Electrode plate, power storage device, and method for producing electrode plate

Abstract

An electrode plate 11 comprises a current collector 34 which has a first surface 34a and a second surface, a first electrode active material layer 36 which is provided to the first surface 34a, and a second electrode active material layer which is provided the second surface. The current collector 34 has a first exposure part 40 on the first surface 34a, and has a second exposure part 42 on the second surface. The first exposure part 40 and the second exposure part 42 are each shaped so as to protrude in the short direction A from an end of the current collector 34 in the short direction A toward the center of the current collector 34. As viewed from the direction C in which the first surface 34a and the second surface overlap each other, the second exposure part 42 has an area greater than that of the first exposure part 40, and the entire first exposure part 40 overlaps the second exposure part 42. The electrode plate 11 is wound such that the second electrode active material layer is located on the inner side of the winding and the first electrode active material layer 36 is located on the outer side of the winding.

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] There is a strong demand for increasing the capacity of power storage devices such as secondary batteries. In response to such demands, for example, in Patent Document 1, a secondary battery is described in which a bare portion where no positive electrode active material layer is provided, that is, an exposed portion of the positive electrode current collector, is provided on the positive electrode current collector, and a positive electrode lead is welded to this exposed portion. By welding the lead to the exposed portion of the current collector in this way, the area of the electrode active material layer can be increased, and the capacity of the power storage device can be increased.

[0003] Japanese Patent Application Laid-Open No. 2003-68271

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

[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 used in a power storage device. 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 have a convex shape from the end portion in the short side direction of the current collector toward the center side of the current collector in the short side direction. When viewed from the direction in which the first surface and the second surface overlap, the area of the second exposed portion is larger than that of the first exposed portion, and the entire first exposed portion overlaps with the second exposed portion. The electrode plate is wound such that the second electrode active material layer is on the inner side of the winding and the first electrode active material layer is on the outer side of the winding.

[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 first electrode mixture sheet having a first notch, a second electrode mixture sheet having a second notch larger than the first notch, and a current collector having a first surface and a second surface facing opposite directions; pressing the first electrode mixture sheet onto the first surface to form a first electrode active material layer and a first exposed portion on the first surface 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 on the second surface 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 each have a convex shape extending from the short-side end of the current collector toward the center of the current collector in the short-side direction, with the second exposed portion having a larger area 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 first electrode mixture sheet having a first notch, a second electrode mixture sheet having a second notch larger than the first notch, and a current collector having a first surface and a second surface facing opposite directions, 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 area 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 area where the second electrode active material layer is not provided on the second surface. When viewed from the direction in which the first and second surfaces overlap, the first exposed portion and the second exposed portion each have a convex shape extending from the short-side end of the current collector toward the center of the current collector in the short-side direction, the second exposed portion has a larger area 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 an energy storage device 1 according to an embodiment. Figure 2 is a perspective view of the electrode group 2. Note that in Figure 1, the current collector 34, the first electrode active material layer 36, and the second electrode active material layer 38 are omitted from the illustration. 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 insulating plate 4, a second insulating 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] A first lead 16 is attached to the first electrode plate 10. A second lead 18 is attached to the second electrode plate 12. Each lead is attached to the current collector 34 of each electrode plate 11 (see Figure 3(A), etc.) by welding or the like. The first lead 16 protrudes from one end of the electrode group 2 in the axial direction X. The second lead 18 protrudes from the other end of the electrode group 2 in the axial direction X. In this embodiment, each lead is attached to each electrode plate at one location in the winding direction Z, but leads may be attached to each electrode plate at multiple locations in the winding direction Z. Furthermore, the attachment positions of the leads on each electrode plate are not limited to those illustrated in Figure 2. The structure of the electrode plate 11 will be described in detail later.

[0017] The first insulating plate 4 and the second insulating plate 6 are arranged so as to sandwich the electrode group 2 in the axial direction X. The electrode group 2, the first insulating plate 4, and the second insulating plate 6 are housed together with the electrolyte (not shown) in an outer container 8. The outer container 8 is a bottomed cylindrical metal container. The first insulating plate 4 is positioned on the opening side of the outer container 8. The second insulating 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 insulating plate 4, the second insulating plate 6, and the electrolyte inside the outer container 8.

[0018] 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.

