Secondary battery

Abstract

Provided is technology for improving the usability of a secondary battery.　A secondary battery 1 including: an active material layer 21; a current collector provided with a resin layer 201, and a pair of metal layers 202 provided on both surfaces of the resin layer 201, the current collector 20 comprising a body that is provided with an active material layer 21, and an end 200 that extends from the body, and the end 200 including an opening 203; a metal foil 3 joined to at least one of the pair of metal layers 202 at the end 200 of the current collector 20, and including a tab join region 30 overlapping the opening 203 in a plan view; and an electrode tab 4 joined to the metal foil 3 in at least a part of the tab join region 30.

Description

Secondary battery

[0001] SUMMARY OF THE INVENTION An exemplary embodiment of the present disclosure relates to a secondary battery.

[0002] In recent years, technology for converting natural energy such as solar or wind power into electrical energy has been attracting attention. Accordingly, various secondary batteries have been developed as electricity storage devices that are highly safe and capable of storing a large amount of electrical energy.

[0003] Among them, lithium secondary batteries, which are charged and discharged by the movement of lithium ions between a positive electrode and a negative electrode, are known to exhibit high voltage and high energy density. A typical lithium secondary battery is a lithium ion secondary battery (LIB), whose positive and negative electrodes have active materials for retaining lithium elements. In a lithium ion secondary battery, charging and discharging are performed by the exchange of lithium ions between the positive electrode active material and the negative electrode active material.

[0004] Furthermore, current collectors have been developed to improve the safety of lithium-ion secondary batteries. For example, Patent Document 1 discloses a lithium-ion secondary battery that aims to provide a positive and negative electrode configuration that prevents ignition in the event of abnormal heat generation during overcharge or at high temperatures, while maintaining electrical resistance at the same level as conventional batteries.

[0005] Furthermore, secondary batteries with low ohmic resistance have been developed to suppress heat generation. For example, Patent Document 2 discloses a cell of an energy storage device that provides more uniform electrical contact between the electrode current collector and the inner surface of the can.

[0006] Japanese Patent Application Publication No. 11-102711 Special Publication No. 2022-512776

[0007] The present disclosure provides a technique for improving the usefulness of secondary batteries.

[0008] In one exemplary embodiment of the present disclosure, there is provided a secondary battery comprising: a current collector including an active material layer, a resin layer, and a pair of metal layers provided on both sides of the resin layer, the current collector including a main body on which the active material layer is provided and end portions extending from the main body, the end portions having openings; a metal foil joined to at least one of the pair of metal layers at the end portions of the current collector, the metal foil having a tab bonding region that overlaps with the opening in a planar view; and an electrode tab joined to the metal foil in at least a portion of the tab bonding region.

[0009] According to one exemplary embodiment of the present disclosure, a technique for improving the usefulness of a secondary battery can be provided.

[0010] 1 is a three-dimensional perspective view showing an example of the configuration of the secondary battery 1. FIG. 2 is a top view showing an example of the configuration of the secondary battery 1. FIG. 3 is a cross-sectional view showing an example of the configuration of the secondary battery 1. FIG. 4 is a cross-sectional view showing an example of the configuration of the secondary battery 1. FIG. 5 is a top view showing an example of the configuration of an end 200 of the secondary battery 1. FIG. 6 is a top view showing an example of the configuration of the end 200 of the secondary battery 1. FIG. 7 is a cross-sectional view showing an example of the configuration of the end 200 of the secondary battery 1. FIG. 8 is a cross-sectional view showing an example of the configuration of the preliminary joining mark 31 of the secondary battery 1. FIG. 9 is a view showing an example of the configuration of the secondary battery 1. FIG. 10 is a top view showing another example of the configuration of the end 200 of the secondary battery 1. FIG. 11 is a top view showing another example of the configuration of the end 200 of the secondary battery 1. FIG. 12 is a top view showing another example of the configuration of the end 200 of the secondary battery 1. Fig. 1 is a top view showing another example of the configuration of the end portion 200 of the secondary battery 1. Fig. 2 is a top view showing another example of the configuration of the end portion 200 of the secondary battery 1. Fig. 3 is a top view showing an example of the configuration of the end portion 200 of the secondary battery 1 according to a comparative example. Fig. 4 is a cross-sectional view showing an example of the configuration of the end portion 200 of the secondary battery 1 according to a comparative example.

[0011] Hereinafter, each embodiment of the present disclosure will be described.

[0012] In one exemplary embodiment, a secondary battery is provided, comprising: a current collector including an active material layer, a resin layer, and a pair of metal layers provided on both sides of the resin layer, the current collector including a main body on which the active material layer is provided and an end portion extending from the main body, the end portion having an opening; a metal foil joined to at least one of the pair of metal layers at the end portion of the current collector, the metal foil having a tab bonding region that overlaps with the opening in a planar view; and an electrode tab joined to the metal foil in at least a portion of the tab bonding region.

[0013] In one exemplary embodiment, the metal foil has a first bonding mark formed by bonding to at least one of the pair of metal layers of the current collector.

[0014] In one exemplary embodiment, the metal foil further comprises a second bonding mark formed by bonding with the electrode tab.

[0015] In one exemplary embodiment, the metal foil has two first bonding marks and a second bonding mark between the two first bonding marks in a plan view.

[0016] In one exemplary embodiment, the metal foil includes a first bond mark around at least a portion of the periphery of the tab bond area.

[0017] In one exemplary embodiment, the metal foil includes a first bond mark around the entire periphery of the tab bond area.

[0018] In one exemplary embodiment, the opening has an open end at the end of the current collector.

[0019] In one exemplary embodiment, the opening is configured in a generally polygonal shape in a plan view.

[0020] In one exemplary embodiment, the opening is configured to have a substantially rectangular shape in a plan view.

[0021] In one exemplary embodiment, the opening is configured to be substantially semicircular, substantially elliptical, or substantially circular in plan view.

[0022] In one exemplary embodiment, the current collector has a region that is recessed in a direction from one metal layer toward the other metal layer of the pair of metal layers in a cross section including the first bonding mark.

[0023] In one exemplary embodiment, the current collector has a region where the pair of metal layers are integrated in a cross section including the first bonding mark.

[0024] In one exemplary embodiment, the metal foil is bonded to the other metal layer.

[0025] In one exemplary embodiment, the first bond mark is a weld mark.

[0026] In one exemplary embodiment, the second bond mark is a weld mark.

[0027] In one exemplary embodiment, the pair of metal layers each have a thickness of 1.0 μm or more and 15 μm or less, and the resin layer has a thickness of 2 μm or more and 15 μm or less.

[0028] In one exemplary embodiment, the active material layer includes a positive electrode active material, and the pair of metal layers each includes aluminum.

[0029] In one exemplary embodiment, the active material layer includes a negative electrode active material, and the pair of metal layers each includes copper.

[0030] In one exemplary embodiment, the resin layer comprises at least one of polyethylene terephthalate and polypropylene.

