Electrode plate, energy storage device, and method for manufacturing electrode plate

Abstract

This electrode plate 11 comprises: a current collector 34 having a first surface 34a and a second surface; a first electrode active material layer 36 provided on the first surface 34a; and a second electrode active material layer provided on the second surface. The current collector 34 has a first exposed part 40 on the first surface 34a and a second exposed part 42 on the second surface. The first exposed part 40 and the second exposed part 42 are both band-shaped, extending in a longitudinal direction B of the current collector 34 at an end part of the current collector 34 in a transverse direction A. When viewed from a direction C in which the first surface 34a and the second surface overlap, the second exposed part 42 is wider in the transverse direction A than the first exposed part 40, and the entire first exposed part 40 overlaps the second exposed part 42. The end part of the current collector 34 is bent so that the second exposed part 42 is on the inner side and the first exposed part 40 is on the outer side.

Description

Electrode Plate, Power Storage Device, and Method for Manufacturing Electrode Plate

[0001] The present disclosure relates to an electrode plate, a power storage device, and a method for manufacturing an electrode plate.

[0002] Conventionally, a battery in which a wound electrode group and an electrolytic solution are housed in a cylindrical exterior can is known. Regarding such a power storage device, Patent Document 1 describes a method in which an exposed portion of a core body, that is, a current collector, in an electrode is bent to form a flat surface, and a current collecting plate is welded to this flat surface.

[0003] Japanese Patent Application Laid-Open No. 2008-166030

[0004] As a result of intensive studies on an electrode plate that uses an exposed portion of a current collector by bending it, the present inventor has found that there is room for improving the quality of a conventional electrode plate.

[0005] The present disclosure has been made in view of such a situation, and one of its objects is to provide a technique for improving the quality of an electrode plate.

[0006] One aspect of the present disclosure is an electrode plate. This electrode plate includes a strip-shaped current collector having a first surface and a second surface facing each other, a first electrode active material layer provided on the first surface, and a second electrode active material layer provided on the second surface. The current collector has a first exposed portion on the first surface where the first electrode active material layer is not provided, and a second exposed portion on the second surface where the second electrode active material layer is not provided. Both the first exposed portion and the second exposed portion are strip-shaped extending in the longitudinal direction of the current collector at an end portion in the short-hand direction of the current collector. When viewed from the direction in which the first surface and the second surface overlap, the second exposed portion is wider in the short-hand direction than the first exposed portion, and the entire first exposed portion overlaps with the second exposed portion. The end portion of the current collector is bent so that the second exposed portion is on the inner side and the first exposed portion is on the outer side.

[0007] Another aspect of the present disclosure is a power storage device. This power storage device includes the electrode plate of the above aspect.

[0008] Another aspect of the present disclosure is a method for manufacturing an electrode plate. This manufacturing method includes preparing a strip-shaped current collector having a first surface and a second surface facing opposite directions, a strip-shaped first electrode mixture sheet having a narrower width in the short-side direction than the current collector, and a strip-shaped second electrode mixture sheet having a narrower width in the short-side direction than the first electrode mixture sheet, pressing the first electrode mixture sheet onto the first surface to form a first electrode active material layer and a first exposed portion where the first electrode active material layer is not provided, and pressing the second electrode mixture sheet onto the second surface of the current collector on which the first electrode active material layer and the first exposed portion are formed to form a second electrode active material layer and a second exposed portion where the second electrode active material layer is not provided. When viewed from the direction in which the first and second surfaces overlap, the first exposed portion and the second exposed portion are each strip-shaped extending in the longitudinal direction of the current collector at the short-side end of the current collector, with the second exposed portion being wider in the short-side direction of the current collector than the first exposed portion, and the entirety of the first exposed portion overlapping with the second exposed portion.

[0009] Another aspect of the present disclosure is a method for manufacturing an electrode plate. This manufacturing method includes preparing a strip-shaped current collector having a first surface and a second surface facing opposite directions, a strip-shaped first electrode mixture sheet having a narrower width in the short-side direction than the current collector, and a strip-shaped second electrode mixture sheet having a narrower width in the short-side direction than the first electrode mixture sheet, and simultaneously pressing the first electrode mixture sheet onto the first surface and the second electrode mixture sheet onto the second surface, or pressing the second electrode mixture sheet onto the second surface and then pressing the first electrode mixture sheet onto the first surface to form a first electrode active material layer and a first exposed portion where the first electrode active material layer is not provided on the first surface, and forming a second electrode active material layer and a second exposed portion where the second electrode active material layer is not provided on the second surface. Viewed from the direction in which the first and second surfaces overlap, the first exposed portion and the second exposed portion are each strip-shaped extending in the longitudinal direction of the current collector at the short-side end of the current collector, the second exposed portion is wider in the short-side direction of the current collector than the first exposed portion, the entire first exposed portion overlaps with the second exposed portion, and the maximum protrusion amount of the portion of the first electrode active material layer that protrudes onto the second exposed portion is 6 times the cube of the thickness of the current collector or less.