[0019] The first lead 16 extends towards the sealing body 20 through a through hole in the first insulating plate 4. The second lead 18 extends towards the bottom of the outer can 8, passing outside the second insulating plate 6. The first 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 lead 18 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.

[0020] 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 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 and 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.

[0021] In 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 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.

[0022] 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 ends of the current collector 34 in the short-side direction A. The short-side direction A of the current collector 34 coincides with the short-side direction of the electrode plate 11. 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 first lead 16 is connected to the first exposed portion 40 and the second exposed portion 42 provided on the current collector 34 of the first electrode plate 10 by welding or the like. The second lead 18 is connected to the first exposed portion 40 and the second exposed portion 42 provided on the current collector 34 of the second electrode plate 12 by welding or the like.

[0023] Both the first exposed portion 40 and the second exposed portion 42 have a convex shape extending toward the center of the current collector 34 in the short direction A from the end of the current collector 34 in the short direction A. Therefore, both the first exposed portion 40 and the second exposed portion 42 have an outer contour portion 44, an inner contour portion 46, and a pair of connecting contour portions 48a and 48b. 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. The longitudinal direction B of the current collector 34 coincides with the longitudinal direction of the electrode plate 11. Each outer contour portion 44 is formed by the edge of the current collector 34. The inner contour portion 46 is located toward the center of the current collector 34 in the short direction A of the current collector 34 than the outer contour portion 44 and extends in the longitudinal direction B of the current collector 34.

[0024] The connecting contours 48a and 48b are arranged at a predetermined interval along the longitudinal direction B of the current collector 34 and extend approximately in the short direction A of the current collector 34, connecting the outer contour 44 and the inner contour 46. One end of the connecting contour 48a is connected to one end of the outer contour 44, and the other end is connected to one end of the inner contour 46. One end of the connecting contour 48b is connected to the other end of the outer contour 44, and the other end is connected to the other end of the inner contour 46.

[0025] In the direction in which the first surface 34a and the second surface 34b overlap, that is, in the thickness direction C of the current collector 34, the second exposed portion 42 has a larger area than the first exposed portion 40, and the entire 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. The pair of connecting contour portions 48a and 48b of the first exposed portion 40 are closer to each other than the pair of connecting contour portions 48a and 48b of the second exposed portion 42 and are located closer to the center of the first exposed portion 40 in the longitudinal direction B of the current collector 34.

[0026] As shown in Figure 2, the electrode plate 11 is wound such that the second electrode active material layer 38 faces the inside of the winding and the first electrode active material layer 36 faces the outside of the winding. In other words, the second electrode active material layer 38 faces the winding center of the electrode group 2, and the first electrode active material layer 36 faces the outside of the electrode group 2. Therefore, the second exposed portion 42, which has a larger area, is located on the inside of the winding of the electrode group 2, and the first exposed portion 40, which has a smaller area, is located on the outside of the winding of the electrode group 2. When the electrode plate 11 is wound, the electrode active material layer located on the inside of the winding has a greater curvature than the electrode active material layer located on the outside of the winding. Since the second exposed portion 42, which is located on the side of the second electrode active material layer 38 with a greater curvature, has a larger area than the first exposed portion 40, which is located on the side of the first electrode active material layer 36 with a smaller curvature, the electrode plate 11 can be wound more easily. In particular, since the second exposed portion 42 is larger in the longitudinal direction B than the first exposed portion 40, the electrode plate 11 can be wound even more easily. Furthermore, it is possible to suppress problems such as excessive load being placed on the second electrode active material layer 38 during winding, which could cause the second electrode active material layer 38 to peel off. Therefore, the quality of the electrode plate 11 and, consequently, the energy storage device 1 can be improved.

[0027] 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.

[0028] The electrode plate 11 having a first exposed portion 40 and a second exposed portion 42 is formed as follows. First, a first electrode mixture sheet 50 having a first notch 50a, a second electrode mixture sheet 54 having a second notch 54a, and a current collector 34 are prepared. 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. Subsequently, a part of the electrode mixture sheet is cut off while it is being conveyed by a rotary die cutter or the like to form a notch in the electrode mixture sheet. The notch has a convex shape that extends from the end in the short direction of the electrode mixture sheet toward the center of the electrode mixture sheet in the short direction.