[0031] Hereinafter, each embodiment of the present disclosure will be described in detail with reference to the drawings. In each drawing, the same or similar elements are denoted by the same reference numerals, and redundant explanations will be omitted. The dimensional ratios in the drawings do not represent actual ratios, and the actual ratios are not limited to the ratios shown in the drawings.

[0032] In this disclosure, the usefulness of the secondary battery 1 includes at least some of the energy density, safety, monetary cost required for manufacturing, and manufacturing efficiency of the secondary battery 1. Furthermore, in this disclosure, the secondary battery 1 is typically described as a lithium-ion secondary battery, but the present disclosure is also applicable to other types of secondary batteries.

[0033] [Overall Configuration of Secondary Battery 1] Fig. 1 is a three-dimensional perspective view showing an example of the configuration of a secondary battery 1 according to this embodiment. The secondary battery 1 includes a plurality of electrode sheets 2, metal foils 3 joined to each electrode sheet 2, and electrode tabs 4 joined to the plurality of metal foils 3. The dotted arrows in Fig. 1 indicate an example of the relationship in which each component is joined. The electrode sheets 2, metal foils 3, and electrode tabs 4 are stacked along the positive direction of the z-axis. The direction along the z-axis can also be referred to as the stacking direction.

[0034] 1 shows an example of the configuration of one of the positive electrode and negative electrode of the secondary battery 1. Also, in FIG. 1, some components that the secondary battery 1 may have, such as a separator 5, are omitted.

[0035] The overall configuration of the secondary battery 1 will be described below with reference to Fig. 1. Note that detailed embodiments of each component included in the secondary battery 1 may be described with reference to Fig. 2 and subsequent figures.

[0036] <Electrode sheet 2> The electrode sheet 2 includes a current collector 20, an active material layer 21 a, and an active material layer 21 b. Hereinafter, when there is no particular distinction between the active material layer 21 a and the active material layer 21 b or when these are referred to collectively, they will be referred to as the active material layer 21.

[0037] (Current collector 20) The current collector 20 is configured by laminating a resin layer 201 and a metal layer 202a and a metal layer 202b provided on both sides of the resin layer 201. Hereinafter, when there is no particular distinction between the metal layer 202a and the metal layer 202b or when these are referred to collectively, they will be referred to as the metal layer 202.

[0038] The current collector 20 includes a main body having an active material layer 21 provided on a metal layer 202, and an end portion 200 extending from the main body. The active material layer 21 is not provided on the end portion 200 of the current collector 20. The active material 21 may be provided on a portion of the end portion 200 of the current collector 20 adjacent to the main body. The end portion 200 of the current collector 20 includes an opening 203. The opening 203 is provided over the entire length of the end portion 200 of the current collector 20 in the z-axis direction. The opening 203 may penetrate the end portion 200 of the current collector 20 along the z-axis direction. In one embodiment, the opening 203 is configured to be U-shaped in a planar view (in this example, when the xy plane is viewed from the positive direction of the z-axis). Such an end portion 200 of the current collector 20 may also be referred to as having a notch. As will be described later, the shape of the opening 203 is not limited to a U-shape.

[0039] Resin Layer 201 The resin layer 201 may be made of, for example, a sheet-like (film-like) or fibrous resin. The resin may be, for example, at least one of thermoplastic resins such as polyethylene terephthalate (PET) and polypropylene (PP). The resin layer 201 may be made by laminating multiple layers of at least one of the resins. In one embodiment, the resin layer 201 is made of a material having a melting point of 130°C or higher and 300°C or lower. In one embodiment, the average thickness of the resin layer 201 may be 2 μm or higher and 15 μm or lower, or 3 μm or higher and 10 μm or lower.

[0040] Configuring the current collector 20 to include the resin layer 201 increases the safety of the secondary battery 1. The resin layer 201 is made of a material that melts when the secondary battery 1 generates abnormal heat due to overcharging, a short circuit, or the like. When the resin layer 201 melts, the electrode sheet 2 is damaged, and the current inside the battery is interrupted. This can prevent the battery from catching fire, etc.

[0041] -Metal Layer 202- The metal layer 202 is a layer for extracting power from the active material layer 21. The metal layer 202 may be made of a type of metal depending on the polarity of the electrode sheet 2. For example, if the electrode sheet 2 is for a positive electrode, the metal layer 202 may contain aluminum. Furthermore, if the electrode sheet 2 is for a negative electrode, the metal layer 202 may contain copper. In one embodiment, the metal layer 202a and the metal layer 202b are formed on the current collector 20 so as to sandwich the resin layer 201. In this case, the metal layer 202a and the metal layer 202b do not conduct electricity in areas other than an area AR1 of the preliminary joining mark 31, which will be described later.

[0042] In one embodiment, metal layer 202 is made of a conductor that does not react with lithium ions. In one embodiment, metal layer 202 is made of at least one material selected from the group consisting of aluminum, titanium, stainless steel, nickel, and alloys thereof. In one example, metal layer 202 is aluminum or an aluminum alloy. In one embodiment, metal layer 202 is formed by vapor deposition, sputtering, electrolytic plating, or lamination of the above material on the surface of resin layer 201. In one embodiment, metal layer 202a and metal layer 202b may have an average thickness of 1.0 μm to 15 μm, 2.0 μm to 10 μm, or 3.0 μm to 6.0 μm.

[0043] (Active material layer 21) The active material layer 21a is a layer provided on the surface of the metal layer 202a opposite to the resin layer 201 (i.e., in FIG. 1 , the surface facing the positive z-axis direction from the metal layer 202a). The active material layer 21b is a layer provided on the surface of the metal layer 202b opposite to the resin layer 201 (i.e., in FIG. 1 , the surface facing the negative z-axis direction from the metal layer 202b). The active material layer 21 contains an active material.

[0044] In one embodiment, the active material layers 21 provided on a single electrode sheet 2 are made of the same type of active material. Specifically, when the active material layer 21a is made of a positive electrode active material, the active material layer 21b that sandwiches the current collector 20 with the active material layer 21a may also be made of a positive electrode active material. When the active material layer 21a is made of a negative electrode active material, the active material layer 21b that sandwiches the current collector 20 with the active material layer 21a may also be made of a negative electrode active material.

[0045] The positive electrode active material is a material for holding the carrier metal in the electrode sheet 2 and can also be referred to as a host material for the carrier metal. The positive electrode active material may be a material for holding lithium ions in the electrode sheet 2. In this case, lithium ions are charged and desorbed from the positive electrode active material by charging and discharging the battery. This can improve the stability and output voltage of the battery. In one embodiment, the positive electrode active material is a metal oxide or a metal phosphate. The metal oxide may be, for example, a cobalt oxide-based compound, a manganese oxide-based compound, or a nickel oxide-based compound. The metal phosphate may be, for example, an iron phosphate-based compound or a cobalt phosphate-based compound. In one embodiment, the positive electrode active material is LiCoO2, LiNixCoyMnzO(x+y+z=1), LiNixCoyAlzO(x+y+z=1), LiNixMnyO(x+y=1), LiNiO ２ , LiMn ２ O ４ , LiFePO, LiCoPO, LiFeOF, LiNiOF, and LiTiS. The positive electrode active material may be used alone or in combination of two or more. In one embodiment, the content of the positive electrode active material in the active material layer 21 may be 50% by mass to 100% by mass or less with respect to the entire active material layer 21.

