the central axis of the molten portion 800 and is parallel to the YZ plane. In Figure 4(a), for the sake of explanation, the top and bottom of Figure 2 are reversed, and the negative Z-axis direction is shown facing upwards. Figure 4(b) is a plan view (top view, bottom view in Figure 2) showing the configuration of Figure 4(a) when viewed from the negative Z-axis direction (upwards, downwards in Figure 2).

[0045] As shown in Figure 4, the current collector 500 and the backing plate 700 are positioned to sandwich the laminated portion 620, which consists of the tabs 641 of the positive electrode plate 640 of the electrode body 600, and are welded together with the laminated portion 620. As a result, a molten portion 800 is formed on the current collector 500, the laminated portion 620, and the backing plate 700, where the current collector 500, the laminated portion 620, and the backing plate 700 are molten.

[0046] The molten portion 800 is a portion formed by laser welding when the current collector 500 is stacked with the laminated portion 620, or when the current collector 500 and the backing plate 700 are sandwiching the laminated portion 620 (a portion that has solidified after melting). In this embodiment, the molten portion 800 is a portion formed by laser welding when the current collector 500, the laminated portion 620, and the backing plate 700 are sandwiching the laminated portion 620. Specifically, the flat portion of the current collector 500 (a portion without recesses or protrusions) and the flat portion of the backing plate 700 (a portion without recesses or protrusions) are arranged sandwiching the flat portion of the laminated portion 620 (a portion without recesses or protrusions). Then, when laser light is irradiated onto these parts, the flat portion of the current collector 500, the flat portion of the laminated portion 620, and the flat portion of the backing plate 700 melt, forming a molten portion 800.

[0047] Of the current collector 500 and the backing plate 700, the member through which the molten portion 800 penetrates in the Z-axis direction is also referred to as the joining member. In other words, the molten portion 800 is formed in a state in which it penetrates the joining member, which is either the current collector 500 or the backing plate 700, in the Z-axis direction (first direction). In this embodiment, the backing plate 700 is an example of a joining member, and a laser beam is irradiated from the backing plate 700 side (Z-axis negative direction) to form the molten portion 800 in a state in which it penetrates the backing plate 700 in the Z-axis direction. The molten portion 800 is formed from the Z-axis negative direction surface of the backing plate 700, penetrating the backing plate 700 and the laminated portion 620 in their thickness direction (Z-axis direction), and extending to the Z-axis negative direction portion of the current collector 500 (the portion close to the laminated portion 620, the portion in contact with the laminated portion 620). In this embodiment, the molten portion 800 has a circular cross-section in the XY plane, and its diameter gradually decreases as it moves toward the Z-axis positive direction.

[0048] In this configuration, the width of the molten portion 800 on the surface 710 of the backing plate 700 (joining member) in a direction perpendicular to the Z-axis direction (second direction perpendicular to the first direction) is referred to as the first width A1. The first width A1 is the width of the surface 810 of the backing plate 700 in the Z-axis negative direction of the molten portion 800 in a direction perpendicular to the Z-axis direction (second direction). Specifically, the first width A1 is the length of the cut portion when the surface 810 is cut by a plane parallel to the Z-axis direction that includes the central axis P of the molten portion 800. In this embodiment, since the surface 810 of the molten portion 800 is circular in shape, the first width A1 is the diameter of the surface 810 and the maximum width of the surface 810. In Figure 4, the Y-axis direction is shown as an example of the second direction, and the length of the cut portion (width in the Y-axis direction) when the surface 810 is cut by the YZ plane that includes the central axis P of the molten portion 800 is shown as an example of the first width A1. The central axis P of the molten portion 800 is a virtual axis that passes through the center of the molten portion 800 and extends parallel to the Z-axis direction when viewed from the Z-axis direction.