[0029] Two sets of conveyor rolls and rotary die cutters are provided, and a first electrode mixture sheet 50 and a second electrode mixture sheet 54 are formed in parallel. A second notch 54a is formed in the second electrode mixture sheet 54, which is larger than the first notch 50a formed in the first electrode mixture sheet 50. As an example, both the first notch 50a and the second notch 54a are rectangular in shape.

[0030] Next, as shown in Figure 4(A), the first electrode mixture sheet 50 having the first notch 50a and the current collector 34 are passed through the gap between a pair of bonding rolls 52. The first electrode mixture sheet 50 is positioned on the first surface 34a side of the current collector 34 and sent to the pair of bonding rolls 52. As a result, the first electrode mixture sheet 50 is pressed against the first surface 34a, and as shown in Figure 4(B), the first electrode active material layer 36 is formed on the first surface 34a of the current collector 34. In addition, the first notch 50a overlaps with the first surface 34a, forming the first exposed portion 40 on the first surface 34a.

[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, which has a second notch 54a, 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 a result, the second electrode mixture sheet 54 is pressed against the second surface 34b, and as shown in Figure 4(D), the second electrode active material layer 38 is formed on the second surface 34b of the current collector 34. In addition, the second notch 54a overlaps with the second surface 34b, forming a second exposed portion 42 on the second surface 34b. As a result, an electrode plate 11 is obtained.

[0032] When viewed from the direction in which the first surface 34a and the second surface 34b overlap, the second notch 54a has a larger area than the first notch 50a. In addition, each notch is positioned such that the entirety of the first notch 50a overlaps with the second notch 54a. As a result, the second exposed portion 42 has a larger area than the first exposed portion 40, and the entirety of the 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. Thus, the first notch portion 50a and the second notch portion 54a, as well as the first exposed portion 40 and the second exposed portion 42, are also divided into two in the short direction A. As a result, each electrode plate 11 has a first notch portion 50a and the second notch portion 54a that are convex in the short direction A from the end toward the center, and a first exposed portion 40 and the second exposed portion 42 that are convex in the short direction A from the end toward the center. In other words, the above-described method for manufacturing the electrode plate 11 includes setting the dimensions and arrangement of the first notch 50a and the second notch 54a, or the first exposed portion 40 and the second exposed portion 42, 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 convex in shape from the end in the short direction A of the current collector 34 toward the center, the area of ​​the second exposed portion 42 is larger than that of the first exposed portion 40, and the entirety of the first exposed portion 40 overlaps with the second exposed portion 42.

[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), the end portion of the first electrode mixture sheet 50 that forms the outline of the first notch 50a will overlap with the second notch 54a or the second exposed portion 42 in the thickness direction C of the current collector 34. Therefore, when force is applied to the end portion from the bonding roll 52, insufficient pressure may not be applied to the end portion, and it may not be possible to firmly press the end portion to the current collector 34. In this case, there is a risk that the end portion will peel off from the current collector 34. 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 portion of the second electrode mixture sheet 54 that forms the contour of the second notch 54a 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 portion, and the end portion can be firmly pressed onto the current collector 34. This 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 notch 50a and the second notch 54a, or the first exposed portion 40 and the second exposed portion 42, 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 the portion sandwiched between the contour of the first exposed portion 40 and the contour of the second exposed portion 42 when viewed from the thickness direction C of the current collector 34. In other words, the portion of the first electrode active material layer 36 is roughly U-shaped, consisting of a portion extending in the short direction A sandwiched between the connecting contour portion 48a of the first exposed portion 40 and the connecting contour portion 48a of the second exposed portion 42, a portion extending in the long 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, and a portion extending in the short direction A sandwiched between the connecting contour portion 48b of the first exposed portion 40 and the connecting contour portion 48b of the second exposed portion 42 (see Figure 3(A)). Therefore, the maximum protrusion amount D can be interpreted as the maximum value of the difference between the contour of the first exposed portion 40 and the contour 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.