[0046] The negative electrode active material is a material that causes an electrode reaction, i.e., an oxidation reaction and a reduction reaction, at the negative electrode. The negative electrode active material may be, for example, lithium metal, an alloy containing lithium metal, a carbon-based material, a metal oxide, a metal that alloys with lithium, or an alloy containing the metal. The carbon-based material may be, for example, graphene, graphite, hard carbon, carbon nanotubes, or the like. The metal oxide may be, for example, a titanium oxide-based compound, a cobalt oxide-based compound, or the like. The metal that alloys with lithium may be, for example, silicon, germanium, tin, lead, aluminum, or gallium.

[0047] As described above, the electrode sheet 2 may include both the active material layer 21 a and the active material layer 21 b from the viewpoint of improving the energy density of the secondary battery 1. However, in one embodiment, the electrode sheet 2 may not include one of the active material layer 21 a and the active material layer 21 b.

[0048] <Metal foil 3> The metal foil 3 is a member for electrically connecting the metal layer 202 and the electrode tab 4. The metal foil 3 may be made of a metal of a type that corresponds to the polarity of the electrode sheet 2. For example, if the electrode sheet 2 is for a positive electrode, the metal foil 3 may contain aluminum. Also, if the electrode sheet 2 is for a negative electrode, the metal foil 3 may contain copper. The thickness of the metal foil 3 may be, for example, 3 μm to 20 μm.

[0049] In one embodiment, the metal foil 3 is joined to the metal layer 202 with a predetermined gap between it and the active material layer 21. By providing the predetermined gap, the risk of short circuiting when the positive electrode sheet 2 and the negative electrode sheet 2 are stacked is reduced. In one embodiment, the predetermined gap may be 0.1 mm to 10 mm, or may be 1 mm to 5 mm.

[0050] In one embodiment, the metal foil 3 is joined to the metal layer 202a by ultrasonic bonding. The joining marks formed by ultrasonic bonding may also be referred to as weld marks because the metal may melt. Ultrasonic bonding makes it possible to join the metal foil 3 to the metal layer 202a in a short time. Furthermore, ultrasonic bonding makes it possible to join the metal foil 3 to the metal layer 202a without applying heat. Furthermore, ultrasonic bonding does not consume any other materials for joining. As described above, ultrasonic bonding can improve the manufacturing efficiency of the electrode sheet 2. In one embodiment, the ultrasonic bonding may be rotary ultrasonic bonding, which allows for continuous processing.

[0051] The metal foil 3 may be joined to the metal layer 202a by any of metallurgical, mechanical, and chemical bonding. Metallurgical bonding includes welding, pressure welding, and brazing. Welding includes, for example, arc welding, electron beam welding, gas welding, and laser welding. Pressure welding includes, for example, ultrasonic welding, friction welding, and diffusion welding. Brazing includes, for example, soldering. Mechanical bonding includes, for example, riveting, caulking, bolting, shrink fitting, and folding. Chemical bonding includes, for example, adhesive bonding.

[0052] The metal foil 3 has a portion that overlaps with the opening 203 of the end 200 of the current collector 20 when joined to the end 200. Hereinafter, the portion of the metal foil 3 that overlaps with the opening 203 of the end 200 of the current collector 20 will be referred to as the tab bonding region 30. The metal foil 3 can be bonded to the metal layer 202 in the end 200 of the current collector 20 in a portion other than the tab bonding region 30. Furthermore, the metal foil 3 is bonded to an electrode tab 4, which will be described next, in the tab bonding region 30.

[0053] For convenience of explanation, the electrode sheet 2 and the metal foil 3 are described as separate components in this disclosure, but this is not limiting. For example, the electrode sheet 2 and the metal foil 3 described in this disclosure may be collectively referred to as an "electrode sheet."

[0054] <Electrode Tab 4> The electrode tab 4 may be a component for supplying power stored in the active material layer 21 to an external electric circuit or the like via the metal foil 3 and the metal layer 202 bonded to the metal foil 3. The electrode tab 4 may also be a component for transmitting power supplied from an external electric circuit or the like to the active material layer 21 via the metal foil 3 and the metal layer 202 bonded to the metal foil 3. When a laminate including multiple electrode sheets 2 and multiple metal foils 3 is housed inside a housing (pouch), a portion of the electrode tab 4 may be exposed from the housing. An external electric circuit or the like may be connected to the exposed portion.

[0055] As described above, the electrode tab 4 is bonded to the metal foil 3 at the tab bonding region 30. In one embodiment, the electrode tab 4 is not bonded directly to the metal layer 202a, but is electrically connected to the metal layer 202a via the metal foil 3.

[0056] [Configuration of End 200 of Current Collector 20] The end 200 of the current collector 20 will be described in more detail with reference to Figures 2-4. Figure 2A shows a top view of the secondary battery 1 of Figure 1 when viewed from the positive direction of the z-axis. The end 200 extends in the positive direction of the y-axis from the main body, which is the portion of the current collector 20 where the active material layer 21a is provided. A metal foil 3 is joined to the positive side of the z-axis of the end 200 of the current collector 20. An electrode tab 4 is joined to the positive side of the metal foil 3 in the positive direction of the z-axis.

[0057] FIG. 2B shows a cross-sectional view of the α-α cross section of FIG. 2A. The α-α cross section is a cross section passing through the opening 203 of the end 200 of the current collector 20. FIG. 2C shows a cross-sectional view of the β-β cross section of FIG. 2A. The β-β cross section is a cross section that does not pass through the opening 203 of the end 200 of the current collector 20. As described with reference to FIG. 1, the opening 203 of the end 200 of the current collector 20 in this example is configured in a U-shape. Therefore, the length of the end 200 in the y-axis direction in FIG. 2B is shorter than the length of the end 200 in the y-axis direction in FIG. 2C by the length of the opening 203 in the y-axis direction.

[0058] 3A is an enlarged top view showing the periphery of end 200 of current collector 20. In one embodiment, opening 203 has an open end at end 200 of current collector 20 as shown in FIG. 3A.

[0059] Fig. 3B shows a top view of a case where a metal foil 3 is bonded to the positive z-axis side of the end 200 in Fig. 3A. The metal foil 3 has a tab bonding region 30 that overlaps with the opening 203 when bonded to the end 200 of the current collector 20. Fig. 3C shows a top view of a case where an electrode tab 4 is bonded to the positive z-axis side of the metal foil 3 in Fig. 3B. The electrode tab 4 is bonded to the metal foil 3 at the tab bonding region 30 of the metal foil 3.