[0049] The width of the molten portion 800 in the direction perpendicular to the Z-axis direction (second direction) at the interface 720 between the backing plate 700 (joining member) and the laminated portion 620 is referred to as the second width B1. The second width B1 is the width of the interface 820 located in the molten portion 800, specifically the interface 820 between the backing plate 700 and the laminated portion 620, in the direction perpendicular to the Z-axis direction (second direction). The interface 820 is a surface that extends the interface 720 between the backing plate 700 and the laminated portion 620 into the molten portion 800, and is a surface located at the same position in the Z-axis direction as the interface 720 within the molten portion 800. Specifically, the second width B1 is the length of the cut portion when the interface 820 is cut by a plane parallel to the Z-axis direction including the central axis P of the molten portion 800. In this embodiment, the second width B1 is the diameter of the interface 820 and is the maximum width of the interface 820. In Figure 4, the Y-axis direction is shown as an example of the second direction, and the length of the cut portion (width in the Y-axis direction) when the interface 820 is cut by the YZ plane containing the central axis P of the molten portion 800 is shown as an example of the second width B1.

[0050] If the surface 810 is not circular when viewed from the Z-axis direction, the definitions of the first width A1 and the second width B1 are as follows. If the surface 810 is elliptical when viewed from the Z-axis direction, the length of the minor axis is defined as the first width A1, and the width of the interface 820 in the same direction as the first width A1 is defined as the second width B1. If the welding is performed so that it extends linearly (straight or curved) when viewed from the Z-axis direction, the surface 810 will have a shape that extends linearly (straight or curved) when viewed from the Z-axis direction. In this case, the maximum width in the direction perpendicular to the direction in which the surface 810 extends when viewed from the Z-axis direction is defined as the first width A1, and the width of the interface 820 in the same direction as the first width A1 is defined as the second width B1. The values ​​of the first width A1 and the second width B1 are measured from the image data obtained by X-ray CT of the molten area 800.

[0051] In the above configuration, when the laminated portion 620 of the current collector 500 and electrode body 600 and the backing plate 700 are welded to form the molten portion 800, the electrode plates may lift away from the current collector 500 in the laminated portion 620, resulting in a decrease in welding quality. The amount of lift of the electrode plates from the current collector 500 in the laminated portion 620 is shown in Table 1 and Figure 5.

[0052] Table 1 shows the amount of lift (μm) of the electrode plates of the laminated portion 620 from the current collector 500 when the number of electrode plates in the laminated portion 620 of the electrode body 600 according to this embodiment and the thickness of the backing plate 700 (thickness C1 in Figure 4) are changed. Specifically, in Table 1, the number of electrode plates in the laminated portion 620 (number of tabs 641 of the positive electrode plate 640) is changed to 20, 40, 60, and 80, and the thickness C1 of the backing plate 700 (thickness in the Z-axis direction) is changed to 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, and 0.6 mm. The thickness of one of the above electrode plates is 12 μm. The amount of lift of the electrode plates of the laminated portion 620 from the current collector 500 is the maximum amount that the electrode plates at the Z-axis positive end of the laminated portion 620 are lifted from the current collector 500 in the Z-axis direction. Because the electrode plates of the laminated section 620 lift up significantly from the current collector 500 around the molten section 800, Table 1 shows the amount of lift (μm) around the molten section 800.

[0053] [Table 1]

[0054] Figure 5 is a graph showing the amount of floating (μm) of the electrode plates in the laminated portion 620 of the electrode body 600 from the current collector 500 when the number of electrode plates in the laminated portion 620 and the thickness C1 of the backing plate 700 are changed. In other words, Figure 5 is a graph of Table 1.

[0055] As shown in Table 1 and Figure 5, when the thickness C1 (thickness in the Z-axis direction) of the backing plate 700 (joining member) is 0.1 mm, the amount of lift of the electrode plates of the laminated section 620 from the current collector 500 is relatively large. However, when the thickness C1 of the backing plate 700 is 0.2 mm, this amount of lift becomes very small. Furthermore, when the thickness C1 of the backing plate 700 is 0.3 mm or more, this amount of lift becomes almost zero. In other words, when the thickness C1 of the backing plate 700 is 0.2 mm, the deformation of the backing plate 700 is suppressed during welding, allowing the laminated section 620 to be effectively pressed against the current collector 500, thus keeping the amount of lift of the electrode plates small. When the thickness C1 of the backing plate 700 is 0.3 mm or more, the deformation of the backing plate 700 is further suppressed, and the amount of lift of the electrode plates is kept even smaller. Therefore, the backing plate 700 (joining member) preferably has a thickness C1 of 0.2 mm or more in the Z-axis direction (first direction), and more preferably 0.3 mm or more. In order to perform laser welding properly, the thickness C1 of the backing plate 700 is preferably 1.5 mm or less.