[0010] Any combination of the above components, as well as any conversion of the expressions of this disclosure between methods, apparatus, systems, etc., are also valid forms of this disclosure.

[0011] According to this disclosure, it is possible to improve the quality of electrode plates.

[0012] This is a cross-sectional view of an energy storage device according to an embodiment. This is a perspective view of the electrode group. Figure 3(A) is a schematic diagram of the region including the first exposed portion of the electrode plate as seen from the first surface. Figure 3(B) is a schematic diagram of the region including the second exposed portion of the electrode plate as seen from the second surface. Figures 4(A), 4(B), 4(C), and 4(D) are schematic diagrams for explaining the manufacturing method of the electrode plate according to the embodiment. Figure 4(E) is a schematic diagram for explaining another manufacturing method of the electrode plate. Figure 5(A) is a schematic diagram of a test specimen used in an evaluation test. Figure 5(B) is a diagram showing the relationship between the amount of displacement between two sides and the pressure applied to the ends in various test specimens with different current collector thicknesses. Figure 5(C) is a diagram showing the relationship between the thickness of the current collector and the allowable upper limit of displacement.

[0013] The present disclosure will be described below with reference to the drawings, based on preferred embodiments. The embodiments are illustrative and not limiting, and not all features or combinations thereof described in the embodiments are necessarily essential to the present disclosure. The same or equivalent components, members, and processes shown in each drawing are denoted by the same reference numerals, and redundant descriptions are omitted where appropriate. The scale and shape of each part shown in each drawing are set for convenience to facilitate explanation and are not to be interpreted restrictively unless otherwise specified. Furthermore, where terms such as "first," "second," etc. are used in this specification or claims, unless otherwise specified, these terms do not indicate any order or importance, but are used to distinguish one configuration from another. In addition, some components that are not important for explaining the embodiments are omitted in each drawing.

[0014] Figure 1 is a cross-sectional view of the energy storage device 1 according to an embodiment. Figure 2 is a perspective view of the electrode group 2. Figure 2 shows the state before the end of the current collector 34 is bent. The energy storage device 1 is, for example, a rechargeable secondary battery such as a lithium-ion battery, a nickel-metal hydride battery, or a nickel-cadmium battery, or a capacitor such as an electric double-layer capacitor. The energy storage device 1 comprises the electrode group 2, a first current collector plate 4, a second current collector plate 6, and an outer casing 8.

[0015] Electrode group 2 is, for example, cylindrical, and has a wound structure in which a strip-shaped first electrode plate 10 and a strip-shaped second electrode plate 12 are stacked with a strip-shaped separator 14 in between, and wound in a spiral shape. Therefore, the first electrode plate 10, the second electrode plate 12 and the separator 14 are stacked alternately in the radial direction Y of electrode group 2. In electrode group 2, the longitudinal direction of each electrode plate and separator 14 is the winding direction Z, and the short direction of each electrode plate and separator 14, in other words, the width direction, is the axial direction X. In this embodiment, the first electrode plate 10 is the positive electrode plate and the second electrode plate 12 is the negative electrode plate. However, the first electrode plate 10 may be the negative electrode plate and the second electrode plate 12 may be the positive electrode plate. Furthermore, in the following, when the polarity of the electrode plates is not distinguished, the first electrode plate 10 and the second electrode plate 12 will be collectively referred to as electrode plate 11. The separator 14 is composed of a microporous film having ion permeability and insulating properties, such as polypropylene or polyethylene.

[0016] The electrode plate 11 comprises a current collector 34, a first electrode active material layer 36, and a second electrode active material layer 38. The current collector 34 is made of a strip-shaped metal foil or the like. In the case of a typical lithium-ion secondary battery, the current collector 34 is made of aluminum foil or the like if it is the positive electrode, and copper foil or the like if it is the negative electrode. The first electrode active material layer 36 and the second electrode active material layer 38 can be formed, for example, by pressing a dry electrode mixture sheet onto the surface of the current collector 34. The dry electrode mixture sheet is obtained by forming a dry electrode mixture containing materials such as electrode active material, binder, and conductive material into a sheet. In the case of a typical lithium-ion secondary battery, the electrode active material is lithium cobalt oxide or lithium iron phosphate for the positive electrode, and graphite for the negative electrode. The binder is polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), etc. The conductive material is graphite, carbon black, acetylene black, etc.

[0017] The end of the current collector 34 in the short direction A is bent toward the winding side of the electrode group 2, that is, toward the winding center of the electrode group 2. The short direction A of the current collector 34 coincides with the short direction of the electrode plate 11. The current collector 34 of the first electrode plate 10 and the current collector 34 of the second electrode plate 12 are bent toward opposite ends. Since the electrode group 2 has a structure in which the electrode plate 11 is wound, the ends of the current collector 34 in the short direction A are arranged in multiple places in the radial direction Y of the electrode group 2.