[0060] FIG. 3D is a see-through view of the metal foil 3 in FIG. 3C . The metal foil 3 has a preliminary joining mark 31a and a preliminary joining mark 31b resulting from joining to the end 200 of the current collector 20. Hereinafter, when the preliminary joining mark 31a and the preliminary joining mark 31b are not particularly distinguished from each other or when they are referred to collectively, they will be referred to as the preliminary joining mark 31. The "preliminary" in the preliminary joining mark 31 comes from the fact that, in one embodiment, the metal foil 3 is joined to the end 200 of the current collector 20 before the electrode tab 4. In FIG. 3D , the preliminary joining mark 31 is formed over a portion of the periphery of the tab joining region 30. Note that the "periphery of the tab joining region 30" may refer to at least a portion of the metal foil 3 excluding the tab joining region 30. The preliminary joining mark 31 may be formed along the circumferential direction of the periphery of the tab joining region 30.

[0061] The metal foil 3 also has a tab bonding mark 32 formed by bonding with the electrode tab 4. The tab bonding mark 32 can be provided inside (i.e., on the negative y-axis side) the tip of the end 200 of the current collector 20 in the positive y-axis direction.

[0062] In one embodiment, the tab bonding marks 32 may be formed at positions that do not interfere with the preliminary bonding marks 31. It can also be said that the tab bonding marks 32 are formed at positions that do not overlap at least a portion of the preliminary bonding marks 31.

[0063] 3A-3C illustrate a portion of the manufacturing process for the secondary battery 1. Specifically, the manufacturing process for the secondary battery 1 may include the following steps (1)-(3) performed in order. Note that this order is merely an example, and the order may be changed as appropriate within the scope of technical inconsistency. (1) An electrode sheet 2 is manufactured including a current collector 20 having an opening 203 formed in the end 200 (see FIG. 3A). (2) A metal foil 3 is bonded to the end 200 of the current collector 20 so as to overlap the opening 203 of the end 200 (see FIG. 3B). This forms a preliminary bonding mark 31 on the metal foil 3 (see FIG. 3D). (3) An electrode tab 4 is bonded in a tab bonding region 30 where the metal foil 3 and the opening 203 overlap (see FIG. 3C). This forms a tab bonding mark 32 on the metal foil 3 (see FIG. 3D).

[0064] By joining the metal foil 3 to the end 200 of the current collector 20 at two or more locations, even if one location is damaged, the metal foil 3 and the end 200 of the current collector 20 can be electrically connected at other locations. In other words, the configuration in which the metal foil 3 is joined to the end 200 of the current collector 20 at two or more locations can improve the availability of the secondary battery 1.

[0065] The metal foil 3 also has a tab joining mark 32 between the preliminary joining mark 31a and the preliminary joining mark 31b. That is, the electrode tab 4 is joined to the metal foil 3 in the region between the preliminary joining mark 31a and the preliminary joining mark 31b. This configuration can prevent damage to the secondary battery 1. The reason for this will be explained below.

[0066] The electrode tab 4 can be joined to the metal foil 3 by a method of applying pressure, such as ultrasonic bonding. At this time, heat may be generated between the electrode tab 4 and the metal foil 3. Such pressure and heat may cause the metal foil 3 to peel off from the end 200 of the current collector 20. In contrast, by joining the electrode tab 4 to the metal foil 3 between the preliminary joining marks 31a and 31b, such pressure and heat are efficiently dispersed. This can suppress damage to the secondary battery 1 and improve availability.

[0067] FIG. 4A shows an enlarged cross section of the preliminary bonding mark 31. In one embodiment, the current collector 20 has, in a cross section including the preliminary bonding mark 31, a recessed region from the metal layer 202b to which the metal foil 3 is not bonded to the metal layer 202a to which the metal foil 3 is bonded. Such preliminary bonding mark 31 can be formed by applying pressure in a direction from the metal layer 202b to the metal layer 202a. That is, the metal foil 3 can be bonded by applying pressure in a direction from the metal layer 202b of the end 200 to the metal layer 202a while the metal foil 3 and the end 200 of the current collector 20 are overlapping. The preliminary bonding mark 31 having the shape shown in FIG. 4A can be formed as a result. In one embodiment, the preliminary bonding mark 31 is formed by pressing an ultrasonic bonding horn from the surface of the metal layer 202b toward the surface of the metal layer 202a. At this time, the metal layer 202a on the opposite side to the metal layer 202b may be deformed due to manufacturing reasons (for example, pressure applied by an anvil corresponding to the horn, etc.).

[0068] In this way, by applying pressure from the side where the metal foil 3 is not bonded to the metal layer 202a, the yield during the production of the electrode sheet 2 can be improved. For example, if an ultrasonic bonding horn is pressed against the metal foil 3, the adhesive strength between the horn and the metal foil 3 may exceed the adhesive strength between the metal foil 3 and the metal layer 202a. This is thought to be because a large amount of heat is generated between the horn and the metal foil 3 during ultrasonic bonding. In such a case, the bond between the metal foil 3 and the metal layer 202a may peel off when the horn is removed from the metal foil 3. In contrast, if the horn is pressed against the metal layer 202b from above, heat generation is relatively suppressed, and therefore peeling of the bond when the horn is removed can be suppressed.

[0069] The current collector 20 has a region AR1 in which the metal layer 202a and the metal layer 202b are integrated in a cross section including the preliminary joining mark 31. In one embodiment, in the region AR1, the metal foil 3, the metal layer 202a, and the metal layer 202b are fused by ultrasonic joining. This allows the metal foil 3 to be electrically connected to the metal layers 202a and 202b provided on both sides of the resin layer 201 via the region AR1. In other words, in order to extract power from the metal layers 202a and 202b, it is sufficient to connect the metal foil 3 to the electrode tab 4.

[0070] 4B shows an enlarged cross section of the tab bonding mark 32. The metal foil 3 and the electrode tab 4 have an area AR2 where they are integrated in a cross section including the tab bonding mark 32. In one embodiment, the metal foil 3 and the electrode tab 4 are fused in the area AR2 by ultrasonic bonding. Note that although only one metal foil 3 is shown in FIG. 4B, multiple metal foils 3 may be bonded to the electrode tab 4 in a stacked state, as shown in FIG. 1.

[0071] [Layer Structure of Secondary Battery 1] Fig. 5 is a diagram showing an example of a layer structure of the electrode sheet 2, the metal foil 3, and the electrode tab 4. The secondary battery 1 in Fig. 5 includes a positive electrode sheet 2p which is the electrode sheet 2 for the positive electrode, a negative electrode sheet 2n which is the electrode sheet 2 for the negative electrode, a positive electrode metal foil 3p which is the metal foil 3 for the positive electrode, a negative electrode metal foil 3n which is the metal foil 3 for the negative electrode, a positive electrode tab 4p which is the electrode tab 4 for the positive electrode, and a negative electrode tab 4n which is the electrode tab 4 for the negative electrode.

[0072] The positive electrode sheet 2p includes a positive electrode current collector 20p, a positive electrode active material layer 21ap, and a positive electrode active material layer 21bp. Hereinafter, when there is no particular distinction between the positive electrode active material layer 21ap and the positive electrode active material layer 21bp or when they are referred to collectively, they will be referred to as the positive electrode active material layer 21p.