[0056] In each case shown in Table 1 and Figure 5, the shape of the molten portion 800 changes, and therefore the values ​​of the first width A1 and the second width B1 also change. Table 2 is a table showing the ratio of the first width A1 to the second width B1 when the number of electrode plates in the laminated portion 620 of the electrode body 600 according to this embodiment and the thickness C1 of the backing plate 700 are changed. Specifically, Table 2 shows the values ​​of the ratio of the first width A1 to the second width B1 (first width A1 / second width B1) corresponding to each case in Table 1.

[0057] [Table 2]

[0058] Figure 6A is a graph showing the ratio of the first width A1 to the second width B1 when the number of electrode plates in the laminated portion 620 of the electrode body 600 according to this embodiment and the thickness C1 of the backing plate 700 are changed. In other words, Figure 6 is a graph of Table 2. Figure 6B is a graph showing the relationship between the ratio of the first width A1 to the second width B1 and the amount of floating (μm) of the electrode plates in the laminated portion 620 from the current collector 500 when the number of electrode plates in the laminated portion 620 of the electrode body 600 and the thickness C1 of the backing plate 700 are changed.

[0059] As described above, when the thickness C1 of the backing plate 700 is 0.2 mm, the amount of lift of the electrode plates in the laminated section 620 from the current collector 500 (amount of electrode plate lift) becomes very small. As shown in Table 2, Figures 6A and 6B, when the thickness C1 of the backing plate 700 is 0.2 mm, the ratio of the first width A1 to the second width B1 (first width A1 / second width B1) is 1.24 to 1.27 when the number of electrode plates in the laminated section 620 is changed. Therefore, the amount of electrode plate lift becomes very small at or above this value. For this reason, the first width A1 in the second direction of the molten section 800 on the surface 710 of the backing plate 700 (joining member) is preferably 1.24 times or more, and more preferably 1.27 times or more, the second width B1 in the second direction of the molten section 800 at the interface 720 between the backing plate 700 (joining member) and the laminated section 620.

[0060] Furthermore, as mentioned above, when the thickness C1 of the backing plate 700 is 0.3 mm or more, the amount of lift of the electrode plate becomes almost zero. When the thickness C1 of the backing plate 700 is 0.3 mm, the ratio of the first width A1 to the second width B1 (first width A1 / second width B1) is 1.41 to 1.54 when the number of electrode plates in the laminated section 620 is changed, so the amount of lift of the electrode plate becomes almost zero at this value or higher. For this reason, it is preferable that the first width A1 is 1.41 times or more the second width B1, and more preferably 1.54 times or more.

[0061] When the thickness C1 of the backing plate 700 is 0.6 mm, the ratio of the first width A1 to the second width B1 (first width A1 / second width B1) is 1.51 to 1.97, and within this range, the amount of plate lift is almost zero. If the thickness C1 of the backing plate 700 is made too thick, it may become a thickness C1 that is unsuitable for laser welding, but since the amount of plate lift is almost zero when the first width A1 / second width B1 is at least 1.97 or less, it is preferable that the first width A1 is 1.97 times or less of the second width B1.

[0062] [4. Explanation of Effects] As described above, according to the energy storage element 10 of the present invention, the molten portion 800 formed by laser welding is formed in a state that penetrates the joining member (in this embodiment, the backing plate 700), which is either the current collector 500 or the backing plate 700. The first width A1 of the molten portion 800 on the surface 710 of the backing plate 700 (joining member) is 1.24 times or more the second width B1 of the molten portion 800 at the interface 720 between the backing plate 700 (joining member) and the laminated portion 620.