[0018] The bent end of the current collector 34 of the first electrode plate 10 is connected to the first current collector plate 4 by welding or the like. By bending the end, the contact area between the current collector 34 and the first current collector plate 4 can be increased. The bent end of the current collector 34 of the second electrode plate 12 is connected to the second current collector plate 6 by welding or the like. By bending the end, the contact area between the current collector 34 and the second current collector plate 6 can be increased. The first current collector plate 4 and the second current collector plate 6 are arranged so as to sandwich the electrode group 2 in the axial direction X.

[0019] The electrode group 2, to which the first current collector plate 4 and the second current collector plate 6 are joined, is housed in an outer container 8 along with an electrolyte (not shown). The outer container 8 is a bottomed cylindrical metal container. The first current collector plate 4 is positioned on the opening side of the outer container 8. The second current collector plate 6 is positioned on the bottom side of the outer container 8. A sealing body 20 is fitted into the opening of the outer container 8. A gasket 22 is provided between the outer container 8 and the sealing body 20. This seals the electrode group 2, the first current collector plate 4, the second current collector plate 6, and the electrolyte inside the outer container 8.

[0020] The sealing body 20 includes a filter 24, a lower valve body 26, an upper valve body 28, an insulating member 30, and a cap 32. Each component of the sealing body 20 has, for example, a disc shape or a ring shape. In addition, each component except the insulating member 30 is electrically connected to one another. The filter 24 has an opening 24a and covers the opening of the outer can 8. The lower valve body 26 and the upper valve body 28 cover the opening of the outer can 8 and close the opening 24a. The lower valve body 26 and the upper valve body 28 are connected at their respective central portions, with the insulating member 30 interposed between their respective peripheral portions. When the internal pressure of the outer can 8 rises due to heat generation caused by an internal short circuit or the like, for example, the lower valve body 26 may rupture. As a result, the upper valve body 28 bulges towards the cap 32 and separates from the lower valve body 26. Consequently, the electrical connection between the lower valve body 26 and the upper valve body 28 is interrupted. A cap 32 is placed over the outside of the upper valve body 28.

[0021] One end of the lead 16 is connected to the first current collector plate 4 by welding or the like. The other end of the lead 16 is connected to the filter 24 by welding or the like. The cap 32 is electrically connected to the filter 24 to form the first electrode terminal. The second current collector plate 6 is connected to the bottom of the outer can 8 by welding or the like. Therefore, the outer can 8 forms the second electrode terminal.

[0022] Next, the structure of the electrode plate 11 will be described in detail. Figure 3(A) is a schematic diagram of the region of the electrode plate 11 including the first exposed portion 40 as seen from the first surface 34a side. Figure 3(B) is a schematic diagram of the region of the electrode plate 11 including the second exposed portion 42 as seen from the second surface 34b side. The current collector 34 has a first surface 34a and a second surface 34b facing opposite directions. The first electrode active material layer 36 is provided on the first surface 34a of the current collector 34. The second electrode active material layer 38 is provided on the second surface 34b of the current collector 34.

[0023] The current collector 34 has a first exposed portion 40 on its first surface 34a. The current collector 34 also has a second exposed portion 42 on its second surface 34b. The first exposed portion 40 and the second exposed portion 42 are located at the end of the current collector 34 in the short direction A. The first exposed portion 40 is the portion on the first surface 34a of the current collector 34 where the first electrode active material layer 36 is not provided, that is, the portion not covered by the first electrode active material layer 36. The second exposed portion 42 is the portion on the second surface 34b of the current collector 34 where the second electrode active material layer 38 is not provided, that is, the portion not covered by the second electrode active material layer 38. The end of the current collector 34 of the first electrode plate 10 where the first exposed portion 40 and the second exposed portion 42 are provided is bent inward towards the winding side of the electrode group 2 and connected to the first current collector plate 4 (see Figure 1). The ends of the current collector 34 of the second electrode plate 12, where the first exposed portion 40 and the second exposed portion 42 are provided, are bent inward towards the winding side of the electrode group 2 and connected to the second current collector plate 6 (see Figure 1).

[0024] Both the first exposed portion 40 and the second exposed portion 42 are strip-shaped and extend in the longitudinal direction B of the current collector 34 at the end of the current collector 34 in the short direction A. The longitudinal direction B of the current collector 34 coincides with the longitudinal direction of the electrode plate 11. Therefore, both the first exposed portion 40 and the second exposed portion 42 have an outer contour portion 44 and an inner contour portion 46. The outer contour portion 44 overlaps with the edge of the current collector 34 in the short direction A and extends in the longitudinal direction B of the current collector 34. Each outer contour portion 44 is composed of the edge of the current collector 34. The inner contour portion 46 is located closer to the center of the current collector 34 than the outer contour portion 44 in the short direction A of the current collector 34 and extends in the longitudinal direction B of the current collector 34.