[0073] Similarly, the negative electrode sheet 2n includes a negative electrode current collector 20n, a negative electrode active material layer 21an, and a negative electrode active material layer 21bn. Hereinafter, when there is no particular distinction between the negative electrode active material layer 21an and the negative electrode active material layer 21bn or when they are referred to collectively, they will be referred to as the negative electrode active material layer 21n.

[0074] The bonding between the positive electrode sheet 2p and the positive electrode metal foil 3p and the bonding between the negative electrode sheet 2n and the negative electrode metal foil 3n may be similar to the bonding between the electrode sheet 2 and the metal foil 3 described above. The bonding between the positive electrode tab 4p and the positive electrode metal foil 3p and the bonding between the negative electrode tab 4n and the negative electrode metal foil 3n may be similar to the bonding between the electrode tab 4 and the metal foil 3 described above. The dotted arrows in FIG. 5 indicate an example of the bonding relationship between each component. Specifically, the positive electrode tab 4p is bonded to the multiple positive electrode metal foils 3p but is not directly bonded to the positive electrode current collector 20p. The multiple positive electrode metal foils 3p are each bonded to the positive electrode current collector 20p. Similarly, the negative electrode tab 4n is bonded to the multiple negative electrode metal foils 3n but is not directly bonded to the negative electrode current collector 20n. The multiple negative electrode metal foils 3n are each bonded to the negative electrode current collector 20n.

[0075] A separator 5 is disposed between the positive electrode sheet 2p and the negative electrode sheet 2n. The separator 5 physically and / or electrically isolates the positive electrode sheet 2p and the negative electrode sheet 2n and ensures ionic conductivity of lithium ions. In one embodiment, the separator 5 may be at least one selected from the group consisting of an insulating porous material, a polymer electrolyte, a gel electrolyte, and an inorganic solid electrolyte. The separator 5 may be formed of one material alone or a combination of two or more materials.

[0076] When the separator 5 includes an insulating porous member, the pores of the porous member are filled with an ion-conductive substance (such as an electrolytic solution, a polymer electrolyte, and / or a gel electrolyte). This allows the separator 5 to exhibit ion conductivity. The material constituting the insulating porous member is not particularly limited, and examples thereof include insulating polymer materials, specifically polyethylene (PE) and polypropylene (PP). That is, the separator 5 may be a porous polyethylene (PE) film, a porous polypropylene (PP) film, or a laminate structure thereof.

[0077] In one embodiment, one or both surfaces of the separator 5 may be coated with a separator coating layer. This may improve the cycle characteristics of the secondary battery 1. In one embodiment, the separator coating layer may be a continuous film with a uniform thickness over 50% or more of the surface area of ​​the separator 5. In one embodiment, the separator coating layer may include a binder such as polyvinylidene fluoride (PVDF), a mixture of styrene butadiene rubber and carboxymethyl cellulose (SBR-CMC), and polyacrylic acid (PAA). In one embodiment, the separator coating layer may be formed by adding inorganic particles such as silica, alumina, titania, zirconia, or magnesium hydroxide to the binder.

[0078] In one embodiment, the average thickness of the separator 5 (including the coating layer if the separator 5 includes the coating layer) may be 3.0 μm or more and 40 μm or less. This can reduce the volume occupied by the separator 5 while isolating the positive electrode sheet 2p and the negative electrode sheet 2n. In one embodiment, the average thickness of the separator 5 may be 5.0 μm or more and 30 μm or less, 7.0 μm or more and 10 μm or less, or 10 μm or more and 20 μm or less.

[0079] The manufacturing process of the secondary battery 1 may include the following steps (1) to (5) performed in order. Note that this order is merely an example, and the order may be changed as appropriate within the scope of technical consistency. (1) Bonding a positive electrode metal foil 3p to each of the multiple positive electrode sheets 2p (see FIG. 3B). (2) Bonding a negative electrode metal foil 3n to each of the multiple negative electrode sheets 2n (see FIG. 3B). (3) Stacking the multiple members manufactured in (1) and the multiple members manufactured in (2) with a separator 5 disposed therebetween. (4) Bonding a positive electrode tab 4p to the multiple positive electrode metal foils 3p all at once (see FIG. 3C). (5) Bonding a negative electrode tab 4n to the multiple negative electrode metal foils 3n all at once (see FIG. 3C).

[0080] 5 illustrates an example in which the positive electrode tab 4p faces in the positive direction of the y-axis and the negative electrode tab 4n faces in the negative direction of the y-axis, but this is not limiting. The secondary battery 1 may be configured so that the positive electrode tab 4p and the negative electrode tab 4n face in the positive direction of the y-axis (or the negative direction of the y-axis). In this case, the positive electrode tab 4p and the negative electrode tab 4n are arranged side by side along the x-axis direction.

[0081] [Method of Using the Secondary Battery 1] The secondary battery 1 is charged and discharged by connecting the positive electrode tab 4p to one end of an external circuit and the negative electrode tab 4n to the other end of an external circuit. The external circuit may be, for example, a resistor, a power source, an apparatus, a device, another battery, or a potentiostat.

[0082] When a voltage is applied between the positive electrode tab 4p and the negative electrode tab 4n such that a current flows from the negative electrode tab 4n through an external circuit to the positive electrode tab 4p, the secondary battery 1 is charged. When the positive electrode tab 4p and the negative electrode tab 4n of the charged secondary battery 1 are connected via a desired external circuit, the secondary battery 1 is discharged.

[0083] [Effects of Secondary Battery 1] The secondary battery 1 of this embodiment can achieve both high safety and low electrical resistance. Because the current collector 20 includes the resin layer 201, as described above, high safety can be achieved even in the event of overcharging, short circuiting, and the like. However, if the electrode tab 4 were to be bonded to a portion of the current collector 20 including the resin layer 201, a relatively large amount of molten resin would be present at the bonded portion, potentially increasing the electrical resistance of the secondary battery 1. In contrast, the electrode tab 4 of the secondary battery 1 is bonded to the metal foil 3 and is electrically connected via the AR2 of the tab bonding mark 32. The metal foil 3 is bonded to the end 200 of the current collector 20 and is electrically connected to the metal layers 202 on both sides of the current collector 20 through the region AR1 of the preliminary bonding mark 31. As a result, the electrical path from the electrode tab 4 to the metal layer 202 of the secondary battery 1 does not contain resin (or contains only a small amount of resin), thereby reducing the electrical resistance of the secondary battery 1.

[0084] [Other Configurations] The secondary battery 1 may have configurations different from or additional to those of the secondary battery 1 described in the above embodiment.

[0085] <Configuration of Preliminary Joining Mark 31 in Metal Foil 3> In the above embodiment, the metal foil 3 has been described as having two preliminary joining marks 31a and 31b, but this is not limited thereto. The number of preliminary joining marks 31 may be any number, and the shape in plan view may also be any shape. An example is shown with reference to FIG. 6 . FIG. 6A shows an example in which, in addition to the preliminary joining marks 31a and 31b, a preliminary joining mark 31c is formed in the negative y-axis direction of the tab joining mark 32. FIG. 6B shows an example in which a U-shaped preliminary joining mark 31 is formed to surround the tab joining mark 32. FIG. 6C shows an example in which one preliminary joining mark 31 is formed in the negative y-axis direction of the tab joining mark 32.