[0063] As described above, since the molten portion 800 penetrates the backing plate 700 (joining member), the laminated portion 620 is laser-welded from the backing plate 700 side while being held down by the backing plate 700, and the lifting of the electrode plates within the laminated portion 620 is suppressed during laser welding. However, if the backing plate 700 deforms when it melts, the hold on the laminated portion 620 by the backing plate 700 weakens, and the electrode plates may lift up. In this case, fracture may occur at the interface between the molten portion 800 and the unmelted area surrounding the molten portion 800, resulting in a decrease in welding quality of the laminated portion 620 and the current collector 500, such as increased resistance and decreased strength. In contrast, increasing the thickness C1 of the backing plate 700 can suppress the deformation of the backing plate 700. Increasing the thickness C1 of the backing plate 700 increases the ratio of the first width A1 of the molten portion 800 at the surface 710 of the backing plate 700 to the second width B1 of the molten portion 800 at the interface 720 between the backing plate 700 and the laminated portion 620. The inventors of this application have found that when the first width A1 is 1.24 times or more the second width B1, the floating of the electrode plate within the laminated portion 620 can be suppressed. Therefore, by making the first width A1 1.24 times or more the second width B1, the occurrence of fracture at the interface between the molten portion 800 and the unmolten portion can be suppressed, thereby improving the welding quality between the electrode body 600 and the current collector 500.

[0064] The inventors of this application have found that if the first width A1 is 1.41 times or more the second width B1, the floating of the electrode plates within the laminated portion 620 can be further suppressed. Therefore, by making the first width A1 1.41 times or more the second width B1, the welding quality between the electrode body 600 and the current collector 500 can be further improved.

[0065] The inventors of this application have found that if the first width A1 is 1.54 times or more the second width B1, the floating of the electrode plates within the laminated portion 620 is almost eliminated. Therefore, by making the first width A1 1.54 times or more the second width B1, the welding quality between the electrode body 600 and the current collector 500 can be further improved.

[0066] The inventors of this application have found that by making the thickness C1 of the backing plate 700 (joining member) thicker, such as 0.2 mm or more, deformation of the backing plate 700 during laser welding can be suppressed. If deformation of the backing plate 700 can be suppressed, the laminated portion 620 can be pressed more firmly by the backing plate 700, and thus the lifting of the electrode plates within the laminated portion 620 can be further suppressed.

[0067] The inventors of this application have found that by forming the backing plate 700 (joining member) with a thickness C1 of 0.3 mm or more, deformation of the backing plate 700 during laser welding can be further suppressed. If deformation of the backing plate 700 can be further suppressed, the laminated portion 620 can be pressed more firmly by the backing plate 700, and thus the lifting of the electrode plates within the laminated portion 620 can be further suppressed. The inventors of this application have found that by forming the backing plate 700 with a thickness C1 of 0.3 mm or more, the lifting of the electrode plates is almost eliminated.

[0068] The above describes the effect of a configuration in which the current collector 500, the laminated section 620, and the backing plate 700 are welded together, but the same effect is obtained in a configuration in which the current collector 500, the laminated section 630, and the backing plate 700 are welded together.

[0069] [5 Explanation of variations] Although the energy storage element 10 according to this embodiment has been described above, the present invention is not limited to the above embodiment. The embodiments disclosed herein are illustrative and not restrictive in all respects, and the scope of the present invention includes all modifications in the sense and scope equivalent to the claims.

[0070] (Variation 1) In the above embodiment, the molten portion 800 is formed in a state where it penetrates the backing plate 700, but it may also be formed in a state where it penetrates the current collector 500. Figure 7 is a cross-sectional view showing the configuration of the current collector 500, the laminated portion 620 of the electrode body 600 and the backing plate 700 in a welded state according to Modification 1 of this embodiment. Figure 7 is a diagram corresponding to Figure 4(a), but the top and bottom of Figure 4(a) are reversed and the Z-axis positive direction is shown facing upwards.

[0071] As shown in Figure 7, in this modified example, the current collector 500 and the backing plate 700 are melted by laser welding with the laminated portion 620 in between, forming a molten portion 801. The molten portion 801 is formed in a state where it penetrates the current collector 500 in the Z-axis direction (first direction). In other words, in this modified example, the current collector 500 is an example of a joining member, and laser light is irradiated from the current collector 500 side (Z-axis positive direction), forming the molten portion 801 in a state where it penetrates the current collector 500 in the Z-axis direction. The molten portion 801 is formed from the Z-axis positive surface of the current collector 500, penetrating the current collector 500 and the laminated portion 620 in their thickness direction (Z-axis direction), and extending to the backing plate 700. In this modified example, the molten portion 801 has a circular cross-section in the XY plane, and its diameter gradually decreases as it moves toward the Z-axis negative direction. The other configurations of this modified example are the same as in the above embodiment, so a detailed explanation is omitted.