[0025] In the direction in which the first surface 34a and the second surface 34b overlap, that is, when viewed from the thickness direction C of the current collector 34, the second exposed portion 42 has a wider width in the shorter direction A than the first exposed portion 40. In other words, the second exposed portion 42 has a larger area than the first exposed portion 40. Also, the entirety of the first exposed portion 40 overlaps with the second exposed portion 42. The thickness direction C of the current collector 34 coincides with the radial direction Y of the electrode group 2. In this embodiment, the outer contour portion 44 of the first exposed portion 40 and the outer contour portion 44 of the second exposed portion 42 overlap each other. The inner contour portion 46 of the first exposed portion 40 is located closer to the outer contour portion 44 than the inner contour portion 46 of the second exposed portion 42.

[0026] As shown in Figure 1, the end of the current collector 34 where the first exposed portion 40 and the second exposed portion 42 are provided is bent so that the second exposed portion 42 is on the inside and the first exposed portion 40 is on the outside. In this embodiment, the electrode plate 11 is wound so that the second electrode active material layer 38 is on the inside of the winding and the first electrode active material layer 36 is on the outside of the winding. The end is then bent toward the winding center of the electrode group 2. Therefore, at the bent end, the second exposed portion 42, which has a larger area, is positioned on the inside of the bend, and the first exposed portion 40, which has a smaller area, is positioned on the outside of the bend.

[0027] When the end of the current collector 34 is bent, the electrode active material layer located on the inside of the bend is more likely to experience a greater load due to the bend than the electrode active material layer located on the outside of the bend. The second exposed portion 42, located on the side of the second electrode active material layer 38 where the load is greater, has a larger area than the first exposed portion 40, located on the side of the first electrode active material layer 36 where the load is smaller, making it easier to bend the end of the current collector 34. Furthermore, it is possible to suppress problems such as the second electrode active material layer 38 peeling off due to excessive load when the end is bent. Therefore, the quality of the electrode plate 11 and, consequently, the energy storage device 1 can be improved.

[0028] Next, a method for manufacturing the electrode plate 11 will be described. Figures 4(A), 4(B), 4(C), and 4(D) are schematic diagrams illustrating a method for manufacturing the electrode plate 11 according to an embodiment. Figure 4(E) is a schematic diagram illustrating another method for manufacturing the electrode plate 11. Figures 4(A) to 4(E) illustrate the view of the gap between the pair of laminating rolls 52 when observed from the transport direction of the electrode mixture sheet and the current collector 34.

[0029] The electrode plate 11 having a first exposed portion 40 and a second exposed portion 42 is formed as follows. First, a current collector 34, a strip-shaped first electrode mixture sheet 50, and a strip-shaped second electrode mixture sheet 54 are prepared. The first electrode mixture sheet 50 has a narrower width in the short-side direction A of the current collector 34 than the current collector 34. The second electrode mixture sheet 54 has a narrower width in the short-side direction A than the first electrode mixture sheet 50. As an example, a dry electrode mixture is formed into a sheet by roll molding or the like to obtain a long electrode mixture sheet. The electrode mixture sheet is conveyed downstream by a conveyor roll. Two conveyor rolls are provided, and the first electrode mixture sheet 50 and the second electrode mixture sheet 54 are formed in parallel.

[0030] Next, as shown in Figure 4(A), the first electrode mixture sheet 50 and the current collector 34 are passed through the gap between a pair of bonding rolls 52. The first electrode mixture sheet 50 is placed on the first surface 34a side of the current collector 34 and sent to the pair of bonding rolls 52. As an example, two first electrode mixture sheets 50 are sent to the pair of bonding rolls 52. The two first electrode mixture sheets 50 are placed at a predetermined distance apart in the short-side direction A of the current collector 34. As a result, each first electrode mixture sheet 50 is pressed against the first surface 34a, and as shown in Figure 4(B), two first electrode active material layers 36 are formed on the first surface 34a of the current collector 34. A first exposed portion 40 is also formed between the two first electrode active material layers 36.

[0031] Next, as shown in Figure 4(C), the current collector 34, on which the first electrode active material layer 36 and the first exposed portion 40 are formed, and the second electrode mixture sheet 54 are passed through the gap between a pair of bonding rolls 52. The second electrode mixture sheet 54 is placed on the second surface 34b side of the current collector 34 and sent to the pair of bonding rolls 52. As an example, two second electrode mixture sheets 54 are sent to the pair of bonding rolls 52. The two second electrode mixture sheets 54 are placed at a predetermined distance apart in the short-side direction A of the current collector 34. The two second electrode mixture sheets 54 are placed so that the distance between them is wider than the distance between the two first electrode mixture sheets 50, and so that the space between the two second electrode mixture sheets 54, when viewed from the thickness direction C of the current collector 34, fits within the space between the two first electrode mixture sheets 50. As a result, each second electrode mixture sheet 54 is pressed against the second surface 34b, and as shown in Figure 4(D), two second electrode active material layers 38 are formed on the second surface 34b of the current collector 34. In addition, a second exposed portion 42 is formed between the two second electrode active material layers 38. As a result, an electrode plate 11 is obtained.