[0086] <Configuration of Opening 203> In the above embodiment, the end 200 of the current collector 20 has been described as having a U-shaped opening 203, but this is not limited thereto. Referring to FIG. 7 , other examples of the opening 203 are shown. FIG. 7A shows an example in which the end 200 of the current collector 20 has a square-shaped opening 203, and the preliminary joining marks 31 a and 31 b are formed on both sides of the opening in the x-axis direction. FIG. 7B shows an example in which the end 200 of the current collector 20 has a square-shaped opening 203, and the preliminary joining marks 31 are formed around the entire periphery of the opening. FIG. 7C shows an example in which the end 200 of the current collector 20 has an oval-shaped opening 203, and the U-shaped preliminary joining marks 31 a and 31 b are formed on both sides of the opening in the x-axis direction. FIG. 7D shows an example in which the end 200 of the current collector 20 has a semicircular opening 203, and the preliminary joining marks 31 a and 31 b are formed on both sides of the opening in the y-axis direction.

[0087] <Configuration Regarding the Number of Metal Foils 3> In the above embodiment, an example in which one metal foil 3 is bonded to one electrode sheet 2 has been described, but this is not limiting. Specifically, the metal foil 3 may be bonded not only to the metal layer 202a but also to the metal layer 202b. This allows two (or more) metal foils 3 to be bonded to one electrode sheet 2. In this case, the metal foil 3 bonded to the metal layer 202a may be bonded by applying pressure in a direction from the metal layer 202b toward the metal layer 202a, and the metal foil 3 bonded to the metal layer 202b may be bonded by applying pressure in a direction from the metal layer 202a toward the metal layer 202b (see FIG. 4A ). This configuration can further improve the availability of the secondary battery 1.

[0088] <Configuration Related to the Direction in Which the Current Collector 20 is Depressed> In the above embodiment, the current collector 20 has been described as having a region in a cross section including the preliminary joining mark 31 that is recessed from the metal layer 202b to which the metal foil 3 is not bonded to the metal layer 202a to which the metal foil 3 is bonded, but this is not limited to this. The current collector 20 may have a region in a cross section including the preliminary joining mark 31 that is recessed from the metal layer 202a to the metal layer 202b. That is, in the above embodiment, an example has been shown in which the preliminary joining mark 31 is recessed toward the positive direction of the z axis, but the preliminary joining mark 31 may be recessed toward the negative direction of the z axis.

[0089] Similarly, in the above embodiment, the current collector 20 has been described as having a region recessed from the metal layer 202b, to which the electrode tab 4 and the metal foil 3 are not bonded, to the metal layer 202a, to which the electrode tab 4 and the metal foil 3 are bonded, in a cross section including the tab bonding mark 32, but this is not limited thereto. The current collector 20 may have a region recessed from the metal layer 202a to the metal layer 202b in a cross section including the tab bonding mark 32. That is, in the above embodiment, an example has been shown in which the tab bonding mark 32 is recessed toward the positive direction of the z axis, but the tab bonding mark 32 may be recessed toward the negative direction of the z axis.

[0090] <Configuration of Active Material Layer 21> In one embodiment, the active material layer 21 may contain a gel electrolyte. The gel electrolyte can improve the adhesive strength between the active material layer 21 and the current collector 20. In one example, the gel electrolyte contains a polymer, an organic solvent, and a lithium salt. The polymer in the gel electrolyte may be, for example, a copolymer of polyethylene and / or polyethylene oxide, polyvinylidene fluoride, or a copolymer of polyvinylidene fluoride and hexafluoropropylene.

[0091] In one embodiment, the active material layer 21 may include a polymer electrolyte. For example, the polymer electrolyte may be a solid polymer electrolyte primarily containing a polymer and an electrolyte, or a semi-solid polymer electrolyte primarily containing a polymer, an electrolyte, and a plasticizer. In one embodiment, the total content of the polymer electrolyte may be 0.5% by mass to 30% by mass or less with respect to the entire positive electrode active material layer 21p.

[0092] In one embodiment, the active material layer 21 may contain a binder. For example, the binder is polyvinylidene fluoride, polytetrafluoroethylene, styrene butadiene rubber, an acrylic resin, a polyimide resin, or the like. In one embodiment, the content of the conductive additive is 0.5% by mass to 30% by mass or less with respect to the entire active material layer 21. In one embodiment, the content of the binder may be 0.5% by mass to 30% by mass or less with respect to the entire active material layer 21.

[0093] In one embodiment, the positive electrode active material layer 21p may include a sacrificial positive electrode material, which is a lithium-containing compound that undergoes an oxidation reaction and does not substantially undergo a reduction reaction in the charge / discharge potential range of the positive electrode active material.

[0094] In one embodiment, the positive electrode active material layer 21p may include a conductive additive, such as carbon black, single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), or carbon nanofibers (CFs).

[0095] <Configuration Related to Electrolyte Solution> In one embodiment, the secondary battery 1 may contain an electrolytic solution. The electrolytic solution is a liquid containing a solvent and an electrolyte, and has ion conductivity. The electrolytic solution may also be referred to as a liquid electrolyte, and acts as a conductive path for lithium ions. Therefore, when the secondary battery 1 contains an electrolytic solution, the internal resistance can be reduced, and the energy density, capacity, and cycle characteristics can be improved.

[0096] The electrolytic solution may be, for example, a solution that fills the housing (pouch) of the secondary battery 1. Furthermore, for example, the electrolytic solution may be impregnated into the separator 5, or may be held in a polymer to form a polymer electrolyte or a gel electrolyte.

[0097] The electrolyte contained in the electrolytic solution may be, for example, a lithium salt, which may be, for example, one or a combination of two or more selected from the group consisting of LiI, LiCl, LiBr, LiF, LiBF, LiPF, LiAsF, LiSOCF, LiN(SOF), LiN(SOCF), LiN(SOCFCF), LiB(OCOH), LiB(COOH), LiB(OCOH)F, LiB(OCOCF), LiNO, and LiSO.

[0098] The solvent contained in the electrolytic solution may be, for example, a non-aqueous solvent containing fluorine atoms (hereinafter referred to as a "fluorinated solvent") or a non-aqueous solvent containing no fluorine atoms (hereinafter referred to as a "non-fluorinated solvent").

[0099] The fluorinated solvent may be, for example, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, and 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether.

[0100] The fluorine-free solvent may be, for example, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,2-dimethoxyethane, dimethoxyethane, dimethoxypropane, dimethoxybutane, diethylene glycol dimethyl ether, acetonitrile, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, chloroethylene carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, trimethyl phosphate, triethyl phosphate, and 12-crown-4.

[0101] The above fluorinated solvents and / or non-fluorinated solvents may be used alone or in any combination of two or more in any ratio. The contents of the fluorinated solvent and non-fluorinated solvent are not particularly limited, and the ratio of the fluorinated solvent to the total solvent may be 0 to 100% by volume, or the ratio of the non-fluorinated solvent to the total solvent may be 0 to 100% by volume.