[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 present inventor derived the relationship between the thickness T of the current collector 34 and the amount of deviation of two sides where the pressure reaches the threshold value Th, that is, the upper limit of the allowable amount of deviation (hereinafter appropriately referred to as the allowable upper limit deviation amount E). For the test body 56 with the thickness T of the current collector 34 being 0.02 mm and the test body 56 with the thickness being 0.03 mm, since the pressure did not reach the threshold value Th within the range of the amount of deviation of two sides of each test body 56, the allowable upper limit deviation amount 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 plots of the allowable upper limit deviation amount E at each thickness T, the formula: E = 6 × T ３ was 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 surely 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, it is possible to suppress the peeling of the end portion from the current collector 34, and improve the quality of the electrode plate 11 and thus the power storage device 1. 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 amount of deviation of the contours of the first exposed portion 40 and the second exposed portion 42, is not less than five times and not more than thirty times the thickness of the second electrode active material layer 38. By setting the maximum protrusion amount D to be not less than five times the thickness of the second electrode active material layer 38, the ease of winding of the electrode plate 11 can be more surely improved. Also, by setting the maximum protrusion amount D to be not more than thirty times the thickness of the second electrode active material layer 38, it is possible to suppress an excessive decrease in the second electrode active material layer 38 due to the installation of the second exposed portion 42 and prevent the quality of the power storage device 1 from deteriorating. 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] As described above, the embodiments of the present disclosure have been described in detail. 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 effects of the combined embodiments and variations respectively. In the above-described embodiments, with respect to the content where such design changes are possible, notations such as "in this embodiment" and "in this embodiment" are added 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 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 items described below. [Item 1] An electrode plate (10, 11, 12) used in an energy storage device (1), comprising: 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 (40) 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, Both the first exposed portion (40) and the second exposed portion (42) have a convex shape extending toward the center of the current collector (34) in the short direction (A) from the end of the current collector (34) in the short direction (A), and when viewed from the direction (C) in which the first surface (34a) and the second surface (34b) overlap, the second exposed portion (42) has a larger area than the first exposed portion (40), and the entire first exposed portion (40) overlaps with the second exposed portion (42), and the electrode plates (10, 11, 12) are wound such 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, electrode plates (10, 11, 12). [Second item] Energy storage device (1) comprising the electrode plates (10, 11, 12) of the first item.[Item 3] Prepare a first electrode mixture sheet (50) having a first notch (50a), a second electrode mixture sheet (54) having a second notch (54a) larger than the first notch (50a), and a current collector (34) having a first surface (34a) and a second surface (34b) facing opposite directions, and press 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 which the first electrode active material layer (36) is not provided. A method for manufacturing electrode plates (10, 11, 12), comprising 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) each have a convex shape extending toward the center of the current collector (34) in the short direction (A) from the end of the current collector (34), the second exposed portion (42) has a larger area than the first exposed portion (40), and the entire first exposed portion (40) overlaps with the second exposed portion (42).[Item 4] Prepare a first electrode mixture sheet (50) having a first notch (50a), a second electrode mixture sheet (54) having a second notch (54a) larger than the first notch (50a), and a current collector (34) having a first surface (34a) and a second surface (34b) facing opposite directions. 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 electrode plates (10, 11, 12), 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) each have a convex shape toward the center of the current collector (34) in the short direction (A) from the end of the current collector (34) in the short direction (A), the second exposed portion (42) has a larger area 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, 50a First notch, 54 Second electrode mixture sheet, 54a Second notch.

Claims

1. An electrode plate used in an energy storage device, 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 the first and second exposed portions have a convex shape extending from the short-side end of the current collector toward the center in the short-side direction, and when viewed from the direction in which the first and second surfaces overlap, the second exposed portion has a larger area than the first exposed portion, and the entirety of the first exposed portion overlaps with the second exposed portion, and the electrode plate is wound such that the second electrode active material layer is on the inside of the winding and the first electrode active material layer is on the outside of the winding.

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

3. The present invention includes preparing a first electrode mixture sheet having a first notch, a second electrode mixture sheet having a second notch larger than the first notch, and a current collector having a first surface and a second surface facing opposite directions; pressing the first electrode mixture sheet onto the first surface to form a first electrode active material layer and a first exposed portion on the first surface 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 on the second surface 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 each have a convex shape extending from the short-side end of the current collector toward the center of the current collector in the short-side direction, the second exposed portion has a larger area than the first exposed portion, and the entirety of the first exposed portion overlaps with the second exposed portion.

4. The present invention includes preparing a first electrode mixture sheet having a first notch, a second electrode mixture sheet having a second notch larger than the first notch, and a current collector having a first surface and a second surface facing opposite directions, and simultaneously performing the pressing of 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 area 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 area 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 each have a convex shape extending toward the center of the current collector in the short direction from the short end of the current collector, the second exposed portion has a larger area 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.

Images