[0032] The strip-shaped second electrode mixture sheet 54 is narrower in width than the strip-shaped first electrode mixture sheet 50. Also, the distance between the two second electrode mixture sheets 54 is wider than the distance between the two first electrode mixture sheets 50, and the space between the two second electrode mixture sheets 54 accommodates the space between the two first electrode mixture sheets 50. For this reason, when viewed from the direction in which the first surface 34a and the second surface 34b overlap, the first exposed portion 40 and the second exposed portion 42 are strip-shaped, extending in the longitudinal direction B of the current collector 34. Also, the width of the second exposed portion 42 in the short direction A of the current collector 34 is wider than that of the first exposed portion 40. Furthermore, the entire first exposed portion 40 overlaps with the second exposed portion 42.

[0033] As an example, the electrode plate 11 is cut in the longitudinal direction B such that the cut surface passes through the first exposed portion 40 and the second exposed portion 42. As a result, the electrode plate 11 is divided into two in the short direction A. Therefore, the first exposed portion 40 and the second exposed portion 42 are also divided into two in the short direction A. Consequently, at the end of each current collector 34 in the short direction A, the first exposed portion 40 and the second exposed portion 42 are formed, extending in the longitudinal direction B along the edge of the current collector 34. In other words, the manufacturing method of the electrode plate 11 described above includes setting the dimensions and arrangement of the first electrode mixture sheet 50 and the second electrode mixture sheet 54 such that, when viewed from the thickness direction C of the current collector 34, the first exposed portion 40 and the second exposed portion 42 are strip-shaped extending in the longitudinal direction B at the end of the short direction A of the current collector 34, the second exposed portion 42 is wider than the first exposed portion 40, and the entirety of the first exposed portion 40 overlaps with the second exposed portion 42. If necessary, the electrode mixture sheet pressed onto the current collector 34 may be subjected to drying or rolling treatments.

[0034] As a method for manufacturing the electrode plate 11, it is also conceivable to first press the second electrode mixture sheet 54 onto the current collector 34, and then press the first electrode mixture sheet 50 onto it. However, in this procedure, as shown in Figure 4(E), one end of the first electrode mixture sheet 50 will overlap with the second exposed portion 42 in the thickness direction C of the current collector 34. Therefore, when force is applied to this end from the bonding roll 52, insufficient pressure may not be applied to this end, and it may not be possible to firmly press this end onto the current collector 34. In this case, there is a risk that this end will peel off from the current collector 34. In particular, when the end of the current collector 34 is bent, the end of the electrode active material layer is subjected to a load due to the bending, making it more prone to peeling. The same situation may occur when the first electrode mixture sheet 50 and the second electrode mixture sheet 54 are pressed together simultaneously.

[0035] On the other hand, in this embodiment, the second electrode mixture sheet 54 is pressed onto the current collector 34 after the first electrode mixture sheet 50 has been pressed onto it. In this case, when pressing the second electrode mixture sheet 54 onto the current collector 34, the end of the second electrode mixture sheet 54 can be supported by the first electrode active material layer 36 via the current collector 34. As a result, sufficient pressure can be applied to the end, and the end can be firmly pressed onto the current collector 34. This suppresses peeling of the electrode active material layer when the end of the current collector 34 is bent, and improves the quality of the electrode plate 11 and, consequently, the energy storage device 1.

[0036] Furthermore, the manufacturing method of the electrode plate 11 according to this embodiment may include a manufacturing method in which the first electrode mixture sheet 50 is pressed onto the first surface 34a and the second electrode mixture sheet 54 is pressed onto the second surface 34b simultaneously, and a manufacturing method in which the second electrode mixture sheet 54 is pressed onto the second surface 34b and then the first electrode mixture sheet 50 is pressed onto the first surface 34a. However, in this case, it is preferable that the sizes of the first exposed portion 40 and the second exposed portion 42 are determined such that the maximum protrusion amount D of the portion of the first electrode active material layer 36 that protrudes onto the second exposed portion 42 is 6 times or less the cube of the thickness T of the current collector 34. In other words, when the first electrode mixture sheet 50 and the second electrode mixture sheet 54 are pressed together simultaneously, or when the first electrode mixture sheet 50 is pressed together after the second electrode mixture sheet 54 is pressed together, the method for manufacturing the electrode plate 11 further includes setting the dimensions and arrangement of the first electrode mixture sheet 50 and the second electrode mixture sheet 54 such that the maximum protrusion amount D of the portion of the first electrode active material layer 36 that protrudes onto the second exposed portion 42 when viewed from the thickness direction C of the current collector 34 is 6 times or less the cube of the thickness T of the current collector 34.

[0037] The portion of the first electrode active material layer 36 that protrudes onto the second exposed portion 42 is a strip-shaped portion extending in the longitudinal direction B, sandwiched between the inner contour portion 46 of the first exposed portion 40 and the inner contour portion 46 of the second exposed portion 42, when viewed from the thickness direction C of the current collector 34. Therefore, the maximum protrusion amount D can be interpreted as the maximum value of the displacement between the inner contour portion 46 of the first exposed portion 40 and the inner contour portion 46 of the second exposed portion 42.