[0102] <Configuration of Negative Electrode Sheet 2n> In the above embodiment, the negative electrode sheet 2n is described as including the negative electrode active material layer 21n, but this is not limited thereto. The negative electrode sheet 2n may be substantially free of negative electrode active material.

[0103] In one embodiment, the negative electrode sheet 2n does not have a negative electrode active material before the initial charge of the battery (the state from the assembly of the battery until the first charge). After the initial charge, the secondary battery 1 may be charged and discharged by depositing lithium metal on the negative electrode and electrolytically dissolving the deposited lithium metal. In this case, the volume and mass occupied by the negative electrode active material are reduced, the volume and mass of the entire battery are reduced, and the energy density is, in principle, increased. Note that "lithium metal deposited on the negative electrode" not only refers to lithium metal being deposited on the surface of the negative electrode, but also includes lithium metal being deposited on the surface of a solid electrolyte interface (SEI) layer or on or inside a buffer functional layer, which will be described later.

[0104] In one embodiment, the thickness of the layer of negative electrode active material deposited on the negative electrode sheet 2n at the end of discharge (e.g., when the open circuit voltage of the battery is 2.5 V or more and 3.6 V or less) is 25 μm or less. In one embodiment, the thickness of the layer of negative electrode active material at the end of discharge may be 20 μm or less, 15 μm or less, 10 μm or less, or 5 μm or less, or may even be 0 μm. Since the negative electrode sheet 2n is substantially free of negative electrode active material, the energy density per volume can be improved in addition to the weight energy density. In this case, the secondary battery 1 can also be called an "anode-free lithium battery," a "zero anode lithium battery," or an "anodeless lithium battery."

[0105] In one embodiment, the mass of lithium metal deposited on the negative electrode when the voltage is 4.2 V is M ４．２ The same mass at a voltage of 3.0 V is M ３．０ In this case, M ３．０ / M ４．２ may be 40% or less, or 35% or less. ３．０ / M ４．２ may be 1.0% or more, 2.0% or more, 3.0% or more, or 4.0% or more.

[0106] [Examples] Next, examples and comparative examples will be described. The present disclosure is not limited in any way by the following examples and comparative examples.

[0107] Table 1 shows examples and comparative examples of the secondary battery 1. Examples A and C show data relating to the secondary battery 1 configured by laminating a positive electrode sheet 2p including a positive electrode current collector 20p whose metal layer 202 is made of aluminum with a thickness of 1 μm and whose resin layer 201 is made of PET with a thickness of 6 μm, and a negative electrode sheet 2n including a negative electrode current collector 20n whose metal layer 202 is made of copper with a thickness of 1 μm and whose resin layer 201 is made of PET with a thickness of 4.5 μm.

[0108] As described with reference to Figures 3A to 3D, the current collector 20 of Example A has a U-shaped opening 203 at the end 200, and is joined to the metal foil 3 at two locations. The electrode tab 4 is joined to the metal foil 3 in the tab joining region 30. At this time, the electrode tab 4 is joined to the metal foil 3 so that a tab joining mark 32 is formed between two preliminary joining marks 31.

[0109] In the current collector 20 of Example C, the U-shaped opening 203 of Example A was changed to a square-shaped opening 203 as described with reference to Fig. 7A. In Example C, as in Example A, the electrode tab 4 was joined to the tab joining region 30 of the metal foil 3 so that the tab joining mark 32 was formed between the two preliminary joining marks 31.

[0110] In comparison with Examples A and C, Examples B and D show data in which the resin layer 201 of the negative electrode sheet 2n was changed from PET to PP.

[0111] The comparative example is data for a case where the end 200 of the current collector 20 does not have the opening 203, as compared with examples B and D. The configuration of the secondary battery 1 according to the comparative example will be described with reference to Fig. 8. Note that the same reference numerals as those in the above embodiment are used.

[0112] 8A shows the configuration of the end 200 of the current collector 20 of the secondary battery 1 according to the comparative example. The end 200 of the current collector 20 is joined to the metal foil 3 and is electrically connected via the preliminary joining marks 31. The metal foil 3 is joined to the electrode tab 4 and is electrically connected via the tab joining marks 32. Compared to the secondary battery 1 according to the example (see FIG. 3D ), the secondary battery 1 according to the comparative example does not have an opening 203 provided in the end 200.

[0113] 8B shows a cross-sectional view of the α-α cross section of FIG. 8A. In the secondary battery 1 according to the comparative example, the preliminary joining mark 31 is formed between the metal foil 3 and the end 200 of one current collector 20 to which the metal foil 3 is joined. In addition, the tab joining mark 32 is formed between the electrode tab 4 and the plurality of metal foils 3 joined to the electrode tab 4.

[0114] For Examples A to D and the Comparative Example, the cell capacity was 8.6 Ah, the applied current was 34.4 A (equivalent to 4 C), and the secondary battery 1 was housed in a housing except for a part of the electrode tab 4. Under these conditions, the temperature of the portion on the surface of the housing of the secondary battery 1 corresponding to the tab joining mark 32 of the positive electrode tab 4 p (the temperature at the base of the positive electrode tab 4 p) was measured.

[0115]

[0116] In Example A, the root temperature of the positive electrode tab 4p was 51 degrees. In Example B, the root temperature of the positive electrode tab 4p was 50 degrees. In Example C, the root temperature of the positive electrode tab 4p was 53 degrees. In Example D, the root temperature of the positive electrode tab 4p was 52 degrees. In contrast to these Examples, in the Comparative Example, the root temperature of the positive electrode tab 4p was 71 degrees. This result shows that in Examples A-D, the rise in the root temperature of the electrode tab 4 is suppressed compared to the Comparative Example. By suppressing the rise in the root temperature, damage to the secondary battery 1 is suppressed. Therefore, according to the present disclosure, a secondary battery 1 with high availability can be provided.

[0117] [Embodiments of the Present Disclosure] The embodiments of the present disclosure further include the following aspects.

[0118] (Supplementary Note 1) A secondary battery 1 includes: a current collector 20 including an active material layer 21; a resin layer 201; and a pair of metal layers 202 provided on both sides of the resin layer 201, the current collector 20 including a main body on which the active material layer 21 is provided and an end portion 200 extending from the main body, the end portion 200 including an opening 203; a metal foil 3 joined to at least one of the pair of metal layers 202 at the end portion 200 of the current collector 20, the metal foil 3 including a tab bonding region 30 overlapping with the opening 203 in a plan view; and an electrode tab 4 joined to the metal foil 3 at at least a part of the tab bonding region 30.

[0119] (Supplementary Note 2) The secondary battery 1 according to Supplementary Note 1, wherein the metal foil 3 has a first joining mark (preliminary joining mark 31) formed by joining to at least one of the pair of metal layers 202 of the current collector 20.