[0072] The width of the molten portion 801 on the surface 510 of the current collector 500 (joining member) in the direction perpendicular to the Z-axis direction (second direction perpendicular to the first direction) is referred to as the first width A2. The first width A2 is the width (diameter, maximum width) of the surface 811 of the molten portion 801 on the Z-axis positive direction of the surface 510 of the current collector 500 in the direction perpendicular to the Z-axis direction (second direction). The width of the molten portion 801 on the interface 520 between the current collector 500 (joining member) and the laminated portion 620 in the direction perpendicular to the Z-axis direction (second direction) is referred to as the second width B2. The second width B2 is the width (diameter, maximum width) of the interface 821 located on the molten portion 801 on the interface 520 between the current collector 500 and the laminated portion 620 in the direction perpendicular to the Z-axis direction (second direction). The interface surface 821 is a surface that extends the interface surface 520 between the current collector 500 and the laminated portion 620 into the molten portion 801, and is positioned in the same location in the Z-axis direction as the interface surface 520 within the molten portion 801.

[0073] Thus, in this modified example, the current collector 500 and the backing plate 700 are reversed compared to the above embodiment. Therefore, the first width A2 and the second width B2 in this modified example correspond to the first width A1 and the second width B1 in the above embodiment. Accordingly, the current collector 500 (joining member) preferably has a thickness (thickness C2 in Figure 7) of 0.2 mm or more in the Z-axis direction (first direction), and more preferably 0.3 mm or more. The first width A2 is preferably 1.24 times or more the second width B2, and more preferably 1.27 times or more. The first width A2 is preferably 1.41 times or more the second width B2, and more preferably 1.54 times or more. Other aspects are the same as in the above embodiment. As described above, this modified example can also achieve the same effects as in the above embodiment.

[0074] (Modification 2) In the above modified example 1, the molten portion 801 is formed by laser welding, with the current collector 500 and the backing plate 700 sandwiching the laminated portion 620; however, the backing plate 700 does not necessarily have to be placed. Figure 8 is a cross-sectional view showing the configuration of the laminated portion 620 of the current collector 500 and electrode body 600 in a welded state according to modified example 2 of this embodiment. Figure 8 corresponds to Figure 7.

[0075] As shown in Figure 8, in this modified example, the backing plate 700 is not placed, and a molten portion 802 is formed by laser welding with the current collector 500 overlapping the laminated portion 620. The molten portion 802 is formed with the current collector 500 penetrating in the Z-axis direction (first direction). In other words, this modified example has a configuration in which the backing plate 700 is removed from the configuration of Modified Example 1. The other configurations of this modified example are the same as those of Modified Example 1, so a detailed explanation is omitted.

[0076] In the configuration of the above modified example 1, by using a backing plate 700 with a high melting point that does not melt when laser-welded, the backing plate 700 does not melt even when the current collector 500 and the laminated section 620 are laser-welded, and therefore the backing plate 700 can be removed from the current collector 500 and the laminated section 620. This makes it possible to realize the configuration of this modified example. In this modified example, the amount of floating of the electrode plate described in the above embodiment can be read as the amount of floating of the electrode plate of the laminated section 620 from the backing plate 700 before the backing plate 700 is removed. As described above, this modified example can also achieve the same effects as the above embodiment or the above modified example 1.

[0077] (Other variations) In the above embodiment, the electrode body 600 is a wound-type electrode body with a winding axis perpendicular to the cover body 120, but it may also be a stack-type electrode body with flat plates stacked together, or a bellows-type electrode body with plates and / or separators folded in a bellows-like manner. The electrode body 600 may also be a wound-type electrode body with a winding axis parallel to the cover body 120. The stacked portions 620 and 630 may not be stacked tabs, but may be ends of the electrode body 600 that protrude from the entire electrode body body portion 610 of the electrode body 600.

[0078] In the above embodiment, the laminated portions 620 and 630 of the electrode body 600 are bent in the Y-axis direction while sandwiched between the current collector 500 and the backing plate 700, but they do not have to be bent in the Y-axis direction. In other words, the laminated portions 620 and 630 are not limited to being positioned sandwiched between the current collector 500 and the backing plate 700 in the Z-axis direction, but may be positioned sandwiched between the current collector 500 and the backing plate 700 in the Y-axis direction or other directions. In this case, the Y-axis direction or other direction is an example of a first direction, and a direction perpendicular to it is an example of a second direction.