[0038] The inventors have discovered through the following evaluation tests that if the maximum protrusion amount D of the first electrode active material layer 36 is 6 times or less the cube of the thickness T of the current collector 34, sufficient pressure can be applied to the end of the first electrode active material layer 36 in contact with the first exposed portion 40, even if a second exposed portion 42 is formed on the second surface 34b.

[0039] Figure 5(A) is a schematic diagram of the test specimen 56 used in the evaluation test. The test specimen 56 has pressure-sensitive paper 58 attached to the first surface 34a and the second surface 34b of the current collector 34. In this evaluation test, multiple test specimens 56 with different thicknesses T of the current collector 34 were prepared. In each test specimen 56, a notch 58a is formed in one of the pressure-sensitive papers 58. A notch 58b is formed in the other pressure-sensitive paper 58. The notch 58a is a rectangle with two sides parallel to the short side A of the current collector 34 and the other two sides parallel to the long side B of the current collector 34. The notch 58b is a parallelogram with two sides parallel to the short side A and the other two sides extending diagonally to the long side B. In the following, the edges extending in the shorter direction A at each notch will be referred to as the shorter edges, and the edges extending in the longer direction B will be referred to as the longer edges.

[0040] The notches 58a and 58b are positioned so that their respective short sides overlap each other. One longitudinal side of the notch 58b is positioned so that the upstream end of the test specimen 56 in the transport direction overlaps with the longitudinal side of the notch 58a, and as it moves downstream in the transport direction, it moves outward in the short side A. The other longitudinal side of the notch 58b is positioned so that the downstream end of the test specimen 56 in the transport direction overlaps with the longitudinal side of the notch 58a, and as it moves upstream in the transport direction, it moves outward in the short side A. Therefore, the amount of displacement between the longitudinal sides of the notches 58a and 58b changes depending on the position in the longitudinal direction B.

[0041] The orientation of each test specimen 56 was determined so that the longitudinal direction B of the current collector 34 was parallel to the transport direction, and each test specimen 56 was passed between a pair of press rolls. This applied pressure to the two pressure-sensitive papers 58 in each test specimen 56. After that, the edges of the pressure-sensitive papers 58 along the longitudinal side of the notch 58b were observed, and the pressure applied to those edges was calculated from the degree of discoloration due to the pressurization. Then, the pressure at each position of the edges was normalized using the pressure applied to the edge of the pressure-sensitive paper 58 in contact with a reference position on the longitudinal side of the notch 58b as a reference. This reference position is the position where the longitudinal side of the notch 58b overlaps with the longitudinal side of the notch 58a. Next, the relationship between the distance between the longitudinal side of the notch 58a and the longitudinal side of the notch 58b in each test specimen 56, i.e., the amount of displacement between the two sides, and the pressure applied to the edge of the pressure-sensitive paper 58 in contact with the notch 58b was derived. The amount of displacement between the longitudinal side of the notch 58a and the longitudinal side of the notch 58b can be considered as the amount of displacement between the inner contour 46 of the first exposed portion 40 and the inner contour 46 of the second exposed portion 42.

[0042] Figure 5(B) shows the relationship between the amount of displacement between two sides and the pressure applied to the end in various test specimens 56 with different thicknesses T of the current collector 34. As shown in Figure 5(B), as the thickness T of the current collector 34 increased, the decrease in pressure associated with the increase in the amount of displacement between the two sides was suppressed. Therefore, it was confirmed that the amount of displacement at which the pressure falls below the threshold Th increases as the thickness T of the current collector 34 increases. The pressure threshold Th is the pressure at which the end can be crimped to the current collector 34 to a degree that suppresses the deterioration of the quality of the electrode plate 11, and is 80% as an example.

[0043] The inventors derived the relationship between the thickness T of the current collector 34 and the amount of displacement between the two sides at which the pressure reaches the threshold Th, i.e., the upper limit of the allowable displacement (hereinafter referred to as the allowable upper displacement E as appropriate) from the graph shown in Figure 5(B). For the test specimen 56 with a current collector thickness T of 0.02 mm and the test specimen 56 with a thickness T of 0.03 mm, the pressure did not reach the threshold Th within the range of displacement between the two sides of each test specimen 56, so the allowable upper displacement E was estimated based on the measured values.