[0120] (Supplementary Note 3) The secondary battery 1 according to Supplementary Note 2, wherein the metal foil 3 further includes a second joining mark (tab joining mark 32) formed by joining with the electrode tab 4.

[0121] (Appendix 4) The secondary battery 1 according to Appendix 3, wherein the metal foil 3 has two first bonding marks (preliminary bonding marks 31) and a second bonding mark (tab bonding mark 32) between the two first bonding marks (preliminary bonding marks 31) in a plan view.

[0122] (Supplementary Note 5) The secondary battery 1 according to any one of Supplementary Notes 2 to 4, wherein the metal foil 3 has a first bonding mark (preliminary bonding mark 31) over at least a part of the periphery of the tab bonding region 30.

[0123] (Supplementary Note 6) The secondary battery 1 according to Supplementary Note 5, wherein the metal foil 3 has a first bonding mark (preliminary bonding mark 31) along the entire periphery of the tab bonding region 30.

[0124] (Supplementary Note 7) The secondary battery 1 according to any one of Supplementary Notes 1 to 6, wherein the opening 203 has an open end at the end 200 of the current collector 20.

[0125] (Supplementary Note 8) The secondary battery 1 according to any one of Supplementary Notes 1 to 7, wherein the opening 203 is configured to have a substantially polygonal shape in a plan view.

[0126] (Supplementary Note 9) The secondary battery 1 according to Supplementary Note 8, wherein the opening 203 is configured to have a substantially rectangular shape in a plan view.

[0127] (Supplementary Note 10) The secondary battery 1 according to any one of Supplementary Notes 1 to 7, wherein the opening 203 is configured to have a substantially semicircular, substantially elliptical, or substantially circular shape in a plan view.

[0128] (Appendix 11) The secondary battery 1 according to any one of Appendices 2 to 10, wherein the current collector 20 has a region that is recessed in a direction from one metal layer 202b to the other metal layer 202a of the pair of metal layers 202 in a cross section including the first bonding mark (preliminary bonding mark 31).

[0129] (Supplementary Note 12) The secondary battery 1 according to Supplementary Note 11, wherein the current collector 20 includes an area AR1 where the pair of metal layers 202 are integrated in a cross section including the first joining mark (preliminary joining mark 31).

[0130] (Appendix 13) The secondary battery 1 according to appendix 12, wherein the metal foil 3 is bonded to the other metal layer 202a.

[0131] (Appendix 14) The secondary battery 1 according to any one of Appendices 2 to 13, wherein the first joining mark (preliminary joining mark 31) is a welding mark.

[0132] (Appendix 15) The secondary battery 1 according to any one of Appendices 3 to 14, wherein the second joining mark (tab joining mark 32) is a welding mark.

[0133] (Appendix 16) The secondary battery 1 according to any one of Appendices 1 to 15, wherein the pair of metal layers 202 each have a thickness of 1.0 μm or more and 15 μm or less, and the resin layer 201 has a thickness of 2 μm or more and 15 μm or less.

[0134] (Supplementary Note 17) The secondary battery 1 according to any one of Supplementary Notes 1 to 16, wherein the active material layer 21 is configured to contain a positive electrode active material, and the pair of metal layers 202 are each configured to contain aluminum.

[0135] (Supplementary Note 18) The secondary battery 1 according to any one of Supplementary Notes 1 to 17, wherein the active material layer 21 is configured to contain a negative electrode active material, and the pair of metal layers 202 are each configured to contain copper.

[0136] (Supplementary Note 19) The secondary battery 1 according to any one of Supplementary Notes 1 to 18, wherein the resin layer 201 contains at least one of polyethylene terephthalate and polypropylene.

[0137] DESCRIPTION OF SYMBOLS 1...Secondary battery, 2...Electrode sheet, 2n...Negative electrode sheet, 2p...Positive electrode sheet, 3...Metal foil, 3n...Negative electrode metal foil, 3p...Positive electrode metal foil, 4...Electrode tab, 4n...Negative electrode tab, 4p...Positive electrode tab, 5...Separator, 20...Current collector, 20n...Negative electrode current collector, 20p...Positive electrode current collector, 21...Active material layer, 21n...Negative electrode active material layer, 21p...Positive electrode active material layer, 30...Tab bonding region, 31...Preliminary bonding marks, 31a, 31b, 31c...Preliminary bonding marks, 32...Tab bonding marks, 200...End, 201...Resin layer, 202, 202a, 202b...Metal layer, 203...Opening, AR1, AR2...Region

Claims

1. A secondary battery comprising: a current collector having an active material layer, a resin layer, and a pair of metal layers provided on both sides of the resin layer, the current collector having a main body on which the active material layer is provided and an end portion extending from the main body, the end portion having an opening; a metal foil joined to at least one of the pair of metal layers at the end portion of the current collector, the metal foil having a tab bonding region that overlaps the opening in a plan view; and an electrode tab joined to the metal foil in at least a part of the tab bonding region.

2. The secondary battery according to claim 1, wherein the metal foil has a first bonding mark formed by bonding to at least one of the pair of metal layers of the current collector.

3. The secondary battery according to claim 2, wherein the metal foil further comprises a second bonding mark formed by bonding to the electrode tab.

4. The secondary battery according to claim 3, wherein the metal foil has two of the first bonding marks and the second bonding mark is located between the two first bonding marks in a plan view.

5. The secondary battery according to claim 2, wherein the metal foil has the first bonding mark over at least a portion of the periphery of the tab bonding area.

6. The secondary battery according to claim 5, wherein the metal foil has the first bonding mark around the entire periphery of the tab bonding area.

7. The secondary battery according to claim 1, wherein said opening has an open end at said end of said current collector.

8. The secondary battery according to claim 1, wherein the opening is configured in a substantially polygonal shape in a plan view.

9. The secondary battery according to claim 8, wherein the opening is configured to be substantially rectangular in plan view.

10. The secondary battery according to claim 1, wherein the opening is configured to be approximately semicircular, approximately elliptical, or approximately circular in plan view.

11. The secondary battery according to claim 2, wherein the current collector has a region recessed in a direction from one metal layer toward the other metal layer of the pair of metal layers in a cross section including the first bonding mark.

12. The secondary battery according to claim 11, wherein the current collector has a region where the pair of metal layers are integrated in a cross section including the first bonding mark.

13. The secondary battery according to claim 12, wherein the metal foil is bonded to the other metal layer.

14. The secondary battery according to claim 2, wherein the first joining mark is a welding mark.

15. The secondary battery according to claim 3, wherein the second joining mark is a welding mark.

16. The secondary battery according to claim 1, wherein each of the pair of metal layers has a thickness of 1.0 μm or more and 15 μm or less, and the resin layer has a thickness of 2 μm or more and 15 μm or less.

17. The secondary battery according to claim 1, wherein the active material layer contains a positive electrode active material, and the pair of metal layers each contain aluminum.

18. The secondary battery according to claim 1, wherein the active material layer contains a negative electrode active material, and the pair of metal layers each contain copper.

19. The secondary battery according to claim 1, wherein the resin layer contains at least one of polyethylene terephthalate and polypropylene.

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