[0079] In the above embodiment, the molten portion 800 is formed by the melting of a flat plate-shaped portion of the joining member (current collector 500 or backing plate 700), but it may also be formed by the melting of a recess or protrusion formed on the joining member. In other words, in Figure 4, the surface 810 of the molten portion 800 is located at the same position in the Z-axis direction as the surface 710 of the joining member (backing plate 700), but it may be recessed in the Z-positive direction from the surface 710, or it may protrude from the surface 710 in the Z-negative direction. Even in this case, the width of the surface 810 in the second direction becomes the first width A1. The same applies to the interface surface 820 (second width B1). However, since forming a recess in the joining member (backing plate 700) reduces the thickness of the joining member, it is preferable that the molten portion 800 is not formed in a recess of the joining member (the surface 810 is not formed in a position recessed from the surface 710).

[0080] In the above embodiment, the above configuration is assumed to be present on both the positive electrode side (laminated portion 620 side) and the negative electrode side (laminated portion 630 side), but it is not necessary for either the positive electrode side or the negative electrode side to have the above configuration. Generally, when the substrate of the electrode plate is made of metal, blowholes are likely to occur, which makes the electrode plate prone to lifting. This is because an oxide film may form on the surface of the metal, and the formed oxide film may adsorb water, making it easier for blowholes to occur when the adsorbed water gasifies during melting. Since the laminated portions 620 and 630 are parts made by laminating multiple substrates, when the substrates are made of metal, the oxide film formed on the surface of each substrate may adsorb water, making it prone to blowholes. Among metals, aluminum is particularly prone to the formation of an oxide film on its surface, making it particularly susceptible to blowholes. For this reason, when the laminated portion 620 of the positive electrode is made of laminated positive electrode substrates made of aluminum or an aluminum alloy, blowholes are likely to occur. Therefore, the above configuration is particularly effective when the positive electrode substrate is made of aluminum or an aluminum alloy.

[0081] The present invention also includes forms constructed by arbitrarily combining the components included in the above embodiments and their modified examples. [Industrial applicability]

[0082] This invention can be applied to energy storage elements such as lithium-ion secondary batteries. [Explanation of symbols]

[0083] 10 Energy storage elements 100 containers 110 Container body 120 Lid 200 electrode terminal 300 Upper gasket 400 Lower gasket 500 Current collector 510, 710, 810, 811 surface 520, 720, 820, 821 interface 600 Electrode body 610 Electrode body part 620, 630 Laminated section 640 Positive Plate 641, 651 tabs 650 Negative plate 661, 662 Separators 700 backing plate 800, 801, 802 Molten section

Claims

1. A power storage element comprising an electrode body having a laminated portion in which electrode plates are stacked in a first direction, and a current collector joined to the laminated portion, The current collector is superimposed on the laminated portion, or the current collector and the backing plate are sandwiched between the laminated portion, and the molten portion is provided by laser welding. The molten portion is formed in such a state that it penetrates the current collector or the joint member which is the backing plate in the first direction. The first width of the molten portion on the surface of the joining member in a second direction perpendicular to the first direction is 1.24 times or more and 1.97 times or less of the second width of the molten portion in the second direction at the interface between the joining member and the laminated portion. The number of plates stacked in the first direction in the aforementioned stacked portion is 80 or less. When the current collector and the backing plate sandwich the laminated portion, and the width of the molten portion in the second direction on the backing plate is greater than the width of the molten portion in the second direction on the current collector, the joining member is the backing plate; and when the width of the molten portion in the second direction on the current collector is greater than the width of the molten portion in the second direction on the backing plate, the joining member is the current collector. If the aforementioned backing plate is not provided, the joining member is the current collector. Energy storage element.

2. The joining member has a thickness of 0.2 mm or more and 1.5 mm or less in the first direction. The energy storage element according to claim 1.

3. The first width is 1.41 times or more the second width. The energy storage element according to claim 1 or 2.

4. The first width is 1.54 times or more the second width. The energy storage element according to any one of claims 1 to 3.

5. The joining member has a thickness of 0.3 mm or more in the first direction. The energy storage element according to any one of claims 1 to 4.

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