[0044] FIG. 5(C) is a diagram showing the relationship between the thickness T of the current collector 34 and the allowable upper limit deviation amount E. As shown in FIG. 5(C), from the plot of the allowable upper limit deviation amount E at each thickness T, the formula: E = 6×T ３ is derived for the approximate curve. From this, by setting the maximum protrusion amount D of the portion protruding above the second exposed portion 42 in the first electrode active material layer 36 to be not more than the allowable upper limit deviation amount E, that is, not more than six times the cube of the thickness T, it was confirmed that the end portion of the first electrode active material layer 36 in contact with the first exposed portion 40 can be reliably crimped by the current collector 34. Thereby, even when simultaneously crimping the first electrode binder sheet 50 and the second electrode binder sheet 54, or when crimping the first electrode binder sheet 50 after crimping the second electrode binder sheet 54, peeling of the end portion from the current collector 34 can be suppressed, and the quality of the electrode plate 11 and thus the power storage device 1 can be improved. Note that the lower limit of the maximum protrusion amount D is 0. Also, as an example, the thickness T of the current collector 34 is 0.008 mm or more and 0.02 mm or less.

[0045] Also preferably, the maximum protrusion amount D, in other words, the maximum value of the deviation amount of the contours of the first exposed portion 40 and the second exposed portion 42, is 5 times or more and 30 times or less the thickness of the second electrode active material layer 38. By setting the maximum protrusion amount D to be 5 times or more the thickness of the second electrode active material layer 38, the ease of bending of the end portion of the current collector 34 can be more reliably improved. Also, by setting the maximum protrusion amount D to be 30 times or less the thickness of the second electrode active material layer 38, an excessive decrease in the second electrode active material layer 38 due to the installation of the second exposed portion 42 can be suppressed, and a decrease in the quality of the power storage device 1 can be suppressed. As an example, the thickness of the second electrode active material layer 38 is 0.008 mm or more and 0.02 mm or less.

[0046] The embodiments of the present disclosure have been described in detail above. The above-described embodiments are merely specific examples for implementing the present disclosure. The content of the embodiments does not limit the technical scope of the present disclosure, and many design changes such as component changes, additions, deletions, etc. are possible without departing from the inventive concept defined in the claims. The new embodiments with design changes have the combined effects of the combined embodiments and the modifications respectively. In the above-described embodiments, with respect to the content that allows such design changes, notations such as "in this embodiment" and "in this embodiment" are used for emphasis, but design changes are also allowed for the content without such notations. Also, any combination of the components included in each embodiment is also effective as an aspect of the present disclosure. The hatching attached to the cross-section of the drawing does not limit the material of the object to which the hatching is attached.

[0047] The structure of the power storage device 1 can be changed as appropriate. For example, the power storage device 1 is not limited to a cylindrical battery, and may be, for example, a rectangular battery provided with a rectangular metal case, a laminate battery provided with a resin exterior, or the like.

[0048] The embodiment may be specified by the following items: [Item 1] A strip-shaped current collector (34) having a first surface (34a) and a second surface (34b) facing opposite directions, a first electrode active material layer (36) provided on the first surface (34a), and a second electrode active material layer (38) provided on the second surface (34b), wherein the current collector (34) has a first exposed portion (40) on the first surface (34a) where the first electrode active material layer (36) is not provided, and a second exposed portion (42) on the second surface (34b) where the second electrode active material layer (38) is not provided, and both the first exposed portion (40) and the second exposed portion (42) are strip-shaped extending in the longitudinal direction (B) of the current collector (34) at the end of the current collector (34) in the short direction (A), Electrode plates (10, 11, 12), viewed from the direction (C) in which the first surface (34a) and the second surface (34b) overlap, the second exposed portion (42) is wider in the shorter direction (A) than the first exposed portion (40), the entire first exposed portion (40) overlaps with the second exposed portion (42), and the end of the current collector (34) is bent so that the second exposed portion (42) is on the inside and the first exposed portion (40) is on the outside. [Second item] Energy storage device (1) comprising the electrode plates (10, 11, 12) of the first item.[Item 3] A strip-shaped current collector (34) having a first surface (34a) and a second surface (34b) facing opposite directions, a strip-shaped first electrode mixture sheet (50) having a narrower width in the short-side direction (A) of the current collector (34) than the current collector (34), and a strip-shaped second electrode mixture sheet (54) having a narrower width in the short-side direction (A) than the first electrode mixture sheet (50) are prepared, and the first electrode mixture sheet (50) is pressed onto the first surface (34a) to form a first electrode active material layer (36) and a first exposed portion (40) on which the first electrode active material layer (36) is not provided. The method includes pressing a second electrode mixture sheet (54) onto the second surface (34b) of a current collector (34) on which a first electrode active material layer (36) and a first exposed portion (40) are formed, thereby forming a second electrode active material layer (38) and a second exposed portion (42) on the second surface (34b), wherein, when viewed from the direction (C) in which the first surface (34a) and the second surface (34b) overlap, the first exposed portion (40) and the second exposed portion (42) are each strip-shaped extending in the longitudinal direction (B) of the current collector (34) at the end in the short direction (A) of the current collector (34), the second exposed portion (42) is wider in the short direction (A) of the current collector (34) than the first exposed portion (40), and the entirety of the first exposed portion (40) overlaps with the second exposed portion (42). A method for manufacturing electrode plates (10, 11, 12).[Item 4] Prepare a strip-shaped current collector (34) having a first surface (34a) and a second surface (34b) facing opposite directions, a strip-shaped first electrode mixture sheet (50) whose width in the short-side direction (A) of the current collector (34) is narrower than that of the current collector (34), and a strip-shaped second electrode mixture sheet (54) whose width in the short-side direction (A) is narrower than that of the first electrode mixture sheet (50), The method includes simultaneously pressing the first electrode mixture sheet (50) onto the first surface (34a) and pressing the second electrode mixture sheet (54) onto the second surface (34b), or pressing the second electrode mixture sheet (54) onto the second surface (34b) and then pressing the first electrode mixture sheet (50) onto the first surface (34a) to form a first electrode active material layer (36) and a first exposed portion (40) on the first surface (34a) where the first electrode active material layer (36) is not provided, and forming a second electrode active material layer (38) and a second exposed portion (42) on the second surface (34b) where the second electrode active material layer (38) is not provided. A method for manufacturing an electrode plate (11), wherein, when viewed from the direction (C) in which the first surface (34a) and the second surface (34b) overlap, the first exposed portion (40) and the second exposed portion (42) are each strip-shaped extending in the longitudinal direction (B) of the current collector (34) at the end of the current collector (34) in the short direction (A), the second exposed portion (42) is wider in the short direction (A) of the current collector (34) than the first exposed portion (40), the entire first exposed portion (40) overlaps with the second exposed portion (42), and the maximum protrusion amount (D) of the portion of the first electrode active material layer (36) that protrudes onto the second exposed portion (42) is 6 times or less the cube of the thickness (T) of the current collector (34).

[0049] This disclosure can be used for electrode plates, energy storage devices, and methods for manufacturing electrode plates.

[0050] 1 Energy storage device, 11 Electrode plate, 34 Current collector, 34a First surface, 34b Second surface, 36 First electrode active material layer, 38 Second electrode active material layer, 40 First exposed portion, 42 Second exposed portion, 50 First electrode mixture sheet, 54 Second electrode mixture sheet.

Claims

1. An electrode plate comprising: a strip-shaped current collector having a first surface and a second surface facing opposite directions; a first electrode active material layer provided on the first surface; and a second electrode active material layer provided on the second surface, wherein the current collector has a first exposed portion on the first surface where the first electrode active material layer is not provided, and a second exposed portion on the second surface where the second electrode active material layer is not provided, both of which are strip-shaped extending in the longitudinal direction of the current collector at the short-side end of the current collector, and when viewed from the direction in which the first surface and the second surface overlap, the second exposed portion is wider in the short-side direction than the first exposed portion, the entirety of the first exposed portion overlaps with the second exposed portion, and the end of the current collector is bent so that the second exposed portion is on the inside and the first exposed portion is on the outside.

2. An energy storage device comprising the electrode plate described in claim 1.

3. The present invention includes: a strip-shaped current collector having a first surface and a second surface facing opposite directions; a strip-shaped first electrode mixture sheet having a narrower width in the short-side direction than the current collector; and a strip-shaped second electrode mixture sheet having a narrower width in the short-side direction than the first electrode mixture sheet; pressing the first electrode mixture sheet onto the first surface to form a first electrode active material layer and a first exposed portion where the first electrode active material layer is not provided; and pressing the second electrode mixture sheet onto the second surface of the current collector on which the first electrode active material layer and the first exposed portion are formed to form a second electrode active material layer and a second exposed portion where the second electrode active material layer is not provided. A method for manufacturing an electrode plate, wherein, when viewed from the direction in which the first surface and the second surface overlap, the first exposed portion and the second exposed portion are each strip-shaped extending in the longitudinal direction of the current collector at the short-side end of the current collector, the second exposed portion is wider in the short-side direction of the current collector than the first exposed portion, and the entirety of the first exposed portion overlaps with the second exposed portion.

4. A strip-shaped current collector having a first surface and a second surface facing opposite directions, a strip-shaped first electrode mixture sheet having a narrower width in the short-side direction than the current collector, and a strip-shaped second electrode mixture sheet having a narrower width in the short-side direction than the first electrode mixture sheet are prepared, and the first electrode mixture sheet is pressed onto the first surface and the second electrode mixture sheet is pressed onto the second surface simultaneously, or the second electrode mixture sheet is pressed onto the second surface and then the first electrode mixture sheet is pressed onto the first surface to form a first electrode active material layer and a first exposed portion where the first electrode active material layer is not provided, and a second electrode active material layer and a second exposed portion where the second electrode active material layer is not provided on the second surface, A method for manufacturing an electrode plate, wherein, when viewed from the direction in which the first surface and the second surface overlap, the first exposed portion and the second exposed portion are each strip-shaped extending in the longitudinal direction of the current collector at the short-side end of the current collector, the second exposed portion is wider in the short-side direction of the current collector than the first exposed portion, the entire first exposed portion overlaps with the second exposed portion, and the maximum protrusion amount of the portion of the first electrode active material layer protruding onto the second exposed portion is 6 times the cube of the thickness of the current collector or less.

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